DOSE-RATE IN THE REACTOR ROOM AND ENVIRONMENT DURING MAINTENANCE IN FUSION-REACTORS

According to the International Thermonuclear Experimental Reactor (ITE R) conceptual design activity, after reactor shutdown, damaged segment s are pulled up from the reactor and hung from the reactor room ceilin g by a remote handling device. The dose rate in the reactor room and t he environment is estimated for this situation, and the following resu lts are obtained: First, the dose rate in the room is > 10(8) muSv/h. Since this dose rate is 10(7) times greater than the biological radiat ion shielding design limit of 25 muSv/h, workers cannot enter the room . Second, lenses and optical fiber composed of glass that is radiation resistant up to 10(6) Gy would be damaged after <100 h near the segme nt, and devices using semiconductors could not work after several hour s or so in the aforementioned dose-rate conditions. Third, during susp ension of one blanket segment from the ceiling, the dose rate in the s ite boundary can be reduced by one order by a 23-cm-thicker reactor bu ilding roof. To reduce dose rate in public exposure to a value that is less than one-tenth of the public exposure radiation shielding design limit of 100 muSv/yr, the distance of the site boundary from the reac tor must be greater than 200 m for a reactor building with a 160-cm-th ick concrete roof.