無液面型及び有液面型蒸気発生基の大リーク・ナトリウム-水反応事象評価 : 大リーク・ナトリウム-水反応解析(第15報)

Evaluation of large leak sodium-water reaction events for the cover-gas type and non-cover-gas type steam generators; Large leak sodium-water reaction analysis (Report No.15)

田辺 裕美*; 鈴木 道博*

not registered; not registered

大型高速増殖炉の蒸気発生器(以下SG)に,カバーガス空間を設置した場合と設置しない場合との,大リーク・ナトリウム-水反応事故時の圧力挙動の違いを明らかにする目的で,SWACSコードによる初期スパイク圧及び準定常圧の評価を行った。評価対象は,要素技術設計研究2)に基づく無液面型SG,及びそのSG頂部にカバーガス部を設置した有液面型SGである。解析結果から次のことが判った。初期スパイク圧では,無液面型SGで自由液面部での圧力波減衰効果が無いため,ホットレグ及び1HXでの圧力が相対的に高く,最高圧は,有液面型の16.2kg/cm2aに対し,27.0kg/cm2aとなる。準定常圧については,有液面型ではカバーガス部の圧力開放板の破裂圧がピーク圧となるのに対し,無液面型では圧力開放板が初期スパイク圧で作動するため,準定常的な圧力ピークは不明確となる。しかしながら,無液面型でも,圧力開放系を反応域の近くに設置すれば,初期スパイク圧低減上,かなりの効果が得られる。本解析により,実証炉のSG型式を選定する上で,SWACSコードが重要な評価手段となり得ることが明らかとなった。

Pressure behaviors in a large scale sodium-water reaction event were analyzed using the SWACS code to clarify the effect of the cover gas region of the steam generator on the pressures as a part of the design study of the Large LMFBR plant of Japan. The non-cover-gas type steam generator handled here comes from "Key Technology Design Study (II) (1985)" and the cover-gas-type was designed by adding cover gas region to the top of the former one. An initial spike pressure analysis, i.e. a short term analysis, revealed that due to the lack of a pressure attenuation effect in sodium free surface, pressures in hot-leg pipes and IHX in the non-cover-gas type were higher than those of the cover-gas type. The maximum pressures were 27.0 and 16.2 kg/cm a in the gasless and gas type, respectively. Even in the gasless type, however, it is possible to reduce the short-term pressures to a certain degree by installing the rupture discs close enough to the steam generators reaction zone. The results of a quasi-steady pressure analysis, a long term analysis, clarified that the rupture disc bursting pressure almost corresponds to the peak pressure in the gas type design while a quasi-steady pressure build-up was minor due to initial disc burst in the gasless type. From such analyses, it reveald that the SWACS code had a sufficient potential for applying to a design evaluation study of the Large LMFBR plant design.