Validation on the lead coolant technology for BREST reactors

The operating experience of reactor facilities with a lead-bismuth coolant and a complex of R and D work done to validate facilities with a lead coolant convince that the coolant technology issues require urgent solution also for the BREST-OD-300 facility. The coolant technology issues include a complex of measures, processes and devices to be developed to ensure the cleanliness of the reactor and heat exchanging surfaces and ensure anti-corrosion protection of materials. In the long run, the coolant technology relates the most important list of issues that determine the preservation of the reactor facility's design thermal-hydraulic characteristics and its trouble-free operation. The coolant technology priorities and capabilities for implementing this technology have been determined for the BREST-OD-300 reactor facility. With regard for the quantitative prediction of all impurity sources for the BREST-OD-300 conditions, key technical concepts for the coolant technology systems have been proposed and validated, including the following: 1. To clean the coolant and the circuit surfaces at the BREST-OD-300 facility, it is proposed to use a hydrogen recovery process based on hydrogen reduction of the lead oxide impurities to lead and its return to the coolant. The hydrogen recovery process in the BREST-OD-300 facility is implemented through introduction of a hydrogen-containing gas mixture immediately to the circulating alloy flow. To exclude negative hydrogen effects on protective passivating films of structural materials, water vapour is added to the reduction gas mixture. 2. To clean the coolant of impurities other than reduced by hydrogen, the BREST-OD-300 facility includes filters. They are used to clean the coolant of oxidized impurities of structural materials that enter the coolant through diffusion, erosion or other processes. 3. To prevent the primary circuit gas volume making dusty in the BREST-OD-300 facility, it will have a special aerosol cleaning system. To ensure the anti-corrosion state of the coolant and protect the steel against corrosion, the BREST-OD-300 project includes a system for the oxygen control in the coolant and a system for keeping the oxygen content in the optimum concentration range by controlled dissolution of lead oxides preliminarily introduced to the circuit. To this end, special designs of mass exchange devices have been developed for the project. Along with particular systems, the project includes a range of organizational and technical measures for maintaining the coolant technology, which provides for an improved BREST-OD-300 facility operation reliability. (author)