April 16th, From Kyodo:
The level of radioactive substances in seawater increased sharply overnight inside a containment fence installed near the Fukushima Daiichi nuclear power plant, the operator Tokyo Electric Power Co. said Saturday.
The utility said the rise suggested that the fence is helping to curb the spread of contaminated water, but the government's Nuclear Industrial and Safety Agency remained cautious, citing the possibility that radioactive water could still be seeping from the complex.
The company said the level of radioactive iodine rose Saturday morning to 260 becquerels per cubic centimeter in seawater inside the fence near an intake leading to the No. 2 reactor.
The figure, 6,500 times the legal limit, was around six times the 42 becquerels detected the previous day, the company said, adding the reading of radioactive cesium had also jumped by four times.
TEPCO also said it plans on Sunday or later to throw sandbags containing zeolite, a mineral that absorbs radioactive materials, into the sea near intakes leading to the Nos. 1, 2 and 3 reactors to reduce the levels of contamination.
Meanwhile, the utility is considering installing circulating water cooling systems for reactors and spent fuel storage pools outside the reactor buildings at the plant in a bid to bring it under control, sources familiar with the matter said.
The new systems would cool nuclear fuel inside the reactors and spent fuel pools in a stable manner. They would involve heat exchangers and circulation pumps to drain reactor coolant water from the containment buildings, cooling it with seawater and then sending it back to the reactors, the sources said.
TEPCO appears to have already placed orders for dozens of gasketed plate heat exchangers -- each measuring 3 meters high, 1 meter wide and 2 meters long -- for such systems, the sources said.
The existing circulating water cooling systems at the plant were crippled by the March 11 earthquake and ensuing tsunami.
The utility has been pumping water into reactors and storage pools in a desperate bid to cool them. But the move has created large puddles of water contaminated with high levels of radiation inside the reactor containment and turbine buildings, as fuel rods in the reactors and storage pools have been partially damaged.
The presence of the large puddles in the buildings has blocked restoration work at the plant.
TEPCO has therefore determined that it is necessary to cool the reactors and storage pools with new circulating water cooling systems to be installed outside the containment buildings, they said.
It is impossible to sufficiently cool the reactors and storage pools simply by pumping water into them without circulating water through the reactors and pools. The pumping operation has also had the negative side effect of raising the water levels of the radiation-contaminated puddles.
It would be necessary to secure five or six heat exchangers to cool one reactor, but the cooling efficiency of the gasketed plate heat exchangers is twice that of conventional heat exchangers for nuclear plants, according to the sources.
Radiation levels inside the containment buildings remain high. TEPCO plans to utilize the pipes that it has been using to pump water into the reactors in the new circulating water cooling loops, so it can minimize the need for work inside the dangerous buildings.
==Kyodo
