Axpo cleared for Beznau vessel head replacements

Wednesday, 11 March 2015

The Swiss nuclear regulator has inspected the new reactor vessel heads destined for the two-unit Beznau nuclear power plant and given plant operator Axpo permission to carry out their replacement this year.

The replacement vessel head for Beznau unit 2 undergoing pressure tests (Image: ENSI)

Axpo announced in 2009 that it would replace the lids of the reactor pressure vessels at the plant as part of a program to prolong the plant's operating life. Westinghouse - the original supplier of the pressurized water reactors - was selected to supply the new vessel heads. As part of the upgrade program, the two units are also to get new emergency power buildings with related systems, as well as new computer systems.

The new vessel heads were delivered to the plant site in December 2013. The upgrades were originally planned to be carried out during scheduled outages in 2014. However, Axpo announced last May that the work had been rescheduled for 2015 because of delays in installing the new emergency power supply systems.

Switzerland's Federal Nuclear Safety Inspectorate (ENSI) has now approved Axpo's plan to conduct the upgrade work. This will involve plasma-cutting through each reactor's concrete and steel containment and removing the old vessel heads to an on-site radioactive waste management building. The new heads, as well as new control rod drives, will then be fitted. The containment will then be sealed again and its tightness demonstrated by an integral leak rate test. ENSI said it will supervise the work.

George Piller, head of ENSI's department for radiation protection, said the focus is on the protection of people and the environment - both outside and inside the installation. He noted that before the units' containment buildings are opened, the fuel will be removed from the reactor cores and placed in storage pools. "The fuel elements will be well protected and the threat of a radioactive release significantly reduced," Piller said.

The installation of the new vessel head and control rod drive at unit 1 is set to be carried out during the first half of 2015, while that of unit 2 will take place in the second half of the year. Each reactor is expected to be offline for some four months while the work is carried out.

Axpo said it is investing some CHF 700 million ($696 million) in "the realization of these three large-scale projects and further enhancing the safety and reliability of the plant." It said its decision to replace the vessel heads, which it earlier said showed no sign of deterioration, is "a purely entrepreneurial one".

ENSI deputy director Georg Schwarz noted that the regulator had not requested the replacement of the vessel heads. "However, we welcome all investments that contribute to long-term maintenance or a safety improvement," he said.

The two 365 MWe Westinghouse units at the Beznau plant are the oldest power reactors in Switzerland. Unit 1 began operating in 1969, while unit 2 entered operation in 1972. In addition to providing power, both units also produce district heating.

Researched and written
by World Nuclear News