Due to the Tohoku-Chihou-Taiheiyou-Oki Earthquake which occurred on March 11, 2011, TEPCO's facilities including our nuclear power stations have been severely damaged. We deeply apologize for the anxiety and inconvenience caused.
With regard to the accident at Fukushima Daiichi Nuclear Power Station, on April 17, 2011, we have compiled the roadmap towards restoration from the accident and on July 19 we accomplished the Step1 target "Radiation dose is in steady decline". Then on December 16 we confirmed the accomplishment of the Step 2 target "Release of radioactive materials is under control and radiation doses are being significantly held down".
In addition, on December 21, 2011, we have compiled the "Mid-to-long-Term Roadmap toward the Decommissioning of Fukushima Daiichi Nuclear Power Units 1-4, TEPCO".
In addition to the maintenance of the plant's stable condition, we will implement Mid-to-Long Term countermeasures towards the decommissioning of Fukushima Daiichi Nuclear Power Units 1-4 to enable evacuees to return to their homes as soon as possible and reduce the anxiety of the people in Fukushima and the whole nation as soon as possible.
Below is the status of TEPCO's Fukushima Daiichi Nuclear Power Station.
*
The updates are underlined.
[Fukushima Daiichi Nuclear Power Station]
·Unit 1 to 4: Abolishment (April 19, 2012)
·Unit 5 to 6: Outage due to regular inspections before the earthquake
-Contaminated water transfer from the underground reservoirs was all completed as of July 1. However, we are continuing to take measures to prevent the expansion of contaminated water, and to conduct sampling activities.
<Measures to prevent the expansion of contaminated water>
· Since the decreases of all-β radioactivity densities in the leakage detection holes (at the northeast side of the underground reservoir No.1, the northeast side of the underground reservoir No.2, and the southwest side of the underground reservoir No.3) have been slow, operations to dilute the underground reservoirs No.1-No.3 by transferring filtered water or desalination-system (RO) treated water (the all-β radioactivity density: approx. 1×10
1Bq/cm
3) into these reservoirs have been conducted as appropriate.
[Recent dilution operations]
Underground reservoir No.1 (since June 19): On August 3, approx. 60m
3 of filtered water was injected.
Underground reservoir No.2 (since June 27): On August 1, approx. 60m
3 of filtered water was injected.
Underground reservoir No.3 (since July 24): On August 12, approx. 107m
3 of water in the drain hole (northeast) of this underground reservoir was injected.
* Approx. 60m
3, approx. 51m
3, and approx. 107m
3 of water were injected on August 5, 11, and 12, respectively, for the purposes of dilution and reduction of the water pressure (uplift pressure) acting on the bottom surface of the underground reservoir.
·
On August 28 and 29, leaked water in the leakage detection holes at the underground reservoirs No.1-No.3 was transferred to the temporary aboveground tank, and leaked water in the drain holes at the underground reservoirs No.1 and No.2 was transferred into these underground reservoirs.
<Sampling>
On August 28, sampling was performed in the drain holes of the underground reservoirs No.1-No.7 (14 locations), the leakage detection holes of the underground reservoirs No.1-No.4 and No.6 (sample could not be collected at 2 out of 10 locations), and the observation holes of the underground reservoirs (22 locations). The analysis results showed no significant change compared to the results from the previous sampling (on August 27). Further, analysis for tritium was conducted on water sampled on August 21 in the drain holes and leakage detection holes of the underground reservoirs No.1-No.4 and No.6. The analysis results showed no significant change compared to the previous results (from sampling on August 14).
-At around 1:00 AM on August 24, in Unit 2, we conducted on-site confirmation of the primary containment vessel (PCV) gas control system, etc. after noticing that the pressure inside the PCV had dropped and that the flow rate of exhaust gas from the PCV gas control system was on a downward trend. As a result of the confirmation, we found airflow through a U-shaped sealing section in a drainage line installed at the entrance side of the line of this system. In response, we closed a valve located upstream of the U-shaped sealing section at 10:40 AM, and have been monitoring the state.
After the valve closure, we confirmed that both of the pressure inside the PCV and the flow rate of exhaust gas from the PCV gas control system were on an upward trend as at 3:00 PM. We are continuing to monitor the parameter No significant change was found in the monitoring post readings after this incident occurred. In addition, for the conformation purpose, we conducted dust measurement on the Turbine Building 1st floor which corresponds to the exit part of the drainage line's U-shaped sealing section. The dust measurement resulted in values below the detection limit values, which we consider to indicate no abnormality.
Later, the pressure in the PCV took on a rising trend, and the flow rate of exhaust gas from the PCV gas control system became stable. As to the cause of the PCV pressure drop, we concluded that: increases in outdoor air temperature and injected water temperature under the summer environment caused a rise in the pressure inside the PCV; and the seal water of the U-shaped seal installed in the drainage line of the PCV gas control system was thereby pushed out and lost. Accordingly, aiming at preventing this problem, from 10:33 to 11:07 AM on August 29, we increased the flow rate of exhaust gas from the PCV gas control system from approx. 14m3/h to approx. 19m3/h so as to prevent the seal water of the U-shaped seal from being lost. Further, we are planning to implement an operational requirement to close the U-seal line drainage valve when the pressure inside the PCV exceeds 10 kPa (gage).
The amount of radioactivity in the gas released with the PCV pressure drop this time is estimated to be approx. 2×104Bq, which is approx. 0.1% of the amount of radioactivity (approx. 1.6×107Bq) released from Unit 2 Reactor Building during July 2013 and is considered to have a small impact on the environment.
-At around 9:50 AM on August 19, a TEPCO employee on patrol found water leaking from a drain valve of a tank dike in the H4 area in the power station. Later, the drain valve was closed. No significant change has been found in the monitoring post readings. As a result of confirmation on the site conditions, a puddle of approx. 1-2cm was found inside the dike, and puddles of approx. 3m×3m×1cm and approx. 0.5m×6m×1cm were found outside of the drain valve of the dike. There is no trace of water having flowed into a public drainage ditch, etc. from the puddles found outside of the drain valve of the dike. Therefore, we consider that the water has not flowed out into the sea.
At 2:28 PM on August 19, we determined that this incident corresponds to "a case when nuclear fuel material (not in the form of gas) or the like has leaked within an area controlled by the company due to an unpredictable event such as a failure of a nuclear reactor facility for power generation" as per Article 18, item 12 of the regulations concerning the operational safety and the protection of specified nuclear fuel material at the TEPCO's Fukushima Daiichi NPS nuclear reactor facilities. The reasons for the determination are as follows:
· Although we have not yet been able to identify the source of contaminated water, water accumulated inside the dike around a tank containing contaminated water has leaked outside the dike through the drain valve.
· It cannot be denied that water stored in a tank has leaked from the tank.
· High β ray and γ ray densities were detected in the puddle of water having leaked outside the dike.
Later, at 7:00 PM on the same day, we started collecting water accumulated inside the dike. The water collection was carried out by pumping up the water with a temporary pump into a temporary tank, and placing absorbent inside the dike.
We found water spread at the bottom level of tanks near the tank No.5 (H4-I-5) in the area. Therefore, we checked the water level of this tank, and found out that the water level has fallen to approx. 3m 40cm from the top of the tank. We confirmed that the current water level is lower by approx. 3m than the normal level, given that the water levels of the neighboring tanks are approx. 50cm from the top of the tanks. Further, we are checking the water levels of the surrounding tanks. Note that the amount of water corresponding to this approx. 3m fall in water level is approx. 300m
3. With regards to water considered to have leaked, we started collecting the water remaining inside the dike and already collected some of the water. However, since the water seems to have flowed out of the dike through the drain valve, we will collect soil in the surrounding area and continue to conduct an investigation to find out the range reached by the water. Later, we found streaky traces of flows on the wall surface of a drainage channel located east of the H4 area tanks. In response, we measured surface dose equivalent rates at this location, and the maximum rate was 6.0mSv/h (γ and β rays (70μm dose equivalent rate)). As this information indicates the possibility that contaminated earth and sand, etc. may have flowed into the drainage channel, we are planning to conduct a detailed investigation and evaluation concerning these traces. Incidentally, we confirmed that no water was flowing on the surface of the ground near the above drainage channel at the time when water leaking this time was found.
At 9:55 PM on August 20, we started transferring water stored in the tank No.5 in the group I in the H4 area and water collected in a temporary tank (water accumulated inside the dike) into the tank No.10 in the same area. At 9:13 PM on August 21, we completed the transfer of the water stored in the tank No.5. At 3:00 PM on August 22, we completed the transfer of the water collected in a temporary tank.
From around 11:00 AM to around 3:00 PM on August 22, we conducted full inspections (appearance inspections and dose measurement) on the flanged tanks in the other areas, which are of the same type as the tank from which water has leaked. Neither leak nor puddle was found by the appearance inspections on the tanks and the drain valves. However, 2 locations locally showing high dose rates were found around the H3 area tanks. The surfaces of these locations were dry, and we confirmed that there has been no water having flowed into the inside of the dike or the outside of the dike. We also confirmed that the water levels of these tanks remain unchanged after they received water. [High dose rate locations, the surface dose equivalent rates at these locations (γ and β rays (70μm dose equivalent rate)), and tank water levels]
· Near the bottom flange of the tank No.4 in the group B in the H3 area: 100mSv/h and approx. 97% of the full water level
· Near the bottom flange of the tank No.10 in the group A in the H3 area: 70mSv/h and approx. 95% of the full water level
No locations around the other tanks and drain valves showed high dose rates.
We conducted nuclide analysis on water from the tank (hereinafter "Tank") No.5 in the group (hereinafter "Group") I in the H4 area from which water has leaked. Based on the analysis results shown below, we confirmed that water from this tank is RO concentrated water.
<Water from Tank No.5 in Group I in the H4 area (sampling performed at 9:00 PM on August 23)>
Cesium-134: 4.4×10
1Bq/cm
3
Cesium-137: 9.2×10
1Bq/cm
3
Antimony-125: 5.3×10
1Bq/cm
3
All β: 2.0×10
5Bq/cm
3
Chloride concentration: 5,200ppm
Additionally, we conducted full inspections (visual appearance inspections and water level confirmation) on the flanged tanks that are in use for storage of accumulated water from Units 5 and 6. The inspections were completed on August 26 and showed no abnormality.
During our inspection of Tank No.5 in Group I in the H4 area from which water has leaked, we found out the following:
· 3 tanks including this tank (Tank No.5 in Group I, Tank No.10 in Group I, and Tank No.3 in Group II in the H4 area) were initially installed in the H1 area.
· Ground subsidence occurred in the H1 area at the foundations on which these tanks had been placed, and these tanks were planned to be installed in the H2 area, but actually, have been placed in the H4 area despite our plan.
Although it is still unclear whether there is a causal relationship between the water leaking of Tank No.5 and the tank's having experienced ground subsidence occurred in the H1 area at the foundation on which it had been placed, we started to transfer water from inside Tank No.10 in Group I in the H4 area to Tank No.10 in Group B in the H4 area at 3:57 PM on August 25 to reduce the risk of leakage. At 2:07 AM on August 27, the transfer was completed.
Further, at 10:30 AM on August 29, we start to transfer water from inside Tank No.3 in Group II in the H4 area to Tank No.10 in Group B in the H4 area.
Following this leakage from a tank, we sampled water in the following locations and
conducted nuclide analysis on the water (sampled on August 28). The analysis results are as follows. No remarkable change was found in the analysis results compared to those obtained the day before (in the samples taken on August 27).
<Seawater near the south water outlet (near the exit of the drainage channel)>
(Sampling performed at 11:00 AM on August 28)
Cesium-134: Below the detection limit value [the detection limit value: 1.3Bq/L (1.3×10-3Bq/cm3)]
Cesium-137: 1.9Bq/L (1.9×10-3Bq/cm3)
All β: Below the detection limit value [the detection limit value: 19Bq/L (1.9×10-2Bq/cm3)]
<Water at the junction of the drainage channels B and C near the H4 area (previously referred to as "water of the side ditch in front of the core warehouse")>
(Sampling performed at 11:20 AM on August 28)
Cesium-134: Below the detection limit value [the detection limit value: 19Bq/L (1.9×10-2Bq/cm3)]
Cesium-137: Below the detection limit value [the detection limit value: 26Bq/L (2.6×10-2Bq/cm3)]
All β: 210Bq/L (2.1×10-1Bq/cm3)
-At around 10:35 AM on August 28, an associated company worker, who had been working on water transfer of the H4 area tanks in Units 1-4, received a contamination examination at the Main Anti-earthquake Building after the work, and was found to have contamination on the head, face and breast. Therefore, the worker was instructed to receive whole body counting. Then, the contaminated parts were cleaned by wiping, etc., and the contamination level became dropped below 13,000cpm (equivalent to 40Bq/cm
2) set as the screening level. Accordingly, at 2:51 PM on the same day, the worker left from the Entrance Area Management Buildings. Note that the worker received smear measurement on the nasal and oral cavities, which showed no contamination. However, the worker was found to have some contamination (5,000cpm) on the head, and therefore,
received whole body counting on August 29, which showed that the worker has no internal intake.
-On August 23, in an effort to investigate the cause of the high-high radioactivity alarm's occurrence at around 10:04 AM on August 19 at a continuous dust monitor installed in front of the Main Anti-earthquake Building, we conducted nuclide analysis on radioactive substances in the air (sampled on August 22) in the upper part of Unit 3 Reactor Building, which was sampled while debris removal work in the upper part of Unit 3 Reactor was not being conducted. As a result of the analysis, a slightly high value compared to the past results was detected from one sample, which was taken during the first sampling (in the downward direction) of 2 times of the sampling in the west-southwest side above the Unit 3 reactor. The other analysis results were found to be within the past fluctuation ranges.
On August 29, after an anti-scattering agent was sprayed, debris removal work in the upper part of Unit 3 Reactor was temporarily conducted from 1:15 to 2:03 PM, and dust sampling was performed in the upper part of Unit 3 in the meantime. The anti-scattering agent was spayed also after the removal work.
-
At 10:00 AM on August 29, accumulated water transfer from the Unit 6 Turbine Building basement to a temporary tank was started. At 3:00 PM on the same day, the transfer was stopped.
-We installed observation holes east of the Unit 1-4 Turbine Buildings, and have been conducting sampling and analysis of groundwater from the observation holes. On June 19, we announced that tritium and strontium were detected at high densities in the observation hole located between Units 1 and 2. Therefore, we have been conducting intensified monitoring.
At 11:35 AM on August 15, we started pumping up groundwater from one of the well points (pumping facilities using vacuum pumps, scheduled to be installed at 28 locations) installed east of Units 1 and 2 Turbine Buildings and transferring the pumped-up groundwater to the Unit 2 vertical shaft C. No abnormality such as leakage has been found in the transfer. Later, we started to use 12 locations at 11:10 AM on August 16, 9 locations at 11:05 AM on August 17, one location at 9:00 AM on August 18, one location at 2:10 PM on August 21, and 4 locations at 8:20 AM on August 23 additionally, thereby starting to pump up groundwater from all of the 28 well points as planned and transfer pumped-up groundwater to the Unit 2 vertical shaft C. At 1:55 PM on the same day, the transfer destination of water from the well points was changed from the Unit 2 vertical shaft C to Unit 2 Turbine Building. At 10:58 AM on August 28, due to construction for adding a groundwater transfer pump, the transfer destination of water from the well points and the water collection pit (south) was changed from Unit 2 Turbine Building to the Unit 2 vertical shaft C.
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Revised past progress
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