Short period tests of hydrogen water chemistry (H\VC) were carried out at Tsuruga-1 and Tokai-2 Nuclear Power Plants. The effects of H\VC at Tsuruga-1, a non-jet pump plant, are larger than those at Tokai-2, a jet pump plant; this is caused by the much higher recombination rate of hydrogen and oxygen at the downcomer region under suitable gamma ray irradiation for the former. The effective oxygen concentrations ([02]err=[02]+1/2[H202]) in water measured at the reactor pressure vessel bottom are suppressed by HWC as effectively as those concentrations at the recirculating lines in both plants.The effects of HWC in both plants were analyzed and compared with literature data on H\VC to evaluate the differences in the effectiveness of H\VC as caused by reactor type. From the evaluation, it was concluded that the effectiveness of H\VC is much more affected by the power density in the core and the average dose rate at the downcomer than by the reactor type itself. The authors propose an evaluation concept for HWC effectiveness. This is the recombination factor, which is defined as a function of dose rate factor at the downcomer.
Short period tests of hydrogen water chemistry (H\VC) were carried out at Tsuruga-1 and Tokai-2 Nuclear Power Plants. The effects of H\VC at Tsuruga-1, a non-jet pump plant, are larger than those at Tokai-2, a jet pump plant; this is caused by the much higher recombination rate of hydrogen and oxygen at the downcomer region under suitable gamma ray irradiation for the former. The effective oxygen concentrations ([02]err=[02]+1/2[H202]) in water measured at the reactor pressure vessel bottom are suppressed by HWC as effectively as those concentrations at the recirculating lines in both plants.The effects of HWC in both plants were analyzed and compared with literature data on H\VC to evaluate the differences in the effectiveness of H\VC as caused by reactor type. From the evaluation, it was concluded that the effectiveness of H\VC is much more affected by the power density in the core and the average dose rate at the downcomer than by the reactor type itself. The authors propose an evaluation concept for HWC effectiveness. This is the recombination factor, which is defined as a function of dose rate factor at the downcomer.
IntroductionTokai-1 (GCR, Gas Cooled Reactor) nuclear power plant of the Japan Atomic Power Company started commercial operation in 1966 as the first commercial nuclear power plant in Japan and ceased its operation in 1998. Spent fuel elements were removed out of the reactor core and shipped to the reprocessing plant by June 2001. JAPC (The Japan Atomic Power Company) launched Tokai-1 decommissioning in December 2001 after the submission of the notification of decommissioning plan to the competent authority. This is the first instance of the decommissioning for a commercial nuclear power plant in Japan. The whole project is planned to take 17years in all, reactor area is safe-stored while first 10 years, as shown in Table 1.Tokai-1 decommissioning project has an important role for demonstrating that the decommissioning of commercial nuclear power plant can be executed safely and economically, and for establishing the key technologies for future LWR decommissioning in Japan.
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