[en] Automatic translation: With the help of the 2-dimensional computer program THERMIX, the temperature and flow processes in the core area of the THTR reactor were examined with residual heat removal operation with small mass flow rates either started directly or interrupted for a longer period of time. When NWA operation starts directly, 2% of the full-load mass flow already ensures a stable flow through the core area; when the start is delayed by 5 hours, this is 3%. Lowering the gas inlet temperature has no significant influence the maximum temperatures in the ball fill.