Assessment of Spent Fuel of Alfa Class Nuclear Submarines
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ASSESSMENT OF SPENT FUEL OF ALFA CLASS NUCLEAR SUBMARINES M.I. BUGREEV, E.I. EFIMOV, S.V. IGNATIEV, D.V. PANKRATOV, V.I. TCHITAYKIN Institute of Physics and Power Engineering, Obninsk 249033, RUSSIA E-mail: [email protected] ABSTRACT At present spent nuclear cores from Alfa class submarines are being stored in temporary facilities, designed to sore them only for a few years (∼3 to 5 years). This paper assesses the problems of nuclear safety during long-term unplanned forced storage of spent fuel because of the delay in building permanent facilities. The Nuclear Submarines (NS) cores use heavy liquid metal lead-bismuth coolant in the primary circuit of nuclear reactor. The radiation parameters of the discharged cores from NS of the Project 705K (this is the number of ship engineering design) are determined. Based on that determination a step-by-step solution is proposed and the technological and other challenges that the Project faces are considered. INTRODUCTION During 1960 – 1990 the Institute of Physics and Power Engineering (IPPE) along with other Russian organizations has developed an unique reactor technology that has been realized in the building of the nuclear reactors (NR) cooled by heavy liquid metal lead-bismuth eutectic alloy (LBEA) in the primary circuit. Such NR were used in high-speed and maneuverable Alfa class Nuclear Submarines (NS). In order to support the coolant technology research a couple of heavy liquid metal test facilities (HLMTF) have been created at IPPE in Obninsk and in Sosnovy Bor near St.Petersburg. Prototypes of such nuclear reactors were operated at these facilities. All of the operated NR in question belonged to the intermediate neutron reactor type. The reactor fuel composition included the inter-metallic compound UBe13 with U235 enriched up to ∼90% and dispersed into the beryllium matrix. Metallic beryllium served as reflector (moderator) in these reactors. At present all Alfa class NS are decommissioned. Unlike to water-cooled reactors the refueling of these NR was implemented through the unloading of a single removable blocks, including reactor core with dropped control rods, reflector (moderator), and upper closure fitting of biological shielding. So, in fact it was the unloading of a sub-critical reactor. The unloaded and non-unloaded (that should be unloaded but for some reasons are still stored on the boards or in the cut reactor modules) spent removable blocks (SRB) have been allocated for a temporal storage either at the coastal repository or inside the cut reactor modules at Kola Peninsula. In the meantime, the permanent storage of the SRB has been delayed. That is why the assessment of nuclear safety during the long-term forced storage of the SRB in the temporary facilities is an urgent task. The purpose of this work was to analyze the radiation parameters of the SRB unloaded from the NS of Project 705K, determine the radioactivity composition and set the problems on treatment of the SRB as a radwaste. STORAGE CONDITIONS OF SRB For temporary storage (from 3 to 5 y
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