Implementation of safety measures
classification of the individual safety-relevant issues was based on the IAEA document
EBP-WWER-03 “Safety issues and their ranking for VVER-440 /V-213 NPPs” with the
difference that the extent of safety-relevant measures has bee extended by the
recommendations of RISKAUDIT, taking into account specific conditions of the NPP Mochovce.
The results of safety measures are documented in the Safety Assessment Report or in other
Before start up of the units safety issues of categories III and II has been fulfilled in
a manner to fulfill requirements of INSAG 3 from the point of view of defense in depth.
The remaining safety measures were implemented depending on the technological
possibilities during the operation, and if such measures required unit shutdown, their
implementation was postponed to outages for refueling. This procedure was continuously
approved and verified by ÚJD.
The safety improvement programme was evaluated after the completion of units 1 and 2
shutdown in 2001. The evaluation confirmed that the implementation of safety measures
adopted within the safety improvement project which was a part of the completion of units
1 and 2 has been principally completed.
From the point of view of the IAEA document EBP-WWER-03 “Safety issues and their ranking
for WWER 440 model 213 NPPs “ the task AA08 “Possible accidents during operation on
low power and shut down” remains to be completed. Until now a comprehensive study of
event trees has been performed including thermal-hydraulic analyses dealing mainly with
the risk of boron dilution in the primary circuit. Their results have been taken into
account in the safety assessment report. Within this task SPSA needs to be completed.
Safety measure I&C 09 “Equipment for monitoring accidents” (II category) remains
to be completed as well which is planned for 2003 and 2004. The present equipment covers
the needs for design bases accidents through EOP’s. The completion of post accident
monitoring is conditioned also by developing procedures for severe accident management.
Additional safety aspects
Besides safety measures implemented during the completion of NPP Mochovce units 1 and 2
attention has been devoted also to other safety questions.
In accordance with the IAEA recommendations arising from expert missions for assessing
seismic data of the site a precision of seismo tectonic and geological data is performed
in 2000 and 2001. These data will be then used for the seismic PSA.
Continuous attention is devoted to the question of the containment . Despite of the fact
that within the safety measures a comprehensive analyses and calculations have been
performed for the whole system under maximal design bases accident, supported by number of
experiments, a comparison of full scope experimental results have been performed with
thermal-hydraulic calculations supported by a series of experiments within a PHARE/TACIS
project. The comparison confirmed the correctness of results for the NPP Mochovce. The
leak tightness of the containment during operation confirms its quality during the outages
of units 1 and 2 in 2001 a leak rate of 1.6% and 1.7% have been measured.
An important step toward safety improvement of NPP Mochovce is the start up of the process
of management of beyond design bases accidents. As it was mentioned earlier the start up
of these works on development of severe accident management guidelines (SAMG) is expected
during 2001 and at present contractual negotiations with selected supplier are going on.