DECOMMISSIONING OF THE NUCLEAR RESEARCH REACTOR IRT-M AND PROBLEMS CONNECTED WITH RADIOACTIVE WASTE

摘要

The nuclear research reactor IRT-2000 is described, along with modifications and upgrades made over the past three decades. Considerations are outlined which followed a decision to shutdown the reactor and to dismantle it. About 50 years has passed since the appearance of the first nuclear research reactors. Most of the first generation reactors have exhausted their operating life and should be dismantled. But nuclear reactor dismantling is a very complex process, fall-scale realization of which generates a lot of problems mainly connected with radioactive waste, solution of which is apparently beyond many countries strength. The construction of the Nuclear Research Reactor IRT-2000 of the Institute of Physics began in early 1957 and was completed in August 1959. Physical start-up of the reactor was done in October 1959 and its regular operation began since 1960 at various power levels up to the designed power 2000 kW. IRT-2000 type nuclear reactor, designed in the Soviet Union, pertains to the group of light water pool-type reactors in which the usual (light) water is used as a moderator and a reflector of neutrons and as a coolant and a part of biological shielding of the reactor. Such type nuclear reactors were built also in Russia (Moscow, Tomsk, Sverdlovsk), Byelorussia (Minsk) and Latvia (Riga) as well. Besides IRT-2000 type research nuclear reactors were constructed in Bulgaria (1961), China (1962), North Korea (1965) and Iraq (1967) [1,2]. The pool of the reactor IRT-2000 is a tank made of 6 mm thick aluminum alloy sheets surrounded by 1.8 m thick biological shielding of reinforced concrete which has different densities in different parts of construction. The height of the pool is 7.6 m, the length - 4.5 m, the width 1.9 m and the whole volume - about 60 m . The following units of the reactor are located on the bottom of the pool under six-meter water layer: the reactor core, ejection pump and pipelines of the primary circuit of cooling system, loading and unloading devices, channels of control and emergency protection systems and 10 horizontal experimental channels of various diameters (100-150 mm) which border the core and serve for outlet of neutron beams to the experimental installations. The pool of the reactor is filled with distilled water up to the height of 7.2 m and is covered with the lid of organic glass. Reactor is also equipped with vertical experimental channels for irradiation of samples in the vicinity and within of the core (see Fig. 1). At the reactor power of 2000 kW the maximum flux of thermal neutrons measured in the center of the core was 2.5-10 n/cm -sec, in the water reflector of the core - 5-10 n/cm -sec, and at the outlet of the horizontal experimental channels - 5-10 -1-10 n/cm -sec.