新規制基準施行後における廃止措置段階にある東海再処理施設のリスクに応じた安全対策

The Safety measures for Tokai Reprocessing Plant under the Decommissioning Stage in line with the upgraded regulatory standards

TRP廃止措置技術開発部

TRP Decommissioning Technology Development Department

東海再処理施設は平成30年6月に廃止措置計画の認可を受けて廃止措置段階に移行したものの、未だに多くの高放射性廃液を貯蔵している。高放射性廃液のガラス固化処理の完遂までには相応の期間を要すること、また立地場所が太平洋沿岸部であって地震・津波によるリスクを有していることから、東京電力福島第一原子力発電所の事故の教訓と反省を踏まえて平成25年7月に大幅に改正された原子炉等規制法(新規制基準)に照らして、リスクに応じた適切な安全対策を実施した。東海再処理施設のリスクの状況として、東海再処理施設内の放射能インベントリの多くが高放射性廃液として特定の施設に集中して貯蔵していること、貯蔵している高放射性廃液は比較的高い崩壊熱を持つこと、さらに、漏えいや沸騰による施設外への放射性物質の放出が挙げられる。また、立地場所が太平洋沿岸部であって地震・津波によるリスクを有していることから、これらの高放射性廃液を取り扱うリスクが集中する高放射性廃液貯蔵場(HAW)及びガラス固化技術開発施設(TVF)ガラス固化技術開発棟を中心に新規制基準を踏まえた安全対策を講じた。主な安全対策工事として、耐震性向上のための地盤補強工事及び排気筒補強工事、津波対策としての津波漂流物防護柵の設置、竜巻飛来物に対する防護扉等の設置、森林火災対策である防火帯の設置、内部火災・内部溢水事象への対策強化を行った。これらの一連の工事は令和2年7月から着工し、令和7年3月までの約5年間で全て完了したことから、今後のガラス固化処理に向けて施設の安全性は大きく向上したものと考える。

After the Tokai Reprocessing Plant (TRP) has received approval for its decommissioning plan in June 2018 and transferred to the decommissioning stage, it still remains an amount of high active liquid wastes. Because it takes a considerable amount of time to complete the vitrification of the high active liquid wastes, and because the plant is located near the Pacific coast and is at risk from earthquakes and tsunamis, appropriate Safety Measures were implemented in accordance with the present risks on TRP and the upgraded regulatory standards which was revised in July 2013 based on lessons learned from TEPCO's Fukushima Daiichi Nuclear Power Station accident in 2011. Most of the radioactivity inventory in the TRP is involved in the high active liquid waste and these wastes are stored in two facilities. The high active liquid wastes have a relatively high decay heat, and therefore there is a risk of releasing radioactive materials outside the facility due to leakage or boiling. In addition, since the location of TRP is near the Pacific coast and there is a risk of earthquakes and tsunamis. Thus, for the two facilities which treat the high active liquid waste, the High Active Liquid Waste Storage Facility (HAW) and the Tokai Vitrification Facility (TVF), we decided to enhance those safety features in line with the upgrade regulatory standards. The notable safety measures include ground reinforcement work and exhaust pipe reinforcement work to improve earthquake resistance, installation of tsunami debris protection fences as a tsunami countermeasure, installation of protective doors against tornado debris, setting of wildfire prevention line, and strengthened measures against internal fires and internal flooding events. These construction works began in July 2020 and were completed in five years, by March 2025. Those provide great improvement in the safety of TRP for future vitrification processing.