Kohopää, Jyrki

Solin, Jussi

Tamminen, Antero

Valo, Matti

The embrittlement rate of the pressure vessel weld material is a dominating factor in life management of VVER reactor pressure vessels. In order to maintain adequate safety level, several backfitting measures have been performed in Loviisa. The neutron flux and embrittlement rate was reduced after receiving the first indications of anticipated problems. An increase of emergency core cooling water temperature and other process related changes followed to eliminate and reduce potential transients. Finally, the core weld of Loviisa 1 was successfully annealed in 1996. A current concern is to verify the post-annealing embrittlement rate in order to enable safe and economic life management of the RPV. Post-annealing re-embrittlement is governed by somewhat different mechanisms than the embrittlement of the first irradiation cycle. A new tentative approach for predicting the re-embrittlement rate has been proposed

Innovations on life management of VVER reactor pressure vessels

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