Design and Safety Criteria for Reactor Relevant Heat Transport Systems

The candidate media (helium and water) for the primary cooling systems of a fusion plant are compared and criteria for the selection of the appropriate coolant developed. Robust formulas are developed to determine the space requirements for the cooling system. The formulas expressing the volumes of a cooling loop are derived from correlations for heat transfer, pressure drop, mass and energy balances. They define the required coolant volumes as a function of characteristic design parameters such as thermal power, temperature increase of the coolant, the temperature difference across the heat exchange surfaces and pumping power. The formulas are validated by comparison with design values of helium cooled fission reactors (High Temperature Reactor HTR) and a pressurized water cooled fission reactor (PWR). For the case of pipe break, the expansion volumes required to avoid an excessive overpressure in the building are calculated (important safety criterion). Mixing of the coolant with air contained in the expansion room is assumed. If high operation temperatures could be realized for the helium cooling (THe, max > 450°C) this would have a safety advantage compared with water cooling at conditions typical of a PWR. For lower allowable inlet temperatures, water requires a smaller expansion volume than helium, at the expense of energy conversion efficiency.