SUBATECH, CNRS-IN2P3, Ecole des Mines de...

Decay Heat calculations with SERPENT 2

[email protected]

SUBATECH, CNRS-IN2P3, Ecole des Mines de Nantes (now IMTA), France

  I. Decay Heat

- Motivations and Method of calculation - Available measurements   II. Decay Heat / Fission Pulses

- Total decay energy: Measurement and Pandemonium effect - Case of 239Pu Electromagnetic Decay Heat - On going pulse calculations with SERPENT 2   III. Assembly benchmarks with SERPENT 2

- Results on Pressurized Water Reactor assemblies - Outlooks   IV. Molten Salt Fast Reactor

- Concept - On going-work & Outlooks

Outline

I. Motivations on Decay Heat

Decay Heat: Thermal power released after the reactor stops Mainly coming from the radioactive decays of fission products isotopes and actinides produced by successive neutrons captures but additionnal sources (fission induced by delayed fissions, reactions indiced by spontaneous fissions)

Nuclear stage impacted Time of cooling

Safety systems of cooling 0.1s to 8 days

Unloading of assemblies from core

5 to 25 days

Fuel transport 1 to 10 years

Reprocessing, vitrification, storage

4 to 3000 years

Storage 50 to 300 000 years and more

~ 7% of nominal power at reactor stop (~290 MW for 900 MWe PWR) ~ 1.5% of nominal power at reactor stop +1h (~40 MW for 900 MWe PWR)


§  Safety/Radiation protection/Economic interests for the complete cycle (Gen II, Gen III)

§  Key issue for new concepts: Gen IV, innovative reactor design, innovative fuels, most of the concepts with fast neutrons => not so many data, limited reactor operation feedback

§  Important design parameter for a spent fuel repository

Summation Formula

ΣDH(t) = f(t) = Ni(t) λi Eii

n Ni : Number of nuclei i at the cooling time t

Ei : Total decay energy of the nucleus iλi : Decay constant of the nucleus i

Depletion calculation within a reactor model + code (e.g with SERPENT)

Ei is usually divided in evaluated librairies(e.g ENDF, JEFF, JENDL) in 3 parts :

Electromagnetic component

Light particles component

Heavy particles component


- Large time range: 10-1 to 106 years

- Complex calculation (reactor modeling + depletion): quality of the code but also of the data !

- ~ 40 000 nuclear data: σ, E, Branching Ratio, λ, Fission Yields, ν

§  Safety/Radiation protection/Economic interests for the complete cycle (Gen II, Gen III)

§  Key issue for new concepts: Gen IV, innovative fuels => not so many data, limited reactor operation feedback

§  Important design parameter for a spent fuel repository

- Important quantity to design the size/capacity of safety systems

- Increasing will of safety authorities to ask for a precise calculation & detailed uncertainty quantification

but also identification of biases in the calculation/data to improve them ….

- Interest of industry to reduce the uncertainty for economic reasons, with keeping the same level of safety

Rigorous calculation with evaluated codes associated to experimental validation

I. Decay Heat Measurements

Calorimetric technique for assembly measurements - Principle: Measure the temperature increase of the water in the calorimeter caused by the decay heat power from a fuel assembly placed in the calorimeter

- Gamma radiation monitors outside: to correct the measured DH for the energy loss due to gamma rays escaping from the calorimeter vessel

- Calibration: electric heater designed as the same shape as a fuel assembly

Measurements uncertainties for CLAB calorimeter:

BWR PWR

- Low sensitivity at long cooling times (10%)

SKB, R-05-62, 2006

I. Fuel Assembly Decay Heat Measurements

GE-Morris Operation facility:

PWR PWR

Handford Engineering Development Laboratory :

Swedish Central Interim Storage Facility for Spent Fuel (CLAB):

Name Type Fuel design

San Onofre 1 Point Beach 2 Dresden 2 Cooper Monticello

Enrichment wt % 235U

BWR BWR BWR

W 14 x 14Sa W 14 x 14 GE 7 x 7 GE 7 x 7 GE 7 x 7 2.25

1.1, 2.5 2.128 3.397 3.865-4.005

Nb of assemblies measured

6 54 1 6 8

Max Burnup (MWd/MTU)

32,363 39,384 5,280

28,048 20,189

Turkey Point PWR W 15 x 15 2.557 4 28,588

- 39 BWR assemblies : Barsebäck 1-2, Forsmark 1-3, Oskarshamm 2-3, Ringhals 1

- 34 PWR assemblies among Ringhals 2-3

systematic error:

- ± 2% for thermal output of 700 W range

NUREG/CR-6972, ORNL/TM-2008-015 and references therein

- ± 4% for thermal output of 200 W range

- ± 5% for thermal output greater than 1000W - ± 10% for thermal output greater than 100W

I. Fuel Assembly Decay Heat Measurements

GE-Morris Operation facility:

PWR PWR

Handford Engineering Development Laboratory :

Swedish Central Interim Storage Facility for Spent Fuel (CLAB):

Name Type Fuel design

San Onofre 1 Point Beach 2 Dresden 2 Cooper Monticello

Enrichment wt % 235U

BWR BWR BWR

W 14 x 14Sa W 14 x 14 GE 7 x 7 GE 7 x 7 GE 7 x 7 2.25

1.1, 2.5 2.128 3.397 3.865-4.005

Nb of assemblies measured

6 54 1 6 8

Max Burnup (MWd/MTU)

32,363 39,384 5,280

28,048 20,189

Turkey Point PWR W 15 x 15 2.557 4 28,588

- 39 BWR assemblies : Barsebäck 1-2, Forsmark 1-3, Oskarshamm 2-3, Ringhals 1

- 34 PWR assemblies among Ringhals 2-3


Serpent2 Benchmarks

- PWR GE-Morris/HEDL done in 2017- early 2018 Comparison with SCALE

- BWR GE-Morris On-going, Half done

- CLAB PWR/BWR Forseen : 2019

I. Decay Heat Measurements

Beta/ Gamma measurements on irradiated actinide samples

- Decay heat is measured in MeV/fission

Ohkawachi et al., Journal of Nucl. Sc. and Technology, Suppl 2, p. 493

- Access to Beta & Gamma components of Decay Heat for a given actinide in MeV/fission

=> Extra data to test the depletion code => Extra data to test the library data, especially fission yields & decay data (Ei) with a summation calculation

Number of fissions determined using nuclides with proper gamma ray and energy (97Nb,135Xe)

High efficiency detectors

- Combinaison of irradiation, waiting and measurement times allows to get fission burst decay heat

I. Selected Decay Heat fission burst pulse experiments

Isotopes Method Author(s) Institute Year 235Uth, 239Puth, 241Puth γ, β Dickens et al. Oak Ridge National Laboratory 1980

235Uth, 239Puth, 239Pufast γ, β

Schier, Couchell et al. Univ. of Massachussetts, Lowell 1997

235Uth,239Puth

γ, β compilation

Tobias Berkeley National Laboratory 1989

233,235,238Ufast,,239Pufast γ, β Akiyama YAHOI reactor, JAEA 1982

232Th, natUfast γ Akiyama YAHOI reactor, JAEA 1983

235Ufast, 237Npfast

γ, β Ohkawachi YAHOI reactor, JAEA 2002

I. Selected Decay Heat fission burst pulse experiments

CCFE-R(15)28, UKAEA, FISPACT-II, 2015

Isotopes Method Author(s) Institute Year 235Uth, 239Puth, 241Puth γ, β Dickens et al. Oak Ridge National Laboratory 1980

235Uth, 239Puth, 239Pufast γ, β

Schier, Couchell et al. Univ. of Massachussetts, Lowell 1997

235Uth,239Puth

γ, β compilation

Tobias Berkeley National Laboratory 1989

233,235,238Ufast,,239Pufast γ, β Akiyama YAHOI reactor, JAEA 1982

232Th, natUfast γ Akiyama YAHOI reactor, JAEA 1983

235Ufast, 237Npfast

γ, β Ohkawachi YAHOI reactor, JAEA 2002

235U thermal

gamma

total

II. Total Decay Energy and Pandemonium effect

ΣDH(t) = f(t) = Ni(t) λi Ei

n Ni : Number of nuclei i at the cooling time t

Ei : Total decay energy of the fission product i

λi : Decay constant of the fission product ii


⇒  Bias in nuclear data bases for some key nuclei and all their applications (safeguards, DH)

J. Hardy et al., PLB 71 (2) 307, 1977

- Decay energy measurements biased by Pandemonium effect for some Fission Products

-  Incomplete decay schemes: overestimate Ebeta, underestimate Egamma

- Total Decay energy (Ei) measurements - Before the 90s, conventional detection techniques: high resolution γ-ray spectroscopy - Excellent resolution but efficiency which strongly decreases with increasing energy - Risk of overlooking the existence of β- feeding into the high energy nuclear levels of daughter nuclei (especially with decay schemes with large Q values)

=> Known as the « Pandemonium effect »

Missing


From A. Algora

From TAS collaboration: contacts A. Algora & J. L. Tain @Valencia, W. Gelletly@Surrey, M. Fallot@Subatech

- Most suitable detection technique to re-measure key nuclei: Total Absorption Spectroscopy IFIC Valencia/Subatech/Surrey TAGS collaboration Experiments @ Jyväskylä, Finland to high precision penning trap (Pure beams)


TAGS Arrays, Valencia

Algora et al., PRL 105, 202501 (2010)

239Pu Electromagnetic Decay Heat

Cooling time (s)

t x f(

t) E

EM D

ecay

Hea

t (M

eV/fi

ssio

n)

II. Case of 239Pu Electromagnetic Decay Heat

- Important improvement with 7 nuclei known from suffering from Pandemonium effect (WPEC-25, IAEA) and re-measured by TAS technique

- No improvement on 235U case

II. Pulse fission calculations with SERPENT 2

Pulse Fission calculations with Serpent 2

Serpent 2 flexibility allows to do:

235U

Example: - Pure sphere of 235U (2cm)

- Irradiation with a thermal neutron source for 1µs + cooling time till 104s - Dedicated work on the normalization to compare with experimental results

x n

n - Serpent 2 adapted to get the individual ELP & EEM parts for fission pulse

- Sensivity studies on fission yields/decay data libraries: all mix possible with data @ ENDF-6 format

- To calculate the impact of a Pandemonium nucleus, remeasured with TAS method on a pulse calculation

=> IAEA interest, Consultant’s Meeting on decay data librairies and their impact on DH, Fev 2018

=> In contact with evaluators (ENDF & JEFF)

- To have access to all individual FP contributions to the DH for each cooling time step => Allows to identify key contributors, and then check their decay schemes to see if real effect or bias due to Pandemonium effect (Python macros developed) => new measurements needed

- Python macros written to extract the FP individual contributions

II. Pulse fission calculations with SERPENT 2

Time (s)-110 1 10 210 310 410

Tot

al d

ecay

hea

t in

MeV

/fiss

ion

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

U Tobias235 U Dickens235

ENDFVII.1JEFF 3.1.1JEFF 3.3JEFF 3.3 + Other TAS Published

U Pulse / Total Heat235

Time (s)-110 1 10 210 310 410

Ele

ctro

mag

netic

dec

ay h

eat i

n M

eV/fi

ssio

n

0.2

0.3

0.4

0.5

0.6

0.7

0.8

U Tobias235 U Dickens235

ENDFVII.1JEFF 3.1.1JEFF 3.3JEFF 3.3 + TAS Published

U Pulse / ELM Heat235

Yields & Decay Libraries: JEFF 3.1.1 Yields & Decay Libraries: JEFF 3.3

Published TAS nuclei already in JEFF3.3 and were not in JEFF3.1.1: 87,88Br, 94Rb, 105Mo, 104,105,106,107Tc + 92Rb

Published TAS nuclei added: 86Br, 91Rb, 101Nb, 102Tc

235U Total 235U EEM

Example of work which be part of IAEA consultant’s report, released at the end of 2018 Studied cases: 235U & 239Pu (Tot, β, γ) Fission yields: JEFF3.1.1 or JEFF3.3 with different decay data libraries: ENDFVII.1, ENDFVIII, JEFF3.1.1, JEFF3.3

III. Assembly benchmarks with SERPENT 2

Measured Decay Heat (W) 0 200 400 600 800 1000 1200 1400 1600

Cal

cula

ted

Deca

y He

at (W

)

0

200

400

600

800

1000

1200

1400

1600

San Onofre Unit 1 reactor

Turkey Point 3 reactor

Point Beach reactor

PWR Spent Fuel

-  Available decay heat measurements using calorimeters from U.S facilities (18 PWR) - Serpent 2 calculations performed by Pyry Savolainen (LUT student, internship @SUBATECH)


- Typically: 3 operation cycles, final cooling period: 1000-3000 days (San Onofre), 800-1700 days (Turkey Point),1600 days (Point Beach 2)

San Onofre (Calc/Meas -1) : -0.3% to 1.2%

Point Beach (Calc/Meas -1) : -1.5% to 0.1%

Turkey Point (Calc/Meas -1) : -2.6% to 5.5%

- NUREG doc used (SCALE benchm.) but not all the time enough to be used as it is….

Performed with ENDFBVII.0

to reproduce SCALE calc.

III. Assembly benchmarks with SERPENT 2/ Outlooks

- BWR calculations : On-going on GE-Morris assemblies, CLAB BWR/PWR for 2019

- Forseen 2018: Decay heat blind test benchmark on new measurements at CLAB (5 PWR assemblies), financed by the Swedish Nuclear Fuel and Waste Management (SKB)

-  PWR Benchmarks: On-going comparison with SCALE

Measured Decay Heat (W) 0 200 400 600 800 1000 1200 1400 1600

Cal

cula

ted

Dec

ay H

eat (

W)

0

200

400

600

800

1000

1200

1400

1600

SCALE

San Onofre Unit 1 reactor

Turkey Point 3 reactor

Point Beach reactor

PWR Spent Fuel

- Turkey Point: SCALE more «off» w.r.t to other calculations

under investigation ~ 1.2% between both

- Will be done with new JEFF3.3

21

Three circuits: Fuel salt circuit

General characteristics: •  Liquid circulating fuel •  Fuel = coolant •  Power: 3 GWth •  Thermal yield: 45% •  Mean fuel temperature: 725°C •  Fast neutron spectrum •  Thorium fuel cycle

IV. Molten Salt Fast Reactor (MSFR)

22

Three circuits: Fuel salt circuit Intermediate circuit Thermal conversion circuit + Draining / storage tanks + Processing units

General characteristics: •  Liquid circulating fuel •  Fuel = coolant •  Power: 3 GWth •  Thermal yield: 45% •  Mean fuel temperature: 725°C •  Fast neutron spectrum •  Thorium fuel cycle

IV. Molten Salt Fast Reactor (MSFR)

IV. MSFR / On-going and Outlooks

ü  On going analysis: Fast fission pulse calculations on 232Th/233U & U/Pu cycles

Time (s)210 310 410

Tot

al d

ecay

hea

t in

MeV

/fiss

ion

0.2

0.4

0.6

0.8

1

1.2

U YAHOI233

JEFF 3.1.1 Fission Products

U Pulse Fast / Total Heat233

Time (s)210 310 410

Tot

al d

ecay

hea

t in

MeV

/fiss

ion

0.2

0.4

0.6

0.8

1

1.2

Pu YAHOI239

JEFF 3.1.1 Fission Products

Pu Pulse Fast / Total Heat239

ü  Mid term Development of Decay Heat calculation for MSFR using a serpent model (STL geometry from A. Laureau, LPSC) for both fuel cycles + identification of key contributors nuclei

233U total 239Pu total - JEFF3.1.1 & JEFF3.3 - Total, beta, gamma

- 233,235,238U, 232Th, 239Pu

- 5 cooling times chose, to cover the range of data - 15 most important contributors identified

First studies (Master student) for this summer

with typical burnt fuel & cooling scenarii

=> New nuclei to measure ?

ü  Longer term: Sensitivity studies & Error propagation for decay heat calculations

Summary

-  On going decay heat calculations at different levels with SERPENT 2 :

Nuclear Data (Pulse fission)

Reactor case

-  DH Benchmarks PWR assemblies performed: good agreement with measured and also w.r.t SCALE BWR assemblies forseen next year

-  Importance of the quality of the decay energy data: Pandemonium effect

Funded intersnships opportunities for M1/M2 J , on one of these subjects, flexible starting date & length Nantes 20 km from Clisson (Hell Fest festival..)

Of course, need of more measurements of DH, especially for fast cases …

-  Forseen activities on MSFR presented

Thanks !

[email protected]

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