Analysis of Fe-56 CIELO Evaluation Issues
Problems detected in the Fe-56 CIELO (ENDF/B-VIII.0) evaluation related to neutron leakage underestimation and overestimation in the resonance range. Solutions discussed involve addressing capture cross-section near 27 keV, patching the evaluation for better accuracy, and observing reduced overshoot in benchmarks.
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Analysis of the Post- CIELO Fe-56 Evaluation Andrej Trkov and Roberto Capote INDEN Structural Materials 13-17 December 2021 1
Background Problems were identified with the Fe-56 CIELO (=ENDF/B-VIII.0) evaluation in the resonance range: Capture in the region below the 27 keV resonance Elastic in the minima between the resonances, particularly near 300 keV INDEN Structural Materials 13-17 December 2021 2
Problems with ENDF/B-VIII.0 (CIELO) 56Fe Underestimation of neutron leakage at 1-4 MeV, overestimation near 300 keV Fig. 32, 35, Nuclear Data Sheets,148 (2018) 214-253 3
Capture cross section near 27 keV resonance 1/v background added ~ direct (n, ) ? ZPR 9/34 (hmi001) criticality reduced by ~1% INDEN Structural Materials 13-17 December 2021 4
252Cf(sf) neutron leakage: 100 cm sphere Up to 30% overestimation of neutron leakage for En~300 keV (B. Jansky et al., CVR, Rez, Czechia,EPJ WoC 239 (2020) 18005, ND2019) INDEN Structural Materials 13-17 December 2021 5
Patching the Fe-56 evaluation: elastic x.s. Sensitive to transmission through thick samples (>5 cm) INDEN Structural Materials 13-17 December 2021 6
Similar observation by M. Diakaki Sensitive to transmission through thick samples (>5 cm) INDEN Structural Materials 13-17 December 2021 7
Reduced overshoot of the spectrum in the Oktavian benchmark INDEN Structural Materials 13-17 December 2021 8
Similarly for the 100 cm Rez sphere INDEN Structural Materials 13-17 December 2021 9
and the IPPE sphere with D-T source INDEN Structural Materials 13-17 December 2021 10
However: new 9 cm thick transmission measurement on iron at nELBE INDEN Structural Materials 13-17 December 2021 11
Observation Current INDEN patch to fill the minima is not supported by the nELBE measurement To decrease the spectrum peak (at the cross section minimum) the cross section needs to be increased Flux attenuation for a narrow collimated beam is: ? = ? ????? ; ???= ? ????= ??+ ???1 ? Cross section can be increased by increasing ??? or decreasing ? The effect of increasing ? is too small INDEN Structural Materials 13-17 December 2021 12
Implications of the nELBE measurement Analytical transmission function based on INDEN data agrees with Monte Carlo simulation, showing that: Multiple scattering is negligible Self-shielding is not applicable Only a very small increase of cross section near 312 keV can be accommodated Possible effect of the angular distributions is too small Spectrum overshoot in the resonance windows remains unresolved INDEN Structural Materials 13-17 December 2021 13
Conclusions Capture below the 27 keV resonance seems to be under control Issues regarding the elastic cross sections in the minima between resonances (near 300 keV and higher) remain unresolved INDEN Structural Materials 13-17 December 2021 14
