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March 25, 2011

Fukushima Daiichi Worker details and the radioactive water and overall levels of Cesium and Iodine

World nuclear news - Tokyo Electric Power Company has been criticized over yesterday's exposure to workers operating in ankle-deep water, but continues to make progress towards stabilising the site two weeks after the natural disasters of 11 March.

Nuclear Energy Institute - Tokyo Electric Power Co. is stepping up efforts to switch from sea water to fresh water for cooling the reactors and used fuel storage pools. The United States government has urged the switch to fresh water as soon as possible and is providing two U.S. Navy barges, each of which can carry up to 1,000 tons of water. The ships are scheduled to reach port about 60 kilometers from the Daiichi plant in about three days. Japanese workers at the site will install pipes and hoses to carry the water to the plant.

It is of course understandable that the lower part of the turbine building of unit 3, in which three workers were installing cables, had not been fully checked. But it is thought that contractors ignored alarms from their dosimeters, while ankle-deep in contaminated water for about three hours. They received doses of 170-180 millisieverts and seem to have suffered shallow burns to their skin from beta radiation.



Nuclear communications network - JAIF also confirmed that three workers were contaminated when laying cables in the turbine hall of unit 3.

The International Atomic Energy Agency (IAEA) said the three were contract workers laying cables in the turbine hall. Two of them were found to have radioactivity on their feet and legs. JAIF said they were exposed to more than 170 millisieverts (mSv).

The workers were washed in an attempt to remove radioactivity, but since there was a possibility of beta-ray burning of the skin, the two were taken to the Fukushima University Hospital for examination and then transferred to Japan's National Institute of Radiological Sciences for further examination. They are expected to be monitored for around four days.

It is thought that the workers ignored their dosimeters’ alarms believing them to be false and continued working with their feet in contaminated water.

According to JAIF, the level of radioactive fission products in the water was about 3.9 million bequerels per cubic centimeter or 10,000 times higher than the reactor water used in the course of normal operations.

Japan’s Nuclear and Industrial Safety Agency (NISA) has asked plant operator Tokyo Electric Power Company (Tepco) to review the radiation control system immediately in order to avoid similar incidents in the future.

As of 24 March at 19:30 Japan time (11:30 central European time), the number of workers at the plant found to have received more than 100 mSv of radiation dose was 17 including the three contract workers. The remaining fourteen are Tepco employees, the IAEA said.

Unit Status At Fukushima-Daiichi 25 March 2011:

Unit 1

Core and fuel integrity damaged.
Reactor pressure vessel integrity: unknown.
Core cooling requiring AC power: not functional.
Building integrity severely damaged by hydrogen explosion.
Water level in the rector pressure vessel (RPV): fuel partially or fully exposed.
Pressure of the RPV: now decreasing after initial increase.
Temperature of the RPV: now decreasing after initial increase.
Water injection to core: continuing.
Water injection to containment vessel: to be confirmed.
Containment venting: temporarily stopped.

Unit 2

Core and fuel integrity: damaged.
Reactor pressure vessel integrity: unknown.
Core cooling requiring AC power: not functional.
Building integrity slightly damaged.
Water level in the rector pressure vessel: fuel partially or fully exposed.
Pressure of the RPV: unknown.
Temperature of the RPV: stable.
Water injection to core: continuing.
Water injection to containment vessel: to be confirmed.
Containment venting: temporarily stopped.

Unit 3

Core and fuel integrity damaged.
Reactor pressure vessel integrity suspected damaged.
Core cooling requiring AC power: not functional.
Building integrity severely damaged by hydrogen explosion.
Pressure of the RPV: unknown.
Temperature of the RPV: now decreasing after initial increase.
Water injection to core: continuing.
Water injection to containment vessel: to be confirmed.
Containment venting: temporarily stopped.

Unit 4

Shut down at the time of the earthquake, no damage to fuel, which had already been removed from the reactor and transferred to the pool. No damage to core or containment. Building integrity severely damaged by hydrogen explosion.

Unit 5

Shut down at the time of the earthquake, no damage to fuel, core or containment. Vent hole opened in roof as precaution against hydrogen explosion.

Unit 6

Shut down at the time of the earthquake, no damage to fuel, core or containment. Vent hole opened in roof as precaution against hydrogen explosion.

Spent Fuel Pool Status At Fukushima-Daiichi 25 March 2011:

Fuel integrity unknown at units 1 and 2, possible damaged at units 2 and 3, safe at units 5 and 6.

Unit 1

Seawater injection being considered.

Unit 2

Seawater injection carried out on 20 March.

Unit 3

Water level low, seawater injection continues.

Unit 4

Water level low, seawater injection continues. Reactor building damaged by explosion and fire on 15 March.

Unit 5 & 6

Pool cooling capability recovered.

Overall levels of Cesium and Iodine

Japan's damaged nuclear plant in Fukushima has been emitting radioactive iodine and cesium at levels approaching those seen in the aftermath of the Chernobyl accident in 1986. Austrian researchers have used a worldwide network of radiation detectors – designed to spot clandestine nuclear bomb tests – to show that iodine-131 is being released at daily levels 73 per cent of those seen after the 1986 disaster. The daily amount of cesium-137 released from Fukushima Daiichi is around 60 per cent of the amount released from Chernobyl.

The difference between this accident and Chernobyl, they say, is that at Chernobyl a huge fire released large amounts of many radioactive materials, including fuel particles, in smoke. At Fukushima Daiichi, only the volatile elements, such as iodine and cesium, are bubbling off the damaged fuel.

For the first two days after the accident, the wind blew east from Fukushima towards monitoring stations on the US west coast; on the third day it blew south-west over the Japanese monitoring station at Takasaki, then swung east again. Each day, readings for iodine-131 at Sacramento in California, or at Takasaki, both suggested the same amount of iodine was coming out of Fukushima, says Wotawa: 1.2 to 1.3 × 10^17 becquerels per day.

In the 10 days it burned, Chernobyl put out 1.76 × 10^18 becquerels of iodine-131, which amounts to only 50 per cent more per day than has been calculated for Fukushima Daiichi. It is not yet clear how long emissions from the Japanese plant will continue.

Similarly, says Wotawa, caesium-137 emissions are on the same order of magnitude as at Chernobyl. The Sacramento readings suggest it has emitted 5 × 10^15 becquerels of caesium-137 per day; Chernobyl put out 8.5 × 10^16 in total – around 70 per cent more per day.

The Chernobyl accident emitted much more radioactivity and a wider diversity of radioactive elements than Fukushima Daiichi has so far, but it was iodine and cesium that caused most of the health risk – especially outside the immediate area of the Chernobyl plant

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