RECONSTITUTION TECHNIQUE FOR SURVEILLANCE PROGRAMMES

摘要

Surveillance programmes of reactor pressure vessel materials play very important role in reactor pressure vessel lifetime assessment. Unfortunately, most of them were designed and manufactured many years ago when knowledge about radiation damage as well of fracture mechanics was substantially nonadequate to present requirements. Reconstitution techniques are very effective methods for obtaining necessary data from irradiated and previously tested surveillance specimens. Electron beam welding technique was chosen for reconstitution of irradiated surveillance specimens from WWER-440 reactor pressure vessels. This method was chosen as an effective one as practically no machining is necessary after welding as specimen dimensions and forms are fully maintained. Reconstitution seems to be necessary for re-assessment of standard surveillance programmes as the original design has some disadvantages: high neutron flux in the centre of specimens chain (lead factor between 13 and 18 for Charpy V-notch specimens) and very steep flux gradient for pre-cracked Charpy specimens determined for static fracture toughness tests. Thus, reconstitution of these specimens into the other type (Charpy V to pre-cracked and vice versa) can serve for finding the correlation between transition temperature shifts of both parameters - notch impact as well as static fracture toughness temperature dependencies. Paper describes the reconstitution method and results obtained from its validation - time dependent temperature in the vicinity of the specimen notch to prove that this method does not affect irradiation damage in reconstituted specimens. Paper also gives results from first tests of re-assessed surveillance programme of WWER-440 RPV: comparison of transition temperature shifts from original Charpy V-notch specimens with transition temperature shifts from reconstituted pre-cracked Charpy specimens.