Results on research of templates from Kozloduy-1 reactor pressure vessel

The studies on the specimens manufactured from the templates cut out from t he weld 4 of Kozloduy NPP Unit 1 reactor vessel have been conducted. The da ta on chemical composition of the weld metal have been obtained. Neutron fl uence, mechanical properties, ductile to brittle transition temperature (DB TT) using mini Charpy samples have been determined. The phosphorus and copp er content averaged over all templates is 0.046 and 0.1 wt.%, respectively. The fluence amounted up to 5 x 10(18) n cm(-2) within 15-18 fuel cycles, a nd about 5 x 10(19) n cm(-2) for the whole period of operation. These value s agree well with calculated data. DBTT was determined after irradiation (T -k) to evaluate the vessel metal state at the present moment, then after he at treatment at the temperature of 475 degrees C to simulate the vessel met al state after thermal annealing (T-an), and after heat treatment at 560 de grees C to simulate the metal slate in the initial state (T-k0). As a resul t of the tests the following values were obtained: T-k, +91.5 degrees C; T- an, + 63 degrees C; and T-k0, 54 degrees C. The values of T-k and T-an obta ined by measurements were found to be considerably lower than those predict ed in accordance with the conservative method accepted in Russia (177 degre es C for T-k and 100 degrees C for T-an). Thus, the obtained results allowe d to make a conclusion that it is not necessary to anneal Kozloduy NPP Unit 1 reactor vessel for the second time. The fractographic and electron-micro scopic research allowed to draw some conclusions on the embrittlement mecha nism. (C) 1999 Elsevier Science S.A. All rights reserved.