Safety of the Mochovce NPP in comparison with Western safety requirements

In the early nineties, plans had foreseen the completion of the Mochovce pl ant to be financed under a loan from the EBRD. One of the preconditions for such a loan to be granted was a commitment by the Slovak government to dec ommission the two older units, 1 and 2, at Bohunice as soon as units 1 and 2 of the Mochovce nuclear power plant would have started long-term commerci al operation. Negotiations dragged on, especially as a consequence of interventions by Au stria, causing the Slovak side to do without Western loans and complete the plant under its Own responsibility. In this way, the West had lost any dir ect influence on the safety level of Mochovce as well as on decommissioning Bohunice. On the other hand, the Slovak side committed itself to implementing all Wes tern recommendations made to improve the safety of this reactor line. For t his purpose, also Western manufacturers were commissioned to carry out engi neering work and supply components. The Slovak regulatory authority accepted the offer made by the EU to verify the safety level of the Mochovce nuclear power plant by accompanying the c ommissioning steps carried out in 1998 and 1999 together with Western exper t organizations within the framework of a PHARE project. The backfitting measures carried out helped to correct the major weak spots in the VVER-440/V-213 reactor line, and improve their relevance to safety, respectively, to such an extent that they can no longer be classified unde r level three. The measures taken affect in particular the leak-before-break criterion, th e emergency feed system of the steam generators, demonstration of the effec tiveness of the pressure suppression system, the reliability of the instrum entation and control systems, improvements in diagnosing and monitoring sys tems, improvements in ergonomics, systematic fire protection measures, and thorough training of personnel at a full-scale power plant simulator. The remaining measures to be carried out in the next two years include a PS A for the final state of the plant after completion of all backfitting meas ures and for the down condition, the inclusion of international large-scale tests of the wetwell yet to be concluded, completion of the multichannel c ontrol room ventilation system, and another review of the seismic activity on site. The Slovak regulatory authority accepted the recommendations by the PHARE p roject and by a special IAEA mission about the seismic hazard associated wi th the Mochovce site and asked the operator to procure reliable verificatio n of the seismic design of the plant. The Mochovce nuclear power station is the first nuclear power plant with a VVER completed in Eastern and Central Europe to have a safety standard comp arable to that of Western plants. This safety standard has model character for other power plants of this type, especially for backfitting the Slovak nuclear power plants of Bohunice-3 and 4.