Status of TEPCO's Nuclear Power Stations after the Tohoku-Chihou-Taiheiyou-Oki Earthquake (Daily Report as of 3:00 PM on July 24)

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

-At around 8:20 AM on July 18, an associated company worker, investigating the site using a camera ahead of debris removal work, encountered a steam-like gas wafting through the air near the central part of the fifth floor (equipment storage pool side) of Unit 3 Reactor Building. No significant change was found in the main parameters related to the plant (temperature, pressure and xenon density of PCV/RPV). Neither was any significant fluctuation found in the monitoring post readings or the continuous dust monitor amounts. At 9:20 AM on the same day, the subcritical state was found being maintained. With regards the measurement result of ambient dose on the upper part of the spent fuel pool protection at Unit 3 Reactor Building, no remarkable change was found compared to the measurement result so far obtained every day before work.
All of the values obtained from dust sampling conducted on the same day in the north side (where the sampling was performed twice) and the northeast side of a space over the reactor at Unit 3 Reactor Building fell within the fluctuation ranges observed during the past half year.
Given the dust sampling results and the status of the plant, we consider that the steam was generated due to rainwater having leaked through gaps near the well cover and having been heated at the head of the primary containment vessel.
At 7:55 AM on July 19, no steam-like gas was found when we investigated through a camera the site where a steam-like gas was wafting.
On the same day, the temperatures near the site were measured and found to be in the range of 20.8-22.3℃ (between 1:44 and 2:54 PM). The outside air temperatures were 21.4℃ (as at 1:40 PM) and 20.1℃ (as at 3:00 PM).
On July 20, the third and fourth rounds of dust sampling were conducted in the north side of the space over the reactor at Unit 3 Reactor Building, and dust sampling was also conducted in the northeast side of the space over the reactor (where the sampling is regularly conducted). As a result, we found that all of the thus obtained values were at levels equivalent to or lower than the levels in the previous measurement (on July 18) and fell within the fluctuation ranges observed during the past half year. Additionally, between 0:39 and 2:40 PM on the same day, an area around the site was measured using infrared thermography. As a result, we found that the temperature of the site where a steam-like gas was wafting was approx. 18-25℃ and at about the same level as the air temperature of the same day (Reference: the air temperature and humidity as at 2:00 PM on July 20 were 21.4℃ and 76%).
At around 9:05 AM on July 23, steam wafting at the site was again observed through a camera. As at 9:30 AM on the same day, no abnormality was found in the plant status, the monitoring post readings, etc. Later, the steam was observed intermittently, but not observed between 1:30 and 2:30 PM. We determined that the steam had disappeared.
On the same day, we conducted radiation dose rate measurement at 25 locations around the site where the steam was found (around the entire shield plug). As a result, the maximum and minimum dose rates were found to be 2170mSv/h and 137mSv/h, respectively. The radiation dose rate at the location where the steam was seen was found to be 562mSv/h.
At around 4:15 AM on July 24, steam, coming from the vicinity of the central part of the Unit 3 Reactor Building fifth floor (equipment storage pool side), was again observed through a camera. The plant status indicator values and the monitoring post readings recorded as at 5:00 AM on the same day showed no abnormality (based on the continuously stable states of reactor water injection and cooling of the spent fuel pool and based on monitoring post readings, temperatures in RPV and PCV, pressure in dry well, and noble gas monitoring. The air temperature and humidity were 18.3℃ and 91.2% as at 4:20 AM). Between 4:40 and 6:04 PM on the same day, an area around the site was measured using infrared thermography. As a result, we found that the temperature of a part from which the steam was coming out was approx. 30-34℃, and that the maximum temperature around the joining section of the shield plug was approx. 25℃. The temperatures measured this time are higher than the previously measured temperatures (approx. 18-25℃) (measured on July 20). However, this is attributed to a difference in measurement accuracy between the latest and previous measurement because we changed heights of the measurement and made it closer to the site. Between 0:30 and 1:30 PM on July 24, ambient dose rate measurement was again conducted in the upper part of the Unit 3 operating floor to collect data so as to supplement the ambient dose rate measurement conducted at 25 locations around the shield plug on July 25. As a result, the maximum and minimum dose rates were found to be 1860mSv/h and 633mSv/h.

-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>
On June 19, since the decrease of all-β radioactivity density in the leakage detection hole (northeast) at the underground reservoirs No.1 has been slow, an operation to dilute the underground reservoir No.1 by transferring desalination-system (RO) treated water (the all-β radioactivity density: approx. 1×10¹Bq/cm³) or filtered water into the reservoir was started (the all-β radioactivity density of residual water in the underground reservoir No.1: 6.6×10⁴Bq/cm³).
[Recent dilution operation] On July 23, approx. 70m³ of water was transferred to a temporary tank.

On June 27, since the decrease of all-β radioactivity density in the leakage detection hole (northeast) at the underground reservoirs No.2 has been slow, an operation to dilute the underground reservoir No.2 by transferring filtered water or desalination-system (RO) treated water (the all-β radioactivity density: approx. 1×10¹Bq/cm³) into the reservoir was started.
[Recent dilution operation] On July 23, approx. 60m³ of filtered water was injected.

On July 23, 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 July 23, 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), the observation holes of the underground reservoirs (22 locations), the groundwater bypass investigation holes a-c (sample could not be collected at 1 out of 3 locations), the groundwater bypass pump wells No.1-No.4, and the observation holes on the sea side (1)-(4). No significant change was found with the analysis results compared to the analysis results from the sampling performed previously (on July 22). Further, analysis for tritium was performed on water sampled on July 15 and 16 in the groundwater bypass (investigation holes a-c and pump wells No.1-No.4; sample could not be collected at 1 investigation hole out of 3 investigation holes) and the observation holes on the sea side (1)-(8). As a result, no significant change was found compared to the previous analysis results (from the sampling on July 8 in the observation holes on the sea side (5)-(8), and on July 9 in the other locations).

-At 9:03 AM on July 23, in Unit2, an alarm went off indicating a failure of the suction pump installed at the dust radiation monitoring system B in the facility (systems A and B) that exhausts air from inside the building after removing the radioactive materials from air inside a building by having the air pass a filter, and then monitors dust at the exit of the exhaust system when exhausting the air. The dust radiation monitoring system B was suspended as a consequence of the giving of the alarm. Since the dust radiation monitoring system A is under repair, both of the dust radiation monitoring systems A and B became unavailable for measurement. However, the exhaustion of air from the building was continued through the filter. No abnormality was found in the plant data (such as temperatures of the RPV bottom and the PCV interior), and no significant change was found in the monitoring post readings. As a result of a later conducted on-site investigation on the dust radiation monitoring system B, the position detector of the airtight device (motor-driven), which clips and fixes dust measurement filtrate paper, was found to have shifted to an improper position. We considered that this positional shift caused the giving of the alarm and the consequent suspension of the dust suction pump. Then, we repositioned the position detector. On the same day, the suction pump of the dust radiation monitoring system B was restarted at 11:43 PM, and dust measurement was restarted at 11:53 PM.
At around 0:00 PM on July 24, an alarm went off indicating a failure (abnormal pressure) of the dust radiation monitoring system B, and the suction pump was suspended again. Since the dust radiation monitoring system A is under repair, both of the dust radiation monitoring systems A and B became unavailable for measurement. As a result of a later conducted on-site investigation, we considered that the abnormal pressure in the device and the consequent suspension of the dust suction pump were caused with the packing part of the filter paper feeding device having shifted to an improper position. Accordingly, we repositioned the packing part. Then, at 2:16 PM on the same day, the suction pump of the dust radiation monitoring system B was restarted. No abnormality in the operation status has been found since the restart. During the suspension period of the dust radiation monitoring, the reactor building exhaust system continued its operation, and the exhaustion of air from the building was continued through the filter.

-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.

-The tritium densities in water sampled on July 18 and 19 in the groundwater observation holes No.1, No.1-2, No.1-3, No.1-4, No.2 and No.3 were measured. The γ nuclide and all-β densities in water sampled on July 22 in the groundwater observation holes No.1, No.1-2, No.1-3, No.1-4, and No.2, and in seawater sampled on July 22 inside the port (other than seawater in the Unit 1-4 water intake north side and seawater between the water intakes of Units 1 and 2 (near the surface and near the bottom)) were measured. (With respect to the groundwater observation hole No.1-2, the γ nuclide densities were measured also after the sample was filtered). The γ nuclide and all-β densities in water sampled on July 23 in the groundwater observation hole No.3-1 were measured. The γ nuclide and all-β densities in the groundwater observation hole No.3-1 were found to be at the same levels as those in the groundwater observation hole No.3. With regards to the densities in the groundwater observation hole No.1-3 (west of the groundwater observation hole No.1), all-β was detected at 150,000Bq/L, which is higher than the past highest density (120,000Bq/L in the sample taken on July 18). With regards to the other densities, no significant change was found compared to the previous results.

-On July 24, a worker who was working on covering the oil fence with a protective sheet near the bank protection south of Unit 5, while pulling the sheet using a rope, fell into the sea behind the worker when a part of the sheet, at which the rope was attached, was torn. The worker immediately climbed up a slider, which is used for fixing the oil fence, and onto the bank protection on his own. Then, the worker immediately received a physical check-up at Main Anti-Earthquake Building, and was found to be uninjured and have neither physical contamination nor internal intake. We will consider measures to prevent workers from falling.

-At around 6:40 AM on July 23, a TEPCO employee on patrol found oil leaking in a trench under the actuation valve oil injection tank of the Unit 6 emergency diesel generator (B) main body. As a result of an on-site confirmation, it was found that the leaked oil had spread across an area of approx. 5m × 5m × 1mm and that the oil supply valve was slightly open. The oil supply valve was closed immediately. At 7:05 AM on the same day, we reported the incident to Tomioka fire station. Tomioka fire station conducted an on-site confirmation, and determined the incident to fall in the category of hazardous material leakage. Later, the leaked oil on the floor was completely wiped out. Then, the oil was continuing to leak at a rate of 1 drop per 3 seconds and being received by a drain pan. On July 23, oil was withdrawn from the actuation valve oil injection tank, so that the amount of the oil was adjusted to the appropriate level. On July 24, we confirmed that the oil leakage had stopped (the leaked oil amounts to approx. 25L).

-At around 5:00 AM on July 22, an associated company worker found oil leaking near a high-pressure pump of the desalination system 3 (reverse osmosis membrane). The high-pressure pump was suspended, and the oil leakage was confirmed to have stopped. The leaked oil is lubricating oil, and amounts to approx. 1.5 liters (approx.1.5m × approx. 1m × approx. 1mm). The oil has not flowed out of a concrete floor provided with a dike. At 5:45 AM on the same day, the incident was reported to Tomioka fire station. Then, at around 11:30 AM on the same day, the leaked oil was completely wiped out. Later, between 11:30 AM to 2:45 PM, we replaced the lubricating oil of the high-pressure pump and conducted test operation, which showed no abnormality. Therefore, we started the operation of the system.

-At 6:49 AM on July 22, cooling of the Unit 4 spent fuel pool was suspended due to inspection on instruments of the Unit 4 spent fuel pool alternative cooling system. At 2:05 PM on July 23, the spent fuel pool alternative cooling system was started up following the completion of the inspection. No abnormality was found in the operation status after the startup. The spent fuel pool water temperature has increased to 37℃ from 29℃ since the start of the suspension. This temperature is sufficiently low compared with the operational limit value of 65℃, and causes no problem in controlling the water temperature of the spent fuel pool.

* Revised past progress

The aforementioned attachments are only available in Japanese.
We apologize for any inconvenience this may cause.