Fig. 4-1 Schematic illustration for reconstitution of reactor pressure vessel surveillance test specimens Construction of compound specimens is achieved by attaching additional material around a sample removed from the undeformed portion of surveillance specimens which have already been tested. Surface-activated joining makes use of rotational friction in a vacuum to join the materials without melting.

Fig. 4-2 Temperature during joining The maximum local temperature during joining falls below the reactor operating temperature of 300 degrees cent. at a distance of less than 2 mm from the seam. Joint seam quality is confirmed.

The pressure vessel of a nuclear plant power is subject to embrittlement caused by neutron irradiation during operation. Surveillance tests using Charpy impact specimens installed in the pressure vessel are performed at regular intervals to evaluate the degree of embrittlement to assure reactor pressure vessel integrity. The level of pressure vessel embrittlement at the projected end-of-life date of older nuclear plants requires that more surveillance data be obtained using the limited original surveillance specimens if the nuclear plant is to be operated for a prolonged period. The technique commonly called "reconstitution" utilizes the undeformed portion of previously tested specimens as the "insert" or central portion of a new specimen. Additional material is attached to the insert to produce compound specimens, as schematically illustrated in Fig. 4-1. One of the important concerns of reconstitution is that heating of the insert during joining should be as low as possible to preclude annealing of irradiation damage and to minimize any other metallurgical changes. We have applied the technique of surface-activated joining (SAJ) to reconstitution. SAJ allows a sound joint seam to be achieved with a low heat input and a narrow heat-affected zone. Fig. 4-2 shows the maximum temperature during joining at varying distances from the interface. A joining temperature below the reactor operating temperature of 300 degrees cent. is achieved at a distance of 2 mm. The integrity of the joint seam has been demonstrated. This reconstitution technique is a powerful tool for providing sufficient surveillance specimens to help assure further safe plant operation.

Reference Y. Nishiyama et al., Reconstitution of Charpy Impact Specimens by Surface Activated Joining, ASTM STP 1329, 484 (1998).

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