STUK notices deficiencies in the welding of pipes at Olkiluoto

15/10/2009

Whilst supervising the Olkiluoto 3 construction site, the Radiation and Nuclear Safety Authority Finland (STUK) has noticed that instructions have not been observed in the welding of pipes and the supervision of welding. STUK requires a report on its observations from Teollisuuden Voima (TVO). This report must be approved by STUK before the subcontractor may continue its welding at the construction site.

STUK’s inspectors noticed deficiencies in the welding of the pipes in the plant’s cooling system between 6th and 8th October 2009. Among the deficiencies observed were that one welder did not have the welding instructions at his disposal, neither was he familiar with the welding requirements, as a result of which an excessive amount of power was being used in the welding. Other deviations noticed concerned the use of shielding gas necessary for welding and the shape of the contact surfaces to be welded.

The pipe installation work commenced during the autumn in systems that are significant from a point of view of the safety of the nuclear power plant. The pipe welding in question is connected to the system, which cools equipment significant from a point of view of plant safety. Pipe welding in accordance with instructions is essential to ensure the integrity of pipes during the operation of the plant. During the autumn, STUK has constantly supervised the pipe welding that has so far begun, and no similar deficiencies in welding had been noted prior to this.

TVO must now explain to STUK why the instructions were not observed in the welding work, and why the supervision carried out by the subcontractor, plant supplier and TVO did not result in these deficiencies being observed. Furthermore, TVO must explain the significance of the deficiencies observed from a point of view of weld quality. The report must suggest remedial measures through which welding work and its supervision can be made to comply with requirements. The subcontractor is not allowed to continue the welding work until the reports have been approved.  

STUK has previously drawn attention to welding quality and its supervision in the welding of the steel lining of the containment building, amongst others. STUK has also required TVO to take into account what has been learned from this experience in pipe welding and its supervision. The matter will continue to require special attention from TVO as the volume of pipe installation work increases in the near future. 

Additional information:
Director, Petteri Tiippana, tel. +358 (0)9 759 88 654
Assistant Director, Tapani Virolainen, tel. +358 (0)9 759 88 671
Information Officer, Leena Hietanen, tel. +358 (0)9 759 88 215

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