1 Managed by UT-Battellefor the U.S. Department of Energy
Simulation of βn Emission From Fission Using Evaluated Nuclear Decay Data
Ian GauldMarco Pigni
Reactor and Nuclear Systems Division
May 2, 2013
2 Managed by UT-Battellefor 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
3 Managed by UT-Battellefor 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 storageReprocessing
• Criticality safety• Radiation shielding• Cross-section processing• Reactor physics• Sensitivity and uncertainty analysis• Spent fuel and HLW characterization
4 Managed by UT-Battellefor 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
5 Managed by UT-Battellefor the U.S. Department of Energy
ENDF/B-VII.1 Nuclear Data LibrariesDecay half lives, branching fractions, energy release− 2226 nuclidesCross sections− ENDF/B-V, -VI, -VII− JEFF-3.0/A special purpose activation fileFission product yields− Energy-dependent yields for 30 actinidesGamma ray production data− X-ray and gamma ray emissions per decayNeutron 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 nuclidesAlpha and beta spectra included in next release
6 Managed by UT-Battellefor 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
7 Managed by UT-Battellefor the U.S. Department of Energy
Decay Heat Standards• ANS-5.1-2005 and ISO 10645 (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-5.1-1971 draft, issued 1979)
• Parameters for exponential fits available for four fissionable nuclides, (MeV/s/fission)
8 Managed by UT-Battellefor 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)
9 Managed by UT-Battellefor the U.S. Department of Energy
235U thermal fission
10 Managed by UT-Battellefor the U.S. Department of Energy
239Pu thermal fission
11 Managed by UT-Battellefor the U.S. Department of Energy
241Pu thermal fission
12 Managed by UT-Battellefor the U.S. Department of Energy
238U fast fission
13 Managed by UT-Battellefor the U.S. Department of Energy
239Pu thermal fission γ energy
The effect of introducing TAGS data from Algora, (2010) to JEFF-3.1.1 decay data
Testing JEFF-3.1.1 and ENDF/B-VII.1, Cabellos et al., ND2013
14 Managed by UT-Battellefor the U.S. Department of Energy
OECD/NEA WPEC 25Decay 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) http://www.nea.fr/html/science/wpec/volume25/volume25.pdf
• 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 239Pu
15 Managed by UT-Battellefor 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)
16 Managed by UT-Battellefor 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
17 Managed by UT-Battellefor the U.S. Department of Energy
ORIGEN βn Calculation – 235U fission
0.000001
0.00001
0.0001
0.001
0.01
0.01 0.1 1 10 100 1000
Neut
ron y
ield
(n/fi
ssion
/sec)
Time (s)
Keepin ORIGEN
0
2000
4000
6000
8000
10000
0 0.5 1 1.5
Dela
yed N
eutro
n Yiel
d [n
/sec]
Energy [MeV]
0.5 s1.0 s1.5 s2.0 s2.6 s
18 Managed by UT-Battellefor the U.S. Department of Energy
Recent Studies at UPM Calculations performed with JEFF-3.1.1 and ENDF/B-VII.1
JEFF 3.1.1: 241 n-emitters, 18 2n-emitters and 4 3n-emittersENDF/B-VII.1: 390 n-emitters, 111 2n-emitters, 14 3n-emitters and 2 4n-emitters
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
0.01 0.1 1 10 100 1000
Neu
tron
em
issi
on b
y 1
fissi
on (n
/s)
Time after fission burst (s)
Keepin-JEFF-3.1.1
n_emiss_rate (JEFF-3.1.1)- My work
Keepin-ENDF/B-VII.1
n_emiss_rate (ENDF/B-VII.1)- My work
Testing JEFF-3.1.1 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 235U
19 Managed by UT-Battellefor 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
20 Managed by UT-Battellefor the U.S. Department of Energy
Frequency Distributions of Sampled Values
Group 1 nu-fission ; 30 GWD/T
Kinf ; 60 GWD/TKinf ; 0 GWD/T
Tc-99 concentration; 50 GWD/T
21 Managed by UT-Battellefor the U.S. Department of Energy
Uncertainty analysis – 235U fission
300 years
22 Managed by UT-Battellefor 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
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