Features of methods for monitoring the fuel cladding tightness in lead-cooled fast breeder reactors

Anastasiya V Dragunova,Mikhail S Morkin,Vladimir V Perevezentsev

doi:10.3897/nucet.7.78372

Anastasiya V Dragunova, Mikhail S Morkin + Show 1 more

Open Access

https://doi.org/10.3897/nucet.7.78372

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Abstract

To timely detect failed fuel elements, a reactor plant should be equipped with a fuel cladding tightness monitoring system (FCTMS). In reactors using a heavy liquid-metal coolant (HLMC), the most efficient way to monitor the fuel cladding tightness is by detecting gaseous fission products (GFP). The article describes the basic principles of constructing a FCTMS in liquid-metal-cooled reactors based on the detection of fission products and delayed neutrons. It is noted that in a reactor plant using a HLMC the fuel cladding tightness is the most efficiently monitored by detecting GFPs. The authors analyze various aspects of the behavior of fission products in a liquid-metal-cooled reactor, such as the movement of GFPs in dissolved and bubble form along the circuit, the sorption of volatile FPs in the lead coolant (LC) and on the surfaces of structural elements, degassing of the GFPs dissolved in the LC, and filtration of cover gas from aerosol particles of different nature. In addition, a general description is given of the conditions for the transfer of GFPs in a LC environment of the reactor being developed. Finally, a mathematical model is presented that makes it possible to determine the calculated activity of reference radionuclides in each reactor unit at any time after the fuel element tightness failure. Based on this model, methods for monitoring the fuel cladding tightness by the gas activity in the gas volumes of the reactor plant will be proposed.

Highlights

The lead-cooled BREST-OD-300 reactor plant using nitride uranium-plutonium fuel is being developed in order to substantiate the possibility of deploying large-scale nuclear power industry based on fast reactors, which could solve the problems of removing restrictions on fuel resources, eliminating severe accidents at nuclear power plants and closing the nuclear fuel cycle to ensure economic competitiveness (Adamov et al 2020)
In accordance with modern standards in the field of nuclear power, in order to determine the number of failed fuel elements, their location and the type of cladding failure, the BREST reactor facility should be provided with a fuel cladding tightness monitoring system (FCTMS), developed on the basis of the experience in designing and operating such systems for existing types of fast reactors (NP-082-07 2008)
The expected effect of this process on the measured gas activity can be calculated using a mathematical model that takes into account the transfer of nuclides, in which the gaseous fission products (GFP) released from the leaking fuel elements enter the lead coolant (LC) passing through the core, into the other parts of by the LC flow, since the lead downward flow rate in the steam generators (SG) is many times higher than the bubble rise velocity