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MOCHOVCE NUCLEAR POWER PLANT

Mochovce NPP consists of four units of WWER 440 , V 213 reactor type with an improved safety level. Unit 1 was commissioned in 1998 and unit 2 in April 2000. Unit 3 and 4 are in a phase of construction which was interrupted in 1994. During the last year a completion of a part of the safety improvement measures prescribed by UJD continued.

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Aerial view of the Mochovce NPP site

Within the second refuelling outage of unit 1 when the reactor core has been fully unloaded, safety improvement measures have been implemented at:

charging lines of core cooling system
fire protection check valves
modifications of equipment and pipelines to mitigate internal hazards raising from a high energy pipeline rupture
improvement of seismic resistance of the equipment

Prior to a re-start of both units after the refuelling outages UJD carried out in form of team inspections a complex evaluation of the state of implementation of requirements followed from generally applicable legal regulations and also from requirements UJD contained in its decisions and protocols. UJD stated a satisfaction with reached results of the fulfilment of its requirements on nuclear safety.
At the site of Mochovce NPP a daughter company SE-MO 3,4 managing a conservation of partially constructed units 3 and 4 was founded on 1 July 2001.

Assessment activity

In 2001 UJD assessed reports on a completion of safety improvement measures included in the Programme of safety improvement of Mochovce NPP. Within the refuelling outages of unit 1 and 2 a corresponding portion of in-service inspection programme of classified equipment was completed in the scope of an adequate in-service inspection cycle. Based on the in-service inspection results the equipment was evaluated as the appropriate one for further operation and a physical condition could be evaluated as a good one.
Throughout of 2001 year on the basis of an evaluation of a pre-service inspection phase the modifications of individual quality assurance programmes and in-service inspection programmes of classified equipment have been assessed.
In 2001 UJD completed the review of Chapter 4 and 15 of the Pre-operational Safety Analysis Report dealing with the licensing of profile fuel which came into use at Mochovce NPP Changes of the in-core monitoring system software linked with the utilisation of profile fuel were one of the most considerable design modifications implemented at unit 1 and 2 of NPP Mochovce.
At the Mochovce NPP 62 events which, according to a relevant regulation have to be reported to UJD, occurred in 2001. This number is higher than at Bohunice NPP, but it does not exceed the frame of event numbers typical for units under commissioning. According to the INES scale 12 events were classified into level 0, 43 events were classified out of the scale. Two events were classified into level 1 what, according to the above mentioned scale, does not represent failures violating the nuclear safety. One of these events was a short time discrepancy of plant parameters from the range of the technical specification during a unit start-up caused by a human factor. Not even this case had a safety significance.
During the whole last year at unit 1 an activation of the automatic reactor protection trip system did not occur, what can be considered as a world wide good result. At unit 2 the reactor protection trip system was activated one time by control room personnel as a consequence of the dropout of 440 kV line, nevertheless the automatics during the event was operating normally.
During the operation of unit 2 a leakage at the steam generator secondary side and also a leakage of the main isolation valve seal occurred. Both leakages were repaired during short time unit outages and after then unit continued in the normal operation. Total number and character of the events at Mochovce NPP unit 1 and 2 do not exceed the frame of usual technical failures and the failure causes which are characteristic for new facilities. Systems and components important to nuclear safety have been operated in a reliable way during the whole last year.

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UJD site inspector M. Bencat in Mochovce NPP during the inspection

Statistical overview of number of operational events at Bohunice V-2 NPP between 1993 and 2001 and their ranking according to the INES scale as well as an overview of collective dose of personnel are given in the tables 3.4 up to 3.6. In the tables only those events are recorded which according to the corresponding regulation have to be reported to UJD.

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Table 3.7. Number of events at Mochovce NPP

* Total number of events in 2001 differs from the event numbers categorised into INES degree (or outside of INES scale), because eight failures of an identical character were grouped into three group and by the INES degree was categorised all group.

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Table 3.8. Number of fast automatic trips at Mochovce NPP

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Table 3.9. Collective dose of personnel at Mochovce NPP (man Sv)

* in 2000 no refuelling outage took place

Inspection activity

The inspection activity of UJD at Mochovce NPP was aimed at the operation and re-start of units after the refuelling outages, the abidance of technical specification and operational procedures and performance of surveillance tests in accordance with adequate test programmes.
The inspections at Mochovce NPP unit 1 and 2 were executed according to the inspection plan. In the area of operation, one unplanned inspection was conducted, focused on the assessment of the utility activities in connection with operational events at unit 2. During this inspection no shortcommings in the operational personnel actions during this event were identified. The operational personnel has been acting in accordance with operational procedures and the nuclear safety principles.
Based on the evaluation of operational events, results of the assessment and inspection activities and also taking into account safety indicators UJD evaluated the operation of Mochovce NPP unit 1 and 2 in 2001 year as safe and reliable one.

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