EDN: NFDLLV
Authors & Affiliations
Gonchar N.I., Dmitriev D.V.
A.I. Leypunsky Institute for Physics and Power Engineering, Obninsk, Russia
Dmitriev D.V. – Junior Researcher. Contacts: 1, pl. Bondarenko, Obninsk, Kaluga region, Russia, 249033. Tel.: +7 (484) 399-70-00 (add. 54-21); e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it..
Gonchar N.I. – Leading Researcher, Cand. Sci. (Tech.).
Abstract
The reactor design must define safe operation limits for fuel element damage (their number and degree of damage), as well as the associated levels of radioactivity in the primary circuit working media, including the concentration of fission products.
NP-082-07 establishes safe operation limits (SOL) for fuel element damage in sodium-cooled fast neutron reactors relative to the number of fuel elements in the core: the maximum number of fuel elements with a gas leakage defect of no more than 0.1 %; fuel elements with direct contact of the fuel with the coolant – no more than 0.01 %. The main task of failed fuel detection systems (FFDS) is timely diagnostics of approaching the SOL.
The physical principle of FFDS operation is recording an increase in the activity of fission products in the primary circuit media when a through defect in the fuel element cladding appears and an increase in the content of delayed neutrons in the coolant in the event of significant cladding damage and the appearance of an open fuel surface. The rate of fission products (FP) entering the coolant and, accordingly, the activity of the environments directly depend on the number of leaky fuel elements, the degree of their damage and the type of fuel.
Spectrometry of the primary circuit protective gas of the BN reactor purified from aerosols allows us to detect the presence of leaky fuel elements by the growth of the activity of gaseous FPs (GFP). To estimate the number of damaged fuel elements with division by the type of defect, a calculation model is required that allows us to compare the GFP activity with the number of leaky fuel elements depending on the type of damage and verified using experimental data on an operating reactor. One of the important parameters of this model is the relative rate of coolant degassing, defined as the ratio of the rate of GFP exit from the coolant into the gas system to their content in the coolant.
The aim of the work is to estimate the relative rate of sodium coolant degassing based on the measured volumetric activity of radioactive argon (Ar-41) in the gas cavity of the reactor.
Keywords
failed fuel element detection, reactor plant, fast neutron reactor, sodium coolant, radiation levels in working areas, inert radioactive gases, relative degassing rate
Article Text (PDF, in Russian)
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UDC 621.039.548
Problems of Atomic Science and Technology. Series: Nuclear and Reactor Constants, 2025, no. 1, 1:17
