1Managed by UT-Battelle for the U.S. Department of Energy Simulation of βn Emission From Fission Using Evaluated Nuclear Decay Data Ian Gauld Marco Pigni Reactor and Nuclear Systems Division May 2, 2013

2Managed by UT-Battelle for the U.S. Department of Energy Nuclear decay data from an end-user perspective. Evaluated decay data have major importance to areas of reactor safety and nuclear fuel cycle analysis Reactor safety applications include analysis of energy release (decay heat) and beta-delayed neutron emission after fission Decay heat impacts safety studies for irradiated nuclear fuel during reactor operation, fuel handling, storage, and disposal Delayed neutrons play an important role in reactor control and behavior during transients Our group is an end user of decay data

3Managed by UT-Battelle for the U.S. Department of Energy 3 SCALE is a nuclear systems modeling and simulate code used worldwide for reactor and fuel cycle applications Disposal Material processing and fabrication Commercial and research reactors Interim storage Transportation and storage Reprocessing Criticality safety Radiation shielding Cross-section processing Reactor physics Sensitivity and uncertainty analysis Spent fuel and HLW characterization Criticality safety Radiation shielding Cross-section processing Reactor physics Sensitivity and uncertainty analysis Spent fuel and HLW characterization

4Managed by UT-Battelle for the U.S. Department of Energy ORIGEN – Oak Ridge Isotope GENeration and Depletion code Irradiation and decay Calculates – Time dependent isotopic concentrations – Radioactivity – Decay heat (based on summation) – Radiation sources (neutron/gamma) – Toxicity Explicit simulation of 2228 nuclides using evaluated nuclear data Fast: 0.02 s per time step ENDF/B-VII.1 nuclear data for: – 174 actinides – 1151 fission products – 903 structural activation materials Simulation of Nuclear Fuel

5Managed by UT-Battelle for the U.S. Department of Energy ENDF/B-VII.1 Nuclear Data Libraries Decay half lives, branching fractions, energy release − 2226 nuclides Cross sections − ENDF/B-V, -VI, -VII − JEFF-3.0/A special purpose activation file Fission product yields − Energy-dependent yields for 30 actinides Gamma ray production data − X-ray and gamma ray emissions per decay Neutron production data from LANL SOURCES code − Alpha decay energies − Stopping powers − α,n yield cross sections − Spontaneous fission spectral parameters − Delayed neutron spectra for 105 precursor nuclides Alpha and beta spectra included in next release

6Managed by UT-Battelle for the U.S. Department of Energy ENDF/B-VII.1 Decay Sublibrary Improvements Decay data based on the Evaluated Nuclear Structure Data File (ENSDF), translated into ENDF-6 format 3817 long-lived ground state or isomer materials More thorough treatment of the atomic radiation Improved Q value information Recent theoretical calculations of the continuous spectrum from beta-delayed neutron emitters New TAGS (Total Absorption Gamma-ray Spectroscopy) data

7Managed by UT-Battelle for the U.S. Department of Energy Decay Heat Standards ANS and ISO (1992) widely adopted in reactor safety codes Experimentally-based curves developed using groups, fit to experimental data at short decay times Groups developed to represent decay times from 1 second to 300 years after fission Necessitated because nuclear decay data inadequate for short decay data times at the time of standard development (ANS draft, issued 1979) Parameters for exponential fits available for four fissionable nuclides, (MeV/s/fission)

8Managed by UT-Battelle for the U.S. Department of Energy Code Calculations using Evaluated Nuclear Data Alternate approach to standards-based methods using nuclear decay data and fission yields for all fission products generated by fission – Simulate all fission products explicitly – Provides greater insight into system performance – Contributions from important nuclides, and gamma, beta, and alpha components – Gamma spectrum for determination of non-local energy deposition – Provides values for isotopes not considered by the current Standards – Can evaluate the impact of changes in fission energy (e.g., fast reactor systems)

9Managed by UT-Battelle for the U.S. Department of Energy 235 U thermal fission

10Managed by UT-Battelle for the U.S. Department of Energy 239 Pu thermal fission

11Managed by UT-Battelle for the U.S. Department of Energy 241 Pu thermal fission

12Managed by UT-Battelle for the U.S. Department of Energy 238 U fast fission

13Managed by UT-Battelle for the U.S. Department of Energy 239 Pu thermal fission γ energy The effect of introducing TAGS data from Algora, (2010) to JEFF decay data Testing JEFF and ENDF/B-VII.1, Cabellos et al., ND2013

14Managed by UT-Battelle for the U.S. Department of Energy OECD/NEA WPEC 25 Decay Heat Analysis International Working Party on Evaluation Co-operation of the NEA Nuclear Science Committee NEA/WPEC-25 VOLUME 25 - Assessment of Fission Product Decay Data for Decay Heat Calculations (2007) Important to – – Reactor LOCA analysis – Delayed gamma analysis from active neutron interrogation Known problems with data WPEC-25 developed a priority list of isotopes for re-evaluation Electromagnetic decay heat following thermal fission burst of 239 Pu

15Managed by UT-Battelle for the U.S. Department of Energy Beta Delayed Neutron Emission Current methods in reactor physics analysis rely on a delayed- neutron group representation (Keepin) ENDF/B 6-group; JEFF 8-group Based on theoretical-experimental approach to delayed neutron emission Isotopes with similar characteristics combined with an effective group half life and emission spectra Ability of nuclear decay data to simulate neutron emission rate and temporal energy spectra is limited (n/s/fission)

16Managed by UT-Battelle for the U.S. Department of Energy βn Emission Simulation with ORIGEN Neutron methods in ORIGEN are based on the LANL SOURCES code ORIGEN tracks production and decay of 1151 fission product isotopes However, the neutron library currently has precursor data for only 105 fission products – in this implementation, delay neutrons are only calculated for the limited number of isotopes in the neutron library (from SOURCES) ENDF/B-VII.1 has more than 500  n-emitters Delayed neutron energy spectra included for each fission product – stored as multigroup representation used in ENDF/B bins

17Managed by UT-Battelle for the U.S. Department of Energy ORIGEN βn Calculation – 235 U fission

18Managed by UT-Battelle for the U.S. Department of Energy Recent Studies at UPM  Calculations performed with JEFF and ENDF/B-VII.1 JEFF 3.1.1: 241  n-emitters, 18  2n-emitters and 4  3n-emitters ENDF/B-VII.1: 390  n-emitters, 111  2n-emitters, 14  3n-emitters and 2  4n- emitters Testing JEFF and ENDF/B-VII.1, Cabellos et al., ND2013  At t=0 s, >100% difference between ENDF/B-VII.1 6-group data and summation calculations using ENDF/B-VII.1 decay and yield data Comparison of delayed neutron emission rate calculated using Keepin 6/8-group formula and Decay&FY Data after a fission pulse in 235 U

19Managed by UT-Battelle for the U.S. Department of Energy New Developments in Uncertainty Analysis A stochastic nuclear data sampling approach is implemented in the next release of SCALE Defines uncertainty distributions and correlations for all nuclear data Reaction cross sections Fission yields Nuclear decay data Executes any SCALE code using perturbed data parameters for uncertainty analysis Performs parallel computations using MPI or OpenMP Response uncertainty computed by automated statistical analysis of output response distribution

20Managed by UT-Battelle for the U.S. Department of Energy Frequency Distributions of Sampled Values Group 1 nu-fission ; 30 GWD/T K inf ; 60 GWD/T K inf ; 0 GWD/T Tc-99 concentration; 50 GWD/T

21Managed by UT-Battelle for the U.S. Department of Energy Uncertainty analysis – 235 U fission 300 years

22Managed by UT-Battelle for the U.S. Department of Energy Summary and Conclusions New detectors are being used to obtain improved nuclear decay data – Gamma calorimeter – Neutron detectors Improved data impact delayed energy release (total and gamma decay heat) and delayed neutron emission Work initiated to integrate new measurements with the ORIGEN simulation code Planned performance evaluation using comparisons with benchmarks and other measurement data Complete uncertainty analysis now possible MTAS 3Hen VANDLE