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Competence fields

The activities of NUBIKI serve to ensure safe operation of nuclear power plants. NUBIKI staff members perform deterministic, as well as probabilistic analyses to improve the safety level of nuclear power plants.

In the frame of deterministic safety analyses, NUBIKI performs computational simulations to analyse different event sequences which can occur in a nuclear power plant. One of the fields of our activities is the analysis of the containment response in case of design basis accidents using computer codes. The computed results are validated with post-test calculations of experiments. Important condition for the safe operation of a plant is the containment leak rate analysis. Our traditional field is the compilation and evaluation of the measured data of numerous leak test measurements performed since the commissioning of the power plant.
Thermal-hydraulic processes and activity release during severe accident sequences has been analysed applying computer models. In this field analyses in the AGNES project dealing with the safety analysis of the Paks Nuclear Power Plant, and during the project for the Level 2 probabilistic safety assessment of the plant have been done. Important field of the severe accident analyses is the evaluation of the hydrogen distribution and management in the containment. For this purpose CFD tools are used. Our computer simulations – among others – support the development of safety management guidelines of the plant. NUBIKI participates in several international experimental projects with post-test calculation of experiments. The objective of this work is the verification and validation of computational models.

We utilise probabilistic safety analyses to identify event sequences that lead to a severe accident and to determine the likelihood of such sequences. We develop detailed event sequence models for a wide range of accident scenarios. The responses of plant systems, system components and the interactions of plant personnel are all subject to in-depth analysis. We apply state-of-the-art analysis methods and computerised tools for model development and quantification. Over and above a quantitative description of nuclear safety, use can be made of our analysis results in support of risk-informed decision-making. The nuclear safety authorities as well as the utilities can take advantage of this decision-making process. We devote substantial efforts to developing appropriate methods and tools for risk-informed applications.
Nowadays we make uses of our experience and expertise from more than two decades of probabilistic safety assessment in providing support to plant time extension activities, design and implementation of plant changes, making decisions related to plant operation and maintenance and preparation for new nuclear builds in Hungary.

We regularly apply deterministic and probabilistic analyses in combination as complementary methods.

Deterministic safety analyses

Containment studies

The team has a long-term history in performing DBA calculations for the VVER-440 containment. The applications included the update of DBA analyses for the Final Safety Analysis Report (FSAR) of Paks NPP. Recently uncertainty analyses were performed to explore the margins of the containment parameters under DBA conditions.

Severe accident analysis

The behaviour of the VVER-440 plant under severe accident conditions was studied with code calculations in the AGNES project, and later in several PHARE projects.
Further studies involved accident progression and fission product transport analyses in the Level 2 PSA project for Paks NPP. Level 2 analyses also served as a basis for the development for a severe accident management strategy for the VVER-440 plant.

Severe accident management

Verification analyses of the severe accident management guidelines (SAMG) with code calculations were performed to support the development of the guidelines and to check the time frames available for the interventions. Hydrogen distribution in the containment and hydrogen management with passive catalytic recombiners was analysed with 3D containment calculations.

Probabilistic safety analyses (PSA)

Level 1 PSA

Level 2 PSA

Regular Analysis Updates

Method Developments to Support PSA

Development of Analysis Tools to Support PSA

Risk-Informed Decision-Making

Additional Uses of Analysis Results and Experience

Support to New Nuclear Builds in Hungary

Contribution to Risk Assessment of a Proton Therapy Facility

For further information on probabilistic safety assessment and its applications please contact Attila Bareith, Head of Risk Assessment Division, by e-mail or phone (+36 1 392 2716).