NISA Fears Leak Of Cooling Water From Fukushima-Daiichi Unit 2
15 Apr (NucNet): Water being used to cool the number 2 reactor at the Fukushima-Daiichi nuclear plant might be leaking into the trench between the reactor and turbine building, Japan’s Nuclear and Industrial Safety Agency (NISA) has said.
The plant's operator, Tokyo Electric Power Company (Tepco), transferred about 660 tonnes of highly contaminated wastewater from the unit 2 turbine building installation trench to a turbine condenser on 13 April 2011.
As a result, the water level in the trench dropped by 8 cm, but had risen again by 3 cm yesterday morning.
The contaminated water needs to be moved because there is a risk it might continue to leak outside the unit’s controlled zone and from there flow into the sea.
Contaminated water has also been found in the turbine hall basements of units 1 and 3, although its level of radioactivity is much lower than the water at unit 2.
The total amount of water to be removed is estimated at more than 60,000 tonnes, the International Atomic Energy Agency said.
The water has been hampering work to restore the reactors’ cooling systems.
Tepco also plans to transfer contaminated water to the plant's waste processing facility, but the facility has not yet been made leak-proof. The utility says it does not know when it can start removing water from reactors other than unit 2.
Yesterday, workers continued to move emergency diesel generators to higher ground where they would be safe from aftershocks and tsunamis, according the Japan Atomic Industrial Forum.
NISA reported that an earthquake that hit Fukushima prefecture on 13 April 2011 had an epicentre 75 km from the Fukushima-Daiichi nuclear power plant and 67 km from Fukushima-Daini, but no unusual events have been reported at either facility.
Meanwhile, interim analysis of water from the spent fuel pool of unit 4 at Fukushima-Daiichi shows higher than normal levels of radiation, which suggests some of the fuel assemblies stored there might be damaged.
Tepco said analysis of samples collected from the pool on 12 April 2011 showed 220 kilobecquerels per litre (kBq/L) of iodine-131, 88 kBq/L of caesium-134 and 93 kBq/L of caesium-137.
The utility also said the water temperature in the unit 4 SFP had risen to about 90 degrees Celsius, significantly higher than the normal temperature range of 20 to 40 degrees Celsius.
To cool the fuel, workers sprayed almost 200 tonnes of water on the SFP for six hours on Wednesday morning.
The condition of spent fuel in the SFPs at units 1 and 2 is not known, while at unit 3 Tepco says it suspects there might be some damage.
Cooling capacity at all four SFPs was lost after the earthquake and tsunami on 11 March 2011 and keeping the fuel cool has been a priority as Tepco works to stabilize the plant.
Stabilizing Fuel Likely To Take Months, Atomic Energy Society Says
15 Apr (NucNet): Once cooling systems have been fully restored at the Fukushima-Daiichi nuclear plant it is likely to take another two or three months before all nuclear fuel can be stabilized, the Atomic Energy Society of Japan has said.
The society’s deputy head, Takashi Sawada, made the projection at a meeting of society members yesterday, the Japan Atomic Industrial Forum (JAIF) said.
He said data published by plant operator Tokyo Electric Power Company (Tepco) show that parts of the fuel rods in reactors 1 and 3 have melted and settled at the bottom of the reactor pressure vessels.
Mr Sawada said Tepco’s most important task is to remove all the contaminated water and rebuild a cooling water circulation system.
Contaminated water has also been found in the turbine hall basements of units 1, 2 and 3. According to the International Atomic Energy Agency the amount of water to be removed has been estimated at more than 60,000 tonnes.
Once these jobs are done, stabilizing the nuclear fuel could take 2 to 3 months, if not longer, Mr Sawada said.
But he warned that the situation could deteriorate if another strong earthquake knocks out power to the plant and makes it impossible to keep the nuclear fuel cool for a few days.
Tsunami Reached Heights Of 15 Metres At Plant, Says Tepco
15 Apr (NucNet): The tsunami that hit the Fukushima-Daiichi nuclear plant in northern Japan on 11 March 2011 reached heights of up to 15 metres, exceeding the plant’s design reference value of five metres, Tokyo Electric Power Company (Tepco) said.
Tepco said that a survey of high water marks at the plant had shown that the tsunami reached up to 15 meters on the ocean side of the reactor and turbine buildings, significantly higher than the original estimate of 5.7 metres.
Tepco said that all six reactors at the plant had been under as much as five meters of water.
Japan Announces Evacuation Plans For More Residents
15 Apr (NucNet): The Japanese government is to evacuate the population of a number of towns and villages to the northwest of the Fukushima-Daiichi nuclear plant to prevent the accumulation of individual exposure doses over the next 12 months.
According to the International Atomic Energy Agency (IAEA), authorities have found that some areas beyond the existing 20 km evacuation zone could be exposed to more than 20 millisieverts (mSv) during the course of the next year, until March 2012.
The evacuation will be a “planned evacuation” with authorities aiming to move people within the next four weeks.
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