Vol 120, No 5 (2016)

The growth prospects for nuclear power are examined: impeding and driving forces. The main problem facing nuclear power today is the management of spent fuel and wastes. Eventually, it will become economically inexpedient to store spent fuel; the natural solution is to reprocess spent fuel, extract the fi ssile isotopes, and recycle it in thermal or fast reactors. Since the fast-reactor fraction in the current system is trivial and the situation will remain the same in the near- and medium-term futures, a variant of plutonium recycling in thermal reactors with a different fuel arrangement is examined. It is shown that a heterogeneous fuel arrangement can give a 10-fold reduction of the radiation load in reprocessing enterprises. Different setups are compared in terms of the potential danger presented by spent-fuel reprocessing. The advantages of the thorium fuel cycle are examined from the standpoint of radiation and environmental safety.

The results of a calculation of critical assemblies and an RBMK core using the STEPAN-MPG code are presented. It is shown that the computational results obtained by calculating the surface harmonics are identical to the measurements for critical assemblies and for real states of an RBMK core without the use of adjustable parameters. In addition, the method of surface harmonics makes it possible to perform a fuelelement-wise calculation of the energy release distribution in any RBMK cell by using neutron fl uxes obtained from coarse-grid calculations.

The effectiveness of control rods is measured in a nonstationary regime at minimum reactor power. The measurement algorithm entails a buildup of reactor power caused by lifting of the measured or any other rod followed by its release, which is due to the need to maintain a detector signal above the background level up to the end of the experiment. It is known that some fission neutrons (the prompt neutrons) are created directly during nuclear fission while others are formed from the decay of the precursors of delayed neutrons, which possess a low-energy spectrum or lower average energy. For fast reactors, this can be reflected on the efficiency of the control rods during measurements and during the development of the processes occurring during an accident. This work is devoted to determining the effect of the conditions preceding the movement of control rods on their effectiveness and the discrepancy between the efficiency of the rods realized in practice and the efficiency calculated on the basis of stationary states.

A structural concept using a sodium cavity located above the core of a reactor is proposed as a means of preventing accidents resulting in the destruction of core elements. The experimental investigations of heat transfer performed on the AR-1 stand with boiling of sodium in a model fuel assembly of a fast reactor with a sodium cavity above the core in a regime with natural circulation have shown that long-time cooling of fuel assemblies is possible. The data obtained are used to refine the computational model of sodium boiling in fuel assemblies and to verify the COREMELT computational code.

The radiation conditions in the dry-storage block for spent nuclear fuel BSKh-3A was characterized by a high dose rate and allowed only brief admission of workers. The plan to normalize the radiation conditions included repeat replacement of workers, whose individual dose limit has been exhausted, and on the whole did not conform to the principle of protection optimization. Analysis of the design and radiation state of BSKh-3A has shown that possibilities for reducing the worker dose do exist. At the stages of current planning and actual performance of the work, it was possible to make changes in the technology used in the work, reduce labor costs, and add and optimize additional protection. As a result, the work was performed in accordance with the radiation safety norms and regulations, worker replacement was not required, and the collective dose was reduced more than 20-fold compared with the nominal level.