Status of TEPCO's Nuclear Power Stations after the Tohoku-Chihou-Taiheiyou-Oki Earthquake (Daily Report as of 3:00 PM on July 26)

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

- With respect to steam found wafting on July 18 and later near the central part of the fifth floor (equipment storage pool side) of Unit 3 Reactor Building, we made detailed examination, and have come to suspect that the steam has been generated by the mechanism described below. We are planning to verify the validity of the assessment through temperature and dose rate measurement after conducting work to reduce radiation dose, such as debris removal. For this purpose, we restarted debris removal at 1:00 PM on July 26. Meanwhile, we regularly conduct assessment through temperature and dose rate measurement at various locations in the premises including the upper part of Unit 3 Reactor Building, which has been indicating an impact that the steam has on the environment is small and limited within the entirety of the premises. In a case where we encounter steam again in association with debris removal work, we will check the plant parameters and the monitoring post readings to verity that there is no abnormality in the subcritical plant state and other aspects.

<Mechanism of how the steam was generated>
In addition to rainwater having leaked through gaps near the well cover and having been heated at the head of the primary containment vessel, the following is suspected as the possible cause. A difference has been observed between the nitrogen amount injected into RPV and PCV (approx. 16m³/h) and the nitrogen amount discharged from them (approx. 13m³/h), which suggests the possibility that a gas fully containing moisture from this difference (approx. 3m³/h) is leaking from the head of PCV, etc. We consider that, when steam from the moisture was released into the upper part of the fifth floor of Reactor Building through an interspace around the shield plug, the steam was cooled and became visible because the surrounding air was relatively cold compared to the steam.

Dust measurement was conducted at a location (the north side of the shield plug) that gave the highest dose rates in the measurement on July 25 and 23, and also at the central part of the shied plug and a location at the west side of the equipment storage pool, which were taken for the purpose of comparison. At all of these locations, the values were found to be in the range of those obtained in the past dust measurement in the upper part of the fifth floor of Reactor Building.

- At 10:33 AM on July 26, accumulated water transfer from the Unit 2 Turbine Building basement to the Unit 3 Turbine Building basement was started.

- At 10:10 AM on July 22, nitrogen injection into the primary containment vessel was started in order to determine whether there is gas flowing from the Unit 2 suppression chamber to the primary containment vessel and whether there is hydrogen remaining inside the suppression chamber. At 11:00 AM on July 26, the nitrogen injection was stopped. No abnormality was found in the parent parameters after the injection was stopped.

- 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 25, approx. 60m³ of desalination-system (RO) treated water was injected.

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 25, approx. 70m³ of water was transferred to a temporary tank.

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 25, 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 25, 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 24).

- 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 γ nuclide and all-β densities in water sampled on July 25 in the groundwater observation hole No.2-1 (east of the groundwater observation hole No.2) were measured. The all-β density in the newly dug-up groundwater observation hole No.2-1 was below the detection limit value. The γ nuclide density was at the same level as those in the nearby located groundwater observation hole No.2 (samples taken on July 18 and 22).

* Revised past progress

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