再処理施設の重大事故時における安全性評価研究; 火災事故の研究

Study on safety evaluation under severe accidents in fire at fuel reprocessing facilities

田代 信介 

Tashiro, Shinsuke

再処理施設等では、飛散性の高い放射性物質はグローブボックス(GB)内で取り扱われる。GB火災が生じると放射性物質が建屋内へ放出され、同時に煤煙も放出される。換気系に設置された高性能エア(HEPA)フィルタは、放射性物質の施設内への閉じ込め機能を担っているため、損傷すると放射性物質の施設外 への放出量の増大が引き起こされる恐れがある。実施設で採用されているGBパネル材を取り扱える大型の装置(ACUA, Apparatus for Evaluating Clogging Effect of HEPA Filter on Confinement Capability Under Fire Accident)を用いて、代表的な複数のGBパネル材料の燃焼試験を行い、煤煙負荷量の増大とHEPAフィルタの差圧上昇の関係を調べた。従来、差圧上昇挙動は、負荷した煤煙重量の増加と関係づけて評価されてきた。それに対して、HEPAフィルタのろ過面閉塞を表現する指標としては、負荷する煤煙粒子の体積の方が適切ではないかと考え、煤煙粒子体積とHEPAフィルタの差圧との関係を検討した。その結果、煤煙負荷体積が少ない領域では、パネル材種類や換気等の燃焼条件の相違に依らず、差圧上昇挙動を統一的に評価できることを示した。

In such as reprocessing facilities, radioactive materials with easy scattering into air are usually treated in the Glove-box (GB). Under the fire accident with GB panels burning, radioactive materials and soot will be together released within the facilities. When the high efficiency particle air (HEPA) filter in the ventilation system, which plays role of the confinement equipment for radioactive materials within the facilities, is damaged during such accident, it may lead to enhance the release of radioactive materials outside them. Based above background, the relationship between the quantity of soot loading onto the HEPA filter and the differential pressure (P) across the one was investigated. The tests with burning of major GB panels materials were performed using the large test apparatus (ACUA, Apparatus for Evaluating Clogging Effect of HEPA Filter on Confinement Capability Under Fire Accident), which enables to burn GB panels materials used as the GBs components in the actual facilities. The rising behavior of P has been evaluated with the increase of loading mass of soot, however, the relationship between loading volume of soot and P was newly examined in this study because the loading volume would be more appropriate than the loading mass as the index for expressing the progress of HEPA filter's clogging by soot loading. As a result, it was found that the rising behavior of P with soot loading in the relatively low region of loading volume could be uniformly represented regardless of combustion conditions such as the kind of GB panels materials and the ventilation in the cell for burning the material.