On Unit 2 of Bohunice V-1 NPP Bohunice, UJD followed and assessed reliable and safe operation of the unit after the reconstruction works, which were completed during last years. During outage of both units, UJD had been performing ongoing control of fulfilment of in-service inspection programmes as well as evaluation of non-destructive testing results. During these activities, any new relevant indications, which would demand extraordinary actions, were not found out.
In accordance with requirements of UJD, the operator after each fuel campaign arranges for evaluation of residual service life of the essential technology equipment in terms of low cycle (i.e. high deformation) fatigue. It is based on history of relevant unit and reactor vessels from the assessment of embrittlement due to neutron exposure point of view during the operation. Residual service life of the essential technology equipment as well as assessment of reactor resistance against brittle fracture are favourable and they do not limit operation of the both units.
In the area of confinement tightness requirements, the activity of UJD was aimed at realisation of the programme of tests and improvement of the confinement tightness. After general overhaul of Bohunice V-1 units, tightness of the confinement has been further improved.
An integrated automatic reactor protection system of the Unit 1 was launched in operation, which has been a significant move towards the increase of the safety and reliability of instrumentation and control systems (I&C) important to the safety. Within the framework of the plant gradual reconstruction, the existing I&C of safety systems has been replaced by a new reactor protection system based on digital TELEPERM XS system. There are functions of fast reactor trip as well as functions of emergency safety features actuation system for postulated accidents mitigation integrated in it. The new digital reactor protection system including the software applied meets requirements and criteria for designing safety systems according to international recommendations and standards. Operational experience with the new digital reactor protection system of NPP V-1 Bohunice Unit 1 and Unit 2 confirm high reliability and availability of this system.
In 2000, the relevant parts of safety report affected by realised design changes were also assessed. These are mainly safety analyses in connection with changes on the accident mitigation and localisation system. These modifications are also related to analyses of beyond design accidents, including their impact on the population. Analyses of generation, distribution and hydrogen burning in conditions of severe accidents of V-1 Bohunice units after their reconstruction were assessed.
The assessment of operational events has been another significant part of the assessment activities of UJD at NPP V-1 Bohunice. According to the new event assessment method introduced in relevant UJD decree on events, 22 events have been recorded. The total number of operational events at Bohunice V-1 in 2000 compared to 1999 has significantly decreased due to perfecting operation staff after previous equipment reconstruction realised. Fast automatic reactor trip occurred once due to external influence (wrong manipulations in superior distribution switchyard - outside of the plant).
From public information point of view, no one event of the kind the public should be informed about occurred. According to the INES scale, 20 events have been assessed by level of “0” and 2 events by level “out of scale”. During 2000, violation of limits and conditions of safe operation did not occur.
Statistical overview of number of operational events at NPP V-1 Bohunice between 1993 and 2000 and their categorisation according to the INES scale is given in the Fig.4.1. Number of reactor scrams at NPP V-1 Bohunice in the Fig.4.2, Collective dose of personnel at NPP V-1 Bohunice (manSv) is in the Fig. 4.3.
Higher collective dose in the year 2000 is caused by a large extent of reconstruction work in the controlled zone.