TOKYO, March 18, Kyodo
An unprecedented attempt to douse an apparently overheating spent fuel pool with tons of coolant water at a stricken nuclear plant in Fukushima bore some fruit Thursday, but the emission of smoke newly confirmed at another pool suggests the difficulties that lie in the way of resolving the crisis triggered by the March 11 quake and tsunami.
Up to 64 tons of water were aimed by helicopters and fire trucks of the Self-Defense Forces as well as a water cannon truck of the Metropolitan Police Department into the pool at the No. 3 unit of Tokyo Electric Power Co.'s Fukushima Daiichi plant.
The utility said vapor rising from the partially destroyed No. 3 reactor building suggests the operation went some way toward cooling down the pool that could otherwise emit highly contaminated radioactive materials.
However, no major changes were seen in radioactive levels at the plant immediately afterward.
Prime Minister Naoto Kan expressed his gratitude to SDF personnel and police officers who were engaged in the daunting mission despite high radiation levels, saying at a government taskforce meeting, ''I thank them for carrying out such dangerous operations.''
No grave health hazard has so far been reported among SDF and police officers who were involved.
Chief Cabinet Secretary Yukio Edano told reporters that the mission will continue Friday in the effort to avert any massive release of radioactive materials into the air from the pool.
The government's Nuclear and Industrial Safety Agency said later in the day that white smoke was confirmed to be billowing from the nearby No. 2 unit at the power plant, suggesting that a spent nuclear fuel pool in the facility may also be boiling.
A rise in the pool's water temperature, usually at 40 C, causes water to dissipate and expose the spent nuclear fuel rods, which could heat up further and melt, and, in the worst-case scenario, discharge highly radioactive materials, experts say.
Hidehiko Nishiyama, an agency spokesman, also said efforts to bring electricity back to the plant by using outside power lines accelerated Thursday.
Electricity could be restored Friday or Saturday to recover the lost cooling functions at the No. 2 reactor building, which he said takes priority over other the troubled reactors as it cannot be doused since the roof of its building is still intact.
TEPCO also plans to install a temporary power source in an area of the plant where the radiation level is low.
Concerns are growing that the level of the water filling the spent fuel pool of the No. 4 unit is also becoming low, and water injection efforts will focus on the pool as well as that of the No. 3 unit, according to Nishiyama.
The pools of both the No. 3 and No. 4 units are no longer covered since they were blown off in apparent hydrogen blasts earlier this week.
The spent fuel pools at the power station lost their cooling function after the quake and tsunami struck last Friday. It is also no longer possible to monitor the water level and temperature of the pools of the Nos. 1 to 4 units.
Among the six reactors at the Fukushima Daiichi nuclear plant, the No. 1, No. 2 and No. 3 reactors that were operating at the time of the quake halted automatically, but their cores are believed to have partially melted as they lost cooling functions after the quake.
The buildings housing the No. 1, No. 3 and No. 4 reactors have been severely damaged by apparent hydrogen blasts, and the No. 2 reactor's containment vessel suffered damage to its pressure-suppression chamber at the bottom.
As for the remaining reactors that along with the No. 4 unit were under maintenance when the quake occurred, Edano said that his understanding is that it would be ''some time'' until the No. 5 and No. 6 units reach a dangerous situation.
The government has set the exclusion zone covering areas within a 20 kilometer radius of the plant, and urged people within 20 km to 30 km to stay indoors.
On Thursday, Tokyo also tried to allay growing concerns over the crisis as the United States advised its nationals living within an 80-kilometer radius to evacuate as a precaution. South Korea, Australia and New Zealand followed suit with the advisory.
==Kyodo
http://english.kyodonews.jp/news/2011/03/79057.html
