NUCLEAR POWER PLANT V-1 BOHUNICE
NPP V-1 Bohunice 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 2000 according to the requirements of the energy dispatch at nominal power, or in a regime of tertiary regulation.
View of JE V-1 Bohunice site
Since 1990, safety improvements and upgradings have been continuously performed at NPP V-1 Bohunice. The objective of them was to enhance the nuclear safety of this NPP to the target level which was in 1994 set by UJD and that is in compliance with the recommendations of the IAEA. Planned activities within the safety improvement programme were completed in 1999 at Unit 2 of this NPP, especially by implementation of accident localisation system, emergency core cooling system, reactor protection system, completing partial works on the air-conditioning system and completing the works of seismic resistance of the unit. On Unit 1, in total 23 modifications and upgradings were implemented still in 1999, however, the programme of reconstruction on this unit was completely accomplished not earlier than during the planned outage of Unit 1 in the first half of 2000. In order to facilitate reconstruction works on common equipment of the NPP V-1, in April and May 2000 the schedule of general overhaul considered also a simultaneous outage both units of the plant. In November 2000, a mission of specialists invited by UJD and delegated by IAEA took place at the Bohunice NPP. Ten mission members from Brazil, Finland, France, Germany, Spain, Bulgaria, and Czech Republic, together with specialists of the plant operator assessed the safety of the units of WWER-440/V-230 of NPP V-1 Bohunice in operation after the reconstruction. Members of the mission have prepared a draft report on the current status of safety of these units for the IAEA. The official IAEA report should be published in February 2001. Tentative assessment is, however, positive
View of JE V-1 Bohunice site
Assessment activities of UJD in 2000 at NPP V-1 Bohunice were focused mainly on actions related to completing reconstruction of Unit 1, completion of the common systems of both units and assessment of safety and stability of Unit 2 operation in the first year after the gradual reconstruction.
Assessment of V-1 NPP Bohunice safety report after the gradual reconstruction was the centre of assessment activity of UJD in 2000, as the report provides overwhole image on nuclear safety of the plant. This assessment was not fully completed at the end of 2000. Modifications of limiting conditions for equipment and systems reconstructed by design changes within the framework of gradual reconstruction have been reviewed. Documentation submitted by the plant operator to 20th refuelling of Unit 2 was also reviewed and approved. PSA Level 1 study for after gradual reconstruction state of the plant has been reviewed. Using the PSA model of the study, a possibility of prolonging allowable outage times of motor-generators in vital Category I power supply system of the plant units based on probabilistic approach have been reviewed and particular recommendations to prolong the times have been specified. This way UJD applied modern approach to their activities based on risk-informed regulation. Within the design preparation to completing reconstruction works on Unit 1 (during general overhaul) at the beginning of the year, the attention was aimed at:
- emergency core cooling system
- essential service water
- sprinkler system
- reactor protection system, reactor power limiting system, reactor power control system, post accident monitoring system (PAMS), in-core measurement system
- modification of 6 kV and 0. 4 kV power distribution switchboards
- replacement of motor-generator and reconstruction of vital Category I power supply
- modification of diesel-generator emergency power supply
- modification of both section an sub-distribution Category I and II power switchboards
- seismic resistance of non-supporting ties and electric equipment.
In this connection UJD performed:
- assessment of design changes in order to issue approvals
- assessment and approving of documentation for quality assurance when implementing the design changes
- reviewing and assessment of safety documentation developed in the process of verification and validation of the new reactor protection system
- reviewing and approving modifications and changes of the applied software for reactor protections,
- reviewing programmes of pre-complex and complex testing of reconstructed systems with the objective to demonstrate and document their functionality and reliability,
- reviewing changes of instrumentation and control system,
- examination, verification and validation of strength calculations of emergency core cooling system nozzles ,
- attending at some selected system tests prior their putting into operation
- following and assessment of tests of digital automatic system of the reactor protection which had already been installed on Unit 1 and until the gradual reconstruction was completed, it had been working only in open loop without connecting to actuators of safety systems. The existing protection and control systems were replaced by this new system during the general overhaul of the Unit 1 ,
- check of the status of assembled or reconstructed facilities.
View of NPP V-1 Bohunice site after the reconstruction