Estimates for Helium Cooling of a Modular DEMO First Wall

摘要

Lifetime studies performed for a modular first wall of a DEMO reactor with 2 MW/m exp 2 neutron wall loading have shown a strong impact of the temperature level at which the wall is operated. This result stimulated closer investigation of the cooling problem. On the basis of helium gas as the coolant, two alternative concepts of cooling the first wall are analyzed which conform to the design requirements imposed by the geometrical restrictions prescribed by the FWLTB life prediction code. In the investigation emphasis is placed on the hemispherical cap which closes a cylindrical cell at the side exposed to the plasma. This cap and a smaller concentric one provide an annular gap in which the coolant flows. In the one concept the coolant is assumed to enter the gap at the bottom of the hemisphere and subsequently to flow upwards along the increasing surface of the hemisphere with decreasing velocity or vice versa. The second concept assumes an essentially rectangular channel wound around the hemisphere inside the annular gap. For both concepts calculations have yielded the coolant-side wall temperatures as a function of the first-wall thickness and the fraction of alpha -power delivered to the wall. While the first concept revealed acceptable temperatures only within a narrow parameter range, the second showed a much higher cooling capacity. To summarize, the results demonstrate that it should be possible to keep the wall temperatures at or below 500 exp 0 C, depending on the parameters chosen. (ERA citation 08:048387)