Preventive and preservation method for neutron flux monitor housing

The reliability for a stress corrosion crack preventive and preservative effect for a neutron flux monitor housing (ICM housing) in a reactor pressure vessel (RPV) of a BWR type reactor is improved. That is, an ICM housing is inserted in a cylindrical welding pad seat attached to the inner surface of the RPV passing through the RPV wall, and it has a cylindrical shape bonded by the welding with the welding pad seat at a weld portion. The vicinity of the weld portion at the inner surface of the ICM housing is applied with machining or polishing. Then, a thin-walled cyclindrical sleeve made of stainless steel comprising ingredients improved with stress corrosion crack resistance is inserted to the portion, and the pipe is expanded, adhered and secured by a pipe expansion device. Next, the thin-walled cylindrical sleeve is welded to the ICM housing, and a pad (build-up) layer of high corrosion resistance is formed at the inner surface. With such a constitution, cracks which may be possibly caused in a small diameter and long ICM housing can be prevented relatively easily. As a result, this contributes to the reduction of the operator's radiation exposure. (I.S.)