Yu. A. Zverkov

Decommissioning of nuclear and radiation-hazardous objects of the russian science center “Kurchatov Institute”

Data are presented on research reactors which form the experimental base used for research in radiation materials science, neutron physics, solid-state physics, and other directions in science and technology. The characteristic features of the decommissioning of research reactors are analyzed. The results of work on the decommissioning of reactors and spent-fuel and radioactive-waste repositories are presented. 3 figures, 2 tables, 12 references.

Decommissioning industrial uranium-graphite reactors

The basic problems in decommissioning industrial uranium-graphite reactors are analyzed, taking account of experience in decommissioning the I-1 and ÉI-2 reactors at the Siberian Chemical Combine. On the basis of the analysis, decommissioning with delayed dismantling of the reactor structures is recommended.

Technical and economic assessments of planned and premature removal of first-generation nuclear power plants from operation in Russia

Four power-generating units are now being removed from operation in the Russian Federation - the first-second units with water-graphite reactors AMB in the Beloyarsk and VVER in the Novovoronezh nuclear power plants; these units were shut down in 1983, 1989, 1984, and 1990. respectively. Work is now being performed on these units in preparation for removal from operation. In connection with the exhaustion of the service life, from 2001 to 2010 another 15 power-generating units with a total electric capacity of about 10 GW will be removed from operation in Russia.

Implementing the principle of self-protection in reactors with a fast-resonance neutron spectrum

The reduced rate at which nuclear power generation develops and the huge reactor accidents of the last few years have increased the interest in the development of reactor plants of a new generation aiming at 1) obtaining increased safety by intrinsic physical and other features of the reactor, i.e., passive safety means, in other works, by self-protection of the reactor plant, and 2) economic efficiency of atomic power stations in the developing nuclear power generation system. Of current interest is the question: Is it possible to provide a reactor with self-protection features while preserving the parameters determining its efficiency? The present article relates to research on the possibilities of building an efficient reactor of increased safety. The concept was discussed for a steam-and-water cooled power reactor [1] which makes it possible to obtain a low operating temperature of the jackets of the fuel elements; a lower stored non-nuclear energy than in water-moderated water-cooled power reactors (replacement of the zirconium jackets of the fuel elements by steel jackets); and non-fuel expenses for the reactor construction resembling those of a water-moderated water-cooled power reactor. Steam-and-water cooled reactors are understood as the family of reactors with a fast-resonance neutron spectrum, UO 2 + PuO 2 fuel, and cooling by dry overheated steam or a steam/water mixture with parameters precluding a possible development of heat exchange stalling. It is a well-known fact that many aspects of the safety of a reactor are given by the dependence of the reactivity upon the density of the coolant. As has been shown in [1-3], a dependence of the reactivity upon the density with a negative void coefficient of the reactivity close to zero, subcriticality of the reactor when it is flooded with water, and a reactivity maximum corresponding to the operating point of the reactor are desirable (Fig. 1). This form of the dependence provides the smallest risk in a reactor accident with the loss of cooling, provides stability of the reactor in termq of neutron physics, makes it possible to use an emergency system of reactor flooding with water as an independent system acting upon the reactivity, provides acceptable times of triggering the emergency cooling and flooding system, and also provides an acceptable emergency flooding process and prevents a significant positive reactivity. The idea of partially using self-protection features in reactors with fast-resonance neutron spectra is by itself not novel: this idea was repeatedly discussed in papers on reactor physics. Thus, the authors of [2] have studied the influence of the geometrical dimensions of the core, the composition and the fraction of its components, and the isotope composition of the plutonium upon the safety and breeding features of a breeder reactor cooled by dry overheated steam. But the authors of [2] did not consider the problem or could not suggest a reactor design with a vanishing or negative void coefficient of the reactivity. Later on [3] the design of a steam-cooled breeder reactor with optimal dependence of the reactivity upon the density of the coolant was considered in greater detail. This design is characterized by large geometrical dimensions of the core and a large spacing of the fuel element grid (relative step width 1.35-1.5). This design has important shortcomings: in order to compensate for the losses resulting from the spacing of the fuel element grid for the production of excess plutonium (r9+1), a coolant of reduced density is required, and this increases the power consumption for the intrinsic reactor requirements in an inadmissible fashion and causes a deterioration of the temperature conditions of the fuel element jackets. Moreover, the large spacing of the fuel element grid increases the specific critical load of the fuel and the supercriticality in the reactor state of flooding with water.