## Laboratory of Nuclear Reactor Physics # 18

Eduard RUDAK, D.Sc. of Physico-Mathematical Sciences

E-mail: rubin@sosny.bas-net.by

Tel.: +375 (17) 375-39-44

Fax: +375 (17) 374-83-35

**History**

The laboratory was founded in 1999 to carry out computational and theoretical studies of the power and research reactors’ neutron characteristics.

**Main research directionss**

- Development of a mathematical apparatus for describing the interaction of a neutron with a multiplying medium based on a particles birth and death model.
- Research work on modeling physical phenomena in the cores of WWER-1000, WWER¬ 1200 reactors, critical and subcritical assemblies.
- Spent fuel characteristics calculation of WWER type reactors (WWER 1000 and WWER 1200): activities of accumulated radionuclides and residual heat release using analytical methods for solving the Beitman problem and via neutron-physical computing codes.
- Computational studies fulfilling to substantiate the safety of the Belarusian NPP.
- Neutron-physical features investigation of processes in advanced fuel assemblies of a WWER-1200 reactor.
- Estimated monitoring of the fast neutron integral fluence and radiation damage in the WWER reactor vessel structures.
- Research work on the creation of computer models for calculating the fuel cycles neutron-physical characteristics based on TVS-M, BIPR-7 and DYN3D analytical codes.
- Estimated determination of the fuel cycle (duration, burnout depth, critical concentration of boric acid, energy release field, etc.) main neutron-physical parameters for the Belarusian NPP WWER-1200 reactor, both under normal operation and in transition modes other than the design.
- Theoretical and computational studies of the technical possibilities of using different storage-stage spent fuel assemblies as a source of gamma radiation for radiation technological processes.
- Research work on the performance calculations of the WWER-1200 reactor with a side reflector detailed description using the MCU code and comparing the calculated multiplication factors and other characteristics with the results of verified computer codes calculations.
- Mastering the calculations of the WWER-1200 reactor using the MCU code with a given distribution of the external source in different approximations and conducting calculations of the reactor based on using the weight window procedure to increase the reliability of the calculated values outside the core.
- Development of data exchange interface through generating the external radiation source, actinide concentrations and fission products data based on the fuel cycle calculation results via the BIPR type code and compiling this data (in appropriate format) to the MCU source files.

**Main projects**

- State Research Program “Energy systems, processes and technologies” subroutine “Nuclear energy and nuclear physics technologies”.
- Labor: Particles’ birth and death model adaptation to describe the interaction of a neutron with a multiplying medium based on U-235 and Pu-239.

2016 – 2020 State Program “High technologies and equipment” subroutine 6 “Scientific support of the nuclear energy development in the Republic of Belarus” economic contract on 30.03.2016 № 2016/2-29.

**Tasks**

- Determine fuel cycles main neutron-physical parameters of the Belarusian NPP WWER-1200 reactor, including the measured parameters, in order to justify the safety and economic efficiency of its operation.
- Perform neutron fluence calculated monitoring over the thickness of the WWER-1200 reactor vessel to justify the safety of its operation.
- Prepare information materials for government agencies and for conducting informational and educational work with the public and the media on nuclear issues.

**Major achievements and developments**

- It is shown that by adjusting the calculation control parameters it is possible to significantly increase (up to several percent) the accuracy of relative energy release determining via BIPR-7 code available in JIPNR – Sosny. The dependences of the fuel temperature reactivity coefficient on the reactor power and the moderator temperature reactivity coefficient on the inlet temperature are obtained.
- A single-time extension of the campaign duration was simulated by reducing the reactor power and coolant temperature. Four subsequent loads are considered to take the reactor back to stationary overloads.
- Simulation of the WWER-1200 reactor operation extension time in the stationary overload mode by reducing the power at the end of the campaign was carried out. The differences in the calculated values of the neutron-physical characteristics from the design ones do not exceed the maximum permissible errors established for the software used in the design of fuel cycles.
- The principal possibility of еру Belarusian NPP WWER-1200 reactor workloads extending through the use of the power reactivity effect was confirmed. Differences between the calculated safety parameters values and the design ones do not exceed the maximum allowable values established for the software used in the design of fuel cycles.
- A comparison was made of the maximum rods energy release values in a fuel assembley and fuel tags obtained using the MCU-PD and DYN3D codes for the first fuel load of the WWER-1200 reactor for the reactor 60° sector. The differences in the maximum fuel assembly values of the relative energy release obtained using the MCU-PD and DYN3D codes for fuel rods do not exceed 5%, and for fuel tags 12%, which is consistent with the permissible energy release errors established for the codes used in fuel cycle design.
- A full-scale model for WWER-1200 reactor fuel calculations at minimum power level using the MCU-PD code with external sources constant over the fuel assembly has been built. As an external source of fast neutrons, the distribution of produced neutrons is taken, obtained in the reference calculation for this code.
- It is shown that the use of the modern concept of low neutron leakage from the core during the fuel cycle of the WWER-1200 reactors, as well as the location of the burned-out fuel assemblies in the places closest to the reactor vessel, allows to reduce the fluxes falling on the vessel by several times.
- Analytical expressions for the most important in practical terms fission products activities of the of the WWER 1200 reactor are obtained.
- The parameters of the WWER-1200 reactor stationary campaign spent fuel are calculated such as radionuclide activities and residual heat generation.
- Works on the mathematical apparatus adaptation based on the birth and death model to describe the processes of interaction of neutrons with the thermal nuclear reactor breeding medium were performed. Analytical expressions are obtained for the evaluation of reactor operating parameters (keff, reactivity, etc.)

**Direction of further research**

- Derivation of a mathematical apparatus describing the interaction of a neutron with a multiplying medium, based on the birth and death model.
- Research work on the physics of nuclear reactors, calculations of WWER type reactors core with various modifications of fuel assemblies, calculations related to ensuring the safety of a nuclear power plant under construction, etc.
- Development of analytical express methods for spent fuel parameters determining of the WWER reactors: fission products and actinides, residual heat generation.
- Development of determination methods of difficult-thttp://sosny.bas-net.by/wp-admin/post.php?post=1232&action=edito-measure activities of radionuclides by easily determined ones using correlation ratios.

**The international cooperation**

- Participation in various international conferences and seminars, presentations. Participation in courses conducted by the IAEA.