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Research Papers

Study on Sensitivity of Control Rod Cell Model in Reflector Region of High-Temperature Engineering Test Reactor

[+] Author and Article Information
Yuki Honda

Japan Atomic Energy Agency, 4002, Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki-ken 311-1393, Japan
e-mail: honda.yuki@jaea.go.jp

Nozomu Fujimoto

Kyushu University, 744, Motooka, Nishi-ku, Fukuoka-shi, Fukuoka-ken 819-0395, Japan
e-mail: n.fujimoto@nucl.kyushu-u.ac.jp

Hiroaki Sawahata

Japan Atomic Energy Agency, 4002, Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki-ken 311-1393, Japan
e-mail: sawahata.hiroaki@jaea.go.jp

Shoji Takada

Japan Atomic Energy Agency, 4002, Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki-ken 311-1393, Japan
e-mail: Takada.shoji@jaea.go.jp

Kazuhiro Sawa

Japan Atomic Energy Agency, 4002, Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki-ken 311-1393, Japan
e-mail: sawa.kazuhiko@jaea.go.jp

1Corresponding author.

Manuscript received November 4, 2015; final manuscript received May 26, 2016; published online December 20, 2016. Assoc. Editor: Emmanuel Porcheron.

ASME J of Nuclear Rad Sci 3(1), 011005 (Dec 20, 2016) (6 pages) Paper No: NERS-15-1226; doi: 10.1115/1.4033813 History: Received November 04, 2015; Accepted May 28, 2016

The high-temperature engineering test reactor (HTTR) is a block-type high-temperature gas-cooled reactor (HTGR). There are 32 control rods (16 pairs) in the HTTR. Six of the pairs of control rods are located in a core region and the remainder are located in a reflector region surrounding the core. Inserting all control rods simultaneously at the reactor scram in a full-power operation presents difficulty in maintaining the integrity of the metallic sleeve of the control rod because the core temperature of the HTTR is too high. Therefore, a two-step control rod insertion method is adopted for the reactor scram. The calculated control rod worth at the first step showed a larger underestimation than the measured value in the second step, although the calculated results of the excess reactivity tests showed good agreement with the measured result in the criticality tests of the HTTR. It is concluded that a cell model for the control rod guide block with the control rod in the reflector region is not suitable. In addition, in the core calculation, the macroscopic cross section of a homogenized region of the control rod guide block with the control rod is used. Therefore, it would be one of the reasons that the neutron flux distribution around the control rod in control rod guide block in the reflector region cannot be simulated accurately by the conventional cell model. In the conventional cell model, the control rod guide block is surrounded by the fuel blocks only, although the control rods in the reflector region are surrounded by both the fuel blocks and the reflector blocks. The difference of the neutron flux distribution causes the large difference of a homogenized macroscopic cross-section set of the control rod guide block with the control rod. Therefore, in this paper, the cell model is revised for the control rod guide block with the control rod in the reflector region to account for the actual configuration around the control rod guide block in the reflector region. The calculated control rod worth at the first step using the improved cell model shows better results than the previous one.

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References

Saito, S., Tanaka, T., Sudo, Y., Baba, O., Shindo, M., Shiozawa, S., Mogi, H., Okubo, M., Ito, N., Shindo, R., Kobayashi, N., Kurihara, R., Hayashi, K., Hada, K., Kurata, Y., Yamashita, K., Kawasaki, K., Iyoku, T., Kunitomi, K., Maruyama, S., Ishihara, M., Sawa, K., Fujimoto, N., Murata, I., Nakagawa, S., Tachibana, Y., Nishihara, T., Oshita, S., Shinozaki, M., Takeda, T., Sakaba, S., Saikusa, A., Tazawa, Y., Fukaya, Y., Nagahori, H., Kikuchi, T., Kawaji, S., Isozaki, M., Matsuzaki, S., Sakama, I., Hara, K., Ueda, N., and Kokusen, S., 1994, “Design of High Temperature Engineering Test Reactor (HTTR),” Japan Atomic Energy Research Institute (JAERI), .
Tachibana, Y., Sawahata, H., Iyoku, T., and Nakagawa, T., 2004, “Reactivity Control System of the High Temperature Engineering Test Reactor,” Nucl. Eng. Des., 233(1–3), pp. 89–101. 0029-5493
Nojiri, N., Shimakawa, S., Fujimoto, N., and Goto, M., 2004, “Characteristic Test of Initial HTTR Core,” Nucl. Eng. Des., 233(1–3), pp. 283–290. 0029-5493
Fujimoto, N., Nojiri, N., Ando, H., and Yamashita, K., 2004, “Nuclear Design,” Nucl. Eng. Des., 233(1–3), pp. 23–36. 0029-5493

Figures

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Fig. 1

Schematic drawings of core and two-step control rod insertion

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Fig. 2

Control rod surrounding condition in the HTTR core: (a) conventional model and (b) revised model

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Fig. 6

Homogenized macroscopic absorption cross section of graphite block where control rods are located (energy range is described in Table 4)

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Fig. 5

Neutron flux distribution on control rod cell model: (a) fast (first) neutron energy groups; (b) upper-thermal (fourth) neutron energy groups; and (c) lower-thermal (sixth) neutron energy groups

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Fig. 4

Cross section for neutron flux distributions in Fig. 5

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Fig. 3

Modeling geometry of control rods for TWOTRAN code calculation: (a) Model A geometry in Fig. 2 and (b) model B geometry in Fig. 2

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