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Year 1998 was a historical milestone for EMO NPP, when after renewing the construction, unit 1 was commissioned. Besides intensive completion of assembly works on unit 1, there were also analytical, design and implementation works going on, resulting from the safety improvement program for EMO NPP and in connection with it also preparation and subsequent tests of the equipment of the NPP. At the beginning of the year phase two of the extended hydro-test was successfully completed, during which the functions and co-operation of NPP systems was tested on unit operational parameters and in non-active conditions, i.e. without fuel being charged in the core of the reactor.

Preparation, approval and distribution of prescribed technical and safety documentation, training and examination of the operation and technical personnel of the operator were done in parallel.

After meeting conditions for launching the first phase of physical commissioning, on 27 April loading of nuclear fuel into the reactor started. The reactor was critical at a minimum controlled power for the first time on 9. 6. 1998. After the physical experiments were completed, in June the power escalation phase of the unit was launched. Another milestone in commissioning of unit 1 was connecting the first turbo-generator to the grid on 4.7. 1998, reaching a nominal power of the unit on 27.8. 1998 and start of the unit trial operation on

28.10. 1998 (when UJD issued its approval). after a successful 144 hours of provable running of unit on full power.

Assessment activity

Assessment activity of UJD at the beginning of 1998 focused on preparation of unit 1 of EMO NPP for commissioning. In this connection UJD evaluated the achieved nuclear safety condition, readiness of the unit to withstand conditions of postulated initiating events assumed in the design, emergency preparedness, plan of physical protection, etc. Based on overall evaluation of the readiness of both the equipment and personnel, UJD issued its approval in April for fuel loading into unit 1 and at the same time it imposed to finalize the safety analysis report in those parts where this extensive document did not contain up to date data or contained incomplete data.

Special attention in evaluating safety documentation was paid to limits and conditions of safe operation. The first version of this document approved prior to fuel loading was modified during commissioning and operation in several steps so that it fully respects specific properties of EMO NPP design, as well as acquired knowledge resulting from the usage this document during commissioning and operation. A separate category in assessment activity was assessment of safety measures gradually implemented within the program of safety improvements on EMO NPP. UJD reviewed the scope, as well as meeting target goals in individual safety measures.

In compliance with the requirements of regulations, all phases of commissioning, as well as work programs of individual tests for the phase of active commissioning were reviewed and approved by UJD still before launching the active phase of commissioning. UJD also issued organizational measures, which allowed flexible review and approval of modifications in this documentation.

When assessing operational events it is necessary to state that in 1998 UJD initiated several working sessions with the EMO NPP management focusing on fine tuning of the methodology for assessment of operational events, record-keeping and system of their reporting.

Despite of the fact that the period of commissioning of the nuclear power plant is used to confirm design properties of the equipment and for finding and removing faults and this activity is performed continuously under the professional supervision of specialists at the unit control room, assessment of operational events during commissioning is one of the components for evaluation of success of commissioning works. The main criterion of commissioning success is the quality of unit tuning-in and operation personnel getting acquainted with it. In general about unit 1 of EMO NPP it can be stated that the whole process of commissioning was permanently under control of UJD and managing bodies for commissioning and there were no significant operational events during commissioning. There was no leakage of radioactive materials into the environment recorded during the entire period of commissioning.

The number of operational events in 1998 on unit 1 of EMO NPP starting from its trial operation was 17. According to UJD the more important operational events were two automatic scrams and non-operability of the two (from three) trains of emergency feed water systems of steam-generators. The last event has been preliminarily evaluated as INES 1, and at the same time this event represents violation of limits and conditions. At the end of 1998 occurrence of operational events on unit 1 of NPP was stabilized and reported the same trend as for example those recorded on previous units commissioned in the former CSFR ( EBO V-1 and V-2 NPPs, and Dukovany NPP ) in the same evaluated period after commissioning.

Inspection activity

The inspection activity of UJD in EMO NPP focused mainly on checking the performance of commissioning programs, control of meeting the test acceptance criteria of in non-active commissioning phase during the second part of extended hydro-test phase, on in-service inspections during the revision phase, on inspection of nuclear materials, checking the physical protection of unit 1, on control of readiness of the personnel, on control of emergency preparedness, meeting the conditions for starting to load the fuel into the reactor core, meeting conditions to start physical tests, meeting conditions for power escalation phase, and on meeting conditions for trial operation. The concept of inspection activities of UJD during the commissioning of unit 1 of EMO NPP is illustrated in Fig. 7. Results of the most important inspections which were used for the decision- -making of UJD, are contained in the following protocols:

  • Checking the results of the second hydro-test


  • Checking the results from pre-operational revision and control of unit readiness to loading the fuel. Material for the resolution of UJD No. 101/98 containing the approval for loading fuel into unit 1.

  • Control of unit preparedness for achieving the first criticality on zero power level. Material for the resolution of UJD No. 146/98.

  • Control of unit readiness for power escalation phase. Material for the resolution of UJD No. 168/98.

  • Control of unit readiness for trial operation.

In all phases of non-active and active testing the UJD inspectors checked the performance of tests, while they were witnesses during selected test. They checked protocols from tests and they reviewed test results. They monitored the activity of commissioning management when deviations were found compared to design, especially non-conformance management and proving acceptable results by repeated tests.

Based on the findings UJD has been continuously imposing measures and for decisive activities in the final phases of commissioning it gave also instructions and directions to achieve acceptable quality of works.

Especially that the results of power escalation commissioning phase would clearly prove the capability of the main controlers, protective devices and automatic devices, to control transient processes also in case of failure of important plant equipment and by that also the capability for safe and reliable operation of unit 1 of EMO NPP.

From evaluation of inspection findings follows that partial shortcomings were found mainly in evaluating results of non-active testing programs for equipment and systems. Other were found in evaluation of some of the programs of active testing, in following technological instructions, in programs of quality assurance, in technical documentation and documentation of the plant actual status, in physical protection of nuclear facility and in communication of service and technical staff. To remove them correction measures were imposed and UJD was checking their fulfillment. Assessment of operational safety in 1998 has limited possibilities, as the power plant was operating full load practically only during the last 2 months. Overall safety assessment of unit 1, EMO NPP, taking in regard also results achieved during the start up show, that unit 1 of EMO NPP has preconditions for safe and reliable operation during the period of its commercial operation.

In 1998, within the policy of transparency and openness, there were 5 international missions visiting EMO NPP, concentrating on independent verification of specific issues of nuclear safety:

  • Mission of Austrian experts in May 1998 focused on verification of safety of the NPP before its commissioning. The mission noted a significant progress achieved in improvements on the original Soviet design. The Austrian team formulated its recommendations. Some, which related the unit operating modes were accepted already during the mission, other were imposed to the operator to improve the design (e.g. improved lightning protection). From the contested positions of the Slovak and Austrian party it is necessary to state mainly the pressure vessel of the reactor, unit 1 of EMO NPP.

  • Expert group of the IAEA established with the aim to review the safety of reactor pressure vessel on unit 1 EMO NPP met in Vienna in September 1998. Its main conclusion was that the pressure vessel of unit EMO NPP is safe and no new issues related to its safety were opened.

  • The IAEA expert mission focusing on assessing the project of safety improvements on EMO NPP was held in October 1998. The preliminary conclusions of the mission stated that the safety improvement program includes and solves all recommendations of the IAEA addressed to WWER440/V213 units. Final report will be available in 1999.

  • Special IAEA mission concentrated on review of site seismic characteristics of the Mochovce (the mission was common for EBO V-1 and V-2 NPP).

  • PHARE Project of assistance to the regulatory authority of SR in licensing of EMO NPP. Project financed by the EC, led by RIS AUDIT, which associates western technical support organizations in the area of nuclear safety ( RS - Germany, IPSN - France, ANPA - Italy and CIEMAT - Spain, and others) was during the project of solution re-oriented also to an independent safety review of EMO NPP.


© Nuclear Regulatory Authority of the Slovak Republic, 1999