Features of Methods for Monitoring the Tightness of the Cladding of Fuel Elements in Fast Breeder Reactors with Lead Coolant
For the timely detection of unpressurized fuel elements in the reactor, a system for monitoring the tightness of the fuel element cladding should be provided. In reactors with a heavy liquid metal coolant, the most effective is the control of the tightness of the cladding of fuel elements by detecting gaseous fission products.
The paper considers the basic principles of constructing a system for monitoring the tightness of fuel element cladding in reactors with a liquid metal coolant based on the detection of fission products and delayed neutrons. It is noted that in reactors with a heavy liquid&metal coolant the most effective is the control of the tightness of the cladding of fuel elements by gaseous fission products. Various aspects of the behavior of fission products in a reactor with a heavy liquid metal coolant are shown such as the movement of gaseous fission products in dissolved and bubble form along the circuit, sorption of volatile fission products in the lead coolant and on the surfaces of the structural elements, degassing of the gaseous fission products dissolved in the lead coolant and filtration of cover gas from aerosol particles of various nature.
General concepts of the transfer of gaseous fission products in a lead coolant and a mathematical model are described, which makes it possible to determine the calculated activity of reference radionuclides in each block of the reactor at any time after the depressurization of the fuel element. On the basis of this model, methods for monitoring the tightness of the fuel element cladding by the gas activity in the gas volumes of the reactor plant will be proposed.
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