Top > Releases ･ Announcements > Press Releases > Status of TEPCO's Nuclear Power Stations after theTohoku-Chihou-Taiheiyou-Oki Earthquake > 2013 > Status of TEPCO's Nuclear Power Stations after the Tohoku-Chihou-Taiheiyou-Oki Earthquake (Daily Report as of 4:00 PM on August 22)
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. 1×101Bq/cm3) into these reservoirs have been conducted as appropriate.
[Recent dilution operations]
Underground reservoir No.1 (since June 19): On August 3, approx. 60m3 of filtered water was injected.
Underground reservoir No.2 (since June 27): On August 1, approx. 60m3 of filtered water was injected.
Underground reservoir No.3 (since July 24): On August 12, approx. 107m3 of water in the drain hole (northeast) of this underground reservoir was injected.
* Approx. 60m3, approx. 51m3, and approx. 107m3 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 21, 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>
-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.
Analysis for tritium was conducted on water in the newly installed groundwater observation hole No.1-8 (located approx. 18m east of the groundwater observation hole No.1, approx. 2m west of the ground improvement area, and approx. 7m from the bank protection) (sampled on August 20).
<Groundwater observation hole No.1-8>
Cesium-134 21Bq/L (previously announced)
Cesium-137 45Bq/L (previously announced)
All-β 1,100Bq/L (previously announced)
Tritium 950Bq/L
With regards to water pumped up from well points, we conducted sampling for the first time (on August 19) to analyze the water. We analyzed the sample for γ nuclides, all-β and tritium.
<Water pumped up from well points> (new)
Cesium-134 1.5Bq/L
Cesium-137 3.4Bq/L
Ruthenium-106 17Bq/L
All-β 190,000Bq/L
Tritium 460,000Bq/L
- 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. 300m3. 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.
After this leakage from a tank, we sampled water in the following locations (on August 21) and conducted nuclide analysis on the sampled water.
<Seawater near the south water outlet (near the exit of the drainage channel)>
(Sampling performed at 12:30 PM on August 21)
Cesium-134:Below the detection limit value [the detection limit value: 1.1Bq/L (1.1×10-3Bq/cm3)]
Cesium-137:2.2Bq/L (2.2×10-3Bq/cm3)
All β:Below the detection limit value [the detection limit value: 17Bq/L (1.7×10-2Bq/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 12:50 PM on August 21)>
Cesium-134:Below the detection limit value [the detection limit value: 18Bq/L (1.8×10-2Bq/cm3)]
Cesium-137:Below the detection limit value [the detection limit value: 25Bq/L (2.5×10-2Bq/cm3)]
All β:140Bq/L (1.4×10-1Bq/cm3)
These analysis results showed no remarkable change compared to the previous analysis results on the samples taken previously (on August 20).
-At 2:55 PM on August 22, in order to block the Unit 2 branching trench (the vertical shaft B and the power cable trench) installed east of Unit 2 Turbine Building, we started transferring contaminated water accumulated in the trench into Unit 2 Turbine Building.
-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 has been found in the operation status since 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. The cause of the residual heat removal system B's stoppage and measures to prevent a recurrence of its stoppage are as follows.
[Cause]
In the above logic verification test, an electric relay for detecting a shortage in voltage in the 6.9 kV metal-clad (power panel) C at Unit 6 was supposed to come into operation. Meanwhile, no action to prevent the electric relay from inputting an operation signal to the reactor protection system M-G set A (safety action) had been taken. As a result, the reactor protection system M-G set A stopped when the electric relay came into operation. This caused the residual heat removal system B, which was then cooling the reactor, to stop.
[Recurrence prevention measures]
1) In order to prevent errors in execution of safety actions in work related to modification construction and testing, use checklists to manage work permits and proper execution of safety actions described in the work procedure.
2) On the Unit 6 central operation panel, put a note that the reactor protection system M-G set A will be stopped when the electric relay for detecting a shortage in voltage in the 6.9 kV metal-clad (power panel) C at Unit 6 is brought into operation. Additionally, include the same note in the operational procedure.
3) Inform the concerned groups of this incident.
Logic verification tests of the Unit 5 emergency diesel generator A and the Unit 6 emergency diesel generator B will be conducted after the above recurrence prevention measures are implemented.
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