Fukushima Daiichi Nuclear Power Plant Status
On 17 May 2011, TEPCO provided a status report against the TEPCO
"Roadmap". Progress has been made during the last month since the
issuing of the Roadmap on 17 April 2011. While the basic policy and
targets defined in the Roadmap remain, several changes were made to
account for new information obtained and progress made to date.
On 13 May TEPCO commenced the preparatory work for the installation of a cover for the reactor building of Unit 1.
The reactor building cover will be installed as an emergency measure to
prevent the dispersion of radioactive substances until mid- to long
term measures, including radiation shielding, are implemented.
TEPCO has reported that information obtained after calibration of the reactor water level gauges of Unit 1 shows that the actual water level in the Unit 1
reactor pressure vessel was lower than was indicated, showing that the
fuel was completely uncovered. The results of provisional analysis show
that fuel pellets melted and fell to the bottom of reactor pressure
vessel at a relatively early stage in the accident.
Tables 1 - 4 track progress made for each of Units 1 - 4
towards fulfilling the three basic safety functions of the IAEA safety
standards: prevention of criticality, removal of decay heat and
mitigation of radioactive releases. The tables replace the three-colour
table that was used previously. The charts are cross-referenced to the
Tokyo Electric Power Company (TEPCO) "Roadmap" plan to bring the nuclear
reactors and the spent fuel pools at the Fukushima Daiichi plant to a
stable cooling condition and to mitigate radioactive releases.
IAEA Briefing on Fukushima Nuclear Accident (12 - 18 May 2011, 17:00 UTC)
Presentations:
→ Summary of Reactor Status: Unit 1, 18 May 2011
→ Summary of Reactor Status: Unit 2, 18 May 2011
→ Summary of Reactor Status: Unit 3, 18 May 2011
→ Summary of Reactor Status: Unit 4, 18 May 2011
On Friday, 20 May 2011, the IAEA provided the following information on the status of nuclear safety in Japan:
TEPCO reported that "most part of the fuel is considered to be
submerged in the bottom of reactor pressure vessel and some part
exposed." TEPCO also reported that leakage of cooling water from the
reactor pressure vessel is likely to have occurred. However, TEPCO
considers that the actual damage to the reactor pressure vessel is
limited, on the basis of the temperatures now being measured around the
reactor pressure vessel.
With regard to the status of the reactor core of Unit 1,
TEPCO believes that because the fuel has been being cooled continuously
by means of water injection, it is unlikely that the situation could
result in a future release of large amounts of radioactive material.
The results of the analysis are provisional; TEPCO will continue to
conduct investigations. Similar analyses will be conducted for Units 2 and 3.
Nitrogen gas is still being injected into the containment vessel in Unit 1 to reduce the possibility of hydrogen combustion inside the containment vessel.
In Units 1, 2 and 3 fresh water is being continuously injected into the reactor pressure vessel; temperatures and pressures remain stable.
To protect against potential damage as a result of future
earthquakes, TEPCO started work on 9 May to install a supporting
structure for the floor of the spent fuel pool of Unit 4.
Fresh water is being injected as necessary into the spent fuel pools of Units 1 - 4.
Stagnant water with high levels of radioactivity in the basement of the turbine buildings of Units 1, 2 and 3
is being transferred to the condensers, the radioactive waste treatment
facility, the high-temperature incinerator building and temporary
storage tanks. Stagnant water in the basement of the turbine building ofUnit 6 is being transferred to a temporary tank.
Countermeasures against the outflow of water to the sea and to prevent
and minimize the dispersion of radionuclides in water have been put in
place.
Full-scale spraying of anti-scattering agent is continuing at the
site with the use of both conventional and remote controlled equipment.
2. Radiation Monitoring
Deposition in 47 Prefectures
The daily monitoring of the deposition of caesium and iodine
radionuclides for 47 prefectures is continuing. Since 12 May negligible
deposition has occurred. I-131 was reported in only one prefecture and
Cs-137 was reported in three prefectures, with a value of 4.8 Bq/m2 for
I-131 and a range of from 4.7 to 10 Bq/m2 for Cs-137.
Gamma Dose Rates in 47 Prefectures
Gamma dose rates are measured daily in all 47 prefectures. The
Ministry of Education, Culture, Sports, Science and Technology (MEXT) of
Japan reports values on the basis of data collected from each
prefecture. On 18 May the value of gamma dose rate reported for
Fukushima prefecture was 1.6 µSv/h. In all other prefectures, reported
gamma dose rates were below 0.1 µSv/h, with a general decreasing trend.
Gamma Dose Rates in Areas More Than 30 km from Fukushima Daiichi Plant
Gamma dose rates reported specifically for the monitoring points in
the eastern part of Fukushima prefecture, for distances of more than 30
km from the Fukushima Daiichi plant, showed a general decreasing trend,
ranging from 0.1 µSv/h to 17 µSv/h, as reported for 17 May.
Maps of gamma dose rates, deposition of Cs-134 and deposition of
Cs-137 within the 80 km zone around the Fukushima Daiichi plant were
produced by means of aerial gamma ray monitoring by the Nuclear Safety
Technology Centre of MEXT and the United States Department of Energy.
The map of the deposition of radiocaesium is presented in Fig. 1.
The values represent the sum of Cs-134 and Cs-137. The areas in green
show a deposition of these two radionuclides of between 0.6 and 1
MBq/m2. The areas in yellow indicate a deposition of between 1 and 3
MBq/m2. The areas in red indicate a deposition of between 3 and 30
MBq/m2. All are normalized to 29 April 2011.
The map shows that the results obtained are consistent with all
previous reported measurements of deposition in soil and of gamma dose
rates.
Air Concentrations of Radionuclides On-site at Fukushima Daiichi Plant
On-site measurements at the west gate of the Fukushima Daiichi plant
indicate the presence of I-131 and Cs-137 in the air in the close
vicinity of the plant (within approximately 1 km). The values observed
in the previous days show daily fluctuations with an overall decreasing
tendency.
Concentrations of Radionuclides in Drinking Water
As of 10 May, the restriction on the consumption of drinking water
relating to I-131 - which had been applied since 1 April as a
precautionary measure for one remaining location (the village of Iitate
in Fukushima prefecture), and only for infants - was lifted.
Food Monitoring and Food Restrictions (12 - 18 May 2011)
Food Monitoring
From 12 to 18 May, the Ministry of Health, Labour and Welfare
reported results of continued monitoring for radioactivity in food.
Over this period, results for 503 food samples from fifteen different
prefectures were reported. Most of this monitoring continues to be
concentrated within Fukushima prefecture (39% of samples reported for 12
- 18 May). The majority of results were below regulation values, but 28
out of these 503 samples (fewer than 6%) were found to have
radioactivity levels above the Japanese regulation values for
radiocaesium. These samples were collected in three prefectures
(Fukushima, Ibaraki and Kanagawa). None of the 503 samples was found to
have radioiodine in excess of the regulation values.
In Fukushima prefecture, 175 of the 194 samples (more than 90%) had
radiocaesium levels below the regulation values set by the Japanese
authorities. However, 19 of the 194 samples (fewer than 10%) exceeded
the regulation values for Cs-134/Cs-137. Samples above the regulation
values were bamboo shoots (ten samples), shiitake mushrooms (five
samples), and four samples of fish (two samples of whitebait, one sample
of ayu and one sample of Japanese smelt).
In Kanagawa prefecture, 6 out of 33 samples (18%) were found to
exceed the regulation values set by the Japanese authorities for
Cs-134/Cs-137, these were six samples of unprocessed tea leaves (an
additional ten samples of unprocessed tea leaves were found to have
levels below this regulation value).
In Ibaraki prefecture, 3 of the 66 samples (4%) reported were above
the regulation values set by the Japanese authorities for Cs-134/Cs-137.
These were unprocessed tea leaves (two samples) and parsley (one
sample).
Fig. 1.: Map of deposition of radiocaesium (sum of Cs-134 and
Cs-137) for the land area within 80 km of the Fukushima Daiichi plant,
as reported by the Japanese authorities (MEXT):
Food Restrictions
As of 18 May, the only food restrictions remaining are in Fukushima
prefecture and for the cities of Kitaibaraki and Takahagi in Ibaraki
prefecture.
In Fukushima prefecture there are restrictions on the distribution
and consumption of sand lance fish. In specified areas of Fukushima
prefecture there are also restrictions on the distribution of raw
unprocessed milk, turnips, bamboo shoots, ostrich ferns and shiitake
mushrooms, and restrictions on the distribution and consumption of
specific non-head type and head-type vegetables (e.g. spinach and
cabbage), flowerhead brassicas (e.g. cauliflower) and shiitake
mushrooms.
In Ibaraki prefecture there is a continuing restriction on the
distribution of spinach produced in the cities of Kitaibaraki and
Takahagi.
3. Marine Monitoring
The marine monitoring programme is carried out both near the
discharge areas of the Fukushima Daiichi plant by TEPCO and at off-shore
stations by MEXT. The increase in the radioactivity in the marine
environment had occurred by aerial deposition and by continuing
discharges and outflow of water with high levels of radioactivity from
the Daiichi plant.
Seawater Monitoring
The activity concentrations of I-131, Cs-134 and Cs-137 in seawater close to the Fukushima Daiichi plant at the screen of Unit 2
have been measured every day since 2 April. Concentrations of Cs-134
and Cs-137 decreased from initial values of more than 100 MBq/L to less
than 5 kBq/L on 7 May, but increased to levels of around 20 kBq/L on 16
May, and to about 10 kBq/L on 17 May. There was a significant increase
in levels of I-131 from about 8 to 80 kBq/L from 10 to 11 May, in
parallel with the increase for both radiocaesium isotopes. This
indicates that there is still some production of fission products. The
I-131 levels decreased to about 20 kBq/L on 17 May.
Monitoring of the marine environment is performed by TEPCO in the
near field area and by MEXT at off-shore sampling positions. The
monitoring of MEXT also includes: measurement of ambient dose rates in
air above the sea; analysis of ambient dust above the sea; analysis of
surface samples of sea water; and analysis of samples of sea water
collected at 10 m above the sea bottom and in a mid-layer, as well as at
several locations for sediments. At most of the offshore stations,
I-131, Cs-134 and Cs-137 reached levels below the detection limit of 10
Bq/L.
