Development of maintenance technology on post irradiation examination facility. An invention of automatic control exhaust valve update method under operated condition of alpha tight hot cell

The inside of Metallography cell, which is an alpha-tight hot cell of post irradiation examination facility, is contaminated by radioactive matters and nuclear fuel materials at high levels, because many fuel pins that were irradiated in nuclear reactor were examined in this hot cell over many years. Therefore, for reasons of safety of workers and of the requirements of the act, the devices for negative pressure controlling (e.g. automatic control exhaust valves) must be updated under the condition of maintained negative pressure in hot cell or under the condition of completion of decontamination of radioactive matters in hot cell. Update method of automatic control exhaust valves of Metallography cell at the design-time of this hot cell was that the automatic control exhaust valves were updated under the condition of no ventilation operation after completion of decontamination. However, this method harmed the experiments of fuel pins because the working period of this method needed over one year. Therefore, a safe and efficient update method of deteriorated automatic control exhaust valves that have been perennially used for control of negative pressure in Metallography cell is invented, and this method was carried out. (author)