Specifics of high-temperature sodium coolant purification technology in fast reactors for hydrogen production and other innovative applications

In creating a large-scale atomic-hydrogen power industry, the resolution of technological issues associated with high temperatures in reactor plants (900°C) and large hydrogen concentrations intended as long-term resources takes on particular importance. The paper considers technological aspects of removing impurities from high-temperature sodium used as a coolant in the high-temperature fast reactor (BN-HT) 600MW (th.) intended for the production of hydrogen as well as other innovative applications. The authors examine the behavior of impurities in the BN-HT circuits associated with the mass transfer intensification at high temperatures (Arrhenius law) in different operating modes. Special attention is given to sodium purification from hydrogen, tritium and corrosion products in the BN-HT. Sodium purification from hydrogen and tritium by their evacuation through vanadium or niobium membranes will make it possible to develop compact highly-efficient sodium purification systems. It has been shown that sodium purification from tritium to concentrations providing the maximum permissible concentration of the produced hydrogen (3.6Bq/l according to NRB-99/2009) specifies more stringent requirements to the hydrogen removal system, i.e., the permeability index of the secondary tritium removal system should exceed 140kg/s. Provided that a BN-HN-type reactor meets these conditions, the bulk of tritium (98%) will be accumulated in the compact sodium purification system of the secondary circuit, 0.6% (∼ 4·104Bq/s), will be released into the environment and 1.3% will enter the product (hydrogen). The intensity of corrosion products (CPs) coming into sodium is determined by the corrosion rate of structural materials: at a high temperature level, a significant amount of corrosion products flows into sodium. The performed calculations showed that, for the primary BN-HT circuit, the amount of corrosion products formed at the oxygen concentration in sodium of 1mln–1 exceeds 900kg/yr with fuel element claddings made of EP-912-VD steel and 464kg/yr with molybdenum alloy claddings. For the secondary circuit, the amount of corrosion products totals 263kg/yr for each loop. Taking into account the high-temperature experiments which demonstrated high efficiency of retaining corrosion product suspensions by the strainers located in the low-temperature area, it is proposed to cool sodium to the required temperature alongside the corrosion products retention on the mass transfer surfaces, including strainers. It is shown that, by using 30% of the power required to produce hydrogen with 50% efficiency, the BN-HT is capable of producing about 0.6·106m3 of hydrogen per 24 hours which is sufficient for modern large-scale enterprises processing medium-grade crude oil or the implementation of other technologies

Investigations for the substantiation of high-temperature nuclear power generation technology using fast sodium-cooled reactor for hydrogen production and other innovative applications (Part 1)

Neutronics and thermal physics studies of BN-VT reactor installation with 600-MW thermal power demonstrated the possibility in principle to achieve the required parameters of high-temperature fast reactor for production of large quantities of hydrogen on the basis, for instance, of one of thermal chemical cycles or high-temperature hydrolysis with high thermal efficiency of use of electric power. Relatively small dimensions, the type of coolant, selection of fissile material and structural materials allow developing nuclear reactor with particular inherent properties (exclusion of prompt-neutron reactor power excursions, removal of decay heat in passive mode) while ensuring enhanced nuclear and radiation safety. Composition of BN-VT reactor facility includes sodium-cooled fast reactor, three cooling loops for emergency heat removal and three sets of equipment of the secondary cooling loop for heat transfer from the reactor to chemical installations generating hydrogen or to gas-turbine plant for supplying chemical equipment with electric power. Composition of each of the cooling loops includes intermediate heat exchanger arranged inside the reactor vessel, centrifugal pump and pipeline for removal and re-introduction of sodium in the reactor core. Contemporary requirements on the safety and financial performance of future generations of nuclear reactors were taken into consideration in the development of the reactor under study. Implemented calculation studies demonstrated that penetration of hydrogen within the limits of permissible allowances produce practically no effect on the neutronics and safety parameters of the reactor. Solution of the problem of fuel pin stability was mitigated due to the selection of low thermal load on fuel pins. Application of EP-912-VD steel as a possible optional structural material was examined. Continued studies of heat-resistant materials and their behavior under irradiation are required