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The magnetic properties of A533B low alloy steel irradiated up to 3 x 1023 n/m2 in a nuclear reactor were measured using a SQUID sensor. The SQUID sensor used in the test is the type with a first-order axial gradiometer. Test specimens were irradiated to 0.5 x 1023 and 3.0 x 1023 n/m2, and then magnetized in a 0.2 T field until saturation before measurement. The specimens were put on a scanning table in a hot laboratory and the SQUID output was recorded while each specimen was gradually moved in a horizontal direction under the SQUID sensor. A superconducting magnet was used to put the test specimen under a magnetic field that changed from +0.01 T to -0.01 T to observe the relation between magnetic field intensity and coercive force (B-H curve). The B-H curve shows a definite tendency towards a higher coercive force for test specimens with higher neutron fluence. The test result also shows a good relation between mechanical properties, such as yield strength, tensile strength, and the Charpy impact test result, with SQUID output. This proves that there is a very good chance of developing a non-destructive evaluation system for nuclear reactor structure. This kind of evaluation system would be a great help in making plant life management even more reliable and reasonable.

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A new method of In-Core Monitor Housing replacement has been successfully applied to Tokai Unit 2 (BWR with 1100 MWe) in April of 2001. It was designed to replace a housing under dry condition of reactor pressure vessel (RPV): this enabled the elimination of water filled-up and drained processes during the replacement procedure resulting in the reduction of implementation schedule. To realize the dry condition, the radiation shields were placed in the RPV and the hollow guide pipe (GP) was adopted to transfer the apparatuses from the top to the bottom work area.