Introducing advanced ISI
Transcript of Introducing advanced ISI
Introducing advanced ISI requirements at
Paks NPP for supporting the LTO
P. Trampus1, S. Rátkai2 1Trampus Consulting & Engineering, Hungary
2MVM Paks Nuclear Power Plant, Hungary
3rd Int. Conf.
Nuclear Power Plant Life Management 14 – 18 May 2012, Salt Lake City, USA
Outline
• Paks Nuclear Power Plant
• Operational life extension project
• ASME BPVC adoption
• Regulatory framework
• Advanced ISI requirements
– General aspects
– Periodic NDE program
– Acceptance standards
– Pressure tests
• Economic benefit
• Summary
Paks NPP, Hungary • Hungary’s sole NPP
• 4 Russian design VVER-440s model 213
• Design life of the units: 30 years
• Expiration of design life: 2012 to 2017
• LTO: 20 more years
• Currently:
• license renewal of Unit 1 in progress
• other units under preparation for LTO
Overall LTO Strategy (1)
• Maintaining business interest of owner / operator
• Completing engineering work needed to
demonstrate safe LTO
• Performing work required by licensing procedure
Engineering and operational practice should integrate
• up-to-date knowledge on ageing phenomena
• vigilance through ageing management and condition monitoring
• ability to recognize unexpected
• application of best practice
• learning from experience
• consideration of VVER-440 features
• graded approach concerning SSC safety relevance
Overall LTO Strategy (2)
• All SSCs have to be covered by a specific plant
program (AM, maintenance, scheduled
replacement,…)
• Safety classified SSCs: programs should comply
with regulations
• Not safety classified SSCs: programs depend on
importance for power production
• All ageing processes should be considered
• All plant activities should be taken into
consideration (synergy of routine activities and
LTO specific ones)
KI < KIc or
Pt < 5∙10-6/y
Change in material
properties (e.g.
embrittlement)
Structural
integrity
assessment
Crack
propagation
(e.g. fatigue,
corrosion)
Decrease
in safety
margin
Loading,
environment
Material properties Flaws
Role of ISI
Goals for ASME BPVC Section XI Adoption
• To facilitate the implementation of
–ISI and IST,
–repair and replacement,
–strength and fracture mechanics analyses
•with state-of-the-art methods, and give the possibility
for their direct comparison with current methods and
requirements SAFETY GOAL
• To serve for the plant life extension
– technically (to make it possible the extension of current
4-year ISI cycle (Class 1 components) up to an 8-year
one COST-EFFECTIVENESS
–„politically” (to support international acceptance of life
extension)
Regulatory Environment
• Current ISI program differs from BPVC Section XI one – based on Russian normative documents (PK-1514; PNAE G-7-008
and 010)
– narrower in its scope
• Major elements: – periodic NDE
– in-service examination (structural examination) equivalent to VT-3
– system pressure test
• No single ISI document like Section XI, instead: – individual documents for various systems (Technical Inspection
Plans)
– NDE framework programs
– acceptance criteria
– NDE procedures (no regulatory license needed)
• Component classification do not show remarkable difference from BPVC Section III
Concept of Introducing Advanced ISI Requirements
• Keeping proven practice as much as possible
• Technical Inspection Plans replaced by ISI Programs
– keeping basic structure (proved in practice)
– integrating concept and requirements of Section XI
– more emphasis on ageing management
• In-service examination
– remains but supplemented by relevant examinations
• ISI interval:
– Currently 4 years for Class 1 components & piping and
Class 2 components; 8 years for secondary circuit
components & piping
– Future: 8 years (instead of 10 as of Section XI)
Periodic NDE
• Appropriate framework programs supplemented by
– IWB-2500 B-M-1 examinations (valve bodies)
– IWC-2500 C-C (welded attachments) and C-G
examinations (valve & pump casing welds)
• In-service examination supplemented by
– IWD-2500 D-A examinations (attachments of welded
components and pipes)
• NDE procedures (not bound by regulatory license)
upgraded to comply with BPVC Section V
• Inspection qualification (instead of performance
demonstration, Appendix VIII)
– requirement for current operating license
– European approach (ENIQ)
Subject NDE
Equipment
NDE
Procedure
NDE
Personnel
Qualifications completed
SG Primary Collector (mechanized UT) + +
SG Heat Exchanger Tube (mechanized ET) + + + *
RPV Welds, Cladding, Nozzle Inner Radius (simplified
mechanized UT from ID) + +
RPV Main Loop Nozzle dissimilar weld (simplified
mechanized UT from ID) + +
RPV Cladding (simplified mechanized ET from ID) + +
Main Loop Circumferential Weld (mechanized UT) + +
Main Loop Longitudinal Weld (mechanized UT) + +
MCP Stud (MT) + +
Small Diameter Tube (PT) + +
Pressurizer Nozzle Dissimilar Weld (mechanized UT) + +
SG Collector Dissimilar Weld (mechanized UT) + +
RPV Welds (mechanized UT from OD) + +
SG Threaded hole (mechanized ET ) + +
MCP Threaded hole (mechanized ET ) + +
RPV Main Loop Nozzle dissimilar weld (mechanized UT
from OD) + +
RPV Safety Injection Nozzle dissimilar weld (mechanized UT
from OD) + +
RPV Stud (mechanized ET and UT) + +
RPV Threaded hole (mechanized ET) + +
Qualifications in progress SG Stud (mechanized ET ) + +
MCP Stud (mechanized ET ) + +
Generic Procedure for PT of nuclear components + +
Status of Inspection Qualification
Registration level
Reference level
(recording level)
Acceptance level (quality control)
Acceptance level
(fitness-for-service)
In
dic
atio
n s
ize
Fla
w s
ize
LEVEL
Evaluation based on flaw
characteristics
Recording
Repair/replacement, or
fracture mechanics analysis
Quality Control Fitness-for-Service
100% PRR (FBH)
+12 dB
20% DAC (SDH)
100% DAC (SDH)
siz
ing
Critical
Not-allowable
Allowable
Acceptance Standards
Current approach Future approach
siz
ing
Level 1 evaluation
Allowable?
Is sizing possible?
Sizing and Level 2
evaluation
Allowable?
Fracture mechanics
calculation
Allowable?
Measures
NDE
OPERATION
Y
N
Y
Y
N
N
Y
N Y
Current standard
IWB, C, D-3000
IWB, C, D-3600
Two-level
evaluation
concept
Pressure Test
• Biggest debate with regulator
• Test pressure of primary coolant circuit:
– 19.1 MPa (until 1993); 16.4 MPa (currently)
– operating pressure: 12.2 MPa
• Fail safe design / operation
– resistance against operation, accident and test loads (flaw size
will not change during hydrotest)
– leakage test (operating pressure)
• Test at elevated pressure:
– no added value to integrity
assessment
– contribution to fatigue
– risk increase
Estimation of Economic Benefit
• Impact of ISI interval extension: USD 300 to 600 M
– NDE volume increase (+) due to ageing management
– longer interval
– outage reduction
• Inspection qualification – usually not quantifiable – allows to use simpler (less time-consuming) NDE
– more reliable NDE – longer inspection interval
– defect repair can be optimized (in earlier stage)
• Risk informed ISI – under consideration
Summary
• To support LTO of Paks NPP
– a complete revision and
– a substantial modification of ISI program
was performed
• Content of ISI program achieved a good agreement
with ASME BPVC Section XI requirements
• ISI program shows more and more features of an
effective ISI (see IAEA-TECDOC 1400)
• Acceptance criteria meet technical requirements of
life extension
– fracture mechanics calculation
– decisions on repair / replacement
• Licensing is under way