Decay Heat calculations with SERPENT 2 - SUBATECH, CNRS-IN2P3, Ecole des Mines de Nantes (now IMTA), France
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Decay Heat calculations with SERPENT 2
SUBATECH,
CNRS-IN2P3, Ecole des Mines de Nantes (now IMTA), France
Lydie.Giot@subatech.in2p3.fr
Outline
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
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)
~ 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)
Nuclear stage impacted Time of cooling
Safety systems of cooling 0.1s to 8 days
Unloading of assemblies 5 to 25 days
from core
Fuel transport 1 to 10 years
Reprocessing, vitrification, 4 to 3000 years
storage
Storage 50 to 300 000 years and
more
I. Motivations on Decay Heat
§ 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 Ni : Number of nuclei i at the cooling time t
n
λi : Decay constant of the nucleus i
DH(t) = f(t) = Σ Ni(t) λi Ei
i
Ei : Total decay energy 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 :
Light particles component
Electromagnetic component
Heavy particles component
I. Motivations on Decay Heat § 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 - Large time range: 10-1 to 106 years - Important quantity to design the size/capacity of safety systems - 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 - Increasing will of safety authorities to ask for a precise calculation & detailed uncertainty quantification - 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 but also identification of biases in the calculation/data to improve them ….
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
- Calibration: electric heater designed as the
same shape as a fuel assembly
- Gamma radiation monitors outside: to correct
the measured DH for the energy loss due to
gamma rays escaping from the calorimeter vessel
- Low sensitivity at long cooling times (10%)
Measurements uncertainties for CLAB calorimeter:
BWR PWR
SKB, R-05-62, 2006
I. Fuel Assembly Decay Heat Measurements
GE-Morris Operation facility:
Enrichment Nb of Max Burnup
Name Type Fuel design assemblies (MWd/MTU)
systematic error:
wt % 235U
measured
San Onofre 1 PWR W 14 x 14Sa 3.865-4.005 8 32,363 - ± 2% for thermal output of 700
Point Beach 2 PWR W 14 x 14 3.397 6 39,384 W range
Dresden 2 BWR GE 7 x 7 2.128 1 5,280 - ± 4% for thermal output of 200
W range
Cooper BWR GE 7 x 7 1.1, 2.5 54 28,048
Monticello BWR GE 7 x 7 2.25 6 20,189
Handford Engineering Development Laboratory : - ± 5% for thermal output greater
Turkey Point PWR W 15 x 15 2.557 4 28,588 than 1000W
- ± 10% for thermal output greater
than 100W
Swedish Central Interim Storage Facility for Spent Fuel (CLAB):
- 39 BWR assemblies : Barsebäck 1-2, Forsmark 1-3, Oskarshamm 2-3, Ringhals 1
- 34 PWR assemblies among Ringhals 2-3
NUREG/CR-6972, ORNL/TM-2008-015 and references therein
I. Fuel Assembly Decay Heat Measurements
GE-Morris Operation facility:
Enrichment Nb of Max Burnup Serpent2 Benchmarks
Name Type Fuel design assemblies
wt % 235U (MWd/MTU)
measured
San Onofre 1 PWR W 14 x 14Sa 3.865-4.005 8 32,363 - PWR GE-Morris/HEDL
Point Beach 2 PWR W 14 x 14 3.397 6 39,384
done in 2017- early 2018
Dresden 2 BWR GE 7 x 7 2.128 1 5,280
Comparison with SCALE
Cooper BWR GE 7 x 7 1.1, 2.5 54 28,048
Monticello BWR GE 7 x 7 2.25 6 20,189 - BWR GE-Morris
On-going, Half done
Handford Engineering Development Laboratory :
Turkey Point PWR W 15 x 15 2.557 4 28,588 - CLAB PWR/BWR
Forseen : 2019
Swedish Central Interim Storage Facility for Spent Fuel (CLAB):
- 39 BWR assemblies : Barsebäck 1-2, Forsmark 1-3, Oskarshamm 2-3, Ringhals 1
- 34 PWR assemblies among Ringhals 2-3
NUREG/CR-6972, ORNL/TM-2008-015 and references therein
I. Decay Heat Measurements
Beta/ Gamma measurements on irradiated actinide samples
- Decay heat is measured in MeV/fission
High efficiency detectors
Number of fissions determined using nuclides
with proper gamma ray and energy (97Nb,135Xe)
- Combinaison of irradiation, waiting
and measurement times allows to get
fission burst decay heat
- 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
Ohkawachi et al., Journal of Nucl. Sc. and Technology, Suppl 2, p. 493
I. Selected Decay Heat fission burst pulse experiments
Isotopes Method Author(s) Institute Year
235U
th,
239Pu
th,
241Pu γ, β Dickens et al. Oak Ridge National Laboratory 1980
th
235U
th,
239Pu
th,
239Pu γ, β Schier, Couchell et al. Univ. of Massachussetts, Lowell 1997
fast
235U 239Pu γ, β Tobias Berkeley National Laboratory 1989
th, th
compilation
233,235,238U
fast,,
239Pu γ, β Akiyama YAHOI reactor, JAEA 1982
fast
232Th, natU γ Akiyama YAHOI reactor, JAEA 1983
fast
235U 237Np γ, β Ohkawachi YAHOI reactor, JAEA 2002
fast, fastI. Selected Decay Heat fission burst pulse experiments
Isotopes Method Author(s) Institute Year
235U
th,
239Pu
th,
241Pu γ, β Dickens et al. Oak Ridge National Laboratory 1980
th
235U
th,
239Pu
th,
239Pu γ, β Schier, Couchell et al. Univ. of Massachussetts, Lowell 1997
fast
235U 239Pu
235U thermalTobias
th, th γ, β Berkeley National Laboratory 1989
compilation
233,235,238U
fast,,
239Pu γ, β Akiyama YAHOI reactor, JAEA 1982
fast
232Th, natU
fast γ Akiyama totalYAHOI reactor, JAEA 1983
235U 237Np γ, β Ohkawachi YAHOI reactor, JAEA 2002
fast, fast
gamma
CCFE-R(15)28, UKAEA, FISPACT-II, 2015II. Total Decay Energy and Pandemonium effect
n
Ni : Number of nuclei i at the cooling time t
DH(t) = f(t) = Σ Ni(t) λi Ei
i λi : Decay constant of the fission product i
Ei : Total decay energy of the fission product iII. Total Decay Energy and Pandemonium effect
- 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)
- Incomplete decay schemes: overestimate Ebeta, underestimate Egamma
Missing
- Decay energy measurements biased by Pandemonium effect for some Fission Products
⇒ Bias in nuclear data bases for some key nuclei and all their applications (safeguards, DH)
=> Known as the « Pandemonium effect »
J. Hardy et al., PLB 71 (2) 307, 1977II. Total Decay Energy and Pandemonium effect
From A. AlgoraII. Total Decay Energy and Pandemonium effect
- 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
From TAS collaboration: contacts A. Algora & J. L. Tain @Valencia, W. Gelletly@Surrey, M. Fallot@SubatechII. 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
239Pu Electromagnetic Decay Heat
t x f(t) EEM Decay Heat
(MeV/fission)
Cooling time (s)
- No improvement on 235U case Algora et al., PRL 105, 202501 (2010)II. Pulse fission calculations with SERPENT 2
Pulse Fission calculations with Serpent 2
Example:
- Pure sphere of 235U (2cm)
235U
- 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
- Python macros written to extract the FP individual contributions
Serpent 2 flexibility allows to do:
- Sensivity studies on fission yields/decay data libraries: all mix possible with data @ ENDF-6 format
=> IAEA interest, Consultant’s Meeting on decay data librairies and their impact on DH, Fev 2018
- To calculate the impact of a Pandemonium nucleus, remeasured with TAS method on a pulse calculation
=> 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 neededII. Pulse fission calculations with SERPENT 2
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
235
235
U Pulse / Total Heat U Pulse / ELM Heat
1.6 0.8
235U 235U EEM
Total
Electromagnetic decay heat in MeV/fission
1.4
0.7
Total decay heat in MeV/fission
1.2
0.6
1
0.5
0.8
0.6 235
U Tobias 0.4
235
U Dickens 235
U Tobias
ENDFVII.1 235
0.4 U Dickens
JEFF 3.1.1 0.3 ENDFVII.1
JEFF 3.3 JEFF 3.1.1
0.2 JEFF 3.3 + Other TAS Published JEFF 3.3
JEFF 3.3 + TAS Published
3 0.2
10-1 1 10 102 10 104 3
10-1 1 10 102 10 104
Time (s) Time (s)
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,
JEFF3.3III. Assembly benchmarks with SERPENT 2
- 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)
- NUREG doc used (SCALE benchm.) but not PWR Spent
all the time Fuel
enough to be used as it is….
1600
San Onofre (Calc/Meas -1) : -0.3% to 1.2%
1400
Point Beach (Calc/Meas -1) : -1.5% to 0.1%
Calculated Decay Heat (W)
1200
Turkey Point (Calc/Meas -1) : -2.6% to 5.5%
1000
800
Performed with ENDFBVII.0
600
to reproduce SCALE calc.
400
San Onofre Unit 1 reactor
Turkey Point 3 reactor
200
Point Beach reactor
0
0 200 400 600 800 1000 1200 1400 1600
Measured Decay Heat (W)
NUREG/CR-6972, ORNL/TM-2008-015 and references thereinIII. Assembly benchmarks with SERPENT 2/ Outlooks
- PWR Benchmarks: On-going
PWR comparison
Spent Fuel with SCALE
1600 - Turkey Point: SCALE more
«off» w.r.t to other calculations
1400
~ 1.2% between both
Calculated Decay Heat (W)
1200 under investigation
1000
- Will be done with new JEFF3.3
800
600
400 SCALE
San Onofre Unit 1 reactor
200 Turkey Point 3 reactor
Point Beach reactor
0
0 200 400 600 800 1000 1200 1400 1600
Measured Decay Heat (W)
- 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)IV. Molten Salt Fast Reactor (MSFR)
General characteristics: Three circuits:
• Liquid circulating fuel Fuel salt circuit
• Fuel = coolant
• Power: 3 GWth
• Thermal yield: 45%
• Mean fuel temperature: 725°C
• Fast neutron spectrum
• Thorium fuel cycle
21IV. Molten Salt Fast Reactor (MSFR)
General characteristics: Three circuits:
• Liquid circulating fuel Fuel salt circuit
• Fuel = coolant Intermediate circuit
• Power: 3 GWth Thermal conversion circuit
• Thermal yield: 45% + Draining / storage tanks
• Mean fuel temperature: 725°C + Processing units
• Fast neutron spectrum
• Thorium fuel cycle
22IV. MSFR / On-going and Outlooks
ü On going analysis: Fast fission pulse calculations on 232Th/233U & U/Pu cycles
233
U Pulse Fast / Total Heat 239
Pu Pulse Fast / Total Heat
1.2
- 233,235,238U, 232Th, 239Pu
1.2
233U 239Pu total
1 total 1 - JEFF3.1.1 & JEFF3.3
Total decay heat in MeV/fission
Total decay heat in MeV/fission
0.8
0.8 - Total, beta, gamma
0.6
0.6
- 5 cooling times chose, to
cover the range of data
0.4
0.4
233
U YAHOI 239
- 15 most important contributors
Pu YAHOI
0.2
JEFF 3.1.1 Fission Products
0.2
JEFF 3.1.1 Fission Products
identified
102
3
10 104
102
3
10 104
=> New nuclei to measure ?
Time (s) Time (s)
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
First studies (Master student) for this summer
with typical burnt fuel & cooling scenarii
ü Longer term: Sensitivity studies & Error propagation for decay heat calculationsSummary
- On going decay heat calculations at different levels with SERPENT 2 :
Nuclear Data (Pulse fission)
Of course, need of more measurements of DH, especially for fast cases …
Reactor case
- Importance of the quality of the decay energy data: Pandemonium effect
- DH Benchmarks
PWR assemblies performed: good agreement with measured and also w.r.t SCALE
BWR assemblies forseen next year
- Forseen activities on MSFR presented
Funded intersnships opportunities for M1/M2 J ,
on one of these subjects, flexible starting date & length
Nantes 20 km from Clisson (Hell Fest festival..)Thanks ! Lydie.Giot@subatech.in2p3.fr
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