After the "Stuck-open of the pressurizer safety valve" incident that occurred in Zaporozhye in 1995, the maintenance work was incriminated and led to a modification of the geometry of valve seat and disk.
Recommendations concerning the modification for periodic testing of safety valves on Zaporozhye site were proposed by Gemeinschaftkernkraftwerk Neckar GmbH, the On-Site Assistance Consulant at Zaporozhye NPP, through the TACIS on-site assistance U1.03/94.
The project consisted in checking, replacing components concerning safety valves of the pressurizer. It included also a training of the local staff in controls and procedures for recording the work.
The work included the overhaul of the two main safety valves (Sempell VS99) on the pressurizer and the pertaining pilot valves (i.e. 4 pilot valves Sempell VS66).
A complete instruction maintenance manual was required according to information mentioned in the IAEA Technical Report Series No. 268: "Manual on Maintenance of Systems and Components Important to safety". The local staff had to be trained in administrative control and procedures for recording the work.
The damaged valves had to be checked and spare parts made available for replacing different components.
This project would be completed with the qualification and certification of the trained staff.
The project was contracted directly with the company Sempell AG, the manufacturer of the original valves.
The work on site was conducted in December 1999 and in spring 2000. A step by step maintenance program has been delivered in Russian language.
The Certificate of Final Acceptance was accomplished in December 1999 for the pressurizer.