Subgroup 29 U-235 Capture Cross Section in the keV to MeV Energy - PowerPoint PPT Presentation

Progress report 2008 Subgroup 29 U-235 Capture Cross Section in the keV to MeV Energy Region O. Iwamoto (JAEA)

Introduction • Fast-neuron critical experiments using U fuels – BFS (IPPE): underestimation of sodium voided reactivity – FCA (JAEA): large dependence of reactivity on neutron spectrum • Capture cross sections of 235 U in keV region

sodium voided reactivity in BFS MOX Sensitivity of 235 U capture cross section sodium voided reactivity

FCA experiment (enriched U + C) criticality of FCA IX assemblies Neutron spectra

Members • ENDF: T. A. Bredeweg (LANL) T. Kawano (LANL), R. McKnight (ANL, Monitor), L.C. Leal (ORNL), C. Lubitz (KAPL) • JEFF: R. Jacqmin (CEA) • JENDL: T. Nakagawa (JAEA), G. Chiba (JAEA), S. Okajima (JAEA), M. Ishikawa (JAEA), O. Iwamoto (JAEA, Coordinator) SG29 started on April 2007.

CONTROL ROD WORTH OF M. Ishikawa (JAEA) ZPPR-18A

Core Configuration of ZPPR-18A Horizontal Vertical

C/E Values of Control Rod Worth

Nuclide- and Reaction-wise Contribution to C/E Changes of Control Rod Worth

G. Chiba and S. Okajima (JAEA) FCA-IX BENCHMARK PROBLEM

FCA-IX benchmark problem • G. Chiba and S. Okajima (JAEA) have prepared a FCA-IX benchmark problem • Cores of the benchmark problem are expressed as simple two-dimensional cylinder. Each core model is composed of two material regions, i.e. , a fuel region and a blanket region. • Tables of the core specifications and the region-wise number densities are given.

O. Iwamoto, G. Chiba, T. Nakagawa (JAEA), and L. Leal (ORNL) IMPACT OF JENDL-3.2 AND ENDF/B-VII.0 RESONANCE REGION IN BENCHMARK CALCULATIONS

Comparisons of cross sections in JENDL-3.2 and ENDF/B-VII.0

Comparisons of cross sections (continued)

capture/fission ratio < σ > < α > = c i < σ > i f i σ 1 ( E ) ∫ E < α > = + i 1 c dE − σ i ( E E ) ( E ) E + i i 1 i f

JENDL-3.2 and ENDF/B-VII.0 resonance parameters combinations Resonance energy range Resonance Region JENDL-3.2 ENDF/B-VII.0 10 -5 eV – 500 eV 10 -5 eV – 2.25 keV RRR URR 500 eV – 30 keV 2.25 keV – 25 keV Energy of the average lethargy causing fission (AVG) Name Spectrum Handbook ID AVG (keV) ZEUS1 Intermediate HEU-MET-INTER-006, case1 5.05 ZEUS2 Intermediate HEU-MET-INTER-006, case2 10.33 ZEUS3 Intermediate HEU-MET-INTER-006, case3 24.02 ZEUS4 Intermediate HEU-MET-INTER-006, case4 FCA-IX-1 Intermediate 29.90 FCA-IX-2 Intermediate 116.52 FCA-IX-3 Intermediate 211.30

JENDL-3.2 for 235 U as reference 500 eV 2.25 kev 25 keV 30 keV Case 1 RR( ENDF) RR (ENDF) (JENDL) (JENDL) 500 eV 2.25 kev 25 keV 30 keV Case 2 RR( ENDF) (JENDL) (JENDL) (JENDL)

ENDF/B-VII.0 as reference 500 eV 2.25 kev 25 keV 30 keV Case 3 RR( JENDL) (JENDL) (JENDL) ENDF FILE 3 500 eV 2.25 kev 25 keV 30 keV Case 4 RR( JENDL) RR (ENDF) (ENDF) ENDF FILE 3 500 eV 2.25 kev 25 keV 30 keV Case 5 RR( ENDF) RR (JENDL) (ENDF) ENDF FILE 3

Effects on the reduction of the 235 U gamma ( > 200 eV) G1 Γ γ − 3 % ( σ γ -2%, σ f +1%) G2 Γ γ − 10 % ( σ γ ‐ 7%, σ f +3%) ‐ 3 % ‐ 10 %

ZEUS2 Sensitivity of ZEUS ZEUS4 ZEUS1 ZEUS3

Sensitivity of FCA FCA ‐ IX ‐ 1 FCA ‐ IX ‐ 2 FCA ‐ IX ‐ 3

Adjustment of U-235 cross section using integral data Sensitivities of U ‐ 235 capture to keff used in adjustment Case 1: Uncertainties of experimental data are assumed to be 0.1%dk/kk’ correlation among the data of the same critical assembly is 0.8. Case 2: Uncertainties of experimental data are assumed to be 1.0%dk/kk’ correlation among the data of the same critical assembly is 0.95.

Result of adjustment C/E values before and after adjustment Relative change in U ‐ 235 capture

Conclusions from the impact of the 235 U capture cross sections in benchmark calculations • It can be seen that ENDF/B-VII.0 capture cross section is much larger than JENDL-3.2 and statistical model calculations in the range of about 100eV to 3keV. Discrepancies are found also in the elastic scattering cross sections below 30 keV. The total and fission cross sections have no such noticeable discrepancies. The ENDF/B-VII.0 α results are in the upper part of the experimental • results. However, JENDL-3.2 agrees well with the experimental results. • Difference between ENDF/B-VII.0 and JENDL-3.2 from 500eV to 2.25keV has a large impact on both the FCA-IX and Zeus calculations while difference below 500eV has an impact only on the Zeus calculations. • Replacement of the ENDF/B-VII.0 resonance parameters by JENDL-3.2 for uranium-235 makes the C/E dependence on spectrum hardness smaller. However, this also results in unacceptable high C/E values. This can be an indication that there exists other energy region which also contributes to the multiplication factor. These cases need further investigation.

Conclusions (continued) • A simple decrease in the capture cross section, i.e. in , reduce the C/E dependence on spectrum hardness. However, it scales the up. These results may indicate that other cross section or combinations of effects may be causing the biases. • Detailed neutron balance analyses indicate that the leakages for the ZEUS benchmark experiments are on the average of 28 % whereas in the FCA it is about 4 %. The contribution of each component to for the ZEUS and FCA benchmark experiments are different from each other. • Through cross section adjustment with the integral data and the covariance information for uranium-235 cross sections, it is indicated that capture cross section in resonance range is overestimated.

Suggestion for the WPEC • Study on the impact of the 235 U capture cross sections in benchmark calculations indicates that there is a problem with the capture cross section. • However, the magnitude of the change on the capture cross section is not well understood. • Existing capture cross section measurements in the energy region from 50 eV to 30 keV shows differences in the average capture cross sections that can be more than 10 %. • It will be helpful to perform new capture cross section measurements in the keV region to improve the resonance parameter evaluation.

Suggestion for the WPEC (continued) • Suggested measurements – Measure high-resolution capture cross section. Existing measurements were done on neutron flight-path of 60-m length or less. Capture cross section measurements done in a flight-path such as 100 meter would be excellent for a better understanding of the data. – Capture-to-fission ratio (alpha measurements) could be essential. • The R-matrix analysis of the new data will lead to a better determination of the 235 U resonance parameters in the keV region.

U-235 capture cross section around 1 keV – Is there a problem? (Ref. JEF/DOC-1250) J. Yoo, KAERI R. Jacqmin, CEA 1. Introduction 2. Benchmark description and calculation 3. Analysis and discussion 4. Summary and conclusion DEN/DER/SPRC WPEC meeting Tokai-mura, June 3-4-5, 2008 1

Introduction � “Inconsistencies” reported by JAEA � Observed in very specific cases, in C/E values for several fast U-fuelled cores: � FCA IX-1, XI-2, XI-3 reactivity measurement � BFS-62-3A sodium void measurement � ZPPR-18A control rod measurement � Tests show discrepant behaviour with JENDL-3.3 vs. JENDL-3.2 � Suspected reason: U-235 capture in the 1-2 keV region in JENDL-3.3 � JAEA proposed to investigate the problem under WPEC → SG29 � SG29, started in April 2007 � FCA core models proposed as benchmarks � Studied by CEA/KAERI as a contribution to SG29 DEN/DER/SPRC WPEC meeting Tokai-mura, June 3-4-5, 2008 2

Benchmark description and calculations � FCA IX-1, IX-2, XI-3 benchmark � Small cylindrical U-metal fuelled cores + graphite � Depleted U metal radial and axial blankets, ~ 35 cm thick � 93% U-235 � Stainless steel � Homogeneous core characteristics IX-1 IX-2 IX-3 Core outer radius (cm) 30.35 23.10 17.89 Core height (cm) 60.96 40.64 35.56 Rel. core volume 1.00 (ref) 0.39 0.20 Core rel. U-235 content 1.00 (ref) 2.00 3.00 Core rel. U-238 content 1.00 (ref) 2.00 3.00 Core rel. steel content 1.00 (ref) 1.00 1.00 Core C-12 rel. content 1.00 (ref) 0.93 0.87 Graphite/Uranium 26.8 12.5 7.77 Spectral hardness r 0.30 0.46 0.62 DEN/DER/SPRC WPEC meeting Tokai-mura, June 3-4-5, 2008 3

Benchmark description and calculations � JAEA results using JENDL-3.2 and JENDL-3.3 + JAEA code system DEN/DER/SPRC WPEC meeting Tokai-mura, June 3-4-5, 2008 4

Benchmark description and calculations � KAERI/CEA results using JEF-2.2 and JEFF-3.1 + ERANOS code 1.01500 0 -0.002 1.01000 Relative sensitivity -0.004 C/E of k-effective -0.006 1.00500 -0.008 -0.01 1.00000 JEFF-3.1 -0.012 JEF-2.2 FCA-IX-1 -0.014 FCA-IX-2 FCA-IX-3 0.99500 -0.016 -0.018 0.1 1 10 100 1000 10000 100000 1e+06 1e+07 1e+08 0.99000 Energy [eV] FCA-IX-1 FCA-IX-2 FCA-IX-3 Experiment no. k-effective C/E Sensitivity of k-eff to the U-235 Capture XS DEN/DER/SPRC WPEC meeting Tokai-mura, June 3-4-5, 2008 5