The containment steel liner weld of Olkiluoto 3 will be repaired

12/09/2007

The Radiation and Nuclear Safety Authority (STUK) on 10 September authorised continuation of the welding work on the containment steel liner of the nuclear power plant under construction in Olkiluoto. On 6 August STUK ordered the work to be discontinued until the problems observed in it have been resolved.

The Radiation and Nuclear Safety Authority (STUK) on 10 September authorised continuation of the welding work on the containment steel liner of the nuclear power plant under construction in Olkiluoto. On 6 August STUK ordered the work to be discontinued until the problems observed in it have been resolved.

Containment steel liner segments, i.e. large prefabricated modules, were welded together in Olkiluoto in June. Post-welding inspections revealed problems in weld quality and deformations in the steel liner. Welding design, implementation and inspection had failed. STUK did not approve of the repair plans first proposed by the constructors.

Due to the problems, STUK in early August ordered all steel liner related welding work to be discontinued until Teollisuuden Voima (TVO) and the plant vendor have thoroughly assessed the matter.

In addition to repair plans, they were asked to propose how to improve the welding process and its quality assurance as well as the supervision of work in future work phases. STUK also required that loads exerted on the weld seam during accident situations be verified by independent calculations. The strength of the steel liner in pre-calculated situations must be demonstrated by laboratory tests later on.

TVO submitted to STUK repair plans and other required documents in early September. STUK gave permission to continue work on 10 September 2007. The steel liner will be repaired by cutting away defective sections and welding new ones in their place.

The steel liner is one of multiple barriers containing radioactive substances

The containment of a nuclear power plant prevents the spreading of radioactive substances into the environment and protects the primary circuit and safety systems from external events.

The walls and dome of the inner containment are made of pre-stressed concrete with a leaktightness-ensuring steel liner on its inner surface. The inner containment is designed to withstand the overpressure and high temperature arising in the severest accident. The steel liner prevents releases into to the environment.

The outer containment is a higly massive pre-stressed concrete structure that withstands aeroplane crashes, among others.

Further information:
Section Head Petteri Tiippana, tel. (09) 759 88 654
Information Officer Risto Isaksson, puh. (09) 759 88 208

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