The formation of nitrous acid has been studied in the 'OC0-y radiolysis of concentrated nitric acid solutions. The yields of nitrous acid are proportional to the electron fraction of nitric acid, on the basis of which, an additional reaction path, NO; O(3P) + NO; with a primary yield of 0.16 pmol J -' , has been verified for the direct action of radiation on nitric acid.

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TiO 2 addition into boiling water reactor (BWR) primary system is being developed as a method to mitigate stress corrosion cracking (SCC) of the BWR structural materials. This technique aims for electrochemical corrosion potential (ECP) decrease of reactor materials by photo-excitation reaction under Cherenkov irradiation. Tests have been conducted in the test loop in both BWR and OECD Halden reactor to investigate the feasibility of the SCC mitigation method with TiO 2 . The test results showed that the ECP of TiO 2 deposited materials was decreased to <-0.3V(vs.SHE) under both UV light irradiation in the BWR reactor water normal water chemistry (NWC) environment and in-core Cherenkov irradiation in the Halden BWR simulation loop under higher dissolved oxygen condition. This TiO 2 technique was confirmed to be feasible as a SCC mitigation method for BWR structural materials.

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