principles of ÚJD issued decisions on safety improvements of nuclear power plants in
similarly as in other countries, there are no officially encoded rules or requirements
concerning safety improvements of nuclear reactors. The requirements of the regulator
therefore are set specifically for the individual reactor types. Safety improvement
programs are developed by operator of nuclear power plants that has primer responsibility
for nuclear safety.
The safety concept of nuclear power plants in Slovakia is based on so-called „defense in
in-depth concept“, a concept generally used world-wide upon designing and operating
nuclear power plants. In reviewing safety of NPGI, ÚJD reviews the ability of the
facility to fulfill safety functions in terms of the design to provide for the required
standard of defense in-depth.
The process of safety improvements follows the current international safety standards.
Some specific measures were taken based on comparisons of some national standards with
those applicable in developed countries. As a rule with respect to WWER-440 reactors,
measures to improve safety are generally oriented towards improving reliability,
redundancy (in particular with respect to V-230 reactors), and physical separation of
The list of safety related shortcomings the solution ,of which is contained in the safety
improvement programs for specific reactor types, has been the result of the recent
developments in the field of primary circuit integrity, evaluation of events at nuclear
installations, results of BDBA analyses, etc.
ÚJD is using deterministic approach to efficient management of the process of safety
improvement, in particular to improve the safety of safety systems (independence,
redundancy). PSA for specific reactor is used to set priorities for individual measures to
improve safety, above all those that make the most significant contribution to core
Requirements on safety improvement are partly set with respect to accident probability.
Acceptance criteria for accident analyses set by ÚJD are generally expressed as
acceptable radiological consequences that differ according to the probability of the
initiating event. Moreover, conservative or so-called best-estimate procedures for
accident analyses have been prescribed. Best-estimate procedures are only accepted for
accidents with a very low probability of occurrence (less than 10-6).
Another principle used by ÚJD in the process of safety improvement is limitation of the
duration of operation of nuclear power plant units through granting approvals for a
limited period of time, which enables a management of the safety measures implementation
process. This approach has so far been applied to units with type V-230 reactors at NPP
Based on previous experience, ÚJD set probability targets of acceptability at systemic
level for safety systems, for the reactor protection system, for core damage, for
so-called early release of radioactive substances, as well as exclusion criterion for
external initiating events of emergency sequences.