Abstract
The purpose of this study is to investigate core design of high-temperature gas-cooled reactor by calculating the effective multiplication factor, thermal neutron flux distribution, and power distribution. The prismatic-type high-temperature gas-cooled reactor chosen is the High Temperature Test Reactor (HTTR) designed by Japan Atomic Energy Agency (JAEA). The prototype design of Gas Turbine High Temperature Reactor of 300MWe nominal capacity (GTHTR300) is also investigated. Reactor core may have certain temperature distribution due to fuel position and helium flow direction. By using cross-section generation code, temperature-dependent cross sections can be generated for the criticality calculation for effective multiplication factor, thermal neutron flux distribution, and power distribution of the core. Using uniform temperature HTTR model may cause ~2 mk overestimate of effective multiplication factor, 13% difference in thermal neutron flux distribution and 14% difference in power distribution, compared with the detailed temperature model. In the original HTTR core design, there are 12 different fuel enrichments used in the core for better power distribution. However, in GTHTR300, there is only one enrichment. Replacing HTTR detailed temperature model by uniform enrichment model will result in 24 mk increase of effective multiplication factor. The radial power distribution in the original design is flatter. The power generated from the bottom fuel in the uniform enrichment model will be 2.5 times of the original one, and the bottom fuel temperature will exceed the design criteria. In the GTHTR300 core design, fuel columns are arranged in outer region of the core, which will result in smoother thermal flux and power distribution. The maximum- to-average ratio of radial power distribution is 1.2, slightly higher than 1.04 of HTTR. In HTTR calculation, it is found that the helium gap between the fuel rod and the cladding will result in increasing of fuel temperature by 88 K. In the GTHTR300 design, by eliminating cladding and the helium gap, the temperature of fuel rod can remain under the design limit. This study established the preliminary coupling of reactor neutron physics and thermal hydraulic calculation, and therefore was able to look into the key issues of the core design of the high temperature gas-cooled reactor.