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「常陽」MK-III性能試験結果に基づくプラント動特性解析コードの整備

Modification of the Mimir-N2 Plant Dynamic Code based on JOYO MK-III Performance Test Results

高松 操 ; 黒羽 隆也*; 吉田 昌宏 

Takamatsu, Misao; Kuroha, Takaya*; Yoshida, Akihiro

高速実験炉「常陽」では、高速炉の固有安全性の実証を目的として、安全特性試験の実施に向けた研究を進めている。本研究では、過渡時のプラント挙動を精度良く予測することが重要であり、「常陽」では、プラント動特性解析コードMimir-N2により、これらの評価を行っている。上記研究では、これまで、MK-IIで実施した運転特性試験、自然循環試験等のデータに基づき、Mimir-N2を整備・検証するとともに、MK-II炉心からMK-III炉心への移行及び冷却系の改造に対応するよう炉心・冷却系モデルの整備を進めてきた。MK-III性能試験では、Mimir-N2の検証データとして、手動スクラム試験及び外部電源喪失試験等のデータを取得した。 MK-III炉心用に整備したMimir-N2の予測値と実測値を比較した結果、プラント各部の温度挙動は、概ね一致するものの、予測した原子炉出ロナトリウム温度や主冷却器入ロナトリウム温度等の降下率は、実測値より大きいことがわかった。これを改善するため、手動スクラム試験及び外部電源喪失試験の実測値に基づき、Mimir-N2の冷却系モデルのうち、原子炉容器上部プレナム部、2次主冷却系ホットレグ配管、主冷却機のモデルの整備を実施した。その結果、原子炉出ロナトリウム温度等の挙動は実測値と一致し、Mimir-N2により、手動スクラム及び外部電源喪失等の過渡変化時のプラント挙動を精度良く模擬できることを確認した。

A study of passive safety test using JOYO has been carried out to demonstrate the inherent safety of sodium cooled fast reactors. In this study, emphasis was placed on the improvement of the accuracy of plant kinetics calculations. The Mimir-N2 analysis code, developed to analyze JOYO plant kinetics, was selected as the standard code for predicting plant behavior during transients. Mimir-N2 was Previously modified based on the data from plant characteristics and natural circulation tests during JOYO MK-II. Recently, the model of the core and the heat transport system of Mimir-N2 was upgraded to correspond to the modified heat transport system for MK-III. The MK-III performance test included manual reactor shutdown test and loss of power supply test etc. as transient tests. Although the sodium temperatures calculated by Mimir-N2 agreed well with the measurement results in the MK-III performance test, it was observed that the calculated sodium temperature descent rate at reactor vessel inlet and dump heat exchanger inlet etc. were slightly larger than measured. In order to further improve the accuracy of the calculation, the Mimir-N2 heat transport system models of the reactor vessel upper plenum, the hot leg of secondary heat transport system and the dump heat exchanger were modified based on the results of the MK-III performance test. As a result of the Mimir-N2 modification, the calculation results had improved agreement with the measurement results and it was confirmed that Mimir-N2 can accurately calculate plant behavior during transients such as reactor shutdown and loss of power supply.

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