Recommendations on Beta-delayed Neutron Emission from IAEA Database
The IAEA Collaborative Research Project focused on compiling neutron data for over 600 precursors to enhance understanding of beta-delayed neutron emission. Their efforts included sensitivity studies, validation of new values, standards evaluation, and systematics development to extend results to unknown nuclei. The project aimed to improve reactor constants, provide theoretical models, and prioritize future measurements. Recommendations from the project's achievements and validated values for U-235, U-238, and Pu-239 are outlined based on thermal and fast neutron induced fission reactions.
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Recommendations from CRP on beta- delayed neutron emission P. (Vivian) Dimitriou Nuclear Data Section International Atomic Energy Agency
IAEA CRP on Reference Database for beta-delayed neutron emission (2013-2017) Microscopic Macroscopic 1. Compile neutron data: half-lives T1/2, neutron emission probabilities (Pn) and neutron spectra for individual precursors (T1/2,Pn) for over 600 precursors the existing beta-delayed 1. Sensitivity studies of delayed nu-bars, delayed neutron spectra, and neutron emission rates with respect to bDN (T1/2, Pn) 2. Validate new recommended (T1/2,Pn) values against integral measurements of nu-bars, <T> and delayed-neutron spectra 2. recommend standards for Pnand reference neutron spectra Evaluate existing (T1/2,Pn) data 3. Re-evaluate the beta-delayed neutron reactor constants in 6- and 8-group format for energy applications and include them in database 3. Produce systematics and theoretical models to extrapolate results to unknown nuclei 4. measurements Provide priority list for new
Validation of new (T1/2,Pn) evaluated library U-235 (thermal neutron induced fission) 2.5 235U thermal 12 (Pn,Ti) IAEA (Pn,Ti) E-W (Pn,Ti) Rudstam (Pn,Ti) P-K-M (Pn,Ti) IAEA Oct 2017 Pn IAEA Pn E-W Pn Rudstam Pn P-K-M Pn IAEA Oct 2017 Recommended value 235U thermal 2.4 2.3 11 Total DN yield (neutr./100 fiss.) 2.2 10 Average half-life <T>,s 2.1 9 2.0 1.9 8 1.8 7 1.7 1.6 6 1.5 5 JENDL-4.0 JENDL-4.0 JENDL-4.0 JENDL-4.0 JENDL-4.0 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JENDL-4.0 JENDL-4.0 JENDL-4.0 JENDL-4.0 JENDL-4.0 JENDL-4.0 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 CY CY c/o: V. Piksaikin
U-238 (fast neutron induced fission) 6.4 238U fast 6.0 (Pn,Ti) IAEA (Pn,Ti) E-W (Pn,Ti) Rudstam (Pn,Ti) P-K-M (Pn,Ti) IAEA Oct 2017 Recommended value Pn IAEA Pn E-W Pn Rudstam Pn P-K-M Pn IAEA Oct 2017 Recommended value 238U fast 6.2 5.8 5.6 6.0 5.4 Total DN yield (neutr./100 fiss.) 5.8 5.2 5.6 Average half-life (s) 5.0 5.4 4.8 4.6 5.2 4.4 5.0 4.2 4.8 4.0 4.6 3.8 3.6 4.4 3.4 4.2 3.2 4.0 3.0 JENDL-4.0 JENDL-4.0 JENDL-4.0 JENDL-4.0 JENDL-4.0 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JENDL-4.0 JENDL-4.0 JENDL-4.0 JENDL-4.0 JENDL-4.0 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 CY CY c/o: V. Piksaikin
Pu-239 (thermal neutron induced fission) Pn IAEA Pn E-W Pn Rudstam Pn P-K-M Pn IAEA OCT 2017 Recommended value 13.5 239Pu thermal 0.85 (Pn,Ti) IAEA (Pn,Ti) E-W (Pn,Ti) Rudstam (Pn,Ti) P-K-M (Pn,Ti) IAEA OCT 2017 Recommended value 239Pu thermal 13.0 12.5 0.80 Total DN yield (neutr./100 fiss.) 12.0 Average half-life (s) 0.75 11.5 11.0 0.70 10.5 10.0 0.65 9.5 9.0 0.60 8.5 JENDL-4.0 JENDL-4.0 JENDL-4.0 JENDL-4.0 JENDL-4.0 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JENDL-4.0 JENDL-4.0 JENDL-4.0 JENDL-4.0 JENDL-4.0 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 ENDF/B-VII.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 JEFF-3.1.1 CY CY c/o: V. Piksaikin
Some conclusions With new CRP (T1/2,Pn) overall trend is to get increased values of d More experimental data available in last 10- 15 yrs (at least 35 new non-zero Pn) Some of the culprits are being scrutinized Small uncertainties due to simplistic error propagation (no correlations) FYs (IFY and CFY) have largest contributions to uncertainties Need to look at FYs carefully
31st Meeting of the International Nuclear Data Committee, 27-30 June 2016 Endorsement of Recommendation for CRP Objective: improve existing evaluated Fission Product Yields (FPY) Scope: Compilation of all new FFY and FPY experimental data Improve systematics and models Incorporate new knowledge in FPY evaluations: correct errors and inconsistencies, update evaluations, provide reliable estimate of uncertainties Agree on treatment of covariances, provide FPY covariance data and propose suitable format for inclusion in ENDF-6 Validation of new evaluations U-235; Pu-239; U-238; Cf-252 Participant countries: Belgium, China, Finland, France, Germany, India, Japan, Russia, Sweden, UK, USA
Recommendation of 6- and 8-group constants (Piksaikin et al, IPPE, Obninsk) Last recommendation: WPEC/SG-6, 1999 - Based on best existing data sets New measurements of delayed-neutron decay curves for: U-233 fast, 235 thermal and fast, 236 fast, 238 fast; Pu-239 thermal and fast; Th-232 fast; Am-241 fast, Np-237 fast Energy dependence Measurements of aggregate delayed-neutron spectra (U-235 thermal) New 6-group and 8-group fits: d, <T> New systematics with predictive power (U-235;U- 238;Pu-239)
Systematics of DN relative abundances in 8-group model using (Ac-2Z) parameter U isotopes only DN group 1 DN group 2 1 U isotopes U isotopes Group 2 Linear Fit 68% Confidence Band 68% Confidence Band 95% Confidence Band 95% Confidence Band Group 1 Linear Fit 68% Confidence Band 68% Confidence Band 95% Confidence Band 95% Confidence Band 0.1 Relative abundance (a1) Relative abundance (a2) 0.1 0.01 0.01 49 50 51 52 53 54 55 49 50 51 52 53 54 55 Ac-2Z Ac-2Z ai= exp[ci+bi(Ac-2Z)]
Relative abundances of U isotopes for Groups 3-8 1 U isotopes Group3 68% Confidence Band of B 68% Confidence Band of B Linear Fit of Sheet1 B 95% Confidence Band of B 95% Confidence Band of B 1 1 U isotopes U isotopes Relative abundance (a3) Relative abundance (a4) Relative abundance (a5) 0.1 0.1 0.1 Group 5 Linear Fit 68% Confidence Band 68% Confidence Band 95% Confidence Band 95% Confidence Band Group 4 Linear Fit 68% Confidence Band 68% Confidence Band 95% Confidence Band 95% Confidence Band 0.01 0.01 0.01 49 50 51 52 53 54 55 49 50 51 52 53 54 55 49 50 51 52 53 54 55 Ac-2Z Ac-2Z Ac-2Z U isotopes 1 1 Group 8 68% Confidence Band 68% Confidence Band Linear Fit 95% Confidence Band 95% Confidence Band U isotopes U isotopes Relative abundance (a8) Relative abundance (a6) Relative abundance (a7) 0.1 0.1 0.1 Group 6 68% Confidence Band 68% Confidence Band Linear Fit 95% Confidence Band 95% Confidence Band Group 7 68% Confidence Band 68% Confidence Band Linear Fit 95% Confidence Band 95% Confidence Band 0.01 0.01 0.01 50 51 52 53 54 55 49 50 51 52 53 54 55 49 50 51 52 53 54 55 Ac-2Z Ac-2Z Ac-2Z
Results of prediction of DN parameters for uranium isotopes lnai=ci+bi(Ac-2Z) ai= exp[ci+bi(Ac-2Z)] Group Number Ci Bi lna1 17.33212 -0.39826 lna2 3.406616 -0.10198 lna3 9.173554 -0.22445 lna4 3.281613 -0.09323 lna5 -2.73211 0.029697 lna6 -18.6346 0.31009 lna7 -8.97534 0.123161 lna8 -24.8399 0.407238
Results of prediction of DN parameters for uranium isotopes lnai=ci+bi(Ac-2Z) ai= exp[ci+bi(Ac-2Z)] U232 U233 U234 U235 U236 U237 U238 Half-life, s Relative abundances 55.6 6.26878 4.20941 2.82656 1.89800 1.27448 0.85580 0.57466 24.5 4.99364 4.50949 4.07227 3.67745 3.32090 2.99893 2.70817 16.3 2.62882 2.10031 1.67805 1.34068 1.07114 0.85579 0.68373 5.21 1.43866 1.31059 1.19392 1.08764 0.99082 0.90262 0.82226 2.37 0.66095 0.68087 0.70139 0.72254 0.74431 0.76675 0.78986 1.04 0.03334 0.04546 0.06198 0.08452 0.11525 0.15715 0.21428 0.424 0.02240 0.02534 0.02866 0.03242 0.03666 0.04147 0.046911 0.195 0.00147 0.00221 0.00332 0.005 0.00751 0.01129 0.016966 <T>, s <T>, 14.2608 12.3608 10.6796 9.18353 7.84142 6.63028 5.537861 recommended data <T>, Wilson et al. 14.35 12.38 9.1 7.37 5.3 14.439 12.36 10.487 7.541 6.896 5.05
Comparison of the average half-life obtained by different methods 16 15 14 U (fast) -recommended U (fast) - Piksaikin et al. U (fast) - Wilson et al. Fit ALL U <T> - systematics 13 12 11 10 9 <T>, s 8 7 6 5 U-232 U-233 U-234 U-235 U-238 U-237 U-236 4 233 234 235 236 237 238 239 (Ac/Z)92 Experimental data, Microscopic approach, Systematics
Energy dependence JEFF-3.1.1 ENDF/B-VII.1
Summary New data on aggregate delayed neutrons allow for improvement of Systematics Energy dependence Energy spectra This will lead to new recommendations for 6- and 8-group constants Work will be published in CRP final report (Nuclear Data Sheets) CRP website: www-nds.iaea.org/beta-delayed-neutron
TOPSY (HEU-MET-FAST-028) 235U sphere covered with a natural U reflector Dimensions: r (core) = 6.1156 cm r (reflector) = 24.1242 cm Composition: Core: 235U (93.24 wt%), 238U (5.74 wt%) and 234U Reflector: natural U keff (exp) = 1,0000 0,0030 eff (exp) = 665 13 pcm natural U HEU core
TOPSY (HEU-MET-FAST-028) Results keff eff(pcm) 665(13) 695(5) 736(5) 882(6) 705(5) 666(5) 747(5) Experimental ENDF/B-VII.1 ENDF/B-VII.1 (v01) ENDF/B-VII.1 (v02) JEFF-3.2 JEFF-3.2 (v01) JEFF-3.2 (v02) 1.00000(300) 1.00286(2) 1.00336(2) 1.00484(2) 1.00506(2) 1.00472(2) 1.00557(2)
BIG TEN (IEU-MET-FAST-007) Big cylindrical reactor. The core is composed by 10 wt% surrounded by an homogenized highly enriched + natural U cylinder. There are two separated natural U annular plates and it has a depleted U cylinder as reflector 235U cylinders with different radii and is Composition: U(10): 238U (89.7 wt%), 235U (10.2 wt%), 236U and 234U HEU and natU: 238U (89.5 wt%), 235U (10.3 wt%), 236U and 234U Natural U: 238U (99.3 wt%), 235U (0.7 wt%) and 234U 10 wt% U HEU and U-nat Depleted U: 238U (99.8 wt%), 235U (0.2 wt%), 236U and 234U natural U Depleted U
BIG TEN (IEU-MET-FAST-007) Dimensions: 3D plot (colors changed) r = 41.91 cm L = 96.428 cm keff (exp) = 1.00490 0.00080 eff (exp) = 720 7 pcm 10 wt% U HEU and U-nat natural U Depleted U 22
BIG TEN (IEU-MET-FAST-007) Results keff eff(pcm) 720(7) 725(3) 736(5) 865(4) 750(3) 729(4) 799(4) Experimental ENDF/B-VII.1 ENDF/B-VII.1 (v01) ENDF/B-VII.1 (v02) JEFF-3.2 JEFF-3.2 (v01) JEFF-3.2 (v02) 1.00490(800) 1.00468(1) 1.00479(1) 1.00611(1) 1.00432(1) 1.00402(1) 1.00463(1)
JEZEBEL (PU-MET-FAST-001) Bare Pu sphere Dimensions: r = 6.385 cm Composition: Core: 239Pu (95.2 at%), 240Pu (4.5 at%), 69Ga (0.6 at%), 71Ga and 241Pu (0.3 at%) keff (exp) = 1.0000 0.0011 eff (exp) = 194 10 pcm Pu core 24
JEZEBEL (PU-MET-FAST-001) Results keff eff(pcm) 194(10) 185(1) 180(1) 197(2) 190(1) 194(2) 224(2) Experimental ENDF/B-VII.1 ENDF/B-VII.1 (v01) ENDF/B-VII.1 (v02) JEFF-3.2 JEFF-3.2 (v01) JEFF-3.2 (v02) 1.00000(110) 0.99870(1) 0.99990(1) 1.00006(1) 1.00021(1) 1.00034(1) 1.00064(1)
