Status of TEPCO's Nuclear Power Stations after the Tohoku-Chihou-Taiheiyou-Oki Earthquake (Daily Report as of 3:00 PM on July 25)

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 11:00 PM on June 15, during dew condensation check, a TEPCO employee found a trace of discolored (brown) water in the leaked water receiving pan under the batch treatment tank (2A) of the multi-nuclide removal equipment system A (currently in trial operation utilizing waste liquid treated at water treatment facility). There is no possibility of water leaking outside the equipment since the trace of water was found in the leaked water receiving pan under the tank.
An operation to stop the multi-nuclide removal equipment system A was started at 6:17 PM on June 17, and the system A was stopped at 11:20 PM on the same day.
Based on the results of the surface contamination measurement using smear filter paper and the radiation dose measurement, the discolored parts showed higher values than the parts not discolored both near the welding line on the surface of the tank and in the leaked water receiving pan. We determined that the results suggest a possibility of concentrated saltwater, which has been contained in the tank, leaking from the welded part of the tank.
On June 18, after water was removed from the tank, a liquid penetrant inspection was performed in the surface investigation on the lower part of the tank. As a result, two very narrow holes (pinholes) were found in the welding line where discoloration was found. We will continue the detailed investigation.
On June 20, a liquid penetrant inspection on the batch treatment tank (1A), which has the same structure as the batch treatment tank (2A), was performed although no discolored water drop trace was found on the 1A tank. As a result, oozing of liquid was found at one location on the surface of the tank. We consider the oozing to have occurred by seeping of liquid having remained in a small amount on the inner surface of the tank, as in the case of the 2A tank. We determined that the 1A tank also has a pinhole as in the case of the 2A tank.
The development of crevice corrosion of the batch treatment tanks was judged as attributable to the following conditions.
･ existence of chloride ions derived from seawater
･ the liquid quality by which corrosion is accelerated when hypochlorous acid or ferric chloride is added
･ crevice environments formed by attached objects such as a scale
As a measure to prevent a recurrence of this problem, we will repair these deteriorated parts, and then apply rubber lining to the inner surfaces of the batch treatment tanks so that these surfaces may be kept from exposing to a corrosion environment. Additionally, an investigation was conducted on corrosion states of the rest of the equipment in the Multi-nuclide Removal Equipment system A, and corrosion was found on the flange surfaces of some of the pretreatment facilities. We considered that this was caused mainly by remaining influence of chemical injected in the batch treatment tanks. Although applying only to some of the pretreatment facilities, the other suspected causes include the following conditions.
･ reduction in residual chloride concentration due to gradual decomposition of hypochlorous acid
･ change in fluid quality into the alkaline quality that occurs in the coprecipitation tank
As measures to prevent a recurrence of this problem, we will interpose a sacrificial electrode between a flange and a gasket, and will study whether to switch to entirely lined pipes for the purpose of reliability improvement. With respect to the Multi-nuclide Removal Equipment systems B and C as well, we will implement the same measures to prevent a recurrence of these problems.

- At around 3:10 PM on May 23, a TEPCO employee, who was conducting inspection of a spent fuel rack at the Unit 6 spent fuel pool, found a foreign object (something like an eye nut^*) at the east-side bottom of the spent fuel pool while checking a video tape having the rack inspection recorded. At 4:50 PM on May 28, the foreign object (one eye nut) was collected. No problem was found with the operation status of the spent fuel pool cooling and filtering system and the temperature and water level of the spent fuel pool.
On June 12, other foreign objects (something like plates) were found. On July 10, the foreign objects (two hanging tags) were collected. These foreign objects and the eye nut collected on May 28 are a kind of objects that would not affect the spent fuel and the facilities. When conducting this inspection, we found scrap and junk, such as a tape remnant, a tube remnant and a flaked remnant, that would not affect the soundness of the spent fuel and the facilities, and collected all the scrap and junk.
* An annular metal part with which a wire is connected when a heavy machine is craned.

- At around 10:16 AM on July 25, the residual heat removal system B, which was cooling the reactor, stopped after the 6.9 kV metal-clad (power panel) C at Unit 6 was suspended during a logic verification test (autostart test) of the Unit 6 emergency diesel generator A. When this stoppage occurred, we saw the following facility conditions.
･ Air conditioning of Reactor Building stopped, and the emergency gas treatment system was started up. (The negative pressure in Reactor Building was maintained.)
･ The spent fuel pool cooling system was operating continuously.
･ The reactor water temperature was 27.1℃ as at 10:43 AM. The increase rate of reactor water temperature was estimated to be approx. 1℃/h.
At 12:06 PM, we have restarted the residual heat removal system B and cooling of the reactor. No abnormality was found in the operation status after the restart of the system. The water temperature of the reactor was 27.6℃ as at 12:00 PM, which is sufficiently lower than the maximum allowed temperature (100℃).
Then, air conditioning of Reactor Building was restarted at 12:22 PM. Consequently, the emergency gas treatment system A was stopped at 12:32 PM and emergency gas treatment system B was stopped at 12:34 PM. No abnormality was found in the operation status after the restart of the air conditioning. The reactor water temperature was 28.0℃ as at 1:00 PM, and has been kept at stable levels. We will continue to investigate the cause of the suspension of the residual heat removal system B.

- At 2:18 PM on July 25, accumulated water transfer from the Unit 3 Turbine Building basement to the Central Radioactive Waste Treatment Facility (Miscellaneous Solid Waste Volume Reduction Treatment Building [High Temperature Incinerator Building]) was started.

- 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 24, since the decrease of all-β radioactivity density in the leakage detection hole (southwest) at the underground reservoirs No.3 has been slow, an operation to dilute the underground reservoir No.3 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 24, approx. 40m³ of desalination treated water was injected.

On July 24, 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 24, 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 sampling previously performed (on July 23). Further, analysis for tritium was conducted on water sampled on July 17 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 performed on July 10).

- 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 density in water sampled on July 23 in the groundwater observation hole No.3-1 was measured. The measured tritium density in water sampled from the newly dug-up groundwater observation hole No.3-1 was 290Bq/L, which is low compared to the density in the nearby located groundwater observation hole No.3 (1,700Bq/L in the sample taken on July 18). In addition, the tritium densities in seawater sampled on July 21 inside the port (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)) and the γ nuclide and all-β densities in seawater sampled on July 23 in the same locations were measured. As a result, no significant change was found compared to the previous results.

* Revised past progress

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