Analysis of Overall Temperature Coefficient of Reactivity of the VHTRC-1 Core with a Nuclear Design Code System for the High-Temperature Engineering Test Reactor

The accuracy of the nuclear design code system for the High-Temperature Engineering Test Reactor (HTTR) is evaluated for the neutronic characteristics that depend on core temperature by analyzing the overall temperature coefficients of reactivity and the effective multiplication factors obtained by an experiment in which the Very High Temperature Reactor Critical Assembly (VHTRC) is heated from ambient temperature to 200°C. The core of the VHTRC consists of block-type fuel containing low-enriched uranium (LEU). The nuclear design code system for the HTTR includes the DELIGHT, TWOTRAN-2, and CITATION-1000VP computer codes. The DELIGHT code is a one-dimensional cell burnup code developed to evaluate the nuclear characteristics of HTTR fuel and to calculate the group constants. The calculated overall temperature coefficients of reactivity between ambient temperature and 200°C agree well with the measured coefficients, and the calculated effective multiplication factors for different temperatures agree with measured factors within an uncertainty of 0.6%. From the results, it is concluded that the nuclear design code system for the HTTR predicts well the temperature-dependent neutronic characteristics of a core containing LEU fuel.