For a long time fast reactors were regarded as unpromising for the production of radionuclides. At the same time, in our opinion, they exhibit good possibilities for producing artificial radioactive isotopes on account of the possibility of combining the production of different types of products (electricity + isotopes), the large volumes for installing targets, specifically, the existence of auxiliary breeding zones, and a high neutron-flux density.In Ref. 1, general approaches to obtaining the widely used 6~ and 14C nuclides in the screens of fast reactors were formulated. To increase the efficiency of the production of these isotopes, it was suggested that the spectrum of neutrons at the location of irradiation of the target be changed with the aid of a moderator --zirconium hydride. To this end, either a special irradiating apparatus should be developed or a subzone of a thermal-column type should be developed to replace part of the lateral breeding zone. In the limiting case, the entire lateral breeding zone can be oriented toward producing radionuclides. The computed production indicators turned out to be fairly good: the specific 6~ activity is 100 Ci/g and higher, and several MCi of a given isotope and up to i-2 kCi of t4c can be obtained in one year at the BN-600 reactor (Beloyar nuclear power plant). The computed data were confirmed in an experiment on the production of 6~ in the BN-350 reactor (Aktau, Kazakhstan) [2].The possibilities associated with the existence of a high neutron flux in fast reactors have nonetheless not been investigated adequately and are not used in full measure. For (anti)neutrino sources, which are studied in the present work, stringent requirements are characteristically imposed both on the overall activity of the source and on the specific activity of the main radionuclide. For this reason, we wish to point out that we are viewing the present work not only as a search for ways to solve the actual problem of producing specific sources for neutron physics and astrophysics, but also as the next step in isotope production in fast reactors, in the development of the ideas advanced in Refs. 1 and 2, and as an attempt to understand and evaluate the limiting possibilities of fast reactors for the production of isotopes with high specific activity.In this connection, we call attention to another method, characteristic for fast reactors, for producing radioactive isotopes with high specific activity --the use of threshold reactors with emission of charged particles, such as (n, c0 and (n, p). The drawback that the cross sections of these reactions are small can be compensated by increasing the mass of the irradiated target. Since in these reactions the nuclides of neighboring elements are formed, after irradiation the target nuclide can be separated from the main mass of the target by chemical methods, i.e. it can be obtained carrier-free. This increases substantially the specific activity of the source to values close to the limiting value for a pure monoisotope.(Anti)neutrino Sources...
A complex of computational and experimental measures for monitoring the distribution of energy release in the core has been perfected over the 25-year history of BN-600 operation in the Beloyarskaya nuclear power plant. Continual monitoring is conducted together with calculations based on three-dimensional multigroup calculations and periodic γ scanning of regular BN-600 fuel assemblies with upgrading of the core of this reactor. At the present time, in the course of switching BN-600 to a new core with four refuelings and maximum fuel burnup increased to 11.1% h.a., the experimental procedure has been upgraded and optimized taking account of the experience gained, three series of such measurements have been completed, and new experimental data on the character of the radial and axial neutron-field distribution have been obtained.One advantage of fast nuclear reactors is the stability of energy release. This made it possible to do without a special in-reactor system for monitoring the power of fuel assemblies in real-time in BN-600 in the Beloyarskaya nuclear power plant. Instead, a complex of measures for monitoring the distribution of the energy release in the core has been developed over the 25-year period of operation of the reactor. The crux of these measures reduces to the following. The fuel-assembly irradiation parameters in a regime with established refueling are continually monitored by computer simulation of the neutron field in a three-dimensional hexagonal geometry using programs for performing neutron-physical calculations, which solve the transfer equation in the multigroup diffusion approximation. During physical startup and upgrading of the core, special experiments are performed which make it possible to follow the actual state and changes of the neutron field in connection with the transition to a new modification. Starting with the physical startup of BN-600 in 1980, the distribution of the reaction rates and energy release in a fuel assembly were measured by means of γ scanning of fuel assemblies and needle activation detectors [1,2]. The former was simpler and adapted for monitoring the power of a fuel assembly under the conditions of a commercial fast reactor in a nuclear power plant and is now standard. The present article presents a description of the method and the application and results of the latest measurements undertaken in connection with the transfer of BN-600 to a new core 01M2 with enhanced burnup.
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