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Wednesday, April 13, 2011

Japan Announces Evacuation Plans For More Residents

THE NUCLEAR COMMUNICATIONS NETWORK
News in Brief/ No. 97 / 13th April 2011

NucNet

Japan Announces Evacuation Plans For More Residents

13 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.

The evacuation area includes Kutsurao village, Namie town, Iitate village, part of Kawamata town and part of Minami Souma City.

The annual dose limit for controlled nuclear workers or medical personnel is 20 mSv per year, but can reach 50 mSv in an exceptional year as long as the five-year average is not higher than 20 mSv per year, according to recommendations by the International Commission on Radiological Protection (ICRP).

In a declared emergency, the recommended limit under Japanese regulations is 100 mSv for controlled individuals. The ICRP backs these regulations, but could sanction a maximum accumulated dose of 250 mSv in extraordinary situations.

The annual dose limit for the general public is lower, at 1 mSv per year as a general guideline. However, according to ICRP recommendations, the total dose may reach 20 mSv from technical sources in an exceptional year.
Japan has adopted these recommendations.

Technical sources include fallout from atmospheric bomb tests, fallout from nuclear accidents, radioactive isotopes released by nuclear installations during normal operation, and radiation released by technical devices such as cathode ray tubes, computers and smoke detectors. They do not include radiation from medical diagnosis and treatment.

Meanwhile, plant operator Tokyo Electric Power Company (Tepco) said workers are spraying resin on debris at the plant in an effort to avoid the release and spread of contaminated dust.

They have started to erect a steel plate in front of the screen of the unit 2 cooling water discharge channel to prevent any further release of highly contaminated water leaking from trenches and pits and the basement of the turbine hall of unit 2.

Yesterday, Tepco started transferring highly radioactive water from a utility trench at unit 2 to the condenser and by this morning had moved about 250 tonnes of contaminated water.

As a result, the water level in the trench had dropped by 4 centimetres by 07:00 local time today (midnight central European time) according to the Japan Atomic Industrial Forum.

The contaminated water needs to be moved from the turbine building basements and from a concrete tunnel and trenches to various storage facilities.

Tepco is transferring the water to the condenser because there is a risk it might continue to leak into cable trenches and pits 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 activity is much lower than the water at unit 2.

The amount of water to be removed is estimated at more than 60,000 tonnes, the IAEA said. The water has been hampering work to restore the reactors’
cooling systems.

Tepco has also taken water samples from the unit 4 spent fuel pool to analyse contamination. The results will allow Tepco to assess the state of the fuel in this pool and to what extent it is damaged.

Dan Yurman 
Mobile: 208-521-5726 

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