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Safety of Armenian NPP

#A-1492


Mathematical model of probabilistic safety analysis for the Armenian NPP with ageing effects consideration

Tech Area / Field

  • FIR-ENG/Reactor Engineering and NPP/Fission Reactors
  • FIR-MOD/Modelling/Fission Reactors
  • FIR-NSS/Nuclear Safety and Safeguarding/Fission Reactors

Status
8 Project completed

Registration date
19.12.2006

Completion date
25.02.2011

Senior Project Manager
Kulikov G G

Leading Institute
Nuclear and Radiation Safety Center of Armenian Nuclear Regulatory Authority, Armenia, Yerevan

Supporting institutes

  • Armenian NPP, Armenia, Metsamor

Collaborators

  • Brookhaven National Laboratory, USA, NY, Upton\nEuropean Commission / Joint Research Center / Institute for Energy, The Netherlands, Petten\nArgonne National Laboratory (ANL) / Nuclear Engineering Division, USA, IL, Argonne

Project summary

As the international industry develops the issue of environment pollution becomes more topical. In case of man-induced accidents, the ecologically hazardous releases into environment could exceed allowed values hundred times. The scientific technological investigations and, as a result of their implementation, determined and accepted standard codes for operation of various ecologically dangerous industrial facilities allow reducing the environment pollution to minimum when operated in standard (design) conditions

The Armenian Nuclear Power Plant (ANPP) operated on the territory of the Republic of Armenia (RA) is one of the facilities in the Southern Caucasus where an accident could result in ecological disaster on a regional scale.

The Armenian Nuclear Power Plant (ANPP) is being operated since 1976. and consists of two WWER-440 Russian design units of 420MW capacity. After 13 years of continuous operation it was shutdown in 1989 following disastrous Spitak earthquake in December 1988.

After 6-year shutdown and implementation of the first stage of the ANPP safety upgrading programme the unit 2 with 300MW was restarted in November, 1995.

Although at present time ANPP is in the period close to the end of the ANPP design life, In regard with great significance of the ANPP for energy development in the region the RA Government made a decision on the ANPP operation up to 2016 provided the required safety level is ensured.

The ANPP safety was mainly assessed with use of deterministic methods that allowed to identify and remove a number of design deficiencies. During the insufficient efficiency of deterministic methods in some issues related to safety it was decided to use probabilistic assessment methods. The initial ANPP probabilistic model allows identifying latent safety issues and implementing activities for their elimination. The major deficiency of the probabilistic safety analysis mathematical model is disregard of equipment ageing issue while for both ANPP and most of the first generation WWER-440 units operated in Russia, Slovakia, Hungary, Czech Republic, etc., the ageing issue is one of the most vital ones.

The issue urgency. Equipment ageing could be characterized as a process resulting in time-dependent change of component, system and different structure parameters. The ageing process could result in equipment reliability degradation below safe operation limits specified in this unit design. Due to equipment ageing the occurrence of initiating events could significantly increase. By "initiating event" (IE) we shall mean violation of a unit normal operation meeting specific criteria (selection criteria), that creates direct and potential (in case of safety functions failure) hazard of occurrence of undesirable consequence for unit. The occurred failure could not be detected in normal operation, testing and maintenance, but could result in a failure or multiple common cause failures in case of an accident. The issue becomes more vital in the period close to the end of the ANPP design life. It is important for this case to monitor equipment condition for timely replacement and repair.

Te methods of probabilistic safety analysis (PSA) are commonly accepted for analysis and decision-making related to NPP safety. The PSA major benefit is a possible in-depth qualitative and quantitative analysis of actual NPP lay-out with identification of contributors to general core damage risk (level 1), radioactive release (level 1) or population contamination (level 3).

The applicability of PSA model for either purpose is limited by detail degree of the given model. The unavailability of ageing effect mathematical model in building PSA live model could affect the correctness of risk profile obtained in quantification result and reduce practical value of the model as a safety related decision-making tool.

The Project main objectives are a) assessment of ageing risk for systems ensuring NPP safety, and b) incorporation of ageing effects in PSA model for WWER-440 type units.

The following tasks are to be addressed in the Project implementation:

  • Analysis and adaptation of a methodology for incorporating ageing effects in PSA model for WWER-440 type units.
  • Analysis of ageing effect on initiating events.
  • Reliability analysis of the ANPP safety important systems taking into account ageing effects.
  • Development of probabilistic safety analysis mathematical model for the Armenian NPP and performance of calculations taking into account the ageing effects.

Two Armenian organizations are involved in the Project:
  1. ANRA Nuclear and Radiation Safety Center
  2. Armenian Nuclear Power Plant

Major scientific and technical potential of Armenia in the area of nuclear power plant safety, modeling of physical and mechanical processes, analysis of loading conditions (regimes), assessment of hazard and risk are concentrated in these organizations.

The Project implementation would facilitate the collection of actually available structural and configuration data. The ageing effect on WWER-440 type units will be specified based on the created experimental data base. New and advanced safety assessment methods will be used.

The results obtained under the Project implementation will be provided, as recommendations, to relevant state organizations and companies concerned in management and reduction of accident and disaster risk.

The studies will be conducted in compliance with IAEA recommendations and corresponding to International Safety Standards.

The Project implementation shall provide:

  • Identification of actual risk profile in regard with the ANPP equipment ageing.
  • Prioritization of modifications related to the ANPP safety.
  • Development of recommendations for correcting of the ANPP equipment testing and maintenance procedures and schedules.
  • Development of recommendation for correcting of ageing monitoring methods.

The developed methodology will allow incorporating ageing effects in PSA models for other operating WWER-440 units. The obtained analysis results will allow specifying the degree of ageing effect on WWER-440 NPP’ s safety.

The Project will allow reorienting of scientists and engineers knowledge and skills engaged earlier in defense industry to peaceful activity.

In the process of information collection on studies, performed in this area contacts were established with European leading experts on ageing (IRC, Ageing PSA Network, etc.) and US experts (Brookhaven National Laboratory) allowing to achieve agreements on co-operation. The main role of European and American experts in the Project will be participation in development of a methodology for incorporating ageing effects in PSA model.

In the process of the Project implementation the collaborators shall continue their cooperation with the Project participants in the following areas:

  • Information and data exchange in the course of project implementation.
  • Selection of a methodology and computational aids in development of specific models.
  • Assitance in the mastering of new reasearch techniques and methodologies.
  • Participation in training courses for young researchers, in workshops and seminars.
  • Providing opportunities to host project participants at western universities and laboratories.


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