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Description
A series of critical experiments was implemented on a mockup PWR-type fuel assembly loaded with B4C neutron absorber rods (B4C rods) in a tank-type critical assembly (TCA) in 1983 [1]. The mockup assembly was a 15x15 lattice consisting of 204 UO2 fuel rods with 3.2 wt% enrichment and 21 water holes. It was surrounded by a driver lattice region composed of 2.6 wt% enrichment UO2 fuel rods. In the experiments, critical water levels were measured by varying the number of B4C rods inserted into the water holes of the mockup assembly. The core radial fission rate distributions in the mockup assembly and driver region were also measured by fuel rod gamma-scanning. In the present study, the experimental results were analyzed using a continuous-energy Monte Carlo code MVP3 [2] with a JENDL-5-based nuclear library. The analysis results were also compared with those with a JENDL-4.0-based nuclear library. The effective neutron multiplication factors (keffs) with JENDL-5 ranged from 0.9998 to 1.0006, exhibiting an increasing trend with the critical water levels, while those with JENDL-4.0 were around 0.9997. The reactivity effects by the updated neutron cross-sections of 1H in H2O, 16O in H2O, 16O in the materials other than water, 235U, and 238U in JENDL-5 were estimated by derivative calculations with the cross-sections in JENDL-5 partly replaced by those in JENDL-4.0. As a result, the differences in the trends in keffs between JENDL-5 and JENDL-4.0 were mainly attributed to the updated cross-section of 1H in water. The C/E-1s in the comparison between the calculated and measured relative fission rates of the fuel rods were obtained for the mockup assembly and driver region. The root-mean-squares (RMSs) of the C/E-1s with JENDL-5 and JENDL-4.0 for the mockup assembly increased with the number of B4C rods and ranged from 1.3% to 2.3%. Those for the driver region were almost independent of the number of B4C rods and ranged from 1.1% to 1.4%. The RMSs with JENDL-5 for the driver region were slightly larger than those with JENDL-4.0.
References
[1] Murakami K, Aoki I, Hirose H, et al. Measurements of reactivity effect of distributed absorber rods and power distributions in a PWR-type fuel assembly. Tokai-mura (Japan): Japan Atomic Energy Research Institute; 1984. (JAERI-M 84-194). [Japanese].
[2] Nagaya Y, Okumura K, Sakurai T, et al. MVP/GMVP version 3: general purpose Monte Carlo codes for neutron and photon transport calculations based on continuous energy and multigroup methods. Tokai-mura (Japan): Japan Atomic Energy Agency; 2017. (JAEA-Data/Code 2016-018).
[3] Iwamoto O, Iwamoto N, Kunieda S, et al. Japanese evaluated nuclear data library version 5: JENDL-5. J Nucl Sci Technol. 2023 Jan;60:1-60.
[4] Shibata K, Iwamoto O, Nakagawa T, et al. JENDL-4.0: a new library for nuclear science and engineering. J Nucl Sci Technol. 2011 Jan;48:1-30.
