The VVER reactor under commissioning at Koodankulam nuclear power project differs from the one featured in the inter-governmental agreement between Russia and India. According to documents published in 2006, there was no weld on the beltline (middle portion) of the reactor pressure vessel (RPV). Now AERB says that there are two welds on the beltline of the RPV installed at KKNPP.VVER beltline welds are one of main causes of accelerated ageing of RPV, known as neutron embrittlement, which may damage the vessel and lead to a major accident. Other known cause of accelerated RPV ageing is the impurities and alloying elements in the base metal and weld metal. Beltline welds have been eliminated in the recent versions and the newest RPVs have lower concentration of ageing-elements.
This is a breach of the contract by the supplier in Russia. NPCIL officers who have known this are guilty of installing an unsafe machine with high risk of RPV failure leading to offsite radiological contamination besides causing financial loss to the company in case of premature retirement of the reactors. By consenting to its erection, AERB has also reneged on its responsibilities. Incidentally, according to the existing compensation regime, the supplier has no liability. These legal issues will have to be investigated and decided upon by appropriate national and international agencies.
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