News in Brief/ No. 83 / 28 March 2011
Efforts Continue To Restore Off-Site Power
28 Mar (NucNet): Attempts to restore off-site AC power are continuing at the
Fukushima-Daiichi nuclear power plant in Japan and lighting is now available
in the central control rooms of units 1, 2 and 3, the International Atomic
Energy Agency (IAEA) said.
Meanwhile, fresh water is being injected into the reactor pressure vessels
(RPVs) of these three damaged units.
The agency said "no notable change" has been reported in the condition of
unit 4, which was shut down at the time of the earthquake and tsunami on 11
March 2011, and where fuel had already been removed from the reactor.
Units 5 and 6 at the six-unit plant were also shut down at the time of the
quake and have been in "cold shutdown" since last week. Cold shutdown means
the reactors are in a safe mode, with cooling systems stable and under
control, and with low temperature and pressure within the reactor.
At unit 1, pressure in the RPV showed a slight increase, but was stable at
units 2 and 3, possibly indicating that there has been no major breach in
the pressure vessels, the IAEA said.
Graham Andrew, senior advisor to the IAEA's director-general told the BBC
today that concerns about the situation at the plant are "understandable and
well-founded", but noted there had been significant developments such as
electricity being restored to the site, and water and boron being injected
into the RPVs.
He said one of the key things is to avoid reactors becoming "re-critical"
through possible melting of the fuel.
Mr Andrew added: "But there is quite a bit in the plant that the Japanese
and the IAEA do not know, so because of that we have to be cautious with our
assessment."
He said it remains a very serious situation. "We are getting a good flow of
information from the Japanese authorities."
Over the weekend, plant operator Tokyo Electric Power Company (Tepco) began
work to remove contaminated water that has accumulated in the turbine
building basements at the plant.
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.
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 on Saturday (26 March). In unit 2 it was more than 1,000
mSv/hr, in unit 3 it was 750 mSv/hr, and in unit 4, where little water was
spilled, it was 0.5 mSv/hr.
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. This suggests the RPVs are
seriously damaged.
The IAEA said today that radiation measurements in the containment vessels
and suppression chambers of units 1, 2 and 3 continued to decrease.
Tepco said contaminated water was found in the trenches of units 1 to 3.
Radioactive emissions on the water surface were 0.4 mSv/hr for unit 1 and
more than 1,000 mSv/h for unit 2.
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.
Dose Rates Still Falling, Latest Figures Indicate
28 Mar (NucNet): Dose rates at the Fukushima-Daiichi nuclear plant site are
continuing to show a downwards trend, according to the most recent figures.
Recent on-site dose rate monitoring by operator Tokyo Electric Power Company
(Tepco) at Fukushima-Daiichi and confirmed by Japan's Nuclear and Industrial
Safety Agency (NISA) shows less activity in the air.
Readings had decreased steadily to 128 microsieverts per hour (microSv/hr)
at midnight Japan time on 27 March (16:00, 27 March central European time).
The dose rates measured by Ministry of Education, Culture, Sports, Science
and Technology (MEXT) at a distance of 20 to about 60 km from the plant site
have also continued to fall slightly. On 27 March, only 11 measuring points
of 87 remained above the alarm level of 5 microSv/hr.
In 28 of the 45 prefectures for which data are available, no deposition of
radionuclides was detected in the period 18 to 25 March, the International
Atomic Energy Agency (IAEA) said. In seven of the other 17 prefectures, the
estimated daily deposition was less than 500 becquerel per square metre for
iodine-131 and less than 100 becquerel per square metre for caesium-137.
On 26 March, the highest values were at a hot spot in the prefecture of
Yamagata to the west of the plant site. Those readings showed 7,500
becquerel per square metre for iodine-131 and 1,200 becquerel per square
metre for caesium-137. In the other prefectures where deposition of
iodine-131 was reported, the daily range was from 28 to 860 becquerel per
square metre. For caesium-137, the range was from 2.5 to 86 becquerel per
square metre.
In the Shinjuku district of Tokyo, the daily deposition of iodine-131 on
27 March was 220 becquerel per square metre, while for caesium-137 it was
12 becquerel per square metre. MEXT said that the resulting local dose rate
had yesterday fallen below 0.1 microSv/hr.
New data from monitoring of the marine environment, carried out about 30 km
offshore from 24 March to 25 March, show a decrease in both caesium-137 and
iodine-131. The IAEA said the measured radiation dose rates above the sea
remain consistently low at between 0.04 and 0.1 microsievert per hour.
Recommendations relating to drinking tap water, based on concentrations of
iodine-131, remain in place in seven locations. In Tokyo, the iodine-131
activity in tap water fell below 20 becquerel per kilogramme yesterday,
according to MEXT.
As far as food contamination is concerned, samples taken from 23 to 25 March
in five prefectures showed iodine-131 in unprocessed raw milk, but the
levels were far below the regulation values set by the Japanese authorities.
Caesium-137 was detected in samples of unprocessed raw milk taken on 23
March in Chiba prefecture, to the south of the plant site, but at levels far
below the Japanese regulation values. Caesium-137 was not detected in any of
the samples taken from 24-25 March in the other four prefectures.
Fukushima-Daiichi Nuclear Plant Status Update
28 Mar (NucNet): The following is a summary of the status of all six reactor
units and the spent fuel pools (SFPs) at the Fukushima-Daiichi nuclear
plant.
Unit Status Summary At Fukushima-Daiichi 28 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. 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 in cold shutdown.
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. Unit in cold shutdown.
Spent Fuel Pool Status At Fukushima-Daiichi 28 March 2011:
Fuel integrity: unknown at units 1 and 2; possibly damaged at units 3 and 4;
safe at units 5 and 6; safe in the common spent fuel pool.
Unit 1
Seawater injection being considered.
Unit 2
Seawater injection carried out periodically since 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.
Units 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.
More details
Major Parameters of the Plant:
http://www.nisa.meti.go.jp/
Conditions of Fukushima-Daiichi Nuclear Plant:
www.nisa.meti.go.jp/english/
Reactor Status and Major Events: www.jaif.or.jp/english
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