13 May (NucNet): Tokyo Electric Power Company (Tepco) is to review its strategy for stabilising the Fukushima-Daiichi nuclear plant after confirming that nuclear fuel in unit 1 has partially melted and formed corium at the bottom of the reactor pressure vessel (RPV).
Corium, also called fuel containing material (FCM) or lava-like fuel containing material (LFCM), is a molten mixture of portions of nuclear reactor core, formed during a nuclear meltdown.
Because corium forms a compact mass and releases heat from the decay of remaining radionuclides inside, its permanent cooling is a particular challenge.
Tepco also confirmed yesterday that coolant water in the reactor had dropped to a level that would completely expose the fuel rods.
But the company said based on the surface temperature of the reactor it believes the corium at the bottom of the RPV has cooled down.
Earlier today workers brought in equipment for connecting a circulating cooling system to the reactor, in line with a plan Tepco decided last month.
Under the plan, the utility was to fill the unit 1 containment vessel with water. A cooling system was to be set up that would circulate this water through a heat exchanger.
But the system will only work if the water in the containment vessel is at least five metres deep.
>>Related reports in the NucNet database (available to subscribers)
Robots Recover First Radiation Data From Reactor Buildings (News in Brief No. 100, 19 April 2011)
Tepco Announces Plans To Flood Unit 1 At Fukushima-Daiichi (World Nuclear Review No. 18, 6 May 2011)
