News in Brief / No. 82 / 27 March 2011
Japan Update: Work Begins To Remove Contaminated Water
27 Mar (NucNet): Tokyo Electric Power Company (Tepco) has begun work to
remove contaminated water that has accumulated in the turbine building
basements at the Fukushima-Daiichi nuclear power plant, the International
Atomic Energy Agency (IAEA) has said.
Workers have started to remove water from the unit 1 turbine building to its
main condenser and are preparing to do the same at unit 2. Work to remove
water from the turbine buildings in units 3 and 4 is being considered.
The Japan Atomic Industrial Forum (JAIF) confirmed that Tepco had taken
"immediate action" to drain off the water so recovery work is not delayed.
Removal of water from the turbine building basements is an important step
before workers can continue efforts to fully restore power to the plant.
Japan's Nuclear and Industrial Safety Agency (NISA) said high radiation
levels were found in water in the basement of the turbine building of units
1, 2 and 3.
The radiation dose rate on the water surface was 60 millisieverts per hour
(mSv/hr) in unit 1 yesterday (26 March), more than 1,000 mSv/hr in unit 2,
750 mSv in unit 3, and 0.5 mSv/hr in unit 4, where little water was spilled.
Iodine-131, which has a half-life of 8.02 days, was the prevailing isotope
in units 2 and 3, and caesium-137 (half-life 30.2 years) in units 1 and 4.
NISA officials believe the contaminated water probably came from the primary
reactor loop rather than the spent fuel pool, because its isotopic
composition indicated it must have been contaminated by leaking fuel
elements that had been recently irradiated.
One of the next challenges will be a detailed radiological assessment of the
entire site, after which decisions will take place on what work will follow,
including repairs and cleaning.
Contaminated Workers
Japanese authorities have confirmed that two workers were contaminated when
laying cables in the turbine hall of unit 3 last week. During examinations
at the National Institute of Radiological Sciences, the level of local
exposure to the workers legs was estimated to be between 2 and 6 sieverts.
The workers did not need medical treatment, but doctors decided to keep them
in hospital and monitor their progress.
The two were among three contract workers who were exposed to radioactivity
in water while laying cables in the turbine hall.
It is thought the workers ignored their dosimeters' alarms believing them to
be false and continued working with their feet in contaminated water. An
investigation has begun to see if their training was adequate.
Radiations Levels
On-site dose rate monitoring by Tepco at Fukushima-Daiichi and confirmed by
NISA shows less activity in the air. Readings had decreased steadily to 140
microsieverts per hour (microSv/hr) last night at midnight Japan time (16:00
central European time) and 135 microSv/hr today at noon.
A spectrum analysis - which reveals the composition of airborne
contamination - showed that in air outside the contaminated buildings all
isotopes are below the limit considered safe for monitored workers. The
highest is still volatile iodine-131 with 300 becquerel per cubic metre,
equivalent to 30 percent of the limit. The second highest is particulate
iodine-131 at 26 percent, and the third tellurium-129 at 13 percent.
Off-site dose rate monitoring by the The Ministry of Education, Culture,
Sports, Science and Technology (MEXT) also showed a steady decrease in
radioactivity. The highest value, at the summit of a mountain chain 30
kilometres northwest of the plant site, was at 45 microSv/hr yesterday (26
March) at noon, down to a quarter of its peak value on 17 March.
At a monitoring post 55 km northwest of the plant site readings showed 5
microSv/hr yesterday, down to a quarter of the peak on 17 March.
There were less marked decreases at monitoring posts in populated areas of
the 20-30 km zone where people have been advised to stay indoors. The
highest levels were to the south and southwest of the plant site with
readings between 2.7 and 3.9 microSv/hr, a decrease of between 20-50 percent
compared to peak readings last week.
Unit Status Summary At Fukushima-Daiichi 25 March 2011:
More details
Major Parameters of the Plant:
www.nisa.meti.go.jp/english/
Conditions of Fukushima Daiichi Nuclear Power Station:
www.nisa.meti.go.jp/english/
Reactor Status and Major Events:
www.jaif.or.jp/english
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. Now using fresh water instead of
seawater.
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. Now using fresh water instead of
seawater.
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. Use of fresh water under consideration.
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), 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 damage at units 2 and 3,
safe at units 5 and 6.
Unit1
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.
Common Spent Fuel Pool
Seawater was sprayed over this pool on 21 March. Pool cooling was restarted
after successful installation of an external power supply line on
24 March.
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