After 8 and a half months of trying to lower the temperature of the Reactor Pressure Vessels (RPV), which by the way are broken and probably devoid of melted fuel, TEPCO announced they would now try to raise the temperature to avoid hydrogen explosion.
It seems like another non-reason why they do and do not want to reduce the amount of water in the building basements. (If they reduce the water level too much too soon, the ground water will seep in more - something like that. The ground water keeps coming in anyway.)
From Yomiuri Shinbun (11/24/2011):
TEPCO announced on November 24 that the work had started on reducing the amount of water being injected to Reactors 1 - 3 at Fukushima I Nuclear Power Plant in order to raise the temperature inside the Reactor Pressure Vessels.
The RPVs are thought to contain hydrogen. If the RPVs are cooled too much, the steam inside the RPVs will become water, making the atmosphere inside the RPV too dry and increasing the danger of igniting hydrogen. At the same time, TEPCO has started the preparation for injecting nitrogen into the RPVs to expel hydrogen inside the RPVs.
The amount of water injected to Reactor 1 will be reduced by 0.5 cubic meter per hour (currently 5.5 cubic meters/hr water is being injected), and the amount of water injected to Reactors 2 and 3 will be reduced by 1.5 cubic meter per hour (current amount is 10 cubic meters/hr). Right now, the temperatures at the bottom of the RPVs of Reactors 1, 2 and 3 are below 70 degrees Celsius. TEPCO wants to raise them to slightly above 80 degrees Celsius to maintain the amount of steam. As soon as nitrogen is injected inside the RPVs, the amounts of water injection will be restored to the existing level, the company says.
So far, nitrogen injection has been to the Containment Vessels.
Well let's see. According to the latest plant status by TEPCO (11/24/2011), the temperatures at the bottom of the RPVs are:
- Reactor 1: 40.4 degrees Celsius
- Reactor 2: 68.3 degrees Celsius
- Reactor 3: 66.6 degrees Celsius
And here's TEPCO's diagram of the effect of the gas management system on Reactor 2's CV. It doesn't make sense whatsoever, as it depicts a reactor that was leaking gas from all over the place but now has stopped leaking, thanks to the gas management system that sucks out the gas from the CV. But isn't it cute that the melted fuel is depicted still nside the RPV?