Degradation of cables insulated with silicone rubber for nuclear power plants by an aqueous solution of naoh sprayed during a severe accident

Some safety-related cables installed in boiling water reactors in Japan are likely to be exposed to an aqueous solution of sodium hydroxide (NaOH) during a severe accident (SA). For examining the degradation mechanism of cables insulated with silicone rubber (SiR) by the aqueous solution of NaOH sprayed during a SA, various tests to simulate a SA were conducted. Namely, after sample cables were pre-aged to simulate the degradation induced in the normal operating conditions, they were irradiated by gamma rays to simulate radiation exposure during a SA. Then, their insulated cores were immersed in the aqueous solution of NaOH with a pH of around 13 at 170 °C. It was found that the scission of siloxane chains in SiR on the surface of insulation and the generation of silicon dioxide occur with the increase in aging time and that the cable insulation is eroded from their surface contacted with the aqueous solution of NaOH.