Nuclear reactor with low-level core coolant intake

A natural-circulation boiling-water reactor has skirts (120) extending downward from control rod guide tubes to about 10 centimeters from the reactor vessel bottom (116). The skirts (120) define annular channels about control rod drive housings (112) that extend through the reactor vessel bottom (116). Recirculating water is forced in through the low-level entrances to these channels, sweeping bottom water (134) into the channels in the process. The sweeping action prevents cooler water from accumulating at the bottom. This in turn minimizes thermal shock to bottom-dwelling components as would occur when accumulated cool water is swept away and suddenly replaced by warmer water.