THE NUCLEAR COMMUNICATIONS NETWORK
World Nuclear Review – week ending 1st April 2011 / WNR N°13/11
Details Released On Exposure Of Fukushima Staff
1 Apr (NucNet): From a combined total of 996 staff working at the Fukushima-Daini and Fukushima-Daiichi nuclear power plants in Japan, 21 have been exposed to radiation doses higher than 100 millisieverts (mSv) and none have been exposed to more than 200 mSv, plant operator Tokyo Electric Power Company (Tepco) has said.
Tepco said 370 staff were working at the Daiichi plant, where authorities have been trying to cool reactors and spent nuclear fuel since an earthquake and tsunami struck on 11 March 2011. Fifty-one of the staff were contractors and the rest employed by Tepco.
At Fukushima-Daini, which was less affected by the quake and tsunami, and where all four units shut down safely, there were 626 staff at the plant. Sixty-four were contractors and 562 worked for Tepco.
Tepco did not say if it had included emergency services staff in its figures.
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 when 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. The ICRP backs these regulations, but could sanction a maximum accumulated dose of 250 mSv in extraordinary situations.
In most countries, the natural background radiation level is about 2 to 4 mSv a year.
Meanwhile, dose rate levels continue to decrease slowly on the site and at the site boundary with outdoor air samples showing it is safe for staff to breathe onsite air, although protection is still needed inside contaminated buildings.
The Japan Atomic Industrial Forum (JAIF) said today that radiation levels were 910 microsieverts per hour (microSv/hr) at the south side of the plant’s main office building, 144 microSv/hr at the main gate, and 65 microSv/hr at the west gate. These readings were taken at 15:00 Japan time (08:00 central European time) on 1 April 2011.
Dose rates were highest on 17 March, showing 4,175 microSv/hr near the main office building, 647 microSv/hr at the main gate, and 313 microSv/hr at the west gate.
Spraying with fresh water has begun of the spent fuel pool (SFP) at unit 1 of the plant and continues at the SFPs of units 1-4.
Tepco said it has been using water from a barge lent by the US military. The barge has been anchored at a pier at the plant.
Yesterday Tepco said it is planning to spray resin, a synthetic chemical, over debris at the plant in an effort to fix radioactive materials and avoid the spread of contamination.
JAIF said Tepco is hoping the adhesive resin will prevent radioactive dust from being carried away by wind and rain.
Work is continuing to remove contaminated water from the basement of the turbine halls at units 1, 2 and 3 by pumping spilled water into the condenser. Preparations have begun to carry out similar work at unit 4, according to Tepco. The delay in removing the contaminated water is hampering work to cool down and stabilise the plant.
Japan’s Nuclear and Industrial Safety Agency (NISA) has ordered Tepco to solve the problem of heavily contaminated water that has leaked into trenches outside the controlled zones of units 1 to 3. Work is continuing to transfer water from the trenches to a storage tank and prevent it from flowing into the sea.
Dan Yurman
Email: dan.yurman@usa.net
Mobile: 208-521-5726
No comments:
Post a Comment