Yu. M. Cherkashov

Increasing the safety of atomic power stations with RBMK reactors

The authors review the operating, safety, and accident records of RBMK reactors in the Soviet Union, perform in-core kinetics assessments of cooling system, fuel element, and control rod behavior during accident scenarios, and make detailed technical recommendations for increasing the operating and safety margins of the plants. Methods for the amelioration of fission product release are also discussed. The Chernobyl accident is included.

Possibilities for Producing Radionuclides in Nuclear Power Plants with RBMK Reactors

It is shown that radiation doping of silicon and the production of medical and industrial radioisotopes in the reactors at the Leningrad nuclear power plant are possible and safe. The production of cobalt with specific activity ~100 Ci/g in an RBMK-1000 reactor is studied. Some promising developments for improving the quality of the radioisotopes produced are described. It is shown that the production volumes can be increased by linking up other nuclear power plants with RBMK reactors into the production chain.

Characteristic Features of the Development of Serious Unanticipated Accidents in RBMK Reactors and Approaches to Controlling Such Accidents

The basic structural features of RBMK reactor systems (absence of an overall external protective shell, disintegrating nature of the circulation loop, multichannel nature of the core, positive steam coefficient of reactivity, large mass of the high-heat-capacity graphite moderator), which predetermine the development of postulated serious unanticipated accidents and their control, are examined. Categories of core behavior for unanticipated accidents and types of accidents resulting in a definite type of damage are determined. The character of the flow of typical unanticipated accidents, possible approaches to controlling the consequences of accidents, and means for performing computational analysis of unanticipated accidents are examined.

Computational Modeling of the Accident in the Fourth Power-Generating Unit of the Chernobyl Nuclear Power Plant

During the accident in the fourth power-generating unit of the Chernobyl nuclear power plant complicated spatially distributed processes (neutron-physical, thermohydrodynamic, chemical, and thermomechanical) were focused and became intertwined. This has made it difficult to model the accident numberically and it has made international collaboration in this field urgent. As a result, specialists in three different countries performed a series of methodological investigations of the effect of different factors on the positive reactive arising as a result of the insertion of the safety and control rods. These works confirmed that the positive reactivity is highly sensitive to the state of the core prior to the accident and they substantiated the need for reproducing in detail the preliminary initial conditions during computational modeling of the first phase of the accident. The first stage of a combined comprehensive computational analysis of the Chernobyl accident were quasistatic estimates of the positive reactivity according the DINA and CITATION codes. The results of the reconstruction of the three-dimensional neutron fields on the basis of information recorded approximately 2 minute prior to the accident by the SKALA system were used as the initial information for constructing the preaccident state of the reactor.

Probability analysis of the safety of the second energy module of the leningrad nuclear power plant

A special international program was undertaken to estimate the safety of the second power unit at the Leningrad Nuclear Power Plant after reconstruction and the effectiveness of the new safety measures introduced. The analysis is based on the IAEA method, modified for RBMK reactors. The calculations employ a full-scale model of the risk of the power unit and the initial data for a 10-year operating period. After reconstruction, the frequency of serious accidents with core damage is 1.4·10−5 per reactor-year and is acceptable in terms of the OPB-88/97 requirements. The influence of reconstruction is considerable: according to the estimates, the risk is reduced by a factor of more than 100. The results of the analysis permit suggestions regarding further increase in safety and reduction in cost of the reconstruction without increasing the risk of accident.

Status and prospects for pressure-tube water-cooled graphite-moderated reactors

An overview is given on the 50 year experience in the development of pressure-tube water-cooled graphite-moderated reactors (WCGMR) in Russia and operation of NPPs with RBMK-type reactors. Advantages and shortcomings of WCGMR are pointed out. Also described is the systematic upgrading effort for some RBMK systems and components meant to enhance their reliability, safety and lifetime. A possibility of further improvement of the economic performance of NPPs is discussed. The paper gives technical features of the MKER-800 reactor plant designed to replace power units with RBMK-type reactors at the end of their lifetime. Pressure-tube and pressure-vessel reactor concepts adopted in the Russian nuclear power system are mutually complementary, which is an important merit and advantage of such a model of power development.

Role of separate factors in the development of the Chernobyl accident

Immediately after the accident in the fourth power unit of the Chernobyl nuclear power plant many computational and analytical investigations of the development of the accident and the values of separate factors in this situation were performed at the NIKIET and other research centers. Foreign research centers, where, in particular, the modern general-loop programs of the type Relap 5, Retran 02, and others were employed for modeling the thermohydraulic processes in the circulation loop of the reactor where the accident occurred, also participated in this process.