Variable Reactivity Control in Small Modular High Temperature Reactors Using Moderation Manipulation Techniques

Abstract

Abstract:With extensive research being undertaken into small modular reactor design concepts, this has brought new challenges to the industry. One key challenge is to be able to compete with large scale nuclear power plants economically. In this article, a novel approach is applied to reduce the overall dependence on fixed burnable poisons during high reactivity periods within a high temperature graphite moderated reactor. To reduce the excess activity, we aim to harden the flux spectrum across the core by removing part of the central moderation column, thus breeding more plutonium, in a later period the flux spectrum is softened again to utilise this plutonium again. This provides a neutron storage effect within the 238 U and the resulting breeding of Plutonium. Due to the small size and the annular design of the high temperature reactor, the central reflector is key to the thermalization process. By removing a large proportion of the central reflector, the fuel within the proximity of the central reflector are less likely to receive neutrons within the thermal energy range. In addition to this, the fuel at the extremities of the core have a higher chance of fission due to the higher number of neutrons reaching them. This works as a method of balancing the power distribution between the central and outside fuel pins. During points of low reactivity, such as the end of the fuel cycle, the central reflector can be reinserted and the additionally bred plutonium and U 235 at the centre of the core will encounter a higher probability of fission due to more thermal neutrons within this region. By removing the central reflector, this provided a 320 pcm reactivity drop for the duration of the fuel cycle. The plutonium buildup provided additional fissile material up until the central reflector was reinserted. The described method created a two-fold benefit. The overall full power days within the core was increased bỹ 31 days due to the additional fissile material within the core and secondly the highest loaded power pins saw a 30% power reduction during the removal of the central reflector column.

Thermodynamic Analysis of Advanced Gas Turbine Combined Cycle Integration with a High-Temperature Nuclear Reactor and Cogeneration Unit

“…Interesting research studies on the potential of nuclear power plant working in cogeneration have been proposed by Hanuszkiewicz-Drapala and Jedrzejewski [17,18]. The promising option can be a connection of two small modular reactors (SMR), which guarantees a significant improvement in efficiency, as well as nuclear reactor flexibility [19,20]. In [21], the authors proposed a new promising solution for an intermediate heat exchanger, which is applicable to the gas turbine high-temperature reactor system and is implemented to cogenerate electric power generation, hydrogen production, and heat.…”

“…Gas-cooled reactor systems possess several essential features that distinguish them from all other types of nuclear reactors and provide an important operational advantage. The reactor fuel in the form of ceramic-coated particles is able to operate at temperatures higher than 1800 • C; the coolant can be carbon dioxide or helium both inert for neutrons and graphite moderator [19]. In [22], the authors proposed an approach to reduce the overall dependence on fixed burnable poisons during high-reactivity periods within a high-temperature graphite-moderated reactor.…”