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Bohunice V-2 Nuclear Power Plant consists of two units with WWER 440 type reactors of improved V-213 type, which were put into operation in 1984 and 1985. Both units operated in 2001 according to the needs of the energy dispatch centre in based load, or also in the regime of “tertiary regulation” and “primary regulation” respectively. From both unit of Bohunice V-2 NPP also the non-electric production heat was used by steam bleeding from the turbine which served as a heat source for heating Trnava, Hlohovec and Leopoldov towns. In 2001 the planned refuelling outage was performed at both units.

Assessment activity

The ongoing review and assessment of the document “Concept of modernisation and safety improvement of Bohunice V-2 NPP”, submitted by the operator based on UJD decision was a significant activity of UJD in connection with safety assessment of Bohunice V-2 NPP in 2001. UJD made an assessment and elaborated comments to the whole conception as well as to the individual topical tasks of safety improvement and by its decision determined the requirements for preparation of tasks implementation according to fixed schedule.

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Aerial view of the Bohunice NPPs site

Consequently the top management of the Slovak Republic power utility SE, a.s. definitely approved the modernisation programme for Bohunice V-2 NPP.
In 2001 a refuelling outages on units 3 and 4 of Bohunice V-2 NPP were performed. UJD reviewed the programmes of in-service inspection for refuelling outages on units 3 and 4 and conducted the current inspections aimed at the fulfilment of these programmes and assessment of the results obtained. During the in-service inspections no significant indication were found which would require an extraordinary measures. State of the plant equipment was assessed as a good one and not limiting further operation of the both units of Bohunice V-2 NPP.
Among the topical design modifications realised on both units of Bohunice V-2 NPP, it is necessary to consider the innovation of in-core monitoring system of reactors WWER 440 on unit 1 and unit 2 of Bohunice V-2 NPP. The existing in-core monitoring systems of both reactor units were supplemented by a new system which is already adapted for operation with the profile fuel. Implementation of this new system and its putting into operation as the back up system had required from the UJD personnel the review and assessment of large amount of safety documentation.

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UJD site inspector I. Moravcik durin the inspection at the Bohunice NPPs

During the refuelling outages in 2002 on unit 1 and unit 2 of Bohunice V-2 NPP the profile fuel with an average enrichment of 3,82 % was loaded into reactor core. Based on this the changes and supplements to corresponding chapters of Safety Analysis Report (SAR) were accomplished. Loading of new fuel was conducted according to licensing procedure contained in the corresponding UJD safety guide. During the planned outages on unit 1 and unit 2 of Bohunice V-2 NPP in 2001 the assessment activities of UJD were focused on reviewing and assessment of the design modifications of systems important to safety which were submitted to the UJD by the utility with the aim of safety and reliability improvement of operating units. In 2001 the programme of systematic improvement of tightness of the containment was realised on unit 1 and unit 2. By realisation of this programme further increase of confinement tightness was reached and the leakage from containment reached the values 5,97 % and 9,34 % for unit 1 and 2 respectively. These values are better as those reached in 2000 and significantly better than it is required by limits and conditions of safety operation of Bohunice V-2 NPP.
In compliance with current regulation 18 operational events at Bohunice V-2 NPP were reported to the UJD. Likewise as at Bohunice V-1 NPP, the number of events is decreasing. The plant is operating reliable and personnel quality increases with operational experience. During the previous year no reactor trip by automatic protection system occurred. The last cases, when the reactor units 1 and 2 of Bohunice V-2 NPP were scrammed automatically occurred in 1999 and 1998 respectively. According to this criterion Bohunice V-2 NPP can be ranked among the best plants in the world.
No violation of the limits and condition was recorded in 2001. According to the INES scale, 10 events have been assessed by level “0” and 8 events by level “out of scale”.

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Remarkable view of the Bohunice V-2 NPP

Statistical overview of number of operational events at Bohunice V-2 NPP between 1993 and 2001 and their ranking according to the INES scale as well as an overview of collective dose of personnel are given in the tables 3.4 up to 3.6. In the tables only those events are recorded which according to the corresponding regulation have to be reported to UJD.

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Table 3.4. Number of events at Bohunice V-2 NPP

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Table 3.5. Number of fast automatic trips at Bohunice V-2 NPP

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Table 3.6. Collective personnel dose at Bohunice V-2 NPP (man Sv)

Inspection activity at Bohunice V-2 NPP

Inspection activities at Bohunice V-2 NPP were conducted mainly through routine inspections. Further there were 18 special inspections and 2 team inspections focused on different fields in compliance with the inspection plan of UJD. Inspections were focused mainly on:

verification of observance of limits and conditions during unit operation
testing of safety systems
safety culture and reliability of operation
preparation and activities of operating personnel
physical protection, storage of spent and fresh fuel
quality assurance control, inspections and control of meeting imposed measures from the previous UJD decisions
emergency training

Based on the evaluation of results of assessment and inspection activities and assessment of safety indicators UJD evaluated the operation of both units of Bohunice V-2 NPP in 2001 as safety and reliable.

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