Radioactive gaseous behavior in the PWR primary coolant system, 3

In the primary coolant cooling the cores of PWRs in normal operation, radioactive fission gas and the hydrogen added for suppressing the corrosion of equipment and piping are dissolved. Among the radioactive fission gas, that exerting serious effect on the radiation exposure of workers in the case of fuel exchange, inspection and maintenance during reactor shutdown is radioactive rare gas. Accordingly, before opening the cover of a reactor vessel, it is necessary to remove the radioactive rare gas and hydrogen contained in coolant. In this study, the analysis model was set up, and the process of removing the radioactive rare gas and hydrogen dissolved in primary coolant was clarified by calculation. This result was verified by using the values measured in a plant in operation. So far, this degassing has taken several days in the period of shutdown for fuel exchange, therefore, on the basis of this analysis result, the method of shortening was proposed and examined by comparison. The system related to the degassing is explained, and the analysis of the degassing in primary coolant and the results are shown. The degassing when the gas phase part of a volume control tank is purged is analyzed. (Kako, I.)