Gas-Net: a two-dimensional network code for prediction of core flow and temperature distribution in the prismatic gas reactor

In the prismatic high temperature gas reactor the coolant that bypasses fueled regions by way of leakage paths can have a significant effect on core temperatures. Large uncertainty in the bypass flow leads to increased operating and safety margins and reduced high temperature performance. The GAS-NET computer code has been developed to investigate the dependence of core temperature distribution on phenomena responsible for coolant bypass. The code is based on a two-dimensional network model for the coolant paths. It solves the one-dimensional conservation balances associated with each elemental flow path through and between fuel, fuel control, reflector control, and solid reflector elements. The code has been used to study the sensitivity of fuel channel coolant temperatures to uncertainties associated with core pressure loss data, leakage past core support seals, leakage from between stacked elements, and leakage past control rods in control rod holes. Ultimately such results can be used to prioritize experiments aimed at reducing uncertainties to achieve reduced operating and safety margins. (author)