格納容器/圧力容器鋼材の耐久性評価

Durability evaluation of steels for reactor pressure vessel/primary containment vessel

中野 純一; 塚田 隆 ; 山縣 諒平

Nakano, Junichi; Tsukada, Takashi; Yamagata, Ryohei

東京電力福島第一原子力発電所では、海水が炉心に注入された。圧力容器(RPV)から落下した燃料デブリおよび核分裂生成物の放出により格納容器(PCV)内が高い放射線量となった。水の放射線分解によりO, 過酸化水素,ラジカル等が生じるため、PCVおよびRPV鋼の腐食が懸念される。希釈人工海水中、50Cでの腐食試験を4.4kGy/hおよび0.2kGy/hの線量率の線照射下、および非照射下での腐食試験を行った。ヒドラジン(NH)を10mg/Lおよび100mg/Lを添加し、線照射下での腐食に及ぼす影響を評価した。NH無添加の場合、0.2kGy/hと非照射下での腐食減量はほぼ同等であり、4.4kGy/hでの腐食減量は非照射下での1.7倍程度であった。

The seawater was injected into the reactor cores in the Fukushima Daiichi Nuclear Power Plant. Dose in primary containment vessels (PCV) increased since the fuel debris fallen from Reactor Pressure Vessels (RPV) and fission products emitted radiation. Since oxygen, hydrogen peroxide, radicals etc. are produced by water radiolysis, it is considered that corrosion on the PCV and RPV steels would be caused. Corrosion tests in diluted artificial seawater at 50C were performed under rays dose rate of 4.4 kGy/h and 0.2 kGy/h, and unirradiation. Hydrazine (NH) of 10 mg/L and 100 mg/L were added to the flasks to evaluate the effects of NH on corrosion under rays irradiation. In situation without NH, weight losses of the specimens irradiated with 0.2 kGy/h were similar to those of the unirradiated specimens. Weight losses of the specimens irradiated with 4.4 kGy/h were approximate 1.7 times those of the unirradiated specimens.