Core performance tests for the JOYO MK-III upgrade

「常陽」MK-III炉心における性能試験

青山 卓史 ; 関根 隆 ; 前田 茂貴   ; 吉田 昌宏 ; 前田 幸基; 鈴木 惣十; 竹田 敏一*

Aoyama, Takafumi; Sekine, Takashi; Maeda, Shigetaka; Yoshida, Akihiro; Maeda, Yukimoto; Suzuki, Soju; Takeda, Toshikazu*

高速実験炉「常陽」は、照射能力向上のため、MK-III炉心への改造を行った。MK-III炉心では、二領域炉心を採用して出力を平坦化し、制御棒配置を変更した。また、原子炉熱出力が1.4倍に増加したことに伴い、冷却系の改造を行って除熱能力を向上させた。MK-III性能試験では、低出力状態で炉心核特性確認のための臨界近接,過剰反応度測定,制御棒校正,等温温度係数測定を実施した。そして、段階的に原子炉熱出力を増加させながら核計装応答,ヒートバランスを確認し、定格の140MWt出力を達成した後、燃焼係数を測定した。本論文は、これらのMK-III性能試験結果のうち、炉心核特性に関する測定・解析評価結果をまとめたものである。

Many changes were made in the recent upgrade of the experimental fast reactor JOYO to the MK-III design. The core changes which were made to achieve a fourfold increase in irradiation capacity include the introduction of a second enrichment zone, an increase in core radius and a decrease in core height. Performance tests done at low power, during the rise to power, and at full power, which focus on the neutronics characteristics, are presented. These tests include the nuclear instrumentation system response, the approach to criticality and excess reactivity evaluation, control rod worth calibration, isothermal temperature coefficient evaluation, the calibration of the nuclear instrumentation system with reactor thermal power, and the burn-up reactivity coefficient evaluation. The measurements and comparisons with calculated predictions are shown. The design predictions are consistent with the performance test results, and all technical safety specifications are satisfied. The JOYO MK-III core will provide enhanced irradiation testing capability, as well as serve as a test bed for improving fast reactor operation, performance and safety. Through the performance test evaluation, the core characteristics of a small size sodium cooled fast reactor with a hard neutron spectrum are clarified.