Yuanzineng kexue jishu (Jan 2023)
Research on Core Physical Characteristics of Prismatic Super-safe Gas-cooled Reactor
Abstract
The prismatic super-safe gas-cooled reactor is one of the advanced reactor types that can be designed as the movable micro nuclear power devices applied in some specific scenarios, such as remote areas, islands, post disaster reconstruction, border national defense and so on. The reactor has superior inherent safety because of graphite core with high temperature resistance and large heat capacity, ceramic particle dispersion fuel almost completely containing fission products, the low power and power density. What’s more, on the basis of high temperature gascooled reactor, the SiC matrix and nofuel zone of fuel pellet further enhances the barrier effect on fission products. Through the design of burnable poison and negative temperature feedback, the reactor can realize automatic shutdown only relying on negative reactivity caused by temperature rise, even if all control rods are pulled out without any emergency measures under accident conditions. From a physical point of view, the risk of core melting and massive release of radioactive materials is avoided. To analyze its core physical characteristics, a core loading scheme and a reactivity control strategy were proposed, and then burnup, distribution of power, distribution of neutron flux density, neutron energy spectrum, reactivity temperature coefficient, xenon oscillation, and xenon reactivity were investigated based on the core model by using Monte Carlo procedure. The results show that the requirement of 5 MW thermal power and 3 a lifetime can be met and the average discharge burnup is 18 700 MW·d/tU. If the fuel enrichment increases from 85% to 15%, the lifetime will increase to 10 a and the maximum discharge burnup is 79 600 MW·d/tU. The radial distribution of power is uniform, while the axial is in the shape of piecewise concave curve similar to the distribution trend of thermal neutrons. The maximum neutron flux density is as low as 43×1013 cm-2·s-1 at the beginning of lifetime, and the neutron energy spectrum is greatly affected by temperature but less by burnup. Reactivity temperature coefficients, including negative fuel temperature coefficient, negative core graphite temperature coefficient, and small positive reflector graphite temperature coefficient, are influenced by burnup and temperature significantly, which makes the core have the safety of automatic shutdown only relying on negative temperature feedback under accident conditions. The amplitude of xenon oscillation is very small and the reactivity of iodine well is only -110 pcm when the reactor is shutdown at full power, thus the core has great stability. These results will instruct the followup development of gascooled reactor micro devices.
