120 water from the rhrs 100 being pumped by the low pressure pump 110 flows into the primary inlet 130 through the primary circuit out of the porimary outlet 140 and into the rcs 170 water flowing through the rcs is recirculated back to the rhrs 100 and is re used valves 23 and 25 provide isolation from the rhrs 100 during normal operation and open to allow flow via the low pressure pump 110 colling water from the coolant tank 10 is circulated though the heat exchanger secondary circuit by the high pressure pump 30 via conduits 20 water from the coolant tank 10 being pumped by the high pressure pump 30 flows into the secondary inlet 150 through the secondary circuit out of the secondary outlet 160 and back to the cws 200 valve 28 and 29 isolate this high pressure cooling from the normal system the heat from water in the primary circuit is transferred to the water in the secondary circuit thereby cooling the water in the primary circuit an independent power source 190 as shown in fig1 is coupled to the high pressure pump 30 low pressure pump 110 and valves e g 23 25 28 29 as needed thereby providing power during a power fail condition fig4 shows a flow chart illustrating automatic activation of the high pressure pump of a preferred cooling system according to the invention upon sensing a loss of power during particular coolant temperature and pressure conditions.