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BOHUNICE. V-1 NUCLEAR POWER PLANT

Bohunice V-1 NPP is equipped with two reactors of WWER 440 type V-230 and was put into operation in 1978-1980 as one of the last nuclear power plants with this type of reactor. Both units of NPP V-1 Bohunice operated in 2001 according to the requirements of energy dispatching at nominal power, or in a regime of tertiary regulation.

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View of the Bohunice V-1 NPPs site

Since 1990, safety improvements and upgradings of Bohunice V-1 NPP have been continuously performed. The objective of them was to enhance nuclear safety of this NPP to the target level which was in 1994 set by UJD and achieve the compliance with the recommendations of the IAEA. Planned activities within the safety improvement programme were completed by the end of 2000. In November 2000, a mission of experts invited by UJD and delegated by IAEA took place at the Bohunice NPPs. The mission members together with experts of the plant operator assessed the safety of the units of WWER-440/V-230 of Bohunice V-1 NPP after the reconstruction. The members of the mission prepared the report on the current status of safety of these units for the IAEA. The report was published at the beginning of 2001 and the results of assessment of NPPs reconstruction are positive. In 2001, UJD by its decision, issued the approval for further operation of both reactor units of Bohunice V-1 NPP.

Assessment activity

A fundamental step of the assessment activity of UJD in 2001 was a control of the tasks fulfilment from the Decision No. 110/94 and task fulfilment from the following decisions and protocols till the end of 2001, whereby the gradual reconstruction was completed from the UJD point of view. Following the review and assessment of the Safety Analysis Report (SAR) after completion of gradual reconstruction and after safety assessment of the reconstructed units the approval of UJD for further operation of Unit 1 and Unit 2 of Bohunice V-1 NPP was issued by the relevant decisions of UJD.
Assessment of Bohunice V-1 NPP safety report after the gradual reconstruction was the centre of assessment activity of UJD in 2001, as the report provides an overall image on nuclear safety of the reconstructed plant.
During outages of both units, UJD had been performing ongoing control of fulfilment of in-service inspection programme 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.
Among the significant design modifications also software changes in reactor protection systems, aimed at reliability improvement were implemented on the units of Bohunice V-1 NPP.
In accordance with requirements of UJD, the operator after each fuel campaign arranges for evaluation of residual service life of the essential technology equipment and the reactor pressure vessel. Based on the evaluation results it can be stated, that the residual service life of the essential technology equipment and of the reactor 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 tightness. After planned refuelling outages of Bohunice V-1 units, tightness of the confinement has been further improved.

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View of the Bohunice V-1 NPP after the reconstruction

In sense of the relevant decree on operational events, 20 events have been recorded, at Bohunice V-1 NPP in 2001. The total number of operational events shows decreasing tendency. The decreasing trend corresponds to a good quality of plant equipment after performed reconstruction as well as to improved activity of operational personnel.
During the start up of Unit 1 of Bohunice V-1 NPP, the fast automatic reactor trip occurred on 0,5 % of nominal power, due to wrong manipulation in distribution switchyard. The unit 2 reliable controlled the nominal power to station service load.
According to the INES scale, 19 events have been assessed by level “0” and 1 event by level “out of scale”. During 2001, violation of limits and conditions of safe operation did not occur. Statistical overview of number of operational events of Bohunice V-1 NPP between 1993 and 2001 and their categorisation according to the INES scale as well as collective dose of personnel at Bohunice V-1 NPP are given in the Tables 3.1-3.3

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Table 3.1. Number of events at Bohunice V-1 NPP

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Table 3.2. Numbers of fast automatic reactor trips at Bohunice V-1 NPP

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Table 3.3. Collective dose of personnel at Bohunice V-1 NPP (man Sv)

The increased collective dose in 2001 was caused by a great scope of reconstruction works in the controlled zone.

Inspection activity at Bohunice V-1 NPP

The inspection activity of UJD is based on internal directive that includes inspection plan, which is amended each year. The inspection activity itself is performed in a form of routine, special, team and extraordinary inspections. The inspection activity in 2001 was focused on standard routine inspections, maintenance, personnel training and actions, technology equipment condition, fire fighting measures from nuclear safety point of view, limits and conditions, maintaining high standards of cleanliness and other areas related to operational reliability and safety culture, and first of all it was aimed at examining UJD´ s requirements resulting from their decision making acts.
In April 2001, a team inspection at Unit 1 was performed aimed at the unit preparedness to further operation after accomplishment of the refuelling outage. Based on the result of the inspection a permit for further operation of the unit was issued.
An equally aimed team inspection was conducted also at Unit 2 in October 2001 after accomplishment of refuelling outage and, on the basis of its results, a permit for further operation of the unit was issued. After accomplishment of safety upgrading programme implementation within framework of gradual reconstruction of both units of Bohunice V-1 NPP, the inspection activity of UJD was primarily focused on:

monitoring of operational reliability of the unit equipped with new systems and instrumentation
regular tests of operational safety systems, particularly of the newly installed systems
monitoring of operational capability and functionality of the new digital integrated system of automatic protection and control of the unit
monitoring of the newly installed or reconstructed systems serving for both units (common systems)

In 2001, within the two units, 21 special inspections and 2 team inspections were conducted in total. Conclusions of routine inspections performed by site inspectors are summarised in protocols developed quarterly. After analysing UJD inspection findings it can be declared, that no major shortcomings occurred. The reconstruction of NPP units has been successfully accomplished.
On the basis of complex assessment, UJD consider the operation of Bohunice V-1 NPP in 2001 safe and reliable.

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