LLNL-PRES-770146 NCSP NUCLEAR CRITICALITY SAFETY PROGRAM Inherently Safe Subcritical Assembly (ISSA) Benchmark Evaluation Presented at the Nuclear Criticality Safety Program (NCSP) Technical Program Review March 26-27 2019 Tony Nelson, Soon Kim, Will Zywiec, Dave Heinrichs Lawrence Livermore National Laboratory Lawrence Livermore National Laboratory, P.O. Box 808, L-384, Livermore, CA 94551-0808 This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344
Inherently Safe Subcritical Assembly (ISSA) • Subcritical benchmark experiments for ICSBEP • Existing asset as a training assembly • Validate time dependent radiation transport modules • Validate nuclear data • Subcritical multiplication monitoring 2
ISSA Fuel • Originally fabricated for the Omega West Reactor • Modified at LLNL • 93.16% 235 U • U 3 O 8 powder + aluminum powder • Sandwiched between aluminum plates • 19 curved plates per assembly • 232 g 235 U per assembly
Experiments • 5 experiments: – 1, 2, 4, 6, and 9 fuel assemblies • Multiplication ranging from 1.2-10 4
Experimental Results 350 300 9 Assemblies 250 Neutron Counts 200 150 100 50 0 0 0.5 1 1.5 2 2.5 3 3.5 4 Time, s (9 Assemblies)
Experimental Results 350 300 9 Assemblies Fission Chains 250 Neutron Counts 200 150 100 50 0 0 0.5 1 1.5 2 2.5 3 3.5 4 Time, s (9 Assemblies)
Experimental Results Time, s (1 Assembly) 0 20 40 60 80 100 120 140 160 180 350 300 9 Assemblies Fission Chains 1 Assembly 250 Neutron Counts 200 150 Fission Chain 100 50 0 0 0.5 1 1.5 2 2.5 3 3.5 4 Time, s (9 Assemblies)
Experimental Results 9 Assemblies 1E+01 1E+00 1E-01 Time Until Next Detection Event, s 1E-02 1E-03 1E-04 1E-05 1E-06 1E-07 0 50 100 150 200 250 300 350 400 450 500 Neutron Counts 8
Experimental Results 9 Assemblies 1E+01 1E+00 1E-01 Time Until Next Detection Event, s Random Source 1E-02 1E-03 1E-04 Fission Chains 1E-05 1E-06 1E-07 0 50 100 150 200 250 300 350 400 450 500 Neutron Counts 9
Experimental Results 9 Assemblies 1 Assembly 1E+01 1E+00 1E-01 Time Until Next Detection Event, s Random Source 1E-02 1E-03 1E-04 Fission Chains 1E-05 1E-06 1E-07 0 50 100 150 200 250 300 350 400 450 500 Neutron Counts 10
Analysis 350 300 250 Neutron Counts 200 150 100 50 0 0 0.5 1 1.5 2 2.5 3 3.5 4 Time, s (9 Assemblies)
Analysis 350 300 250 Neutron Counts 200 150 100 50 0 0 0.5 1 1.5 2 2.5 3 3.5 4 Time, s (9 Assemblies)
Analysis 0.06 Fraction of Segments with k Counts (b k ) 0.05 ISSA Experimental Data 0.04 Poisson Distribution 0.03 0.02 0.01 0 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88 92 96 100 104 108 112 116 120 124 128 132 Number (k) of Counts Recorded in Segment
Analysis 350 300 250 Neutron Counts 200 150 100 50 0 0 0.5 1 1.5 2 2.5 3 3.5 4 Time, s (9 Assemblies) 14
Analysis 350 300 250 Neutron Counts 200 150 100 50 0 0 0.5 1 1.5 2 2.5 3 3.5 4 Time, s (9 Assemblies) 15
Analysis 350 300 250 Neutron Counts 200 150 100 50 0 0 0.5 1 1.5 2 2.5 3 3.5 4 Time, s (9 Assemblies) 16
Analysis 5 4.5 4 3.5 3 Y 2F 2.5 2 1.5 1 0.5 0 0 5000 10000 15000 20000 25000 30000 Time Gate, µs
Analysis 5 4.5 4 1 Assembly 3.5 2 Assemblies 3 4 Assemblies 6 Assemblies Y 2F 2.5 9 Assemblies 2 1.5 1 0.5 0 0 5000 10000 15000 20000 25000 30000 Time Gate, µs
Simulation 19
20
Simulation Results 0.30 0.25 Experimental 0.20 Y 2F 0.15 0.10 0.05 0.00 0 100 200 300 400 500 Time Gate Size, ms
Simulation Results 0.3 0.25 COG Experimental 0.2 Y 2F 0.15 0.1 0.05 0 0 100 200 300 400 500 Time Gate Size, ms
Simulation Results • Neutron start time determined 2 by: 1.8 (Random Number) 1.6 X 1.4 Time Until Next Detection, s (Total simulation duration) 1.2 • Random number generator is 1 single precision 0.8 • Smallest difference between random numbers is ~1E-7 0.6 • For simulation duration 1E6 s, 0.4 smallest time between source neutrons is 1E-7*1E6 = 0.1 s 0.2 0 0 500 1000 1500 2000 2500 Time, s
Simulation Results 0.30 0.25 COG Experimental 0.20 Y 2F 0.15 0.10 0.05 0.00 0 100 200 300 400 500 Time Gate Size, ms
Simulation Results 0.3 Fixed COG 0.25 COG Experimental 0.2 Y 2F 0.15 0.1 0.05 0 0 100 200 300 400 500 Time Gate Size, ms
Simulation Results 20.00% COG with ENDF/B-VII.1 15.00% 10.00% 5.00% R 2F (C-E)/E 0.00% 1 2 3 4 5 6 7 8 9 -5.00% -10.00% -15.00% -20.00% Number of Assemblies 26
Simulation Results 20.00% COG with ENDF/B-VII.1 COG with ENDF/B-VIII.0 15.00% 10.00% 5.00% R 2F (C-E)/E 0.00% 1 2 3 4 5 6 7 8 9 -5.00% -10.00% -15.00% -20.00% Number of Assemblies 27
Simulation Results 20.00% COG with ENDF/B-VII.1 COG with ENDF/B-VIII.0 MORET with ENDF/B-VII.1 15.00% MORET with JEFF3.2 MORET with JEFF3.2 and FREYA 10.00% 5.00% R 2F (C-E)/E 0.00% 1 2 3 4 5 6 7 8 9 -5.00% -10.00% -15.00% -20.00% Number of Assemblies 28
Conclusions – Identified non-physical artifact in radiation transport code – Demonstrated improvement of nuclear data from ENDF/B-VII to ENDF/B-VIII – Points towards further improvements from FREYA – Provided a dataset for multiplicity community to validate new theories and techniques 29
Acknowledgements This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA273444 and was made possible through the support of: – Wilfried Monange, Jesson Hutchinson, Boukhmès Mechitoua – DOE Nuclear Criticality Safety Program – DOE Office of Fissile Materials Disposition – DOE NNSA Livermore Field Office – LLNL Nuclear Operations Directorate 30
Questions? 31
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