原子炉格納容器フィルタベント用の有機ヨウ素フィルタの開発

摘要

A design for an organic iodine filter was developed for filtered containment venting systems of nuclear power plants. After the Fukushima Dai-ichi nuclear accident, filtered containment venting systems were developed and installed at nuclear power plants in Japan employing aerosol filters, which are typically combinations of alkaline water scrubbers and metal fiber filters. Using silver zeolite, the newly designed filter absorbs organic iodine, which cannot be captured with alkaline water scrubbers and metal fiber filters. Methyl iodide absorption performance tests were conducted with various gas velocities and compositions, which covered the operating conditions of filtered containment venting systems. The test results demonstrated that the decontamination factors of the silver zeolite were over 50 if an appropriate gas contact time was ensured, even though steam condensation and the existence of hydrogen during vent startup had negative effects on the absorption performance. It was also revealed from the tests that intermittent venting might dampen the silver zeolite and reduce its absorption performance. Flow control of the vent gas was found to be an effective counter measure to maintain the performance even under such conditions. Filter unit tests and numerical analyses of the gas flow within the filter vessel confirmed that the gas contact time was uniform in the filter and appropriate for achieving a decontamination factor of 50.%福島第一原子力発電所の事故では，津波による被害から原子炉停止後の冷却に失敗して炉心が溶融し，さらに原子炉格納容器(以下，格納容器)の一部が損傷して大量の放射性物質が環境へ放出された。この事故の教訓を踏まえて，深層防護の観点から様々な対策が取り組まれているが，その一環として重大事故時に格納容器を過圧破損から守るとともに，放射性物質の放出量を大幅に低減するフィルタべントシステム(Filtered Containment Venting System:以下，FCVS)が開発されている。