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8/9/2019 Comparison of the Methods of Seismic Analysis Applicable to Fast Reactors in the EEC Countries
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Commiss ion of the European Communi t ies
n u c l e a r s c i e n c e a n d t e c h n o l o g y
C O M P A R I S O N O F T H E M E T H O D S
O F S E I S M I C A N A L Y S I S
A P P L I C A B L E T O F A S T R E A C T O R S
IN T H E E E C C O U N T R I E S
R e p o r t
EUR 10586 EN
Blow-up f rom mic ro f iche or ig ina l
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8/9/2019 Comparison of the Methods of Seismic Analysis Applicable to Fast Reactors in the EEC Countries
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Commission of the European Communities
n u c l e r s c i e n c e n d t e c h n o l o g y
COMP RISON OF THE METHODS
OF SEISMIC N LYSIS
PPLIC BLE TO F ST RE CTORS
IN THE EEC COUNTRIES
M. DEFALQUE, P. KUNSCH, A. PREUMONT
BELGON U C LEAIR E
Place du Champs de Mars, 25
- 1050 Bruxelles
Contract No. RAP-020.B.
FINAL REPORT
This work was performed under the aegis of the
Commiss ion of the European Communit ies
fo r the : WORKING GROUP CODES AND STANDARDS
Activ i ty Group 2 Structural Analys is
w i th in the FAST REACTOR COORDINATING COMMITTEE
Directorate-General Sc ience, Research and Development
1986 EUR 10586 EN
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P u b li s h e d b y th e
C O M M I S S I O N O F T H E E U R O PE A N C O M M U N I T I E S
D i r e c t o r a t e - G e n e r a l
T e l e c o m m u n i c a t i o n In f o r m a t i o n In d u s t r ie s a n d I n n o v a t io n
B t i m e n t J e a n M o n n e t
L U X E M B O U R G
L E G A L N O T I C E
Neither the Com miss ion of the European Com mun it ies nor any person act ing on behal f
of the Commiss ion is responsib le for the use which might be made of the fo l lowing
information
ECSC EEC EAEC Brussels-Luxe mbo urg 1986
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III
Resum
COMPARAISON DES METHODES D'ANALYSE SISMIQUE APPLI
CABLES AUX REACTEURS RAPIDES DANS LES PAYS DE LA CCE.
Les pays de la Communaut concerns sont ceux qui parti
cipent actu ellem ent l'exploitation ou la mise au point
des racteurs rapides savo ir:
- FRANCE (F) : Phnix - Supe rph nix
- RFA - BELGIQUE - PAYS BAS associs au sein du
DeBe Ne : SNR - 300
- Le ROYAU ME UNI (UK) : PFR-CDFR
- I TALI E (I) : PEC
Le premier object if de cette tude est de mettre en vi
dence les points communs et les divergences existant entre
les rgles nationales pour l'analyse sismique de Racteurs
Neutrons Rapides
(RNA).
Ces diffrences peuvent survenir diffrentes tapes de la
concep tion sav oir : dans la dfin ition s des donnes sismi-
ques d'entre, dans le choix des limites admissibles et dans
le conservatisme associ aux mthodes de calculs.
Pour chacunes de ces trois tapes, il convient d'identifier
les points pouvant influen cer les rsultats de l'analyse et
par consquent la marge de scurit globale vis--vis de
l'vnement concern.
Summary
COMPARISON OF THE METHODS OF SEISMIC ANALYSIS APPLI
CABLE TO FAST REACTORS IN THE EEC COUNTRIES.
The countries in the Community which are concerned by this
study are those currently involved in the operation or deve
lopment of fast reactors, namely:
- FRANCE (F) : Phnix - Sup erph nix
- FRG - BELGI UM - THE NETH ERLA NDS associated within
DeBeNe : SNR - 300
- UNITED KI NGDOM (UK) : PFR-CDFR
- I TALY (I ): PEC
The first aim of the study is to enumerate the common points
and differences in the national rules and regulations for
the seismic analysis of fast breeder reactors (FBR).
Such divergences may be encountered at different design
stages, namely: in the definition of the seismic input data,
in the choice of design limits and in the degree of conser
vatism applied to the calculation methods employed.
For every one of these three stages, it is necessary to
identify the points likely to influence the results of the
analysis and consequently the over-all safety margin with
regard to the event concerned.
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TABLE OF CONTENTS
I. Introduction. j
1. Subject of study . j
2.
Framework of the study. ]
3. Methodology. 2
4.
Execu tion of the study. 5
II.Seismic analysis in EEC .
0. Preliminary remark.
1. Reference ground motion. 7
2.
Seismic classification of components - Safety prescriptions - Design
criteria. g
3. Methods for analysis of seismic systems and subsyst ems.
\
III.Synthesis of national answe rs. 25
25
26
0. Introduction.
1. Ground motio n.
2.
Seismic classification of components - Safety prescriptions - Dimensional
criteria. 29
3. Seismic analysis meth ods. 49
IV.
Prospects and further developments . 55
1. Part common to all types of react ors. 55
2.Fast reactors characteris tics. 56
Bibliography. eg
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I. INTRODUCTION
1.1. Subject of study
The Commission of the European Communities has awarded BELGONUCLEAIRE a
study contract (No RAP-020-B) entitled: Comparison of the methods of seismic
analysis applicable to the fast reactor components in the EEC countries.
This study is being monitored by activity group AG2 of the working
group Codes and standards (WGCS) which itself is under the aegis of the Fast
Reactor Coordinating Committee.
The countries of the Community which are concerned by this study are
those currently involved in the operation or development of fast reactors, name
ly:
- FRANCE (F ): Phnix - Superphnix
- FRG - BELGIUM - THE NETHERLANDS associated within DeBeNe: SNR - 300
- UNITED KI NGDOM (UK ): PFR-CDFR
- ITALY (I ): PEC
The first aim of the study is to enumerate the common points and diffe
rences in the national rules and regulations for the seismic analysis of
fast
breeder reactors (FBR).
Such divergences may be encountered at different design stages,
namely:
in the definition of the seismic input data, in the choice of design limits
and
in the degree of conservatism applied to the calculation methods employed.
For every one of these three stages, it is necessary to identify the
points likely to influence the results of the analysis and consequently the over
all safety margin with regard to the event concerned.
1.2. Framework of the study
Since fast breeder reactors are still in the development stage and,
except for France, far from the stage of commercial operation, practices and
regulations are still changing and are mainly based on practices for light water
reactors and, in particular, on American rules and regulations such as Regula
tory Guides (RG) , Standard Review Plan (SRP) , ASME Code Section III and its
Code Cases .
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A fruitful comparison of aspects not yet dealt with in that type of
document is not possible at the present time.
Hence we feel it would be desirable to limit the study to the following
aspects:
(1) ground motion;
(2) classification of components;
(3) methods of analysis.
With regard to point (2), the present study will be limited to mechani
cal components; experimental methods will be excluded from point (3).
This approach deliberately does not take into account certain fundamen
tal aspects which are specific to fast breeder reactors and result from their
operating conditions:
- large masses of liquid sodium, especially in the pool concept;
- low pressures entailing thin walls;
- high temperatures and irradiations entailing problems of material behaviour;
- severe thermal gradients and temperature fluctuations.
Problems arising as a result of these conditions will include the
fol
lowing:
(1) fluid/structure interactions;
(2) instabilities (elastic or plastic
buckling);
(3) creep and plasticity problems.
At the moment, these would seem to belong more to the field of research
than to that of established practices.
1.3. Methodology
In order to specify the different factors which influence the result of
an overall seismic analysis and the associated safety margin, each of the three
aspects that we have identified in 1.2. has been included in a questionnaire (see
para.
I I ).
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(1) Ground_mot ion
This questionnaire aims at comparing the definitions of the two refe
rence earthquakes, the associated probabilities, the corresponding ground accele
rations and response spectra.
(2) Safe_ty_provisions_ -_Classj^fica_tion of_cmonent
s
- Dein_c,iteri
The principle of the classification procedure has been described in a
working document prepared by activity group No 4 (WGCS-AG4) under the title So
dium cooled fast reactors - Classification of the mechanical systems and compo
nents .
The questionnaire proposed here aims at applying that procedure to the
specific framework of earthquakes, considering the following steps :
A. definition of functional requirements for the reference earthquakes;
B. classification of reference earthquakes in relation to the various categories
of operating conditions (normal, upset,
. . . ;
combination with other types of loads, and
definition of the resulting categories of operating conditions;
C. criteria allowing the classification of components into safety classes (e.f.
RG 1.16) and seismic classes (e.g. RG
1.29).
Starting from these classes, the
component function, the consequences of its failure and the normal loading
conditions, definition of its quality level and the corresponding ASME code
subsection;
D.specification of the design rules for mechanical components based on:
1. quality level;
2.functional requirements.
These steps are described in the table given below.
A double entry table is appended to the questionnaire; this enables a
definition to be made for each mechanical component, of its safety class and the
operating condition category corresponding to the reference earthquakes. This
table must be adapted to meet national technologies, in particular for pool and
loop concepts.
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DFINITION
A N D
CLASSIFICATION
; O F
EARTHQUAKE-
:
INDUCED S ITUATIONS
k,
k.
r
W^
SELECTIONO F DESIGN
CATEGORYO F
OPERATING
CONDITIONS
NORMAL
UPSET
EMERGENCY
Tr n
FUNCTIONAL
REQUIREMENTS
1
w
SELECTIONOF A
SET
O F
CRITERIA
A^
RULES (SCHEMATIC DI AGRAM)
w
^\C0DE
CRITERIA
LEVELA
LEVEL
LEVELC
LEVELD
SAFETY CLASSIFICATIONO F EQUIPMENTS
SELECTIONO F ADESIGNAN D FABRICATION COD E ^
@
CLASS
1
CLASS
2
\
\
CLASS
3
\
CONTAIN-
MENTS
SUPPORTS
V
A
I
J-
I
1. The rules of corresp ondence between category of operating conditions
and service level take into account
:
- the
type
of
functional r equirement (act ion, leakti ghtness, structur al
integrity)
- the
possibilities
fo r
inspection
a nd
repair (accessible components) .
2.
Example
of
rule
:
qua lit y level (class)
safety class.
For each block, there is a corresponding
set
o f
design
a n d
construction rules.
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(3) Methods^ for
analys
is_of_
seismic systems_ and subsystems
The questionnaire aims at comparing the analytical verification methods
and the associated degrees of conversatism.
It deals with:
1. rules for modal superposition;
2. decoupling criteria for subsystems;
3. determination of floor spectra;
use of artificially generated accelerograms;
4.
acceptability of approximate methods;
5. damping (reference values, composite structures, etc.).
It follows approximately sections 3.7.2. and 3.7.3. of the SRP.
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1.4. Execution of the study
The questionnaire was sent to members of the working group Codes and
Standards , who contacted the relevant bodies in each country. Various meetings
of experts took place.
The reports of these meetings were drafted by BELGONUCLEAIRE represent
atives, then revised and amended by the national experts.
The French position was sent to BELGONUCLEAIRE after an internal mee
ting held in France.
Contacts were established with the following organizations:
France: CEA - EdF - Novatome;
Italy: ANSALDO - ENEA - NIRA;
United Kingdom: CEGB - UKAEA - NNC;
FRG: IA.
Belgium and the Netherlands are associated with the SNR project in the
FRG. Their representatives (Belgium: BELGONUCLEAIRE; the Netherlands: TNO-Nera-
toom) have approved the document issued by the FRG.
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II.
SEISMIC ANALYSIS IN EEC
11.0.
Preliminary remark
As the present comparison must reflect the evolution of regulation with
time, answers to the questionnaire may consider separately several aspects: rules
and regulations applicable to reactors operating or under construction, rules and
regulation applicable in the future. Differences with LWR practices will be
indicated, if any.
11.1.
Reference ground motion
1. Safety levels
1.1. Could you explain the philosophy that led to setting up two safety levels
(OBE and SSE in the US Regulatory Guides terminology)?
1.2. What are the corresponding probabilities of occurrence?
2. Maximum ground acceleration
2.1. USNRC recommends that maximum ground acceleration be at least equal to
0.1 g for SSE and at least half the SSE value for OBE.
Is such a rule also applied in your country?
2.2.
Is maximum acceleration defined on a site dependent basis or is it
considered constant throughout the country? On what basis has its value
been chosen?
3. Response spectra
USNRC has defined standard shapes for horizontal and vertical spectra. They
must be normalized according to the maximum horizontal acceleration.
3.1. Is a similar rule applied in your country?
3.2. Are the design spectra site dependent or not?
3.3. If the design spectra differ from those of RG 1.60, could you make them
available to us?
4.
Duration
4.1. Is there any specification concerning the duration of the two reference
earthquake?
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I I.2.
Seismic classification of components - Safety prescriptions - Design crite
ria
0. DEFINITIONS AND REMARKS
51 level 1 earthquake: OBE, SB, SNA, AEB, TBE;
52 level 2 earthquake: SSE, SM, SMS, SEB, TSS;
Rl last reactor built or already in construction (Superphnix, SNR-300,
... );
R2 reactor* to follow to Rl (reactor in design phase, reactor in construc
tion).
Where applicable, a distinction should be made between criteria defined
for reactors Rl and R2.
Questions are purposedly redundant. They can be answered by referring
to an official document or an appended document and also by referring to an ans
wer given to another question.
*Fast neutron reactor, excluding research reactors.
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A. FUNCTIONAL CRITERIA.
AO - Are there any official documents defining functional requirements in case of
earthquakes? If so, what are these documents?
Al - What are the safety related functional requirements after an SI earthquake?
A2 - What are the safety related functional requirements after an S2 earthquake?
A3 - Which are (therefore) the circuits and systems that shall remain functional
in the case of an S2 earthquake?
A4 - If the concept of containment [or barriers] appears in the safety regula
tions,
which containments should remain tight after S2?
A5 - Is earthquake detection considered in the safety regulations? If so,what
are the prescribed actions and what are the thresholds triggering them?
A6 - What are the functional consequences of earthquakes that must be taken into
account (emergency shut-down, external electricity supply loss, water flow
failure,
leaks, ...)?
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.
CLASSIFICATION OF EARTHQUAKES WITH REGARD TO OPERATING CONDITIONS.
BO - Are there any official documents specifying earthquake classification? If
so,
which are these documents?
Bl - How are operating conditions classified in the safety regulations?
B2 - With which operati ng conditions should an SI earthquake be combined? In
whic h category of operating conditi ons should the so defined combination be
classified?
B3 - With which operating conditions should an S2 earthquake be combined? In
whic h category of operating condi tions should the so defined combination be
classified?
B4 - In particular , should the simultaneous occurrence of earthquake and the
followin g events be considered? If so , how should the combined situation be
classified?
- Normal shut-down
- Emergency shut-down
- Failure in the steam generator
water supply
- Secondary loop failure
- Loss of external power supply
- Normal handling operations
- Exceptional handling operations
CLASSIFICATION OF THE
COMBINED SITUATION
SI S2
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C . C L A S S I F I C A T I O N O F M E C H A N I C A L C O M P O N E N T S
C O - Are t h ere any o f f i c i a l d o c u m e n t s s p e c i f y i n g t h e c l a s s i f i c a t i on
c r i t e r i a
of
com ponents acc ording to their safet y relate d functions? If
0 ,
wha t a re
t h e s e d o c u m en t s ?
C I - Wh ic h are the safety clas ses of c omp onents and whic h ar the
c l a s s i f i c a t i o n
criteria?
C2 - Is there an additional component classification with regard to
e a r t h q u a k e
(" s e i s m i c cl a s s i f i c a t i on" ) ? I f s o:
- wh a t are t h e c l a s s i f i c a t i on cri t eri a ?
- wh a t are t he re l a t i o n s h i p s wi t h t h e g enera l s a f e t y c l a s s i f i c a t i on ( q u e s -
t i on C I ) ?
- wh i c h re l a t i on s h i p s wi t h t h e d e s i gn cri t eri a m u s t b e a p p l i e d t o t h i a c bw -
ponent with regard to earthquakes? 'M.>:
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D. MECHANICAL DESIGN CRITERIA
DO - Are there any official documents specifying the choise of design rules?
Dl - Which design codes* are used? How are the design and fabrication rules
applying to a specific component to be chosen? (example, in relation to the
safety class, the type of component, the temperature,
etc.).
D2 - Are those design criteria classified in a way comparable with the A, B, C
and D levels found in ASME III?
D3 - What is the relationship between the category of operating conditions and
the level of criteria to be associated with
it**
(with regard to equipment
type and functional requirements)?
D4 - On which basis is fatigue damage assessed (number of cycles per earthquake,
number of earthquakes to be considered)? Are the aftershocks taken into
account?
E. MISCELLANEOUS
El - How are the seismic load specifications officially transmitted to the compo
nent manufacturers? (equivalent of ASME Design Specification).
*A code is defined as a complete set of design and fabrication rules such as the
subsections of ASME III and some code cases.
**In the USA, NRC has defined this relationship for light water reactors in Regu
latory Guide 1.48.
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DESIGN CRITERIA APPLICABLE TO THE VARIOUS COMPONENTS
REACTOR :
Component
1. Reactor block
1 - Main tank
2 - Safety tank.
3 - Roof slab
. 4 - Large rotating plug
5 - Small rotating plug
6 - Core cover plug
7 - Control rod mechanism
8 - Core diagrid
9 - Core support plate
10 - Internal structures of
primary circuit
11 - Internal structures for
thermal shielding
12 - Dome
Safety
class of
component
TYPE :
POOL*
Design criteria level
Earthquake
SI
Earthquake
S2
*A loop version is presented in the appropriate national answers
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DESIGN CRITERIA APPLICABLE TO THE VARIOUS COMPONENTS
REACTOR :
TYPE : POOL
Component
Safety
class of
component
Design criteria level
Earthquake
SI
Earthquake
S2
2. Heavy components
- Primary pumps
+ rotating parts
+ static parts
> -I HX (intermediate heat
exchangers,
normal and
emergency circuits)
+ exchange tubes
+ secondary sodium pipework
+ protective shell (sup
ports and cover gas ple
num seals)
- Secondary pumps
+ rotating parts
+ static parts
- Steam generators
+ exchange tubes
+ protective shells
- Integrate purification
circuits
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15
DESIGN CRITERIA APPLICABLE TO THE VARIOUS COMPONENTS
REACTOR :
Component
3. Handling
- Fuel transfer machine
- Transfer lock
+ cover-gas plenum seals
+ handling mechanism
+ rotating transfer lock
+ charge/discharge ramps
- Storage drum for new and
irradiated fuel
+ vessel(s)
+ drum
+ cover plug
- Handling flasks
- Secondary handling lines
Safety
class of
component
TYPE : POOL
Design criteria level
Earthquake
SI
Earthquake
S2
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DESIGN CRITERIA APPLICABLE TO THE VARIOUS COMPONENTS
REACTOR : TYPE : POOL
Component
Safety
class of
component
Design criteria level
Earthquake
SI
Earthquake
S2
4.
Circuits
- Secondary circuits
+ main pipework
+ sodium storage tanks
+ auxiliary circuits
+ double jacket in dome
+ expansion tank
- Decay heat removal circuits
(in reactor and in storage
drum)
+ main pipework
+ pumps
+ sodium/air exchangers
+ auxiliary circuits
- Primary argon gas circuits
+ piping and vapor traps
+ primary storage tanks
+ argon purification
- Storage drum auxiliary
circuits
- Water/steam circuits
+ up to safety valves
+ beyond safety valves
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I I.3.
METHODS FOR ANALYSIS OF SEISMIC SYSTEMS AND SUBSYSTEMS
1. RULES APPLIED IN CONNECTION WITH THE MODAL SUPERPOSITION METHOD
1.1. Combination of modal responses - Closely spaced modes
The most popular rule for the combination of the modal responses is the
so-called square root of the sum of the squares (SRSS). This can be justified
theoretically if it is accepted that the modal components are statistically inde
pendent. For closely spaced modes, the combination rule must be modified in
order to allow for the correlation between the modal components of the response.
A conservative rule generally accepted for these closely spaced 'modes is the rule
of the absolute sum. The following combination rule is proposed by the USNRC
(SRP, Section
3.7.2.):
- N
R =
k=l
R,R
1 m
1/2
(3.1)
where N is the total number of modes and the second sum includes all modes whose
frequencies are within 10% of each other (of the lowest frequency of the
pair).
A similar rule is given in R.G. 1.92.
Q_.l_.l_.
Is this combination rule applicable in your country?
If not, what is the rule used?
1.2. Combination of three spatial components
In order to estimate the maximum response R of the structure subjected
to a three dimensional excitation (2 horizontals + 1 vertical) from the maxima
R, (i = 1, 2, 3) obtained separately for each of the components of the excita
tion,the USNRC (R.G.1.92) recommends the use of the SRSS rule:
A
2 2
+ R^ + R3
(3.2)
(see Chu, Amin & Singh, NED 21 (1972),
126-136).
This approach has been critici
zed as too conservative whenever R^ are obtained by a modal superposition me
thod, because of the statistical independence of the various components of the
seismic accelerogram (C.W. Lin, NED 24 (1973), 239- 241).
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Q_.K2. Is rule (3.2) applicable in your country?
What other rule is applied, if any?
1.3. Significant Modes
Usually, the combination rule for the modal contributions applies to
those modes whose frequencies are below the excitation cut-off frequency (fre
quency at which the acceleration spectrum reaches its asymptote - 33 Hz in the
case of NRC spectra).
This can sometimes cause certain modes of important effective mass to be ignored
and can lead to substantial errors, especially concerning the support reactions
and the stresses. This approach can, however, be improved by introducing a resi
dual mode which takes into account the rigid part of the response (see for exam
ple, G.H. Powell, SMI RT-5, paper K 10/3, 1979). This mode is then combined with
the others by the SRSS rule.
(}.1_.3_.1_.
What rules are applied in your country, concerning the modes to be con
sidered? (Criteria on frequencies? Criteria on effective masses?).
>1_.3_.2^
What procedures allow the high frequency modes to be taken approximately
into account?
2.
DECOUPLING CRITERIA FOR SUB-SYSTEMS
According to Section 3.7.2. of the USNRC's SRP, the decoupling criteria
are based on the mass R^ and frequency Rf ratios:
Total mass of supported subsystem
m Mass which supports the subsystem
Fundamental frequency of subsystem
f Dominant frequency of support motion
The decoupling can be carried out under the conditions:
(1) R
m
< 0.01
(2) 0.01 < R
m
< 0. and R
f
>
1.25 or R
f
< 0.8
(3.3)
(__.2_. Are these criteria applied in your country? If not, what other criteria are
used?
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3. DETERMINATION OF FLOOR SPECTRA - CONSIDERATIONS ON THE USE OF ARTIFICIALLY
GENERATED ACCELEROGRAMS
3.1. Calcula tion methods
Several procedures have been proposed for determining the floor spec-
tra:
- app roxi ma te m ethod of t he Biggs'.type (J. Bigg s, SMIRT-1, pap er K 4/7,
1971).
- time-history analysis.
- pr obabil ist ic methods (Singh & Ang, SMIRT-2, pa per K 6/1, 1973 or Scania n &
Sachs, Keswick 1978, for ex a m p le) .
C__._3_.l_.
Which of these are r egarded a s a ccepta ble in your country?
3.2. Combination rule for non-symmetric structures
For a non-symmetric structure, the motion in each direction will con-
tain a contri but ion from each of the three components of the seism ic excita tion
(2 horizontal + 1
v e r t i c a l ) .
R.G.1.12 2 st ipu lat es that, if the effect of each of
these components is analy sed s epara tely, the correspondin g ordinates of the floor
spectra should be combined acc ording to the SRSS ru le. A three-dimensional an a-
lysis of the structure subjected to a simultaneous excitation in the three direc-
tions will use statis ticall y independent time-histories ( C. Chen, proc. ASCE,
ST2,
pp . 449-551, 1975).
__.3^__.
Is a similar rule applied in your country?
3.3. Number of ti me-histories - Duration
_._3.3_.__.
- Is there a recommendat ion concerning the min imu m num ber of. st at is ti -
cally independent tim e-histories (of a spectru m enveloping the design
spect rum ) to be used for g enerating floor spectra?
0_3_3___ - Is there a rec omm end at ion con cer ni ng the min im um du ra ti on of t he a c c e-
lerograms to be taken into account in a time-history analysis (C.W.
Lin, SMIR-4, paper 1/11, 1977)?
3.4.
Spectrum broadening
In order to take into account the uncertainties in the properties of
the mat erial and in the models (see for examp le, B.J. Benda et a l. , NED 67, pp .
109-123 (1981)), the computed spectra are smoothed and broadened.
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The USNRC imposes the following broadening (R.G.1.122)
A f .
=
J
r
(0.05 f.)
2
+ ) (. )'
n=l
/2
(3.4)
wit h a minimum of 0.1 f.. In this formul a, Lt . is the amount of broadening
to be applied (on both sides of f.) ; A f j
n
represents the variation of the
j-th natural frequency resulting from the uncertainty on the n-th parameter; the
sum extends over all possible parameters affecting the structural response. The
foregoing procedure can be avoided providing a peak broadening of + 0 . 1 5 f .is
applied.
0;.3_.4_. Is a simi la r r ule appl ied in your c ount ry? If no t, wha t is the curr ent
rule?
3.5. Account of uncertai nties in a time-history analysis
In the case of a syst em analysis by the time-history metho d, the SRP,
Section 3.7.2.
(II.9),
rec ommends that account be taken of the uncertainty in the
properties of the mat erial and in the structure model by using the same values of
acceleration but for several values of the time step (N.C.
TSAI,
Transformation
of Time Axes of Accelerog rams, Proc. ASCE , Vol. 95, EM3, pp. 807-812,
(1969)).
At lea st, the follow ing three values of the time step shall be considered: At and
At(l + ./f . , where f. is the dominant frequency of structural response
Hoc
r
or the floor concerned and
represents, as in the foregoing section, a
measure of the uncertainty on f.. If, in addition, one of the frequencies of
the equipmen t, f lies withi n the range f. + f., the time step
At[l - (f -
AltA will also be considered.
An alternative to this method consists in generating artificially an
accelerogram which would be consistent with the broadened spectrum mentioned in
the preceding section.
Q.3.5. What procedures are permitted in your country?
4. APPROXIMATE METHODS
4.1. Analysis method for multiply-supported equipments
As an alternative to the time time-history analysis [see, for example,
Leimbach, NED 51, pp. 245-252, (1979) ; NED 5 7, pp. 295-307 (1980) ; C.W. Lin &
F. Loceff, NED 60, pp. 347-352 (1980)], Section 3.7.3.(11.9) of the SRP recom
mends the following conservative approach for the response spectrum analysis of
multiply supported equipments with distinct inputs.
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(a) Use a response spectrum which is the envelope of the individual spectra at
the various supports and analyse the structure assuming that the motion is
identical at all supports. This gives an estimate of the dynamic response.
(b) Analyse the structure statically, under the effect of the support maximum
relative displacements. These will either result from the response of the
supporting structure or will be conservatively computed from the floor res
ponse spectra. In the latter case, the maximum support displacement is
evaluated by means of the relationship:
S. - S / w
2
(3.5)
d a
where S is the high frequency asymptote of the acceleration spectrum (i.e.
the maximum absolute acceleration for the floor under consideration) and is
the fundamental frequency of the supporting structure. The relative displa
cements are combined in the most unfavourable manner.
The dynamic and static responses are then combined using the absolute
sum method. Stresses associated with the differential support displacements are
to be considered as secondary in the ASME sense.
.4_.__.
Is a similar rule applicable in your country?
4.2. Equivalent static load method
The dynamic response of systems can be estimated in an approximate and
generally conservative way (see, for example, J.D. Stevenson & W.S. Lapay, ASME
paper 74-NE--9) by a static analysis performed with an acceleration of 1.5 times,
the maximum ordinate of the acceleration spectrum for frequencies larger than the
system's first natural frequency.
The combination of the dynamic response with the contribution from the
support differential motions has to be done as indicated in the previous section.
Q_.4_.2_.
Is a similar procedure accepted in your country? Which one?
4.3. Use of a static factor for the vertical direction.
According to Section 3.7.2.(11.10) of the SRP, an equivalent static
analysis is acceptable [in the vertical direction] if it can be proved that the
structure is rigid in this direction; that is if the first natural frequency of
the structure in the vertical direction is larger than the cut-off frequency of
the excitation (33 Hz in the US A) .
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C_.__.3_.__.Is a similar rule applicable in your country?
Q_.4_.3_.__.Wha t is the corresponding c ut-off frequency?
5. DAMPING
5.1. Reference values for the modal damping
Maximum damping values to be considered in the dynamic analysis of
structu res are recommended by the US NRC . These values depend on the type of
struc ture, the material and the types of joint. Two sets of values have been
defi ned, one for the SS E, one for the O BE , thus reflecting the fact that damping
increase s wit h deforma tio n ampl itu des . Thes e values are given in R.G. 1.61 (see
also Newmark B lume , Kapp ur, Proc. AS M E V ol. 99.P02, November
1973).
Damping
val ues larger tha n those giv en in the R.G. 1.61 may be used in the des ign,
pro-
vidi ng they are justifie d by experimental data .
C_.__.l_.l_. Are su ch st and ard va lu es use d in your co untry?
Q_.5_.l_.2 .
If t hey are d ifferent from those give n in the R.G. 1.61, what are they?
5.2.Damp ing val ues to use in a diiect integration method
The US NR C rec omm ends the us. of the R.G. 1.61 st andard d ampi ng valu es
for all modes considered in the dynamic analy sis . These values cannot be direct-
ly used in case of a di rect integration meth od where a full damping matrix is to
be used . It is common pratice to assume a Rayleigh damping (see, for example,
Bathe & Wilso n, Prentice
H a l l ,
197b, paragraph
8.3.3.
: in this cas e, the dam-
ping ma trix is a l inear combination of the mass and stiffness matrices :
C = + K (3.6)
The resulti ng matrix C can be diagonalized simultaneously with M and K.
Coe ffic ients and
ca n be determined in order to fit two modal danping val ues .
The major drawback connected with this procedure is that it leads to high
fre-
quency mode s considerably more damped than the low frequency modes for which the
constants were chose n. The refore, this leads to non conservative resul ts.
Q.._5.__. Is there a regulation in your country, concerning the use of Rayleigh
damping?
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23
5.3. Composite structures - C ombination of various modal d amping.
The systems involved in the seismic analysis of nuclear power plants
are often composed of substructures having different modal dampi ng. This is
particularly true for models considering soil- structure interaction. The fol low-
ing formula are recommended by the U SN RC (S RP , sect ion 3.7.2. (11.15)) for the
determination of the modal damping values of a composite structure. They result
from the use of the mass or stiffness matrices of the various subst ructures, as
weighing functions for the damping :
_, - i j
5
i i
( 3
7
>
d_ K d
.
~ (3.8)
where _ is the i-th modal damping of the composite structure;
dj is the i-th M- normali zed eige nmode (eig enmode normalized with
regard to mass
matrix);
and M are the modified mas s and stiffness matrices constructed f rom
the substructure matrices by multi plying them by the co rresponding
modal damping;
is the assembled stiffness matrix.
In the case of a direct integration method with Rayleigh damping, the
damping matrices of the various parts of the structure can be calculated from
(3.6),
comp uting the and
coefficients in order to fit two of the modal da m-
ping values for the corresponding subst ructure. The assembled damping matrix is
no longer simultaneously diagonal with the mass matrix. As already mentioned,
this method has the drawback of overdamping the high frequency mo de s.
Of all the approximate methods, equation (3.8) leads to results that
are the closest to those of a more sophisticated method based on the use of sub-
system modal properties to evaluate the damping matrix of the complete structure
(see K.
Koss,
Element Associated Damping by Modal Synthesis, Water Reactor Sa fe-
ty Conference, Salt Lake City, 1973). The damp ing mat rix obtained by t h latter
method is also not simultaneously d iagonal with the mass matrix.
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Q.5.3. What are the procedures accepted in your country for treating structures
composed of substructures having different modal damping?
C_._3.___.J_. In case of a modal superposition method?
Q.5.3._2_.
In case of a direct integration method?
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25
I I I .
SYNTHESIS OF NATIONAL ANSWERS
1II.O.
Introduction
Based on the national answers to the questionnaire, gathered in the
appendix, a tentative synthesis has been made.
The subdivisions of the questionnaire and the various national.repprts
have been adopted.
Proposals are also made to continue and complete the present study.
The following abbreviations are used:
F France
GB Great Britain
D Federal Republic of Germany
I Italy
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III.1.
Ground mot ion
1. Sa_fej_y_l_2vels
1.1. Philosophy leading to the establishm ent of two safety levels :
51 = OBE in American terminology
52 = SSE in American terminology
General ly spea king , the reference earthquake S2 is the only one to be
defined by safety conside rati ons. In all the countries considered, it is defined
in agreement wi th the American SSE philosophy ; it is the maximum hypothetical
eart hquake, taking into account the geological site conditions. For this earth
quake,
it must be possi ble to shut down the reactor and cool it in order to keep
it in a safe shutdown c ondition. This earthquake may not entail any significant
release of fission gas outside the plant.
Earthquake SI represents the normally acceptable earthquake (D,F,I),
that is to say the one that can be borne by the plant without any significant
dam age . It can be defined as the historical earthquake of the highest intensity
(D).
It is frequently defined as being 1/2 S2 (F,I). In Great Britain, an
eart hquake of very low intensity is defined (0.05 g ) ; it is not used at all in
the desig n. Shutdown and a new analysis be fore restart would required if it were
to be exceeded.
1.2. The reference earthquakes are generally defined on a deterministic
basis. Probab ilitic meth ods are generally only accepted as back-up to a dete rmi
nistic analysis (exception : D ) . The probabilities per annum of it being exceed
ed have been quoted as follows :
D
GB
S2
I O
4
( SN R : 3 I O
- 4
) *
1
S I
1 0 - 3
( SN R = 8 I O
- 4
) *
-
*A posteriori calculations.
2 .Maximum __ro_und__acjce_lej:a_t__o__.
2.1 . In some cou ntr ies , a lower bound is specified for the maximum ground
acceleration at the time of an earthquake S2 (see
Table).
2 . 2 .
The maximum acceleration of earthquake S2 is , in principle, defined on
a site-dependent basi s. In some countr ies, however, for the sake of simplicity
and sta ndardization, a single acceleration is defined (GB).
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3. Re__p__n__e_spe__trum
I The R.G. 1.60 spect ra are appl icab le for grounds whose natural freq uen-
cy verifies 3 f 9 H z. A proposal is being studied to modify the lowfre-
quencies spectra for soft ground.
F In principle, the spectra are site dependent. In practice, an envelope
spectrum is used for several sites . This spectrum is different from that
defi ned in R.G. 1.60. The vertic al spe ctrum = 2/3 horizontal sp ect rum.
GB Standard spect ra have been defined for three types of ground. The
vertical spectrum is equal to 2/3 of the horizontal spectrum.
D For SNR , Housner's average spectrum has been used ; the questi on re-
mains open for the future : site-depe ndent shapes or standard shapes which
may or may not be those of the R.G. 1.60.
4.
Du__a__ion
GB The following durations are used for articially generated acce lero-
grams :
soft ground 13 s
medium 12 s
hard 11 s
The minimum duration for q ualific ation tests is 6 s for AGR and 10 s
for PWR.
I Not specified by the safety auth orities . For the mechanical calc ula-
tions,
it is comp rised between 15 s and 30 s.
For PE C, the following numbers of cycles are used:
- 10 cycles corresponding to the S2 peak val ues ;
50 cycles corresponding to the SI = 1/2 S2 peak valu es .
F No formal rule. For SP X1, the durati on has been fixed at 20 s.
D For SNR , the strong motio n period is set at 8 s. In the futu re,
the
duration will be shorter and site- dependent.
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DEFINITION OF GROUND MOTION FOR SI AND S2 EARTHQUAKES
Definition of SI
Minimum value of
a
ma x
f o r s 2
Way of defining
the maximum
acceleration for S2
Response spectrum
Relation between the
vertical spectrum and
the horizontal spectrum
Duration
GB
a
max.=
5
g
not used in design
-
Standard value*: 0.25 g
Standard shapes defined
as a function of the
soil conditions
2/3
11 - 13 s
Ground dependent
F
1/2 S2
o.i g
Site-dependent
So far, envelope
standard values are used:
0.15 g - 0.2 g **
Site-dependent
So far, envelope
spectra have been defined
for several sites
2/3
SPX1 : 20 s
I
1/2 S2
0.18 g
Site-dependent
PEC = 0.3 g
PEC : Housner. Future :
RG 1.60 for the grounds
whose natural frequency
verifies
3 < f < 9 Hz
PEC : 2/3
Future : RG 1.60
15 - 30 s
D
SNR = 0.5 m/s
2
0.5 m/s
2
Site dependent
SNR =1.2 m/s
2
SNR: Housner
In the future, site-
dependent or standard
shapes
1/2
SNR : 8 s
00
*Could become site dependent (0.20 + 0.05) g.
**Two standard shapes are used: one for Superphnix and the 900 MWe PWR's, with a corresponding maximum acceleration of 0.2 g
one for the 1300 MWe PWR's,with a maximum acceleration of 0.15 g.
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I I I .2.
Seismic classification of components - Safety provisions - Dimensional
criteria
A. FUNCTIONAL CRITERIA
A.O.
Official documents
General_
__emark
No official regulations applicable to fast reactors in general exist
at the present time. Safety prescriptions relating to earthquakes are defined
for every reactor, generally on the basis of the operator's proposal. They are
usually included in the safety reports issued for the reactor.
In some countries
(F,D),
there exist official regulations applicable to
pressurized water reactors.
A.l.
Functional requirements after a SI earthquake
_lj_ssi cal _~riteria
Subsequent operation of the plant must be possible without any inspec
tion of the safety related components.
Emissions of radioactive products must remain below the limits imposed
during normal operation.
__xcet__o__s_v__r__an^s_:
GB There is no SI earthquake in the standard sense. There exists a low
intensity earthquake (OSE) beyond which the reactor must be shut down. It
must be inspected before any new start-up.
D The possibility of a restart without inspection is not required. The
criterion failure, which must be foreseen is specified
(SNR-300).
Other
minor differences.
I An inspection is required before restart. The radiological risks in
curred by the operating staff cannot exceed the normally acceptable limits.
F No damage is tolerated to parts which cannot be inspected or repaired.
For other parts', damage must remain extremely low.
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. 2 . Functional requirements after an earthquake S2
Classical reguiremen_ts:
Devic es with a safety function must be designed to withstand earthquake
S2 and must continue to function.
The fo llowing systems have a safety function :
1. devices necessary for reactor shutdown and maintenance of safe shutdown condi
tion (including equipment ensuring core cooling and residual heat
evacuation);
2 . devices designed to prevent or limit releases of radioactive material, which
could result in an accident or would be dangerous for the population.
Ad ditio_n__l_r__q__i__ement__ :
G B :
Add to the list of sy stems having a safety function :
3. devices ensuring containment of radioactive material.
D: Additional requirement s:
. to prevent radio activ e releas es which would prohibit access to reactor
building;
. to fulfil the above mentioned conditions without manual intervention for 10
hours;
. to foresee fai lure of an active componen t and the unavailability of compo
nents which undergo maintenance during reactor operation.
I: Add to the list of systems with a safety function :
3. devices ensuring containment of highly radioactive material;
4 . the sodium envelope.
F: Safe shutdown conditio ns imply :
. no leaks in active circuits (including inside the reactor
b uilding);
. no water sodium reaction;
. no out of control sodium fire.
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. 3 .
Equipment which must remain functional after an S2 earthquake
The comparison of answers is made difficult because of the fundamental
design differences between the fast breeders developed in the various countries.
We will limit ourselves to indicating the equipment which cannot be
immediately associated with a fundamental functional requirement and wh ich , n e
vertheless, is designed to continue to function or to remain leaktight after S2 .
F(R1): The primary pumps are designed to operate after an S2 earthquake, the
secondary pumps are not .
The handling system is designed to withstand an S2 earthquake.
The secondary circuits are designed to withstand an S2 earthquake.
The steam generators are designed to withstand an S2 earthquake.
D(R1): Primary pumps are designed to operate after an S2 earthquake.
The secondary circuit parts external to the reactor building are not d i
mensioned- for earthquake S2 _they are designed to withstand an SI ear th
quake
.
The part of the handling system inside the reactor building is designed to
withstand earthquake S2 (the part of the handling system outside the reac
tor building is designed to withstan d an SI
earthquake).
GB:
Primary pumps are designed to operate after an S2 earthquake.
The handling system is designed to operate after an S2 earthquake.
The secondary sodium envelope is designed to withstand an S2 earthquake
(the aim is to avoid sodium fires and sodium-water
reactions).
I: Primary pumps are designed to operate at reduced rate after an S2 ear th
quake.
The fuel element transfer machine is not dimensioned for earthquake S2 .
However, its collapse must not damage the core and its replacement must be
possible.
These results are summarized in Table Al .
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Remark:
It seems that, in general, three types of earthquake-related require
ments may be distinguished:
- a system or component may be required to remain functional (during and) after
the earthquake;
- a system or component may be required to retain its leaktightness (during and)
after the earthquake;
- finally, a system or component may be required to resist collapse (because of
the consequences of this collapse on equipment having a safety
function).
However, the consequences of this distinction on the mechanical design
are not always clear. This subject is covered in paragraph 3.8. of the KTA
2201.4 standard, as well as in the various countries'answers to question C.2.4.
A.4. Containments that must remain tight after S2
The only containment barriers considered here are those of radioactive
core material. Comparison between the various reactors is difficult (see table
A2).
Nevertheless, the following conclusions can be drawn:
1) The first barrier (except fuel rod cladding) is always the envelope of the
primary circuits. It is always designed to remain leaktight after an S2
earthquake.
2) There is always a second barrier remaining leaktight after an S2 earthquake.
This barrier is not always metallic.
A.5. Earthquake detection - Planned actions
Earthquake detection is planned in all countries.
There is a German standard which defines the detection system in de
tail (KTA 2201.5).
Exceeding a threshold always entails reactor shutdown. According to
the country, the shutdown type is either an automatically triggered emergency
shutdown or a normal shutdown controlled by the operator as a response to an
alarm triggered by the earthquake detection system.
A more complete comparison is given in Table A3.
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. 6 .
Functional consequences of an earthquake to be considered
The principl es seem clear : it is necessary to consider:
- emergency reactor shut down (triggered by the earthquake detection system or by
a condition resulting from the earthquake detected by the reactor safety
system);
- loss of external electricity supplies;
- collapse of component whi ch has not been shown to withstand earth quakes;
- unavailabilit y of systems whose functi oning (during an d) after the earthquake
has not been demonstrated.
Application of these principles in the various countries is compared in
T a b le A 4 .
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TABLE Al - EQUIPMENT WHICH MUST WITHSTAND EARTHQUAKE S2 *
Primary pumps designed to
operate after S2
Secondary pumps designed to
operate after S2
Secondary circuits and steam
generators designed to
remain leaktight after S2
Fuel element handling system
designed to operate after
S2
D (1)
X
0
(2)
(2) (4)
F (1)
0
GB
0
(3)
(5)
(5)
(3)
0 (6)
* Only components for which a doubt may exist are mentioned in
this table.
(1) Answers relating to reactor under construction Rl (SUPERPHENIX,
SNR-300).
(2) Only the part insid e the reactor building is dimensioned for S2 ;
the part outsid e the reactor bui lding is designed to withstand SI,
(3) Only the sodium envelope (not the argon
circuits).
(4) Operation not required.
(5) Operation at reduced rate.
(6) Replacement of the fuel handling system must be possible.
X = yes .
0 = no.
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TABLE A2 - RADIOACTIVE MATERIAL CONTAINMENT BARRIERS
Primary circuit envelope
(sodium + gas)
Double walled primary
circuit (+ dome)
Wall of primary cells
(metal clad)
Reactor building
Safety metallic shell
D(l)
S2
S2
SI
F(l)
S2
S2
GB
S2
S2
I
S2
S2 (2)
S2
(1) Answers relating to reactor Rl (SNR-300,SUPERPHENIX).
(2) Reduced leaktighness is accepted after S2:
51 = dimensioned to remain leaktight after SI.
52 = dimensioned to remain leaktight after S2.
? = answer not supplied.
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TABLE A3 - DETECTION OF EARTHQUAKES AND ASSOCIATED ACTIONS
Earthquake detection requi-
red
Shutdown (A: automa tic,
M: manual)
Shutdown (E: emergency,
N:normal)
Threshold
Required inspection
D
X
M
N
s 0.25 S2
X ( D
F
X
A (1)
E (1)
X
GB
M
(1)
s 0.25 S2
X (2)
I
X
A (1)
E
S 0.5 S2
X
(1) Interpretation of answers supplied.
(2) An instrumentation is planned in order to assess the state of the
plant before restart.
X yes.
? = answer not supplied.
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TABLE A4 - CONSEQUENCES OF EARTHQUAKE S2 TO BE TAKEN INTO ACCOUNT
Loss of external electricity
supplies
Emergency shut down of
reactors
Loss of water flow to steam
generators
Leakages of slightly radio
active products
Sodium circuit leaks
Water/steam leaks
D
X
X
X
X (D
X (D
F
0 (2)
0 (3)
(1)(4)
GB
0
0
(1)
-
0
0
-
(1) External to reactor building .
(2) The design of the nuclear boiler system is such that no radio active
leak must result from the earthquake.
(3) Rl : the design of the boiler system is such that no sodium leak
must result from the earthquake;
R2 : not yet decided (small leaks in auxiliaries ? ) .
(4) Inside the reactor and steam generator build ing, steam and water
pipes are designed to withstand earthquake.
X = to be taken into account,
0 = not taken into account.
- = not relevant.
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. EARTHQUAKE CLASSIFICATION IN OPERATING CONDITIONS
B . l .
Categories of operating conditions
In all co unt rie s, four categories of operating conditions are defined;
they are designated:
- category 1: normal conditions;
- category 2: upset condition s;
- category 3: emergency conditio ns;
- category 4: faulted conditi ons.
These categories are not defined in a precise way:
- categor y 2 conditions ofte n correspond to transient states ;
- category 3 conditions correspond to exceptional circumstances which have to be
taken into consideration;
- category 4 conditions correspond to hypothetical failures of equipment.
. 2 .
Combination of SI and classification of combined conditions
Co__d__t__ons_to c_ombine with__S1_
The pri nciple s seem clear : it is necessary to combine:
- the initial conditions;
- the earthquake;
- the possible consequences of that earthquake (cf. A 6 ).
Usually, all conditions in categories 1 and 2 are considered as possi
ble initial co nditi ons. The conditions whose total duration is low are an excep
tion : such situations are not considered as possible initial conditio ns, or else
the corresponding combined conditions are classified in a different way (i.e.
analysed with less severe
criteria).
Remark : The same remark as in point B3 is applicable here.
l_is__ifica__ioji_ojf omb__ne_d_cc_nd_i__i__ns_
T he c o n d i t i o n s r e s u l t i n g fro m t h e c o m b i n a ti o n s a r e c l a s s i f i e d i n t h e
s e c o n d o r i n t h e t h i r d c a t e g o r y d e p e n d i n g on t h e c o u n t r y .
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.3.
Combi nation of S2 and classifi cati on of combined conditions
C_ondi_t__or_s_to_ __omb__ne_
w
_iJ^h_S2^
Here as w e l l , it is necessary to combine:
- the initial conditions;
- the earthquake;
- the possibl e consequenc es of that earth quake (cf. A . 6 . .
Usually, all conditions in categories 1 and 2 are considered as possi
ble initial cond itions . The conditions for whic h total duration is low are an
excep tion: these conditions are either not considered as possible initial condi
t i o n s , or the corre spond ing combined co nditio ns are analysed off desi gn (fifth
c a t e g o r y) .
Remark :
An elegant s oluti on consist s in using integr ated du ration as a cr it e
rion distinguishing upset conditions from normal operating conditions and to
impose only, as initial con ditio ns, normal operating conditions.
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TABLE Bl - CLASSIFICAT ION OF EARTHQUAKE SI
Category of operating condi
tions resulting from
earthquake SI
Category of operating condi
tions which must be com
bined with earthquake SI:
- categories
- exception for operating
conditions with a small
cumulated duration
- special cases:
.normal handling
.exceptional handling
D
3
1 + 2
X
X
X
F
3
1 + 2
(2)
GB (1)
-
-
-
-
I
2
1 + 2
(3)
(1) Earthquake SI has no influence on plant design.
(2) Rl : the classification of combined conditions depends on the total
duration of the handling operations considered.
R2 : these combined conditio ns are analysed off des ign .
(3) The classif icatio n of combined conditions depends on the total dura
tion of the handling operations considered.
X = yes .
- = not relevant.
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TABLE B2 - CLASSIFICATION OF EARTHQUAKE S2
Classification of operating
conditions resulting from
earthquake S2
Categories of operating co n
ditions which must be
combined with earthquake
S2:
- categories
- exceptions for opera
ting conditions having
low total duration
- threshold (total dur a
tion limit)
- special cases:
.normal handling
.exceptional handling
D
4 (1)
1 + 2
?
X
0 (3)
F
4
1 + 2 (1)
? (2)
0 (2)
GB (1)
4
1
0
-
4
1 + 2
?
0
(1) Interpretation of answers received.
(2) On RI, the threshold is determined by probabilistic calculations
On R2 , exceptional conditions are not analysed off design .
X = yes .
0 = no.
? = answer not supplied.
- = not relevant..
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C. CLASSIFICATION OF MECHANICAL COMPONENTS
C.l. Safety classes
There is no general rule :
F: Three safety classes exist in addition to unclassified equipment.
I and
D(R1):
the safety class concept is not used. On the other hand, a quality level
(equivalent to ASME code class) is attributed to components.
D (KTA) and perhaps GB:
The safety class concept is not used. Standards are established per compo
nent type rather than per quality level.
C.2.1.
Seismic classes
There is no general rule.
F(R1) and D(R1):
There exist three classes :
- equipment to be designed to withstand SI ;
- equipment to be designed to withstand S2;
- equipment not designed to withstand earthquake.
I: There exist three classes :
- equipment with a safety function;
- necessary equipment with in the long run a safety function (equipment ne
cessary for a long duration operation in safe conditions)(see Italian ans
wer for more details in appendix of the french version of this report).
- equipment not designed to withstand earthquake.
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GB: There exist four classes :
- systems which must function after earthquake S2;
- components not required to function after S2 but for which structural inte
grity and leaktightness must be ensured;
- components not designed for earthquakes;
- buildings and systems for handling and storing radioactive material.
D
(KTA):
There exist two classes :
- components with a safety function. These components must be capable of
operating after several SI occurrences. They must ensure their function
after one S2 earthquake;
- other components; it must be demonstrated that no component with a safety
function will be damaged by collapse or malfunction of the other compo
nents.
C.2.2. Relationship between component classification design criteria
The design criteria used during seismic stress analysis depend on the
requirements applicable to the component and on its accessibility.
Rules differ from one country to another: they are compared in Tables
CI and C2 and discussed hereunder.
Special
f_u__c__ions
In some countries, systems ensuring some specific safety functions are
subjected to more severe criteria during seismic analysis.
For example, in Great Britain, components ensuring reactor shut-down,
core cooling, residual power evacuation, and so on, are dimensioned for S2 with
special criteria. On the other hand, components ensuring a containment function,
are dimensioned with normal criteria (level D ) .
In other countries, there is no distinction between safety functions.
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__c__i__e_c__mp_onent_^
Active components are sometimes subjected to special criteria:
- Are called active , components which are not static in performing their safety
function (pumps for which an operation is required, valves which must change
state, etc.).
- A demonstration of the correct operation of such equipment after the earthquake
is often required . This demonstration can be experimental (tests or trials).
In some countries, this experimental demonstration can be avoided by
using more severe design criteria.
(_ompo ne n__s_f_ r_wl_i_;h_c_ ll_ap_se_ must be_ avoided
In some cases, less detailed analyses are permitted when it is only
the collapse of the components which must be avoided.
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TABLE Cl - COMPONENT CLASSIFICATION AND DESIGN CRITERIA FOR SI
Level of criteria relating
to SI (principle)
Distinction accessible/not
accessible:
- applicable
- overclassification not
accessible
Distinction active/passive:
- applicable
- overclassification
active
D
RI KTA
C
0
0
(2)
F
C (4)
(5)
C (4)
(5)
C (4)
GB (1)
-
I
(1) Earthquake SI does not influence the plant design.
(2) An additional analysis of the possible causes of malfunctioning
is required.
(3) Level criteria are imposed, except if it is demonstrated that the
function remains assured.
(4) Rl : C;
R2 : probably C.
(5) Distinctions accessible/not accessible or active/passive have no
consequences on the level of criteria, but affect the class (quality
level) of the component. As an example, inaccessible components are
always class 1.
X = yes.
0 = no.
- = not relevant.
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TABLEC2 -COMPONENT CLASSIFICATIONANDDESIGN CRITERIAFOR S2
Criteria level relatingto
S2
( withstand )
Distinction special func
tion :
- applicable
- overclassification
Distinction active/passive:
- applicable
- overclassification
Distinction( withstand /
collapse avoided):
- applicable
- underclassification
Rl
0
X
(3)
X
(5)
D
KTA
D
X
B/C
(1)
0
-
X
(6)
F
D
(7)
(7)
GB (1)
D
?
0
-
0
I
D
(2)
B/C (4)
0
(1) This overclassification
is not
required when
a
strain analysis
demonstrates correct functioning.
(2 ) A strain analysisisrequired.
(3)
An
additional analysis
of the
possible causes
of
operational failure
is required.
(4) Level
criteria
are
imposed, except
if it is
demonstrated that
the
function remains ensured.
(5) More simple criteria
are
used.
(6) Reduction
of
design effort
as a
function
of
risk
to be
taken.
The
designof thesupportsand thebucklin g analysisareunchanged.
(7) Anadditional analysisisrequired,inordertodemonstrate that
components subject
to
additi onal functional requirements after
S2
are abletomeet them. This analysisisspecifiedon acasetocase
basis. Design rulesdo notensureanyfunctional guaran tee.
X
= yes.
0
= no.
-
= not
relevant.
?= answernotsupplied.
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D. MECHANICAL DESIGN CRITERIA
D.I.
Design codes used
The ASME III code (subsections + code cases ) still is the joint refe
rence code.
In some countr ies, national codes have been drawn up for the design and
construction of pressurized water reactors .
D . 2 .
Classification of design criteria
Criteria levels A,B,C,D of ASME code section III are generally used for
the design of mechanical components with a safety function.
In France, levels A and are grouped together.
D.3.
Relationship between categories of operating conditions and levels of cr ite
ria
With regard to earthquakes, this topic has been analysed in paragraphs
C.l. and C.2 .
D.4. Fatigue analysis
Analysis of earthquake induced fatigue is required by some countries .
Table Dl compares the data gathered.
E .TRANSMISSION OF SEISMIC LOADINGS
Depending on the country, seismic loadings are part of the general
design specification or are dealt with in special specifications.
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TABLE Dl - ANALYSIS
Fatigue analysis required
Number of SI earthquakes
Number of cycles/Si earth
quake
Number of S2 earthquakes
Number of cycles/S2 earth
quake
Are the aftershocks taken
into account ?
OF EARTHQUAKE INDUCED FATIGUE
D
RI KTA
SI 0
1
10-15'
-
? -
? -
? -
F
RI R2
?
?
1
(D
0 ?
GB
0
-
-
-
-
-
I
5
10
1
10
(1) Fatigue analysis not required for S2,
X = ye s.
0 = no .
? = answer not supplied.
- = not relevant.
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III.3. Seismic analysis methods
With the exception of Germany (KTA
2201.4),
no written rules exist re
garding seismic analysis methods. Consequently, answers refer to current practi
ces rather than to rules in the real meaning of the word. The analysis procedu
res are in principle the result of an agreement between equipment supplier and
safety authorities; the trend Is towards using more refined analysis methods for
more sensitive equipment, for which the excessive degree of conservatism of the
seismic analysis methods may constitute a functional hindrance (excessive rigidi
ty, too many snubbers,
. . . .
1. Rules used in connection with the modal superposition method
1.1. orab__ntion of modal __r eeoo ns es
F: SRSS (square root of sum of
squares),
without considering interaction of
closely spaced modes.
D:
SRSS below cut-off frequency, without special modification to tak int ac
count interaction closely spaced modes.
GB :
SRP 3.7.2 practices are acceptable (formula (3.1) of questionnaire).
I: RG 1.92 is used. The CQC* method (Complete Quadratic Combination) la also
used.
To the authors' knowledge, the CQC method represents the first attempt
to rationally take into account the correlation between closely spaced modes. It
is based on the hypothesis that the correlation coefficients of the various medal
responses to a wide band excitation may be approximated by those of the stationa
ry response to white noise**.
*E.L.
Wilson, A. Der Klureghian & E. Bayo, A Replacement of the SRRS Method in
Seismic Analysis , Earthquake Engineering and Structural Dynamics, 9, 187-192
(1981).
**See also: A. Der Klureghian, Structural Responses to Stationary Excitation ,
Proc. ASCE, Vol.
6,
6, pp. 1195-1213, December 1980.
. Der Klureghian, A Response Spectrum Method for Random Vibration Analysis of
MDF Systems , Earthquake Engineering and Structural Dynamics, Vol. 9, 419-435
(1981).
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1.2. __omb__natio_i of_the_tliree_Sa_ti
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3. Determination of floor spectra, considerations on the use of artificially ge
nerated accelerograms
3.1. The time history method is the most popular of the methods in use . It
is the only method accepted in Great Britain. In other countries (D.F.I),
direct or probabilistic methods are accepted subject to appropriate valida
tion*.
3.2.
The spatial components combination rule was discussed In paragraph 1.2.
In the case of a time history analysis, accelerograms used in the ,,
directions must be statistically independent.
3.3. With regard to the use of artificially generated accelerograms, rules
exist in Germany on the agreement between the accelerogram spectrum and the
sig
spectrum. Most often, a single set (I) or two sets (GB ) of accelero
grams are used for the calculation**. The duration of artificially generat
ed accelerograms was discussed in the chapter on Ground motion .
3.4. A spectrum-broadening procedure similar to that described in RG 1.122
is most often used (+_
15Z)(F,I,GB).
It may or may not take Into account the
uncertainty of soil properties. The latter is particularly significant for
soft soils ( D) and was the only one to be taken Into account for SNR-300
3.5. When taken into account in a time history analysis, uncertainties on
structural properties are either treated by a procedure similar to the SRP
procedure described in the questionnaire (F ), or included in the accelero
gram by generating the latter on the basis of a broadened spectrum (G B ).
*It may be interesting to mention a recent study devoted to the direct determina
tion of floor spectra including interaction between equipment and supporting
structure: J.L. Sackman, A. Der Klureghian & B. Nour-Omid, Dynamic Analysis of
Light Equipment in Structures : Modal properties of the Combined System , Proc
ASCE, V ol. 109, EMI, February 1983, 73-89.
A. Der Klureghian, J.L. Sackman, B. Nour-Omid, Dynamic Analysis of Light Equip
ment in Structures : Response to Stochastic Input , Proc. ASCE, Vo l. 109, EMI,
February 1983, 90-110.
** A. Kurosakl and M. Kozekl : Statistical Uncertainty of Response Characteristic
of Building Appendage System for Spectrum Compatible Artificial Earthquake Motion.
SMIRT-6, Paris (1981),Paper K7/ 7.
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4 Approx ima te me thods
4.1. E_quij_ment wi__h_mulj_ip_le supports
The SRP practice described in the questionnaire is generally applicable
in the countries considered (GB,F,I,D) but with differences regarding treatment
of the stresses resulting from the relative displacements of the supports (D) .
Multiple support modal methods are also used in several countries (I,D,F)*.
4.2. Equivalent_s_tat_ic me__hod
The approximate procedure described in the questionnaire is generally
applicable (F,I,D) to small diameter circuits or to circuits of little importance
(cold
piping).
The coefficient changes from 1 to 1.5 as a function of the model-
lization (1 or several degrees of freedom)(I) or of the structure type (D ); it is
reduced to 1 if the first frequency is above the cut-off frequency.
4.3. _5_ta_ti_c_fc_to foj_ vert_Lcal_d___recti on
A static analysis is generally allowed for the directions in which the
structure can be considered as rigid (first natural frequency cut-off frequen-
cy)(F,GB,I,D).
The acceleration used is the spectrum asymptotic value, without
any increase factor.
*It may be of interest to mention recent studies: A. Der Kiureghian, A. Asfura,
J.L. Sackman & J.M. Kelly, Seismic Response of Multiple Supported Piping Sys
tems , SMIRT-7, paper K7/ 7, Chicago 1983.
M.C.
Lee & J. Penzien: Stochastic Analysis of Structures and Piping Systems
Subjected to Stationary Multiple Support Excitation , Earthquake Engineering
Structural Dy namics, Vol. 11, 91-110
(1983).
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5. Damping
5.1. Reference _va_lues__fo_r_m__d__l__d__mp_ing
Standard values of modal damping are generally applicable (F,GB,I,D).
They are mostly identical to those of RG 1.61 (F,GB,I). Higher values can be
used, subject to adequate experimental justification.
5.2. D_i__ect_integraj_i on
Direct integration is rarely used in seismic analysis. An analysis in
the modal basis is often preferred, because of the low frequency content of the
excitation. However, when Rayleigh damping is used, the and coefficients
must be chosen in such a way that all significant modes have a modal damping
lower than the limits fixed in RG 1.61 (GB,I).
5.3. Composi_te j truc.tu.r
s
The SRP procedure outlined in the questionnaire is generally applied
(F,GB,I,D). Formula (3.8) is often preferred to formula (3.7)(F,I).
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IV. PROSPECTS AND FURTHER DEVELOPMENTS
IV.1.
Part common to all types of reactors
It was found necessary to limit this study to the traditional aspects
of the seismic calculation methods for nuclear reactors not only because of the
broad scope of the subject, but also because these traditional aspects are the
only ones to be standardized in codes or official documents and, hence, the only
ones which may be systematically compared.
This report indicates a great similarity between the various European
countries: with regard to the methods, especially in the areas which are not
contested, and with regard to preoccupations as far as more controversai issues
are concerned.
Some of the topics that still remain open are, in our opinion:
- The SI earthquake definition (does earthquake SI have a safety function?).
Three functions can be attributed to it :
(i) to remedy the insufficiencies of level D criteria;
(ii) to define the earthquake beyond which it is necessary to shut down the
reactor;
(iii) to define the earthquake beyond which inspection Is required.
- The integration of seismic rules in design rules:
Is it necessary to add a seismic classification to the safety classifi
cation?
Does a basic difference exist between the earthquake and the other
reference accidents (possibility of common failure
modes?).
- The effect of functional requirements on the design criteria (active compo
nents, leaktightness assured, collapse avoided).
I s this distinction justified? What are the consequences for design?
- Conditions which must be combined with earthquakes:
What are the operating conditions (handling, for example) during which
the occurrence of an earthquake must be considered? The answer could result from
an overall risk analysis.
A substantial improvement of the calculation methods should result from
the application of random vibration theory. As examples, we shall quote:
- The combination rules for closely spaced modes, a particularly important pro
blem in thin shells*. The CQC method (Complete Quadratic Combination)**,based
on the theory of random vibration in conjunction with reasonable hypo
theses,
offers hope of improvement in this field.
*I .
Elishakoff, A.Th. Van Zantem, S.H. Crandall: Wide-Band Random Axisymmetric
Vibration of Cylindrical Shells, J. of Applied M echanics, Vol. 46, p. 417, June
1979.
**E.L.
Wilson et al, op.cit. p. 49.
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- The application of the theory of random vibrations to the direct calculation of
floor spectra
1
and to piping calculation. In addition to taking into account
the correlation between the modal responses of closely-spaced frequencies, in
the latter case the method offers a unique possibility of taking into account
the correlation between excitations at the various supports*.
Finally, the following suggestions from the British experts seem of
particular interest :
1. Methods of analysis of soil-structure interaction should have been included in
the survey. Although the methods are not unique to the fast reactor plants,
such a survey has not been previously conducted with European countries and is
fundamental to seismic assessment of all types of reactors.
2.
Damping. Although the questionnaire was quite exhaustive, the answers were
insufficiently detailed (including my own ). This is regrettable since the
damping values are crucial to the outcome of the seismic analyses. It would
be worthwhile to follow it up with further enquiries to find out what damping
values are used for individual components such as cranes, steam generators,
heat exchangers, sodium pumps, fuel transfer routes, rotating shields, etc.
3. Design criteria - stress limits. Once again the answers were often superfi
cial, e.g. level D , where many different ways exist to satisfy this crite
ria.
This item is of a particular interest to WGCS-2 and should be followed
up if a co-operation of WGCS-2 members can be obtained.
IV.2.
Fast reactor characteristics
The following specific characteristics of fast reactors:
- thin walls resulting from low pressures;
- high temperatures and neutron flux entailing problems of material behaviour;
- severe thermal gradients and temperature fluctuations;
- structures of very large dimensions (especially in the pool concept) containing
large masses of sodium;
- presence of water and sodium,
B.J. Sullivan : A Method for Generating Floor Response Spectra through Power
Spectra/Response Spectra Relationship . SMI RT-7, Chicago (1983),Paper Ml/9.
*M.C.Lee, J. Penzien, o p.cit., p.52.