Western European Nuclear Regulators' Association

Nuclear safety in
EU candidate countries
October 2000

In order to reach Western European standards, it is recommended that the Government of Bulgaria considers the following issues, several of which were addressed in the draft Act amending the CUAEPP that was rejected by the Council of Ministers in February 2000:
There is no substitute for a strong, independent and competent regulator. Over recent years, the technical competence, strength and continuity of the Bulgarian regulator has been strongly supported by Western experts. Major efforts are still needed to ensure that the regulatory authority achieves a status that is comparable with that considered acceptable in Western European countries. The independence of the CUAEPP from bodies concerned with the promotion and supply of nuclear power needs to be made explicit,


......


Despite recent efforts that have led to significant reductions (by a factor of 10), the confinement system leak rate is still excessive, and effort is required to further reduce it. A necessary confinement improvement, the jet vortex condenser discharging through a water pool, is planned to ensure the confinement's structural integrity in case of large break LOCA accidents up to 500-mm breaks. Implementation on units 3 and 4 is planned for installation before 2002. This design solution is completely different from that already installed at Bohunice. However, the jet vortex condenser still requires confirmation of the claimed performance and a proof of the absence of unwanted side effects under the whole spectrum of conditions.

.....

In addition to the limitations in the core cooling and confinement capability, the VVER-440/230 plants had two other major safety concerns:
Internal hazards such as fires or floods, and external hazards such as seismic events or aeroplane crash, were not adequately considered in the original design. Thus the redundant parts of the safety systems were not adequately separated from each other, and were vulnerable to common cause failures. Some important safety systems were installed close to high-energy systems or in high fire risk areas (e.g. the turbine hall). Consequently, an event in one part of the plant could have resulted in complete loss of vital safety functions,
The auxiliary systems, such as electrical power supply or cooling systems, which support the safety functions, were designed with inadequate redundancy. Consequently, a single failure in a critical component of an auxiliary system could have resulted in the loss of that support function and thus also a loss of the main safety functions.

Погледни към себе си