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Nuclear Power Plant V-2 Bohunice consists of two units with WWER 440 type reactors of improved V-213 type, which were put into operation between 1984 and 1985. Both units operated in 2000 according to the needs of the energy dispatch centre in based load, or also in the regime of “tertiary regulation”. From both unit of NPP V-2 Bohunice also the non-electric production -heat - was used by off take from the turbine, which served, as needed, as a heat source for heating Trnava, Hlohovec and Leopoldov towns. In 2000 both units underwent planned overhaul connected with refuelling, while on unit 4 an extended overhaul was performed. The most important activity during the planned extended overhaul on unit 4 was in-service inspection of equipment, both in primary and secondary circuit, including the inspection of the reactor pressure vessel.

Remarkable view of NPP V-2 Bohunice

Assessment activity
The review and assessment of the document “Concept of modernization and safety improvement of NPP V-2 Bohunice” submitted by the operator based on UJD decision was a significant activity of UJD in connection with safety assessment of NPP V-2 Bohunice in 2000. UJD made an assessment and elaborated comments to the whole conception as well as to the individual actual tasks of safety improvement and determined the requirements for preparation of tasks implementation according to fixed schedule.
In 2000 an extended overhaul on unit 4 of NPP V-2 Bohunice was performed within which a defectoscopic in-service inspection of the reactor was carried out. UJD reviewed the programmes of in-service inspections for extended overhaul on unit 4 and for the planned overhaul on unit 3 and conducted the current inspections aimed at the fulfilment of these programmes and assessment of the results obtained. The results of in-service inspections were agreed by the commission for evaluation of in-service inspections and the results were also accepted and approved by UJD.
During in-service inspections no significant indications were found out which would require an extraordinary approach. State of plant equipment can be assessed as a good one and not limited further safety operation of units 3 and 4.

View of reactor hall of NPP V-2 Bohunice

Documents submitted by the utility concerning the 16th and the 15th refuelling campaign on unit 3 and 4 respectively of NPP V-2 Bohunice were reviewed and approved.
The revised PSA study for unit 3 of NPP V-2 Bohunice, which was supplemented by the probability safety assessment of the reactor in shut down state, was also reviewed. A study model was implemented into the EOOS Monitor programme. (Equipment Out Of Service). This programme is a part of programme package Risk and Reliability Workstations, which was developed at the EPRI institute in USA. The above mentioned software was provided to UJD and NPP Bohunice in frame of the contract with the US/DoE.
During the planned outages on unit 3 and 4 of NPP V-2 Bohunice in 2000 the assessment activities of UJD were focused on reviewing and assessment of the project modifications for the system important to safety which were submitted by the utility with the aim of safety and reliability improvement of operating units. As the most important the following project modifications were reviewed and assessed:

  • installation of the fixed fire extinguishing equipment on the board of main circulating pumps,
  • protective constructions of suction sieves in the suction pump system of the emergency core cooling on the steam generator floor on unit 4 (on unit 3 this was done already in 1999),
  • maximum level measurement in traces of bubble condenser,
  • the change of level measurement principle in the tanks of safety systems,
  • relay replacement in the circuits of the ESFAS,
  • signalling of operation of 1MPa demi-water pumps at main control room.

On unit 4 within the extended overhaul the original programme of operational controls was performed including inspection of the pressure reactor vessel from inside. Based on the request of UJD in 2000 also an inspection on the reactor pressure vessel from outside on the same unit was performed, using innovated equipment for non-destructive inspection. It can be stated that during the in-service inspections at NPP V-2 Bohunice no new indications were found out and the conditions of components of both units can be evaluated as good. Assessment activities of UJD also focused on realisation of measures to increase tightness of the containment (requested by UJD). In 2000 the achieved leakage from the containment on Unit 3 was improved by 2,87 % per day in comparison with the result in previous campaign. In both cases the measured values are better than the prescribed limits and conditions of safe operation.
The report “Principal aims and conception of I & C modernization for unit 3 and 4 of NPP V-2 Bohunice was a further document submitted to UJD for review. The review and assessment of I & C modernisation include a serie of aspects as safety classification of functions, systems and equipment, determination of the scope of the requirements and applicable standards, guidelines and recommendations, design criteria and requirements of I & C important to safety, reliability and availability requirements and requirements for quality assurance.
The assessment of operation events was an important part of the assessment of operational safety on NPP V-2 Bohunice from the side of UJD for the year 2000. According to a new methodology for event assessment in compliance with current regulation there were 22 events in total on both units. There was one event at which three workers of the external supply organisations were exposed due to their own cause. The dose, however, was lower than permitted by the Ministry of Health. With regard to the whole consideration the event was classified as level 1 on the INES scale, which means a failure that does not represent the risk but shows to small shortcomings in operational procedures. In this connection UJD informed the public and ordered the remedy provisions to the organization. The remaining events were classified either at level 0 or out of the INES scale. Neither reactor scram by automatic protection system, nor violation of the limits and conditions for safe operation were recorded.
Statistical overview of the number of operational events at NPP V-2 Bohunice between 1993 and 2000 and their categorisation in INES scale is given in the Fig. 4.4. Number of reactor scrams at NPP V-2 Bohunice is in the Fig. 4.5 and Collective dose of personnel at NPP V-2 Bohunice (manSv) is in the Fig. 4.6.

fig. 4.4

fig. 4.5

fig. 4.6

Inspection activity
Inspection activities at NPP V-2 Bohunice were conducted mainly through routine inspections. Further there were 19 special inspections focused on different fields, in compliance with the inspection plan of UJD. Inspections focused mainly on:

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

During May and June 2000 an extended overhaul on unit 4 was performed. After its finishing a team inspection of this unit was conducted focused on inspection of the overhaul performed, and of the readiness to further operation and also on the control whether measures imposed by the previous UJD decisions were met. The next team inspection was focused on shift personnel emergency exercise.
Based on the result evaluation of assessment and inspection activities and assessment of safety indicators UJD evaluated the operation of both units of NPP V-2 Bohunice in 2000 as safety and reliable.

Control room of NPP V-2 Bohunice after a partial reconstruction



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