Grid Failure + ECCS Failure Part 2 – reactor 2.

The following post consists of highly selected quotes from the TEPCO document chronologies given by the text “Measures Taken at Fukushima Daiichi Nuclear Power Station and Fukushima Daini Nuclear Power Station (December 2011 Edition)”. The quotes are taken from the 166 page appendices of the document and focus upon the timing of events and the consequences of grid and ECCS failures at Fukushima Diiachi. The document is authored by TEPCO, Japan and the appendix only is available at :
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/111222e18.pdf
(Yes, Wally, I am cherry picking. Read the whole document and come to a different conclusion if you have an inculcated clock for a brain instead of independent cognition.)

Chronology of Main Events at Fukushima Daiichi Nuclear Power Station
Unit 2 from Impact of Earthquake through Tuesday, March 15

Friday, March 11, 2011
14:46 The Tohoku-Pacific Ocean Earthquake occurred. Automatic proclamation
of Level 3 State of Emergency.
14:47 Automatic reactor SCRAM. The main turbine shut down automatically. The
emergency diesel generator started up automatically.
14:50 The Reactor Core Isolation Cooling system (hereafter the “RCIC”) was
started up manually.
14:51 The RCIC shut down automatically (reactor water level high).
15:01 The reactor in a subcritical status confirmed.
15:02 The RCIC started up automatically.
15:27 A first tsunami wave arrived.
15:28 The RCIC shut down automatically (reactor water level high).
15:35 A second tsunami wave arrived.
15:39 The RCIC started up automatically.
15:41 All of the AC power supplies were lost.
16:36 The Emergency Countermeasures Headquarters was able to check
neither the reactor water levels nor the water injection conditions. Thus,
the Emergency Countermeasures Headquarters decided and reported to
the competent government departments and agencies on the occurrence
of a specified event (Inability of Water Injection by the Emergency Core
Cooling System)
subject to the provisions of Article 15 Clause 1 of the
Nuclear Disaster Prevention Act at 16:45.
21:02 Since the headquarters was able to check neither the reactor water level
nor the water injection in the reactor through the RCIC, the Emergency
Countermeasures Headquarters reported to the competent government
departments and agencies that the reactor water level might reach the
top of active fuel (hereafter the “TAF”).
21:13 The Emergency Countermeasures Headquarters assessed the TAF reach time
as 21:40 and reported to the competent government departments and
agencies.
21:50 The reactor water level was confirmed as being at TAF+3400mm. The
Emergency Countermeasures Headquarters assessed that it would take
time before reaching the TAF and reported the assessment to the
competent government departments and agencies at 22:10.
2:55 It was confirmed that the RCIC was in service.
4:55 It was confirmed that radiation dose in the Power Station site rose (Near the main
gate: 0.069μSv/h (4:00) → 0.59μSv/h (4:23)). The rise was reported to the
competent government departments and agencies.
5:00 Shifting the water source for RCIC completed.
15:36 An explosion occurred at the reactor building of Unit 1.
16:27 Surrounding of monitoring post No. 4 measured a radiation dose beyond
500μSv/h (1,015μSv/h). The Emergency Countermeasures Headquarters
accordingly decided on the occurrence of a specified event (Abnormal rise in
the radiation dose on the site boundary) subject to the provisions of Article 15
Clause 1 of the Nuclear Disaster Prevention Act and reported the event to the
competent government departments and agencies.
8:10 The vent valve (MO valve) of the Primary Containment Vessel (hereafter the
“PCV”) was opened.
8:30 An HVPS car was started up to re-supply electricity to Unit 2 P/C. Due
overcurrent relays activated , however, no electricity was transmitted.
8:56 Surrounding of monitoring post No. 4 measured a radiation dose beyond
500μSv/h (882 μSv/h). The Emergency Countermeasures Headquarters
accordingly decided on the occurrence of a specified event (Abnormal rise in
radiation dose on the site boundary ) subject to the provisions of Article 15
Clause 1 of the Nuclear Disaster Prevention Act and reported the event to the
competent government departments and agencies at 9:01.
10:15 The Site Superintendent ordered operators to operate Venting.
11:00 The formation of a Venting line, except for the rupture disk, was
completed.
12:05 The Site Superintendent ordered operators to promote preparation for
using seawater.
13:10 A formation was completed where a battery was connected to the Safety
Release Valve (hereafter the “SRV”) control panel so as to control opening
operation on the operation switch.
14:15 Surrounding of monitoring post No. 4 measured a radiation dose beyond
500μSv/h (905μSv/h). The Emergency Countermeasures Headquarters
accordingly decided on the occurrence of a specified event (Abnormal rise in
radiation dose on the site boundary) subject to the provisions of Article 15
Clause 1 of the Nuclear Disaster Prevention Act and reported the event to the
competent government departments and agencies at 14:23.
15:18 The Emergency Countermeasures Headquarters again reported to the
competent government departments and agencies the result of its dosage
assessment in the event that Venting was operated.
11:01 An explosion occurred at the Reactor Building of Unit 3.
12:50 It was confirmed that the circuit for the solenoid valves that excite the largevalve of the vent valve (AO valve) of the suppression chamber (hereafter the”S/C”) had been dislocated into a “closed” state.
13:25 Since the reactor water level declined, there was a possibility that the RCIC
function had been lost. The Emergency Countermeasures Headquarters
accordingly decided on the occurrence of a specified event subject to the
provisions of Article 15 Clause 1 of the Nuclear Disaster Prevention Act
(Loss of reactor cooling function) and reported the event to the competent
government departments and agencies at 13:38.
15:28 The Emergency Countermeasures Headquarters assessed the TAF reach time
as 16:30 and reported the assessment to the competent government
departments and agencies.
16:30 Fire engines were started up to inject seawater in the reactor.
16:34 The Emergency Countermeasures Headquarters started reduction of the
reactor pressure and reported its plan to start seawater injection from the Fire
Protection System line to the competent government departments and
agencies.
17:17 The reactor water level reached the TAF. At 17:25 of the day, the Emergency
Countermeasures Headquarters reported the event to the competent
government departments and agencies.
18:00 (Approx.) Reduction of the reactor pressure started (reactor pressure : 5.4MPa → 19:03
0.63MPa).
18:22 The reactor water level reached TAF-3,700mm. The Emergency
Countermeasures Headquarters estimated that the entire fuel had been
exposed and accordingly reported the event to the competent government
departments and agencies at 19:32.
19:20 It was confirmed that the fire engine to use for seawater injection in the
reactor has been out of fuel and halted.
19:54 Fire engines started seawater injection in the reactor through the Fire
Protection System line (individual fire engines started up at 19:54 and
19:57, respectively).
21:00 (Approx.) The small valve of the vent valve (AO valve) of the S/C valve was opened.
The formation of a vent line, except for the rupture disk, was completed.
21:20 Two SRV valves were opened. It was confirmed that the reactor water level
was being restored. The Emergency Countermeasures Headquarters reported
the formation to the competent government departments and agencies at
21:34 (as of 21:30, the reactor water level was TAF-3,000mm).
21:35 Surrounding of the main gate measured a radiation dose beyond 500μSv/h
(760μSv/h). The Emergency Countermeasures Headquarters accordingly
decided on the occurrence of a specified event (Abnormal rise in radiation
dose on the site boundary ) subject to the provisions of Article 15 Clause 1 of
the Nuclear Disaster Prevention Act and reported the event to the competent
government departments and agencies at 22:35.
22:50 Since the drywell (hereafter the “D/W”) pressure exceeded the maximum
allowable working pressure of 427kPa[gage], the Emergency
Countermeasures Headquarters decided on the occurrence of a specified
event (Abnormal rise in the pressure of the Primary Containment Vessel) subject
to the provisions of Article 15 Clause 1 of the Nuclear Disaster Prevention
Act and reported the event to the competent government departments and
agencies at 23:39.
23:35 (Approx.) Since the pressure on the S/C side was lower than rupture disk working pressure and the pressure on the D/W was on the rise, the Emergency
Countermeasures Headquarters decided to operate venting by opening the
small valve of the vent valve.
Tuesday, March 15, 2011
0:01 It was confirmed that the small valve of the vent valve (AO valve) of the
D/W was closed several minutes after the small valve had been opened.
3:00 Since the D/W pressure exceeded the maximum allowable working pressure
in design, the Emergency Countermeasures Headquarters tried reducing the
pressure and injecting water in the reactor. However, the pressure was not
successfully reduced. The Emergency Countermeasures Headquarters
reported the situations to the competent government departments and
agencies at 4:17.
6:00 to 6:10 (Approx.) A large impulsive sound thundered. The indication value of the
S/C pressure turned 0 MPa[abs].
6:50 Sounding of the main gate measured a radiation dose beyond 500μSv/h
(583.7μSv/h). The Emergency Countermeasures Headquarters accordingly
decided on the occurrence of a specified event (Abnormal rise in the radiation
dose on the site boundary) subject to the provisions of Article 15 Clause 1 of
the Nuclear Disaster Prevention Act and reported the event to the competent
government departments and agencies at 7:00.
7:00 The Emergency Countermeasures Headquarters informed the competent
government departments and agencies of a temporary evacuation of
personnel to Fukushima Daini except for the personnel needed for
monitoring and other operations.

8:11 Sounding of the main gate measured a radiation dose beyond 500μSv/h
(807μSv/h). The Emergency Countermeasures Headquarters accordingly
decided on the occurrence of a specified event (Abnormal emission of
radioactive materials on fire or explosion, etc.) subject to the provisions of
Article 15 Clause 1 of the Nuclear Disaster Prevention Act and reported the
event to the competent government departments and agencies at 8:36.
8:25 It was confirmed that smoke (something like steam) was rising from around
the 5th floor of the reactor building. The Emergency Countermeasures
Headquarters reported the event to the competent government departments
and agencies at 9:18.
11:00 The Prime Minister issued an order of in-house evacuation to the local residents
staying in the areas ranging from a 20km up to a 30km radius of Fukushima
Daiichi Nuclear Power Station.
16:00 Sounding of the main gate measured a radiation dose beyond 500μSv/h
(531.6μSv/h). The Emergency Countermeasures Headquarters accordingly
decided on the occurrence of a specified event (Abnormal rise in the radiation
dose on the site boundary) subject to the provisions of Article 15 Clause 1 of
the Nuclear `Disaster Prevention Act and reported the event to the competent
government departments and agencies at 16:22.
23:05 Sounding of the main gate measured a radiation dose beyond 500μSv/h
(4584μSv/h). The Emergency Countermeasures Headquarters accordingly
decided on the occurrence of a specified event (Abnormal rise in the radiation
dose on the site boundary) subject to the provisions of Article 15 Clause 1 of
the Nuclear Disaster Prevention Act and reported the event to the competent
government departments and agencies at 23:20.

Fukushima Daiichi Nuclear Power Station Unit 2
State of Alternate Coolant Injection

Activities after “16:36 on March 11 when “Inability to Inject Water of the Emergency Core Cooling System” was determined and reported on
[Study and preparation for alternative means of water injection]

Considering the radiation dose in Unit 1, the Emergency Countermeasures Headquarters decided to form an alternative line of water injection into the reactor via the residual heat removal system (RHR) before the radiation dose rose. After completing the formation of an alternative line of water injection for Unit 1, from around 21:00 on March 11, operators started forming such
line for Unit 2. However, the operators were unable to work in the
Main Control Room due to the lack of power. The operators thereforewore full-face masks, took flashlights to light their way in complete darkness to
the Reactor Building, and manually opened four solenoid valves, including the
RHR valve. During March 11, they completed the formation of an alternative line
of water injection.
・ In particular, the RHR injection valve fixed on a pipe of approx. 60 cm diameter, pipe had a manual handle, also approx. 60 cm in diameter, which was very heavy to rotate. In addition, since the stroke of the stem was a large and long valve, operators had to climb up a ladder into the small spot for operation. A total of ten operators in rotation rotated the handle and it took approx. one hour to open the valve. (Normally, it takes approx. 24 seconds to fully open the valve electrically by operating switches at the Main Control Room.)

The status indicator of the diesel-driven fire pump (hereafter the “DDFP”) in the Main Control room had gone out. Since the basement of the Turbine Building
where the DDFP was installed was submerged in approx. 60 cm of water,
operators were unable to enter the FP pump room. However, operators confirmed
that the DDFP was in service because they saw smoke from the DDFP exhaust
duct outside the building. Even subsequently, the operators continued to check the exhaust duct for smoke. At 1:20 on March 12, however, operators saw no further smoke from the exhaust duct and confirmed that the DDFP had halted.

[Checking the state of the Reactor Core Isolation Cooling System (RCIC)]

At around 1:00 on March 12, operators headed for the work site to check the state of the RCIC operation, wearing self-contained breathing apparatus and with flashlights. Dedicated boots, used for entering controlled areas, had been washed away and submerged, hence operators wore long rubber boots,
normally used for outside patrols. The water in front of the RCIC room in the basement of the Reactor Building was deep, meaning their long boots were almost submerged in the water. When an operator opened the door of the RCIC
room, water flowed from the room, hence the operator soon closed the door. Although operators were unable to enter the RCIC room, they heard metallic clank screaming. Since operators were unable to check the rotary unit, they
were also unable to determine the operating state. Because no PHS was available
for communication, they returned to the Main Control Room and reported the
・ At around 2:10 on March 12, operators headed back to the RCIC room to check
the operation state. Although the water level in front of the door exceeded before, operators opened the door to check the operation state of the
RCIC. Although water slowly flowed from the room, the operators
entered the room and identified the pointer of the pump inlet pressure meter
shaking in the pressure instrumentation rack at the entrance to the RCIC and again heard the operation sound. Subsequently, the operators confirmed that the RCIC instrumentation rack on the 1st floor of the Reactor Building indicated an RCIC discharge pressure of 6.0MPa and that the reactor pressure in the instrumentation rack of the Reactor Pressure Vessel system on the 2nd floor of the Reactor Building indicated 5.6MPa. Since the RCIC discharge pressure exceeded the reactor pressure, the RCIC was seemingly in service (functioning). The operators returned to the Main Control room and reported the situation at 2:55 to the Emergency Countermeasures Headquarters.

[Checking the state of the high pressure coolant
injection system (HPCI)]

Since all of the DC power supplies needed for operation control were lost and the status indicators of the Main Control room had gone
out, the HPCI was no longer workable.
・ From 16:39 on March 11, the restoration team started checking the on-site conditions of power supply facilities after the earthquake
and tsunami. Since the service building where DC power supplies are installed was submerged approx. 1.5-meter deep on the basement floor
, the restoration team gave up checking.

○ Activities after “2:55 on March 12 when confirming the RCIC in service”
[Shifting water source of the RCIC]
・ Operators decided to shift the water source to the S/C from the CST, considering the fact that the water level of the condensate storage tank (hereafter “CST”), the water source of the RCIC, was declining, the water level of the suppression pressure (hereafter the “S/C”) was likely to rise: and that the CST would be the water source for alternative water injection facilities. From 4:20 on March 12, four operators, putting on C equipment
and full-face masks, headed for the RCIC room.

Amid the echoing operating sound of the RCIC, operators using flashlights manipulated three solenoid valves to shift the water source formation line from the CST to the S/C. All the valves, with long stem strokes and manual handles, were very heavy to rotate. In addition, since the operating site was located so high and without scaffolding, operators had to climb up a ladder from and extend their arms to rotate the handle.
・ One operator was assigned to the entrance of the RCIC room to monitor the
pressure indicated by the pump inlet pressure meter in the instrumentation rack
near the entrance, while two operators in rotation engaged in handling the valves. The remaining operator carefully played the role of lighting and coordinating worker, with the operator monitoring the pressure to prevent the RCIC from halting. The operation was completed at 5:00 on March 12. (Normally, such a shift would take no more than five minutes by manipulating the electrical operation switch in the Main Control Room.)

[Confirming the RCIC operation state]
Under circumstances where the DDFP and the HPCI, which are facilities to inject water into the reactor requiring no power supply, were unavailable for operation, operators continued periodical checking of the operating state of the RCIC, the only water injection facility left.

At around 10:40 on March 13, an operator confirmed that the discharge pressure
indicated pressure ranging from 6.0 to 6.4MPa in the RCIC instrumentation rack
installed on the 1st floor of the Reactor Building, while the reactor pressure
indicated 6.1MPa in the Reactor Pressure Vessel instrumentation rack installed on the 2nd floor of the Reactor Building. Thus, the operator confirmed that the
RCIC discharge pressure exceeded the reactor pressure.
 At around 13:50 on March 13, an operator confirmed that the discharge pressure
in the RCIC instrumentation rack installed on the 1st floor of the Reactor
Building showed 6.3MPa, indicating the continuous operation of the RCIC.

Preparing for a reduction in reactor pressure by seawater injection and with the safety release valve (hereafter the “SRV”)]

For Unit 3, ten 12V batteries as a DC power supply (125V) were needed to drive the SRV that would reduce the reactor pressure by injecting water. At around 7:00 on March 13, the Emergency Countermeasures Headquarters asked its employees staying the Seismic Isolated Building to offer the batteries of their private cars.
Such batteries would also be required for Unit 2 later. Thus, at the same time, the Emergency Countermeasures Headquarters asked its employees to offer batteries. The required number of persons who were ready to offer batteries gathered together.
Each removed the battery from his/her vehicle and took it to the front of the Seismic Isolated Building.
・ Five members of the restoration team transported batteries in their private cars to the Main Control Room of Unit 3, and then returned to the Anti-Earthquake Building to transport batteries to Unit 2. When they reached the entrance of Units 1 and 2, they received temporary evacuation instructions, because the Primary Containment Vessel of Unit 3 was going to have venting operation. Thus, the members of the restoration team moved toward the main gate of the Power Station and stood by there. They confirmed that smoke was flowing from the main stack of Units 3 and 4.

At 13:10 on March 13, the operators connected batteries to the SRV control panel in the Main Control Room so as to open the SRV valve on the operation switch of the SRV control panel, as they had done for Unit 3, to maintain the reduction in the reactor pressure.

Operators connected ten 12 batteries serially to supply the DC power needed to start up the SRV. Wire-cutting and coat stripping needed fine finger work. Wires and terminals were directly connected and fastened with insulation vinyl tape, which could have resulted in accidental electric shock and/or short circuit. Using flashlights alone, the full-face mask provided a narrow view. The insulation vinyl tape sometimes twisted around the rubber gloves. At times, the wire accidentally came into contact with the battery,
sparking and fusing part of the terminal.
 The utmost caution was needed for workers wearing two pairs of rubber gloves in picking and grasping small screws for terminals while tightening them with a screwdriver.

Activities after “11:01 of March 14 when an explosion occurred at the reactor building of Unit 3” (added : as relevant to responses to the emergency at Reactor 2)
[Resuming the formation of a seawater injection line]

After the explosion, workers were suspended from operation at their work sites.
However, following the instruction by the Site Superintendent, the fire brigade
headed for the work sites at 13:05 on March 14. Exposed to a high radiation dosecaused by scattered debris, the fire brigade checked the target sites. The water injection line, the formation of which had already been completed, had sustained damage to the fire engines and hoses, which were no longer usable.
・ Since the fire engine that had been supplying seawater to the reversing valve pit of Unit 3 from the Shallow Draft Quay was undamaged in the explosion, the fire brigade decided to use it to inject seawater into the reactors of Units 2 and 3 from the Shallow Draft Quay as the water source. Thus, the fire brigade promoted efforts to establish an alternative line of water injection by, for example, replacing damaged hoses.
At 13:18 on March 14, the reactor water level was found to be declining. At 13:25, the Site Superintendent decided that the RCIC had lost its function, and anticipated reaching the TAF (top of active fuel (in the core) around 16:30, judging from the facing conditions. The fire brigade continued preparation for seawater injection into the reactors. At around 14:43, the fire brigade succeeded in connecting the fire engine to the water supply outlet of the FP.
・ From past 15:00 to 16:00 on March 14, aftershocks occurring in a Fukushima offing as the seismic center led to the suspension of work and temporary evacuation.

At around 16:30 on March 14, the fire brigade started up a fire engine and made
arrangements to restart water injection after reducing the reactor pressure.

[Reducing the reactor pressure]

Prior to starting water injection with a fire engine, operators needed to open the SRV to reduce the reactor pressure. The previous day, the SRV was set to a state to perform opening operation. However, the S/C had high temperature and pressure (149.3℃ and 486kPa[abs] pressure as of 12:30 on March 14). Thus, there was the possibility that even if the SRV had been opened, steam in the S/C might not have condensed and the pressure could not have been reduced. Thus, the Emergency Countermeasures Headquarters decided to prepare to vent the Primary Containment Vessel (hereafter “Vent/Venting/”) prior to opening the SRV to reduce the reacto pressure and perform seawater injection.
・ At around 16:20 on March 14, it was forecast that it would take time before the vent valve could be opened. Around 16:28, the Site Superintendent prioritized reducing the reactor pressure by using the SRV and instructed operators to promote venting preparation concurrently.

At 16:34 on March 14, the SRV puffing sound, along with rises in the reactor
pressure, reached the calm Main Control Room. Operators tried opening the SRV on the operation switch but the SRV did not open.

All ten batteries were once disconnected from the wiring and then all re-connected serially.・ At around 18:00 on March 14, the serial batteries were connected directly to solenoid valves that opened a discrete SRV for excitation. During the 5th SRV opening operation, the reactor pressure began to decease.

At around 16:30 on March 14, a fire engine was started up and members of the fire brigade started operation to reduce the reactor pressure from 16:34. Although pressure reduction started at around 18:00, the S/C had a high temperature and pressure that were unlikely to have condensation.
Reactor pressure: 6.998MPa (16:34) → 6.075MPa (18:03) → 0.63MPa (19:03)
・ At 19:03 on March 14, the reactor pressure declined to 0.63MPa.
・ During this time, members of the fire brigade had to check the operating conditions of the fire engine, etc. in rotation amid high radiation doses at the work site. At 19:20 on March 14, a member found that the fuel of the fire engine used to inject the water had run out and it was no longer functional. After refueling the fire engine, the fire engine started seawater injection into the reactor through the Fire Protection System line. (At 19:54 and 19:57 on March 14, fire engines were started up respectively.)

At around 21:00 on March 14, the reactor pressure rose. One more SRV was added to open, but did not open. When another SRV was used for the opening operation, the SRV opened at 21:20. While the reactor pressure was decreasing, the indicator showing the downscaled reactor water level meter showed an increase.
Subsequently, the Emergency Countermeasures Headquarters continued reading the
reactor water level, reactor pressure and D/W pressure every few minutes. While
focusing on plant behavior, the headquarters continued water injection into the
reactor.

Fukushima Daiichi Nuclear Power Station Unit 2
Circumstances of Venting of Containment Vessel

At 23:40 on March 14, the reactor pressure was 1.170MPa[gage], whereas the D/W
pressure was 740kPa[abs]. The S/C pressure was 300kPa[abs]. The reactor pressure was declining, the D/W pressure remained constant. At 23:46, the D/W pressure indicated 750kPa[abs].
・ The Emergency Countermeasures Headquarters and the Main Control Room that was
operating the D/W small vent valve (AO valve) had only two hot lines to communicate.

(Works on March 15)
・ At 0:01 on March 15, the Emergency Countermeasures Headquarters excited the
solenoid valves to open the D/W small vent valve (AO valve). However, it wasconfirmed several minutes later that the small valve was closed.

At 0:05 on March 15, the reactor pressure was 0.653MPa[gage]; the D/W pressure was 740kPa[abs]; and the D/W pressure remained constant. At 0:10, the reactor pressure was 0.833MPa[gage]; the D/W pressure was 740kPa[abs]; and the S/C pressure was 300kPa[abs] or so and remained unchanged. The reactor pressure began to rise. The recovery team received an order to prioritize connecting batteries to excite the SRVsolenoid valves required to open the SRV. The recovery team continued the operations.

At 0:22 on March 15, the reactor pressure was 1.170MPa[gage]. The D/W pressure was 735kPa[abs]. Since the reactor pressure was rising, the operators tried opening another SRV. However, at 0:45, the reactor pressure rose to 1.823MPa[gage], hence the SRV did not open and the operators tried to open other SRVs.
・ At 1:10 on March 15 when the operators tried opening an SRV, the reactor pressure began to decline. The D/W pressure, however, remained constant at around 730kPa[abs].
The S/C pressure remained at around 300kPa[abs] and stable. Subsequently, the reactor pressure remained at around 0.63MPa[gage] and stable. At 2:22, the reactor pressure was rising and reached 0.675MPa[gage]. Thus, the operators began to open the next SRV. In addition, the D/W pressure rose slightly and at 2:45 reached 750kPa[abs].
・ The recovery team at the Main Control Room engaged in opening the SRV to reduce the rising reactor pressure and opening the vent valve to reduce the rising pressure of the D/W since the evening of March 14. Following the instructions of the Emergency Countermeasures Headquarters to cope with the plant conditions, members of the recovery team put on full-face masks and rubber gloves. With the help of flashlights, members connected wires, while keeping the SRV open to stabilize the reactor pressure and strove to form a venting line.

Activities “after 6:00 to 6:10 on March 15 when a large impulsive sound thundered, causing the S/C pressure to show a reading of 0 kPa[abs]

At around 6:00 to 6:10 on March 15, a large impulsive sound thundered.
・ An operator who engaged in monitoring the plant at the Main Control Room of Units 1 and 2 felt shocks that differed from the explosion at Unit 1. The operator who engaged in collecting data almost at the same time confirmed that the S/C pressure had an indication value of 0kPa[abs] and reported it to the Emergency Countermeasures Headquarters .
・ At around this time, the ceiling on the Unit 4 side of the Main Control Room of Units 3 and 4 shook with an impulsive sound.

Three operators heading for the Main Control Room of Units 3 and 4 for a work
shift at 6:00 on March 15 felt wind pressure on their backs when entering th service building of Units 3 and 4. After entering the Main Control Room and checking the situation, the power generation team informed them of the
temporary evacuation.
Six operators, consisting of three operators and a further three operators staying at the Main Control Room, started to evacuate into the Seismic Isolated Building. When they left the service building of Units 3 and 4, the surroundings were full of debris. The six operators got in the car that they had just came in and headed for the Seismic Isolated Building. When they looked up at the Reactor Building of Unit 4 on the way, they confirmed that the area around the 5th floor was damaged.
The road near the Reactor Building was full of scattered debris and the car could no longer advance. The six operators left the car, ran away from the Reactor Building of Unit 4, and then walked toward the Seismic Isolated Building. On their way there, they came across cars heading for the main gate to evacuate the Power Station. The six operators finally reached the Seismic Isolated Building and reported on the conditions of Unit 4 to the Emergency Countermeasures Headquarters.

At around 6:30 on March 15, the Emergency Countermeasures Headquarters decided to temporarily move personnel into Fukushima Daini Nuclear Power Station, except for the personnel monitoring the plant and needed for emergency recovery. Each of the team leaders of the Emergency Countermeasures Headquarters appointed the persons needed for the above mentioned operations. Approx. 650 workers started to move into Fukushima Daini. Immediately after the evacuation, some 70 workers were left in the Emergency Countermeasures Headquarters.

At around 11:25 on March 15, operators confirmed that the D/W pressure had
declined. (730kPa[abs](7:20) → 155kPa[abs](11:25)) (ie Reactor 2 Dry Well)

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