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EBO V-1 NPP is equipped with two reactors of WWER 440, V-230 type and was commissioned in 1978-1980 as one of the last NPP with this reactor type. Safety enhancement on V-1 NPP have been performed continuously since 1990, with the aim to improve safety of this NPP to a level required by UJD which is in compliance with the IAEA recommendations. Planned activities in the program of safety enhancement will be completed in 1999 for unit 2 and in 2000 for unit 1. The current status of EBO V-1 NPP is characterized by stable energy operation utilizing both units for so called "tertiary regulation" of capacity supplied to the power grid. On both units overhaulings were performed during the extended outages based on a long-term maintenance plan.

During the extended outage on unit 1 of EBO V-1 NPP the works of gradual reconstruction planned for 1998 were realized. The system of automatic reactor protection system was installed and its demonstration operation was launched in the so called "open loop" mode (i.e. without sending signal to actuators), modifications on the system of (super)emergency feed water system of steam-generators were completed, modifications in control (revolutions and excitation) were made and new electric protections were installed on 4 diesel--generators, the system of measuring outlet coolant temperature from fuel assemblies was replaced, modifications of the venting systems were made, partial modifications of electric distribution lines of 6 kV and 0.4 kV were made, etc.

From the program of gradual reconstruction on unit 2 of EBO V-1 NPP in 1998 the works related to reconstruction of emergency core cooling system and spraying system for hermetic zone, reconstruction of the hermetic zone with installation of jet condensers to decrease the pressure in hermetic zone in case of an LOCA accident were completed. Also on electric systems - their separation into two redundancies and the measures to improve fire safety continued to be implemented. An important part of reconstruction is realization of automatic reactor protection system. After twenty years of operation a new integrated reactor protection and control system was installed, designed and supplied by REKON (Siemens & VUJE Trnava). It is the first of its kind to be installed on WWER 440 type reactor. Through realization of safety improvement measures in 1998 on unit 2 of EBO V-1 NPP the most important requirements contained in the resolution of UJD No. 1/94 were met.

Assessment activity

Assessment activities of UJD in 1998 were focusing mainly on activities related to preparation and implementation of a gradual reconstruction of safety systems on EBO V-1 NPP. One of the most demanding of technical knowledge was the new automatic reactor protection system and related modifications on instrumentation of reactor control system. This programmable system integrates the following functions: automatic reactor scram, control of safety systems, system of measuring the neutron flux, reactor power limitation system, actuation of emergency core cooling system, start up of a diesel generator and load sequencer , reactor protection for case of steam generator pipe break and reactor power control system. Other assessment tasks, characteristic by their high demand on UJD inspectors, were mainly:

  • Review of extensive design changes related to emergency core cooling systems, spraying system and essential service water system, for unit 2 of EBO V-1 NPP. The focus of assessment was a totally new concept of the above mentioned systems, so far not used in this scope on units of WWER 440/V230 type, application of new control components in the mechanical and I&C areas as well as analysis of the proposed seismic resistance of the new systems.

  • Obr.
    Assessment of brittle fracture conditions of reactor pressure vessels of units 1 and 2 of EBO V-1 NPP. Compact samples of materials were taken and results of analysis were submitted already in 1997. After evaluation of these analyses of compact samples from pressure vessels of reactors UJD requested to precise interpretation of analysis results with the aim to determine for each pressure vessel of the reactor a critical brittle fracture temperature. Assessment procedure and methodology used correspond to the recommendations of the IAEA which were developed specifically for evaluation of embrittlement of pressure vessels of WWER 440/V230 type reactor. Results are suitable also for long-term operation of both units.

When evaluating safety of operation of EBO V-1 NPP for the past period UJD concentrated mainly on operational events. During the operation of both units of EBO V-1 NPP in compliance with the methodology approved by UJD, in 1998 there were 34 operational events recorded in total. In one case the automatic reactor protection system of unit 2 scram the reactor and in three cases it was spurious actuation of safety systems. Two operational events were assessed as INES level 1. In two cases the limits and conditions of safe operation were violated. Both cases were independently evaluated by UJD. In general it can be stated that the safety significance of recorded operating events was not high and it did not deviate from a long-term monitored average. During the whole year there was no uncontrolled releases of radioactive substances recorded into the working environment of NPP, nor into environment in the vicinity of NPP. The most important conclusions from the evaluation of the operational events on EBO V-1 NPP for 1998 are the following:

  • lack of precision in operating instructions and shortcomings in the training of operating personnel which led to the event of loss of natural circulation and by that to degradation of the safety function of residual heat removal from the primary circuit

  • repeated occurrence of foreign objects in the primary circuit during maintenance - non-adherence to the instructions at surveillance test of safety system which led to spurious start up of the high pressure injection pump,

  • Insufficient communication between the operation personnel, violation of operating instruction, of obligations and competencies of service personnel, which led to a temporary non-operation of diesel generators for emergency powers supply of category 2.

Statistical overview on the number of operational events at EBO V-1 NPP and their categorization in INES scale is shown in Fig. 1.




Inspection activity

Inspection activity of UJD at EBO V-1 NPP, besides planned inspections, focused mainly on control related to implementation of requirements requested by UJD for the program of safety improvements and by meeting these UJD conditioned further operation of both units of EBO V-1 NPP. In this connection and before the start up of unit 1 after the extended outage a team inspection was carried out. Based on positive status an approval was issued for operation of unit 1 of EBO V-1 NPP for the 18th fuel cycle.

Inspection activity on unit 2 of EBO V-1 NPP focused on implementation of safety improvements, on in-service inspection programme, on quality assurance at implementation of modifications, on verification of compatibility of parameters of equipment and systems status with safety analysis report, on pre-operational and operational testing, and also on control of meeting the imposed measures from the previous resolutions and protocols from UJD inspections. With regard to the large scope of works realized during the extended outage, start up of unit 2 and with that also finishing the inspection before start-up, will be realized in 1999. The analysis of inspections findings shows that there were no serious shortcomings. The most significant are those shortcomings in meeting the program of quality assurance by the contractor of gradual reconstruction, non-adherence to rules of clean assembly on the equipment of the primary circuit, incomplete technical documentation and operating instructions prior to commissioning of EBO V-1 NPP units after the extended outage.

Certain new facts were brought by the inspection activities of the authority which UJD started to perform based on competencies according to the new Act No. 130/1998 Coll. Based on inspections at construction tests on classified safety important equipment it can be stated that UJD found gross lack of preparedness for construction tests by the relevant supplier organizations, as practically in none of the cases it would be possible to confirm success of the construction test at the first attempt. Shortcomings were mainly in incomplete technical documentation. Based on the overall evaluation results of the status of both the equipment and personnel, including assessment of operational events, and taking in regard the favorable development of operational indicators (see Fig. 1, 2 and 3), as well as satisfactory results of inspection activity, in 1998 UJD evaluated the operation of both units of EBO V-1 NPP as safe and reliable .

Within the principle of transparency and openness, in 1998 there were 3 international missions at EBO V-1 NPP. These missions were invited by the Slovak side and focused on independent review of specific areas of nuclear safety:

  • Mission of the IAEA was realized in June 1998. It focused on the overall assessment of gradual reconstruction of EBO V-1 NPP. In its conclusions the mission stated that after the completion of the program of gradual reconstruction all recommendations of the IAEA addressed to the reactor of WWER 440/V230 type will be met.

  • The World association of nuclear operators (WANO)

  • made a review of the operational safety in October/November 1998. Representatives of WANO stated that in most of evaluated indicators EBO V-1 NPP belonged to the better half of NPPs in the world.

  • Special mission of the IAEA, which was invited to review the seismic characteristics of the site, was held in November 1998.

© Nuclear Regulatory Authority of the Slovak Republic, 1999