Latest Articles

Volume 24-1

Extension of the Lifetime of the Existing NPPs – M. Manolov

This paper presents the activities undertaken by Kozloduy NPP to operate the units 5 and 6 beyond an established time frame defined by the licence and the original plant design – so called Long Term Operation /LTO/ which should be justified by safety assessment. Among the topics covered by the safety assessment, specific consideration were […]

Volume 24-1

Specific Aspects of the Emergency Arrangements when Establishing ERO – S. Filipov

Considering the requirement for the adequate emergency arrangements and accident management, some areas in this field are still blank or not well addressed. Among all the factors which play role during accident management and emergency activities, there is one which is a kind of underestimated in most of the emergency arrangements. That is the operators’ […]

Volume 24-1

Innovative Approaches for Nuclear Knowledge Transition within the European Union – M. Krusteva

The consequences of the three major accidents in nuclear energy, and in particular that of the Chernobyl nuclear power plant in terms of their impact on nuclear energy regulation and the availability of staff for the nuclear energy are discussed in this paper. The lack of common standards for evaluation of the safe operation of […]

Volume 24-1

Challenges for Introducing Nuclear Energy Program in Small Embarking Country – A. Causevski, S. Nikolova-Poceva, N. Popov, P. Groudev, N. Zaharieva

Nuclear Energy Program (NEP) for each country, especially for newcomer countries is a long-term process with lot of challenges for the political establishment of the country, as well as for the institutions and all involved stakeholders. According the IAEA recommendations, the process can be divided in 3 continuous phases. The achievement of the infrastructure conditions […]

Volume 24-1

Modeling and Analysis of Portable Diesel-Pump Mitigation Strategy Implemented as a Post-Fukushima Safety Measure – B. Kuzmanov

In accident situations involving Beyond-Design-Basis External Events (BDBEE) taking place in a nuclear power station, there is a necessity for an external portable pump equipment to be delivered on site, in order to avoid fuel melting and to preserve the containment building integrity. It can thus be guaranteed the long-term provision of all the key […]

Volume 24-1

Radiological Analysis of Spent Fuel Transportation Container – A. Yordanov

The transportation of Kozloduy NPP’s WWER-1000 spent nuclear fuel requires design and validation of a special transport equipment. The exploitation of such equipment requires the fulfillment of IAEA Safety Standards Series Safety Guide No. NS-G-1.4 recommendations and compliance with the Bulgarian legislation, which states that the maximal dose rate at the external cask surface shall […]

Volume 24-1

Analysis of the Containment Phenomena, Including Thermal-Hydraulic Processes and Fission Products Behaviour after Inadvertent Withdrawal of the Regulating Control Rod Group During Full-Power Operation – V. Saraeva, N. Rijova

The inadvertent withdrawal of the regulating control rod group during full-power operation leads to an increase in the reactor power and thus to an increase in the primary circuit temperature and pressure. The fuel assemblies with the highest power peaking factors reach the state of boiling crisis and may be damaged. The present analysis of […]

Volume 24-1

Extension of the TRACE Model for NPP Gösgen for MSLB and MB LOCA – E. Borisov, K. Mancheva, D. Papini, R. Kaulbarsch, J.-U. Klügel

Traditionally, the deterministic safety analyses are performed at the NPP Gösgen by the vendor AREVA (now Framatome), which developed an own version of the RELAP5/Mod 3.3 code (S-RELAP5). In the framework of building in-house expertise, the NPP Gösgen – together with the GCR Ltd. team – have been developing an additional thermal-hydraulic model of the […]

Volume 24-1

TRANSURANUS Capabilities for Uncertainty Analyses of Fuel Performance – M. Mitev, N. Mihaylov, S. Boneva, M. Manolova

Uncertainty analysis of important parameters that characterize nuclear fuel behavior during accident conditions were performed using the TRANSURANUS code. The possible values of these parameters during transients in the fuel vicinity were evaluated. The most critical among the parameters are presented by means of fractional frequency in this paper. The obtained results are in good […]

Volume 24-1

Halden LOCA Test Simulation by TRANSURANUS Code with Different Thermo-Hydraulic Boundary Conditions – N. Mihaylov, S. Boneva, M. Manolova, M. Mitev

This paper summarizes the work performed by the Institute for Nuclear Research and Nuclear Energy (INRNE, BAS) – Sofia, Bulgaria in the IAEA’s Coordinated Research Project “Fuel Modelling in Accident Conditions (FUMAC)”. The IFA 650 LOCA experiments in Halden are integral in-pile tests on fuel behaviour under simulated LOCA conditions. Object of the proposed analysis […]

Volume 24-1

Progress of IVMR Investigations in WWER1000 Reactor Type with ASTECv2.1.1.3 Computer Code – R. Gencheva, A. Stefanova, P. Groudev

It has been investigated the In-Vessel Melt Retention (IVMR) strategy with external vessel water cooling after the initiation of Large Break LOCA (2  850 mm) simultaneously with full station blackout (SBO) at WWER-1000 reactor. The reference nuclear power plant for this analysis is Units 5 and 6 of the Kozloduy NPP. Two calculations have […]

Volume 24-1

Optimization of the Maintenance Period for WWER Safety Systems with Taking in Account the Maintenance Quality – V.N. Kolykhanov, I.L. Kozlov, K. Sova, D. Koba

The specificity of NPP safety systems is that they must be in a state of constant availability, but they are not used and, therefore, are not spend the life of the equipment. Verification of readiness through periodic maintenance or testing can lead to the deterioration of some elements of the system and increases their vulnerability […]

Volume 24-1

Local Shielding of Target for Production of 18F – Numerical Optimization – A. Demerdjiev, K. Shegunov, G. Asova, D.T. Dimitrov, N. Goutev, D. Tonev

The results presented in the current paper are part of the studies which we are conducting in regards with the radiological characterization of the cyclotron facility that is currently being built by the Institute for Nuclear Research and Nuclear Energy at the Bulgarian Academy of Sciences. The facility is going to be dedicated to research […]

volume-23-1

Distortion of the Neutron Flux Profile in Reactor Core Induced by Control Rods, V.N. Kolykhanov, I.E. Kozlov – V.I. Skalozubov

The method designed to calculation the axial profile of neutron flux in reactor core based on diffusion theory are presented. The core model describes two zones – upper part containing control rods (additional absorber) and unrodded bottom part of core. The solution of the system of diffusion equations is obtained using the criticality condition. The […]

volume-23-1

Investigation of IVMR Strategy with External Vessel Water Cooling in VVER1000 Reactor Type with ASTECv2.1.1.0 Computer Code – R. Gencheva, A. Stefanova, P. Groudev

It is investigated the applicability of In-Vessel Melt Retention (IVMR) strategy with external vessel water cooling for the VVER-1000 reactor type. The investigation concerns a calculation made with ICARE and CESAR module of ASTECv2.1.1.0 computer code. ASTEC computer code was developed by IRSN (France) and GRS (Germany) to be a European computational tool for simulation […]