Long-term high-temperature operation in the HTTR, 2; Core physics

HTTRによる高温連続運転,2; 炉物理評価

後藤 実  ; 藤本 望; 島川 聡司; 橘 幸男 ; 西原 哲夫 ; 伊与久 達夫

Goto, Minoru; Fujimoto, Nozomu; Shimakawa, Satoshi; Tachibana, Yukio; Nishihara, Tetsuo; Iyoku, Tatsuo

ブロック型高温ガス炉では、反応度制御を制御棒と可燃性毒物(BP)で行うが、運転時に制御棒を炉心深く挿入した場合、軸方向の出力分布が大きく歪み、その結果、燃料温度が制限値を超えるため、制御棒の炉心への挿入深さは燃焼期間を通して浅く保つ必要がある。そのため、運転時に制御棒により制御可能な反応度は小さく、反応度制御は燃焼期間を通しておもにBPで行う。ブロック型高温ガス炉については、反応度制御におけるBPの有効性は、これまで確認されていなかった。高温工学試験研究炉(HTTR)は世界で唯一稼働中のブロック型高温ガス炉で、2010年に高温運転モードによる50日間の高温連続運転に成功するとともに、その燃焼度は約370EFPDに到達し、これにより燃焼データを用いたHTTRの反応度制御におけるBPの有効性の確認が可能となった。そこで、制御棒の炉心への挿入深さの燃焼に伴う変化を調べ、HTTRの反応度制御におけるBPの有効性を確認した。また、制御棒の挿入深さの燃焼変化について、計算値と測定値を比較し、HTTRの炉心燃焼計算手法の妥当性を確認した。

In the High Temperature Engineering Test Reactor (HTTR), which is a Japanese block-type HTGR, reactivity is controlled by control rods (CRs) and burnable poisons (BPs). The CRs insertion depth into the core should be retained shallow during burnup period, because the large insertion depth leads to significant disturbance of the power distribution, and consequently fuel temperature rises above the limit. Thus, the controllable reactivity with the CRs during operation is small, and then reactivity control through the burnup period largely depends on the BPs. It has not been confirmed an effectiveness of BPs on reactivity control on block-type HTGRs. The HTTR succeeded in long-term high temperature operation, and its burnup reached about 370EFPD. Thereby it became possible to confirm the effectiveness of BPs on reactivity control on the HTTR using its burnup data. We focused on a burnup change in the CRs insertion depth into the core to confirm whether the BPs functioned as designed. Additionally, we compared the change in the CRs insertion depths between analysis results and the experimental data to confirm validity of a whole core burnup calculation with the SRAC/COREBN. As a result, the experimental data showed that although the CRs insertion depth into the core was increased with burnup, it was retained the allowable depth. Meanwhile, the analysis result of the CRs insertion depth was in good agreement with the experimental data.