File:DecayRateFukushima.gif

Estimatee for the evolution of the decay heat at the reactors at the Fukushima nuclear plant after shut-down, related to the Fukushima disaster.

Source: http://www.world-nuclear.org/info/fukushima_accident_inf129.html

Fukushima Accident 2011. (updated 12 July 2011)

Description:

The heat from the fuel in the reactor cores was estimated by France's ISRN as 2.5 MW thermal in unit 1 and 4.2 MW in units 2 & 3 after almost three weeks. Tepco's estimate is 1.5 to 1.8 MW in unit 1 at 8 weeks. The IRSN estimates represent enough heat to boil away 95 cubic metres and 160 m3 of water per day respectively if all external circulation to heat sinks ceases, indicating the need for constant top up while the heat is not being dumped in the normal or replacement heat exchanger circuits. From 30 March, 5 to 11 m3/hour has been injected into each reactor. The heat production levels will diminish only slowly from this point. Tepco intends to rig up cooling circulation for each reactor to an atmospheric heat exchanger, similar to those being used for the fuel ponds. Work has started for unit 1. Meanwhile injection into the RPVs of water circulated through the new water treatment plant is seen as relatively 'stable cooling'.