National Report of The Slovak Republic , september 2001

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5.3.5 Analysis of events at nuclear installations

ÚJD Regulation No. 31/2000 Coll.LL. on events at nuclear installations (NIE) came into force in 2000. The Decree lays down detailed regulations concerning the classification of the individual types of events (failures, incidents, accidents), based on Act No. 130/98 Coll.LL. It also sets the method of notification of events, method of identification of event causes, and sets the method of informing the public.

Pursuant to Regulation No. 31/2000 Coll.LL., the operator adjusted the whole process of notifications and management of events (see National Report as of September 1998.) as well as internal regulations to provide for feedback from NIE. Definition and classification of events at nuclear installations

Pursuant to Act No. 130/1998 Coll.LL., an event at nuclear installation means an event which is associated with the threat or violation of nuclear safety of nuclear installation during the commissioning, operation or decommissioning of the latter. The Act recognizes three categories of NIE according to their severity:

  1. Failures are events that caused a discrepancy with requirements on nuclear safety of nuclear installation or were identified upon the operation, maintenance or inspection of the nuclear installation, and might result in an incident or accident.
  2. Incidents are events that caused damage of low importance to nuclear installation or damage to the health of the employees; they however caused the nuclear installation to be automatically shut down, or forced a shutdown of the nuclear installation for the purposes of repair, because of violation of limits and conditions, release of radioactive substances within the premises and on the site of the nuclear installation or contamination or irradiation of employees.
  3. Accidents are events associated with severe damage to the nuclear installation or followed by a severe damage or potential severe damage to health due to ionizing radiation or release of radioactive substances into the environment.

Generally, operator classifies operating events (OE) as follows:

  1. events subject to notification to regulatory and supervisory bodies - they are most important from the viewpoint of nuclear safety and reliability; they include the above mentioned NIE classified pursuant to Act No. 130/1998 Coll.LL.,
  2. events subject to internal notification within the individual single branch plants (so-called recorded); they include events of lower safety relevancy. Operator investigates the reasons of such events so as to prevent them from repeating.
  3. events with no consequences or so-called near miss events - they include incorrect activity resulting in no actual untoward consequences that, under different circumstances, may have resulted in untoward consequences.

Criteria for the classification of NIE are defined in internal QA documents. Documenting and analysis of events at nuclear installations

The schedule of the procedures for investigating NIE, including the method of notification of the regulatory body is shown in the corresponding QA (flow diagram) for event notification and analysis. The Shift Engineer (ZI) completes a notification slip on the event, using the prescribed form, and attaches to it statements by the corresponding staff.

NIE analysis is the responsibility of SSV that conducts it based on positions by expert units and own analyses and/or results provided by working groups.

For NIE meeting the criteria of investigation of the root cause, SSV (Feedback Group) in cooperation with the corresponding divisions, conducts a comprehensive analysis using one of the following methods and/or their combination:

  • HPES - "Human Performance Improvement" developed by INPO, USA. This method includes analysis of tasks, barriers and changes, and offers a general view of NIE.
  • ASSET-" Assessment of Safety Relevant Events“ developed by IAEA.

Analysis of NIE subject to external notification is completed by drafting of a Report on Operating Event to be presented to the Failure Commission for review. The commission is a collective advisory body to power plant directors on NIE management. Failure Commissions usually meet on a monthly basis and approve conclusions of analyses, and impose targeted remedial measures that become binding upon all employees. NIE reports are presented to regulatory bodies, whose representatives are entitled to attend Failure Commission meetings.

So-called recorded events are subject of a similar analysis, but no separate report is drafted on them. Slip notification is presented to the Failure Commission on the event and on remedial measures. The implementation of remedial measures is documented by the corresponding division in charge via computer network, where it stays archived. The status of the implementation is verified by the Failure Commission.

The whole NIE investigation and analyses agenda is kept in a computer network where all network users have access to. Every network user may make a statement on operating events, comment on them or inform on serious findings. Editing interventions may only be done by SSV members who deal with the investigations of the reasons for events at nuclear installation.

Extraordinary Failure Commission

Extraordinary Failure Commission (MPK) is convoked by Deputy Plant Manager for operations (and/or head of the Failure Commission on duty) immediately after having obtained information from ZI on an accident or incident having occurred, provided that such events are not subject to management according to internal emergency plan by Emergency Commission. MPK is also convoked upon the occurrence of other NIE that meet the criteria for it being convoked. The task of MPK is to identify the direct cause of the event, and to define immediate remedial measures.

Protocols of MPK meetings are presented to ÚJD and SE, a.s.´s headquarters. They are included in interim reports on operating event. The final analysis, including the analysis of the root cause, is drafted by SSV as a standard report on operating event, and the report is then presented, together with remedial measures, to regular Failure Commission for approval. Completed „Surveillance Program“ is presented to MPK, serving post-accident inspection.

Independent NIE assessments

Operating event reports are presented to also VÚJE that periodically (at yearly intervals) makes independent assessments of events and suggests remedial measures. The report is also made available to operator.

Reporting of events

Pursuant to ÚJD Decree No. 31/2000 Coll.LL., operator is responsible to inform in a given time frame state authorities on NIE. The first information on incidents or accidents must be provided to ÚJD by operator by phone, facsimile or in person without any delay, within 30 minutes of the event having been identified. Interim reports must be presented to ÚJD by operator in writing within 72 hours of the identification of an incident or accident, and final report must be presented within 30 days of identification. Data required are defined by the Decree and have been reflected in internal QA document. As part of the documentation, also interim NIE assessment according to INES scale must be recorded.

Operator presents to ÚJD a summary written report on failures by the 20th day of the subsequent calendar month.

Upon identifying shortcomings in notification and/or NIE analysis, ÚJZ requests their elimination and/or performs an independent investigation of the event, and issues binding measures.

Provision for feedback from events at nuclear equipment of other NPPs

Operator uses international information systems on operating experiences from nuclear power sector (WANO and IAEA) to apply measures based on analyses of failures by foreign operators to his own units, and also presents his own experiences to foreign operators. The purpose of such an activity is to prevent similar failures from repeating, through implementation of preventive measures as well as to prevent redundant safety analyses and non-standard approach towards the solution of problems. QA document „Feedback from NIE at Other NPPs“ regulates the detailed procedure of processing and using information on NIE that occurred at other NPPs.

Evaluation of the efficiency of remedial measures implemented

The main indicator of the efficiency of the feedback from own NIE is the trend of failures with an analogical mechanism of failure. SSV develops at yearly basis summary statistical evaluation of the occurrences of repeated events, and assesses them with respect to the efficiency of measures implemented.

Efficiency of remedial measures depends on the type of the measure, and is provided for under the quality assurance system:

  • remedial measures implemented as design changes are evaluated according to the directive „Documentation of Equipment Changes",
  • changes in operating instructions, testing programs, “Surveillance Programs” and organizational adjustments concerning the keeping of operating documentation are evaluated after their application to unit operation if allowed by the nature of the change. They are evaluated in a standard manner under amendments to operating procedures on a 3-year cycle basis,
  • for measures resulting in changes of procedures for abnormal and emergency operation whose correctness cannot be verified during real unit operation, the system of effectiveness control of changes is connected with the mechanism of validation of such regulations.

Information flows on NIE within SE,a.s.

Heads of the corresponding departments and divisions are responsible for :

  • continuously make themselves familiar with NIE database,
  • continuously make them familiar with reports on events and with protocols from meetings of regular and Extraordinary Failure Commissions every month,
  • include applicable knowledge to training programs for employees reporting to them. In cooperation with the department of human resources training and with employees of the VÚJE training center, they take care of the incorporation of knowledge derived from NIE into programs of initial and repeated training (re-training).

It is the obligation of every employee to know the results of NIE analyses, in particular of those he/she was involved in. If the inputs or results of analysis contradict their observations or understanding of the event, they are entitled to request the Head of the SSV department to complete the solution to NIE or to provide an explanation for the discrepancy.

Near miss events

Aiming at preventing severe events as well as a measure to improve the safety culture, operator introduced in 2000 a system of notification and feedback from minute events, so-called near miss. Employees are encouraged on the part of the branch plant management to notify small events. Any employee may notify such events, either in writing, by phone or in person to his/her direct supervisor, or electronically to SSV. Forms for notification of near miss events are available at every working place of operating staff. Notifications on near miss events are recorded and evaluated by SSV. Criteria for notification were defined in six areas: documentation, man-machine interface, working environment, working practices, organization of labor, and staff training. SSV makes suggestions for remedial measures that are presented to Failure Commission. Statistical evaluation of events at nuclear installation, developmental trends

This section presents data on events that occurred at nuclear installations in the Slovak Republic in 2000, and developmental trends for the recent period of time.

Overall, the numbers of events at NPP Bohunice has stabilized in recent years. No event has been recorded that would have severely impacted upon nuclear safety. At no nuclear installation there was an event exceeding level of a failure.

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Fig. 5.3.1 Development of the overall numbers of events at NPP Bohunice

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Fig. 5.3.2 Development of numbers of events, by INES - NPP V-1

Fig. 5.3.3 Development of numbers of events, by INES - NPP V-2

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Fig. 5.3.4 Development of overall numbers of events
at NPP Mochovce

Fig. 5.3.5 Development of overall numbers of events at SE-VYZ


Prior to 1999, operating events were classified into two categories, thereby only events of category I being safety relevant. Since 2000, the events have already been classified according to the above mentioned system.

The increase in numbers of events at NPP Mochovce in 2000 was due to the commissioning of unit 2. The numbers of events at SE-EMO unit 2 in the said year were markedly smaller than those at unit 1 in 1998, i.e. the year of trial operation (128 events in 1998 at unit 1, 69 events in 2000 at unit 2). This fact is also connected with the power plant staff having acquired more operating experiences and using them. As compared to the preceding year, there was an approx. 50% reduction in numbers of operating events at unit 1 in 2000.

Table 5.3.1. shows a summary of the numbers of operating events of all NI by their INES grades. There were two INES 1 operating events in 2000, one at Bohunice unit 4 and Mochovce unit 1 each.

Table 5.3.1.


out of scale



































The most frequent causes of OE at all NI are failures of equipment, with the highest contribution by control and instrumentation equipment and electro. Ranking second are staff errors. Figures 5.3.6. through 5.3.8 show the shares of the individual causes for events in 2000 at the individual NI.

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Fig. 5.3.6 Causes of OE at NPP V-1 units in 2000

Fig. 5.3.7 Causes of OE at V-2 units in 2000

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Fig. 5.3.8 Causes of OE at SE-EMO units in 2000

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