PURPOSE: To shorten the heating time of piping in a pressure range and to reduce a load on an RW system (radioactive material disposal system) and exposure by connecting the piping in the pressure range to a circulation system by connecting piping for testing.

CONSTITUTION: As for a pressure leak test of RPV (nuclear reactor pressure containment) 1, the pressure in the RPV 1 is raised by closing an isolation valve 8 and the range of the main piping 3 of a CS (reactor core spray) system 2 from the RPV 1 to the valve is the piping 3A in the pressure range. Then this piping 3A, a PLR (nuclear reactor recirculation) system 15 as the circulation system, and the RPV 1 constitute a circulation loop by the connecting piping 44 for the test. A circulating cooling material is heated by Joule's heat by the pump 18 of the PLR system 15 and the piping 3A is heated with the heated cooling water. Consequently, when the piping 3A is heated, fresh cooling water need not be supplied and heated and the heating time of the piping 3A can be shortened. Further, the heated cooling water circulates and is not discharged to reduce the load on an RW system.