The discussion of the RSK extended to the following subject maters:
- Corrosion at the reactor pressure vessel of the Davis Besse nuclear power plant (USA),
- non-availability of valves at the Unterweser nuclear power plant (KKU), and
- criticality safety for the final disposal of plutonium.
In March 2002, a corrosion cavity (width of 100 to 125 mm) and a gap (length of about 180 mm) - caused by boric acid leaks - was detected on control rod drive mechanism nozzles of the RPV head. The major part of the steel of the reactor pressure vessel with a wall thickness of about 168 mm was corroded down to the cladding. The medium thickness of the remaining cladding in this area was about 6.5 mm. Laboratory analyses showed a crack at the surface of the cladding with a length of about 9.5 mm which was not through-wall. This event to be regarded as severe one, gave reason to examine its applicability to nuclear power plants in Germany. In the opinion of the RSK, the event is mainly due to deficiencies in the maintenance management of this US-American plant operator. At German plants, there is a more stringent maintenance management and monitoring system. The RSK will discuss in depth questions related to the materials, corrosion processes and plant management before it concludes its statement.
Regarding the reportable event at the Unterweser nuclear power plant (KKU) of 6.6.1998 (unavailability of one of four main steam safety and relief valves when demanded), the RSK adopted a statement [107 KB] (in German) prepared by the RSK Committee on REACTOR OPERATION (RB) (soon available under www.rskonline.de). It arrives at the conclusion that the plant operator established an appropriate programme in the organisational/administrative area in order to counteract a recurrence of such events. The programme includes a modern, process-oriented management system which the RSK regards as relevant also for other plants.
On the criticality safety for the final disposal of plutonium, the Committee on SUPPLY AND WASTE HANDLING (VE) had submitted a status report to the RSK. The report includes the procedures and boundary conditions that would have to be considered when emplacing plutonium-containing radioactive wastes and irradiated fuel elements in a repository in order to avoid also over geological periods of time that a condition may occur which leads to criticality. In view of the geometric, geological and geochemical conditions changing over very long periods of time, some of the scenarios to be considered could only be based on processes in an idealised form and a conservative approach. The status report (soon available under www.rskonline.de), shall contribute to the continuation of the scientific discussion and the promotion of the further development of the methods so that the scenarios and boundary conditions for the future selection of a repository site can be derived specifically for the host rock selected.