Officials this week restored electrical power at the stricken Fukushima nuclear power plant in Japan.
In reactors one, two and three officials were worried about an increase in pressure due to seawater being pumped in.
Intense heat in the reactor caused the water to turn to steam increasing pressure in primary containment buildings surrounding the reactors (NCE last week).
Independent nuclear expert Tony Roulstone said the challenge for officials is now split into two areas, cooling the reactor and spent fuel ponds.
With electricity restored to the reactors, engineers can now use cooling pipes containing water to remove heat from the system and reduce pressure and temperature to about 40˚C. Seawater is now only being pumped into reactor three, with reactors one and two using just the heat exchangers to reduce temperatures.
Roulstone said it could take many weeks for the reactors to cool down, but once stabilised attention could turn to public health issues affecting the area around the plant.
Elsewhere at the plant, spent fuel rods are in ponds outside the primary containment building for reactor four in a secondary containment building.
When electricity was cut because of the tsunami, the temperature in the ponds increased and caused a fire in reactor four.
With electricity now restored, cold water is now being circulated in the ponds, and cooling pond water temperatures have been reduced to around 40˚C.