The search for a loose part in the reactor pressure vessel (RPV) of block 1 of the nuclear power plant in Philippsburg 1 (NPP Philippsburg 1) has led to first results. Like already reported, the nuclear power plant was disconnected from the power system over the weekend by the operator, EnBW Energie Baden-Württemberg AG for reasons of safety and precaution. Beforehand, the permanent sonic monitoring of the RPV had sent signals for a loose part in the area of the recirculation pumps.
The inspection work with an underwater camera has now shown that the loose part has to do with an attachment screw from one of four feeder water junction boxes. The feeder water junction boxes are installed in the upper part of the RPV and provide for an even distribution of feeder water in the RPV. The functional capability of the feeder water distribution was not impaired by the absence of the screw.
According to the present state of knowledge, the screw has come off and like the washer too, has reached the floor of the RPV passing through the recirculation pumps. After having localised the screw and washer there, they will be retrieved. Together with the plant manufacturer and the suppliers of the pumps, the entire procedure is presently being analysed and the cause identified. The goal is to eliminate a repetition as far as it is technologically possible.
In this context an incident from the year 1986 is also being investigated. At the time it had been noticed that two screws had come off , one in the same position like now. As a remedy, the screw thread was reworked in 1986 and the screws professionally fastened and secured. The principle of screw fixing complies with the mechanical demands. Purpose of the analysis is also to find out whether a direct and causal relationship exists between the then incident and the present notifiable event.