Re-evaluation of nuclear criticality characteristics for infinite and finite heterogeneous lattice systems composed of uranium-zirconium hydride fuel rods used in the TRIGA annular core pulse reactor NSRR

Yanagisawa, Hiroshi; Motome, Yuiko

JAEA-Research 2025-010, 197 Pages, 2025/11

JAEA-Research-2025-010.pdf:3.5MB

For understandings of nuclear criticality risks of TRIGA fuel rods and review of safety measures for handling them, nuclear criticality characteristics for infinite and finite heterogeneous lattice systems composed of the NSRR fuel rods were re-evaluated with the use of a detailed computational model for the fuel rod. The MVP version 3 code was used with the JENDL libraries including the latest version, JENDL-5, for the re-evaluation. As the criticality characteristics, variations of neutron multiplication factors of the infinite and water-reflected finite systems were examined in detail with parameters of the lattice pitch and density of moderator water. From the results of the re-evaluated criticality characteristics, the minimum critical number of fuel rods for the water-reflected hexagonal shaped lattice system was obtained to be 46.8 0.2 using the JENDL-5 library. Moreover, the attainability of criticality without the water as moderator and reflector was examined because the zirconium hydride moderator and graphite reflector are equipped with the TRIGA fuel rod. It was found that the criticality is possible to be attained by 115.7 0.6 of the number of fuel rods, which is the smaller number of fuel rods than loaded in the NSRR standard core, even though no water exists.

Annular core experiments in HTTR's start-up core physics tests

Fujimoto, Nozomu; Yamashita, Kiyonobu*; Nojiri, Naoki; Takeuchi, Mitsuo; Fujisaki, Shingo; Nakano, Masaaki*

Nuclear Science and Engineering, 150(3), p.310 - 321, 2005/07

https://doi.org/10.13182/NSE03-79

Annular cores were formed in startup-core-physics tests of the High Temperature Engineering Test Reactor (HTTR) to obtain experimental data for verification of calculation codes. The first criticality, control rod positions at critical conditions, neutron flux distribution, excess reactivity etc. were measured as representative data. These data were evaluated with Monte Carlo code MVP that can consider the heterogeneity of coated fuel particles (CFP) distributed randomly in fuel compacts directly. It was made clear that the heterogeneity effect of CFP on reactivity for annular cores is smaller than that for fully-loaded cores. Measured and calculated effective multiplication factors (k) were agreed with differences less than 1%k. Measured neutron flux distributions agreed with calculated results. The revising method was applied for evaluation of excess reactivity to exclude negative shadowing effect of control rods. The revised and calculated excess reactivity agreed with differences less than 1%k/k.

Startup core physics tests of High Temperature Engineering Test Reactor (HTTR), 1; Test plan, fuel loading and nuclear characteristics tests

Yamashita, Kiyonobu; Fujimoto, Nozomu; Takeuchi, Mitsuo; Fujisaki, Shingo; Nakano, Masaaki*; Umeta, Masayuki; Takeda, Takeshi; Mogi, Haruyoshi; Tanaka, Toshiyuki

Nihon Genshiryoku Gakkai-Shi, 42(1), p.30 - 42, 2000/01

https://doi.org/10.3327/jaesj.42.30

no abstracts in English

Preliminary analyses for HTTR's start-up physics tests by HTTR nuclear characteristics evaluation code system

Fujimoto, Nozomu; Nojiri, Naoki; Nakano, Masaaki*; Takeuchi, Mitsuo; Fujisaki, Shingo; Yamashita, Kiyonobu

JAERI-Tech 98-021, 66 Pages, 1998/06

JAERI-Tech-98-021.pdf:2.63MB

no abstracts in English

Conceptual design study of pebble bed type high temperature gas-cooled reactor with annular core structure

Yamashita, Kiyonobu; Zinza, Keisuke*

JAERI-M 90-153, 48 Pages, 1990/09

JAERI-M-90-153.pdf:1.39MB

no abstracts in English