Swiss regulator calls for steam generator checks

14 December 2016

The Swiss nuclear safety regulator has requested a review of documentation to check the design and quality of the forgings of the steam generators at the Beznau and Gösgen nuclear power plants. The regulator said it was "reacting to information from France".

The Swiss Federal Nuclear Safety Inspectorate (ENSI) has asked that in-depth reviews are carried out of the manufacturing documents for the components. These reviews are to include such information as: the manufacturer, manufacturing period, material, applied design specification and regulations, deviations during the manufacture, manufacturing with details of the forging process, the size of the ingots, acceptance tests carried out including test certificates, test requirements, inspection company and acceptance authorities. ENSI said non-destructive testing of the material will also be required "for further clarification of the facts".

The plant operators are required to submit their review results to ENSI by the end of April.

Following questions over quality control and carbon content of steel in the reactor pressure vessel of the EPR under construction at Flamanville, France, Areva was asked by the French nuclear safety regulator to review its records for some 400 heavy steel components made at the Creusot Forge plant since 1965. The steel in parts of some steam generators produced at the forge were subsequently found to contain high concentrations of carbon.

The steam generators at the Beznau plant were replaced in the 1990s with replacements partly produced by the Creusot Forge in France. The forged components of the steam generators at Gösgen were produced in Germany.

In June, ENSI requested Swiss plants check whether components from the Creusot Forge with possibly incorrect production documentation were or still are in use. All the plants were able to confirm that the manufacturing and material certificates for all forgings used for the safety-related main components are fully documented.

ENSI deputy director Georg Schwarz said, "Thus far we have no evidence to indicate that the steam generators in Beznau and Gösgen are affected by impermissible deviations in the material properties."

Steam generators are used in pressurized water reactors. They act as heat exchangers between the water circulating in the reactor's primary coolant circuit and the water in the secondary circuit that supplies steam to the turbines. Their domed lower head is part of the primary circuit and therefore has an important safety role in ensuring cooling water is always available.

Researched and written
by World Nuclear News