Lessons-Learned from the Research on BWR, and its Applicability to PWR

Extremely Confidential

Type

Cause

Applicable
to PWR?

Events / Issues

Measures / Lessons

・ Auto stop (scram) of core reactor activated according to design. Recovery operations performed on DG auto
activation due to external power failure. Operator responded as planned.

・ Nuclear reactor earthquake response as per design.

○・ Same as above

・ After the auto scram was triggered by earthquake, some DGs were activated by mistake in plants that didn't
experience external power outage (because of generator field failure?). DG is an important emergency powersource, so we need to consider whether this activation was appropriate.

・ Investigate the cause of "false-positive" activation.
・ Change to DG auto-activation interlock onearthquake scram.

○×・ Same as above

・ No major damage to the facilities from the earthquake. Detailed examination of the earthquake disaster will
require some time, so whether lessons learned from Kashiwazaki were effectively applied has yet to be verified.

・ Check lessons learned from Kashiwazaki-Kariwa
Nuclear Power Plant on Chuetsu offshore earthquake.

○・ Same as above

・ The earthquake disrupted communications. There were major issues in sharing information, giving
instructions or commands, and making decisions. Whether the emergency satellite phone, or the fire department
and local government hotlines were functioning and utilized has yet to be verified.

・ Secure and reinforce means of communications incase of disasters such as earthquakes.

○

・ Same as above

・ Recovery process delayed due to difficult access over roads to facilities caused by road liquefaction fromearthquake and debris from the tsunami.

・ Reinforce main road to prevent liquefaction, andsecure multiple access routes.

○

・ Same as above

・ The seismic action recorded in Onagawa and Fukushima Dai-Ichi were as predicted. Aside from the
movement in some areas where the actual quake was stronger, the readings were on par with predictions. This
indicates that the designed seismic parameters are reliable.

・ Anti-earthquake design was appropriate.

○・ Same as above

・ The earthquake happened during the day on a weekday, but we need to verify whether workers would havebeen able assemble at the power plant according to the manual if it occurred at night time or on a holiday.

・ Consider response procedures for disasters
occurring on holidays and at night.

○

・ Tsunami impact exceeded the prediction made by the Japan Society of Civil Engineers (JSCE) in 2002.
(Fukushima Dai-Ichi = 5.7M, Dai-Ni = 5.2M) This greatly affected the safety of the plant. Furthermore, it's notclear whether the accuracy of the tsunami estimate data had been seriously reviewed for the past 7 years.

・ Is the prediction from JSCE really enough?
・ Automatic and regular assessment for Tsunami
need to be considered.

○○・ Seawater pump flooded by tsunami

・ The height of the tsunami that hit the Onagawa Power Plant Tokai Dai-Ni Power Plant was on par with that
estimated by the Japan Society of Civil Engineers (2002 estimate). However, some areas of the plant were notsealed properly, so seawater still entered the facility. The emergency seawater pump malfunctioned due toflooding, causing the emergency DG to malfunction.

・ Tsunami countermeasures for seawater pumps.
(Reinforce pressure and water protection.)○・ Tsunami risk assessment system basedon "height"

・ Tsunami impact destroyed power plant structures and equipment, scattering debris everywhere. The debris
became an obstacle during the recovery process. When deliberating anti-tsunami measures the discussion
shouldn't be limited to just the height of the tsunami but should also include its power.

・Revise risk assessment to include consideration of
power of the tsunami.

○

・ Gasoline tanks wiped away by tsunami

・ In Fukushima Dai-ichi and Onagawa power plants the tsunami swept the gasoline tanks onto the road,blocking access to the plant. This affected the speed of the recovery process, while the gasoline was also
released into the sea.

・ Bolt down the gasoline tanks○

・ Debris created from the tsunami.

・ The debris scattered by the tsunami greatly affected mobility and supply transport. There needs to be acountermeasure to enable swift actions in securing the safety of the plant.

・ Secure heavy equipment and operators for clearing
debris.

○・ Seawater coolant pump vulnerable
against tsunami

・ Although the facilities in Fukushima Dai-Ichi and Dai-Ni were built on an area higher than the estimatedtsunami height, the seawater pumps were not. The pumps were damaged by the tsunami and malfunctioned.

・ Store additional mobile power supplies andseawater pumps.

○

Large capacity pumps have been placed as
substitutes for the sea water pumps(December), currently training operators.

Earthquake ・ Major flooding (seawater) of turbine
・Tsunami building from the tsunami③

・ Buildings connected to the turbine building and the nuclear reactor building were badly flooded, andequipment in the basement and ground floor were damaged and stopped functioning. The plant's cooling system
was greatly affected due to flood damage of the emergency diesel generators, DC and AC power panels, etc.

・ Reconsider the location of Diesel generator, DC
power panel, and AC power panel. Stock mobile
power supply vehicle.

○

Alternate proposal for watertightcountermeasures.

・ The tsunami hit when the turbine
building's supply transport entrance wasopen.

・ During regular inspections, the turbine building's large entrance is used for delivery of supplies. The entrance
was left open during and after the earthquake, allowing seawater from the tsunami to enter the turbine building.
The flooding resulted in the loss of the DC power supplies.

・ Revise operations of the wider entrances since
they are vulnerable to flooding. Conduct training.

○・ Important quake-proof building
emergency power lost from the tsunami.

・ There was no power in the Fukushima Dai-Ni emergency response room following the tsunami. Limitationsin the emergency response room's infrastructure affects the speed of the plant's recovery process.

・ Reinforce the durability of important quake-proof
buildings against tsunami. Secure emergency power
supply.

○・ Seawater pumps malfunctioned due todamage from tsunami.

・ In Fukushima Dai-Ichi, almost all of the seawater pumps malfunctioned from the tsunami. There wasn't muchdamage to the pumps themselves, but most suffered damage to the motor's insulators.

・ Keep motor coil washing equipment within the siteand stock spare parts.

○

・ Insufficient AM and training for
simultaneous SBO occurrences on allplants.

・ The tsunami instantly compromised the entire power plant. The AM was not designed for response to instantdevastating blows to the entire power plant. Further, measures against disasters with low probabilities ofoccurrence may not have been seriously taken into account because of the application of the PSA method. To
learn from this, it's important not just to make hard and soft preparations for responding to instant damage to theentire plant, but to enhance plant-wide trainings as well.

・ Reinforce hard and soft preparations for plantwide SBO. Reinforce Training.

○

Earthquake ・ Earthquake
・Tsunami ・ External power outage①
・ Communication function problem
・ Liquefaction of road & infrastructure,and scattered debris from the quake andtsunami.

Earthquake ・ Design estimate for tsunami set too low
・Tsunami②

apdx_applicability_to_pwp.xls

Team H2O

1/13

Comments

If there is external power, activation of DG
is unnecessary.
Consider the risk of damage fromearthquake during operation.

Elevation of important anti-seismic wing.

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Lessons-Learned from the Research on BWR, and its Applicability to PWR

Extremely Confidential

Type

Cause

Power loss ・ DC power supply flooded by the（Fukushima tsunami
Dai-Ichi）①
・ Flood entered through the air inlet

apdx_applicability_to_pwp.xls

Team H2O

Applicable
to PWR?

Events / Issues

Measures / Lessons

AC and DC power supplies in the turbine building's first floor and basement were lost due to the tsunami. It is
important to improve the facility's air tightness, water-tightness, and pressure resistance to protect the power
supplies.

・ Improve air and water protection, and pressure
tolerance of power facilities○

Comments

Emergency DG malfunctioned due to seawater entering the air inlet.

・ Apply water proof solution for air inlet○

・ Instant loss of DC power supply fromflooding

DC power is the most important power source in the plant. It powers the high pressure cooling devices and themain control room instrumentation and lighting. In Fukushima Dai-Ichi, the DC battery room was located in thebasement of the turbine room, so it was lost instantaneously from flooding. With no power, the high pressure
cooling system couldn't function. When the pressure in the reactor dropped, attempts to cool the nuclear reactor
core with the alternative low pressure cooling system failed. This resulted in core meltdown and eventually tothe hydrogen explosion (Fukushima Unit 1).

・ Secure alternative DC power supply. It's importantto have diversity○

・ Complete external power outage

Fukushima Dai-Ichi Reactors 1 – 6 lost external power from the earthquake. Plants that didn't experience power
outage and those that were able to recover partial power with the emergency power supplies achieved cold
shutdown. Securing external power supply directly led to the prevention of fuel damage.

・ Improve earthquake resistance of external power
supplies
・ Increase the number of external power supply
routes (multiplex)
・ Link external power to each plant (multiplex)○

・ Emergency power supplies located ataltitudes below the tsunami crest・ Power supplies relied on seawatercooling system.

In Fukushima Dai-Ichi, only the Unit 6 emergency diesel generator was functioning. It was located in thenorthern part of the plant which is at a higher altitude (OP13) than Reactors 1 - 4. The height of the flooding
only reached up to 1m. In addition, the Reactor 6 emergency DG used air instead of seawater for its coolingsystem, so it wasn't affected by the flood.

・ Consider placing emergency DGs at higher
locations.
・ Secure emergency power supplies with various
cooling systems and different power types.

○○

Current DG relocation is difficult. Substitute
power (power supply vehicle, air coolingemergency generator device, 3rd power
future location) should be located uphill, andimplement air cooling.

Power loss ・ Not anticipated in AM (SBO AC power（Fukushima recovery rate)
Dai-Ichi）②
・ Concurrent AC and DC power outage
・ Instant power loss of all DC power
supplies from flooding. Unable to charge
DC power supply batteries.

・ Only a short-period station blackout was anticipated in the AM countermeasures. However, in Fukushima
Dai-Ichi, the power outage lasted up to a few days. This sort of situation was not covered in the recovery
procedure manual.

・ Revise the procedures for anticipating SBO
duration.

○

Procedure reevaluated.

・ The countermeasures in the AM all assume definite recovery from station blackout, so there aren't any
countermeasures against the loss of all AC and DC power at once. The plant was designed to supply 8 hours of
DC power in case of AC power outage. In Fukushima Dai-Ichi Unit 3, where DC power was retained, the DC
power lasted more than a day (1.5 – 3 days) by cutting off all unnecessary consumption, but they failed to set up
the low pressure cooling system for backup during this period. When the batteries were depleted, the plant lostits high pressure cooling system, and instrumentation in the main control room stop functioning.

・ Secure alternative AC power supply
・ Secure alternative DC power supply
・ Create manual for swift installation of these
supplies○

Confirmed in training that substitute AC
power connection is completed before
battery depletion. Improvement
implemented for reducing procedure time inresponse to the training results.

・ Dai-Ichi Reactors 5 & 6 shared power;
unable to supply power to Reactors 1 - 4

・ The emergency DG in Fukushima Dai-Ichi Unit 6 remained operational and workers were able to connect it
to power Unit 5. This together with the use of the power supply vehicle allowed cold shutdown in Dai-Ichi
Reactors 5 & 6. There was no power line cross-connecting Units 5 & 6 to Units 1 - 4.

・ Improve power supply lines within the site (pervoltage class)○

Deliberating power accommodation between
plants through backup transformer on
secondary side.

・ Delay due to insufficient number of
power supply vehicles

・ After the tsunami, some plants were able to partially restore power with the power supply vehicles.
Utilization of power supply vehicles was effective.

・ Increase number and variety of power supply
vehicles, revise designations, define connection areasand procedures, and reinforce training.

○

・ Complete darkness in the main control
room due to DC power outage
・ Instant loss of parameter monitoring andcontrol functions

・ The greatest fear and cause of despair for operators is the loss of instrumentation. In a severe accident suchas this one, operators need to be calm and utilize their knowledge and skills acquired through training tostabilize the plant and bring it to cold shutdown. In order to achieve this, it is crucial to maintain the monitoring
functions of the measurement instruments and control switches (and the power for it).

・ Increase number and variety of alternative DC
power supplies for maintaining monitoring
functionality.

○

Power loss ・ Loss of power from earthquake and(Fukushima aftershock
Dai-ichi,Dai-ni,
Higashidori,
Onagawa,
Tokai Daini) ①
・ Failure of the emergency DG, seawater
coolant pumps, and cooling system causedby the tsunami and flooding.

・ External power: On 3/11 Fukushima Dai-Ichi, Tokai Dai-ni, and Higashi Dori experienced external power
outage. On 4/7 external power in Higashi Dori was cut-off again (emergency DG automatically activated in bothcases). For deep defense it's important to have power transmission equipment that doesn't rely on emergency
DG, especially in Higashi Dori where external power outage occurred twice in 1 month. The vulnerability ofthe power transmission system was evident. Earthquakes caused the power outages in both cases, so it's
recommended that the power transmission network be expanded, and earthquake resistance improved on theswitching stations and substations.

・ Expand power supply network.
・ Reinforce earthquake resistance of power
substation facilities and switch stations.

○○・ Emergency DG Power: Emergency DGs stopped working either from flooding in the DG or seawater pumpfacility by the tsunami in Fukushima Dai-Ichi and Dai-Ni, Onagawa, and Tokai Dai-Ni.

・ Identify how the floodwater entered theEmergency DG room and implement
countermeasures.
・ Flood prevention and reinforcement of water
protection for the coolant pump.
・ Secure spare parts for emergency DG.
・ Reconsider location of DC power.
・ Flood defense measures.
・ Upgrade battery capacity.
・ Secure alternative DC power, DC power supply
vehicle, and means of chargiing batteries.

○○○

・ Consider relocating power panels to higher areas
・ Prepare power supply vehicles, cables, connection
terminal systems, and connection route・ Equip specific procedures and reinforce training○○

・ No anticipation of, or procedures forhandling instant DC power outage andproviding alternative power backup.

・ Emergency DG Power: Emergency DGs stopped working either from flooding in the DG or seawater pumpfacility caused by the tsunami in Fukushima Dai-Ichi and Dai-Ni, Onagawa, and Tokai Dai-Ni.

・ Loss of power paths via M/C and P/Cdue to flooding.

・ The tsunami flood damaged the power paths including the M/C and P/C in Fukushima Dai-Ichi and Dai-Ni.
In other plants M/C and P/C stopped functioning from partial loss of power. In both cases, crucial responses
such as cooling and venting of the reactor were affected .

2/13

DC main line board DC power was not lostat Unit 3 where it was located 1 floor
underground in the turbine building. At
Units 1, 2 and 4 where it was located in thecontrol building 1st floor, DC power was
lost.

○
○
○
○

○

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Lessons-Learned from the Research on BWR, and its Applicability to PWR

Extremely Confidential

Type

Measures / Lessons

Power loss ・ Insufficient number of power supply(Fukushima vehicles.
Dai-ichi,・ Delay in arrival of additional vehicles.
Dai-ni,・ Insufficient backup batteries,, temporary
Higashidori, orders, compact generators, etc.
Onagawa,
Tokai Daini) ②
・ Restoration of power, high pressure
cooling system, and depressurization
functions under severe and adverse
environments, and insufficient AM
countermeasures.

・ Power supply vehicles: If necessary load for power supply vehicles had been predetermined, sufficientnumber of units secured, and vehicles arrived quickly, the result could have turned out better, especially inFukushima Dai-Ichi.

・ Increase number of permanent power supply
vehicles (multiplex) (DC, AC, mix)
・ Prepare emergency kit for power blackout(batteries, lights, compact generators, fuel, cables,etc.).
・ Create manuals for aforementioned items, andconduct training.

○○○・ Emergency DG, all AC power, DC power, and emergency seawater pumps ceased functioning instantly fromthe tsunami flooding in Fukushima Dai-Ichi. Restoration was conducted in an overwhelmingly adverse
environment. It was extremely difficult to maintain the high pressure cooling system and to switch to low
pressure cooling (preparations, etc.) This chain of events is one of the main causes of the hydrogen explosionthat occurred in the plant.

・ Increase number of permanent power supply
vehicles (multiplex) (DC, AC, mix)
・ Prepare emergency kit for power blackout(batteries, lights, compact generators, fuel, cables,etc.).
・ Create manuals for aforementioned items, andconduct training.

○

Loss of sea ・ Secure emergency DG
water
・ Power sharing functions
cooling
・ Reconstruct seawater cooling system
functionsthat doesn't compromise time
（Fukushima requirements
Dai-Ichi）

・ The tsunami didn't reach the Fukushima Dai-Ichi Unit 6 air-cooled emergency DG. Power was shared
between Reactors 5 and 6, and supplied to the RHR pumps. By preparing temporary seawater pumps and power
supply vehicles, workers were able to reconstruct the seawater cooling system and achieve cold shutdown.
Learning from this experience, the connection route should be defined (i.e. in the manual) and training
conducted periodically to enable prompt response to such situations.

・ Reaffirmed the importance of emergency DG andPower sharing functions
・ Conduct periodic training for simulating similar
events○○・ Vulnerability of emergency DG (watercool) cooling function (seawater pump,
motor, etc.)

・ In Fukushima Dai-Ichi Reactors 1 – 6, all seawater pumps stopped functioning due to flooding by thetsunami, resulting in the loss of the seawater cooling system (ultimate heat sink). Although the emergency DG
was also flooded and malfunctioned, even if it did survive the tsunami impact, the DG would still have stopped
with the loss the of cooling equipment (seawater pumps, motors, etc.). When emergency DG stops, a chain
reaction causes the ECCS pump to stop working as well.

・ Secure seawater cooling system, backup water
pump, power supply, fuel, etc.
・ Prepare line of air-cooled DG (not dependent on
seawater)・ Consider using motor with strong water protection○○○

・ Loss of seawater cooling function

・ Fukushima Dai-Ichi 1 – 3 was not able to achieve cold shutdown due to loss of seawater cooling function.

・ Same as above.

○

・ Retained external power・ Retained main control room function
・ Secured time for recovering the highpressure cooling system.
・ No delay in the restoration and operationof seawater cooling system.

・ Plants that were able to secure external power supply achieved cold shutdown.
－ Fukushima Dai-Ni was able to secure 1 external power system.
－ They lost DG and the seawater cooling system from the tsunami impact but with the external power they
were able to maintain main control room functions. With DC power, they were able to maintain high pressure
cooling by using the RCIC and SR valve.
－ This bought them time to restore the emergency seawater pumps and power the necessary pumps.

・ Reaffirmed the importance of external power.
・ Reaffirmed the effectiveness of AM when external
power and DC power are available.

○○

・ Same as above.

・ In Onagawa power plant, Reactors 2 & 3 were able to secure 1 external power system which allowed themto maintain the seawater cooling system and succeed in implementing standard cold shutdown.
－ Unit 1 lost external power, and DG was activated.
－ Achieved cold shutdown by maintaining seawater cooling function.
Cold shutdown can be achieved by maintaining power and securing seawater pump function.

○
○
○
○

・ Same as above.

・ Partial flooding of seawater pump caused emergency DG to stop in Onagawa Unit 2 and Tokai Dai-Ni. (2DG units in Onagawa Unit 2, and 1 unit in Tokai Dai-Ni.)－ There's no denying that the situation could have been the same as with Fukushima Dai-Ichi 1 – 3 if all
external power and DG failed at the same time.

・ Same as above.
・ Importance of seawater cooling function.
・ Secure alternative equipment to replace amagedunits・ Affirmed the importance of recovery processtraining.
・ Plants that achieved cold shutdown shouldn't simply
celebrate their successful recovery. They should
acknowledge the potential risks faced and review thecountermeasures and training needed for
improvements.

・ 1F Unit 1: Parameter data: The facility lost DC power right after the earthquake and tsunami. Without power,
instrument panels weren't functioning, so it was impossible to acquire important parameters such as the corewater level. As a result, they weren't able to grasp the actual situation in the core and make appropriate
decisions. They started out making the wrong decisions in handling the high pressure cooling system.

・ Countermeasure for main control room power
outage.
・ DC power flood prevention (location, water seal,water protection for batteries), DC power supply
flood prevention (location, water seal, water
protection for batteries)
・ Secure backup batteries (battery, DC power supply
vehicle)○○○・ Loss of all AC/DC power
・ IC valve operation failed

・ 1F Unit 1: High pressure IC water injection and depressurization: Similarly, without AC/DC power,
operators were unable to adjust the valves of the High pressure system (IC). As a result, operating the highpressure system was almost impossible. It can be inferred that water injection and depressurization failed. Our
theory is that the core's water level was decreasing while temperature and pressure kept rising. Damage isestimated to have started 3 hours after the tsunami.

・ Restore AC & DC power within 2 hours?
・ In addition (to AC), allow direct valve control.?
・ Consider valve adjustment mechanism that doesn't
rely on electricity (manual & auto).

○－○

・ Loss of all AC/DC power
・ HPCI valve operation failed

・ 1F Unit 1: High pressure HPCI water injection and depressurization: Similarly, without AC/DC power,
operators were unable to adjust the valves of the HPCI system and failed to perform water injection.

・ Same as above.

○

・ Incomplete multiplexed defense in the
AM・ Delay in depressurization andpreparations for low pressure cooling・ 1F Unit 1: AM ineffective due to unavailable measurement data and high pressure cooling system: When thecomplete AC/DC power outage occured, the plant didn't have enough time to prepare for transition from highpressure to low pressure cooling as given in the AM (+αexpertise of site personnel) because everyone was busy
securing AC power (power supply vehicle), securing DC power (car batteries), vent line setup (manual), lowpressure coolant injection setup (fire truck, hose, water supply for fire extinguisher), etc.

・ Design AM to anticipate instant and concurrent lossof entire AC and DC power (unable to recharge
batteries due to flooding).

○

・ Activation of RCIC・ Effectiveness of the RCIC: Unit 1lost its IC system and wasn't able to maintain high pressure cooling. But
in Unit 2, RCIC was activated and continued working. It is believed that the RCIC kept the pressure in the S/Cwithin the estimated limit of 0Ka (abs) for 3 – 4 days after the tsunami, before the containment vessel was
eventually damaged.

・ Reaffirmed effectiveness and importance of
maintaining the high pressure cooling system.
・ Important to provide procedures and training for
preparing and setting up low pressure cooling system
while the high pressure cooling system is stillworking.

○○

High・ Loss of all DC powerpressure・ Unable to view instrumentation
cooling・ Main control tower functions failed
function ①

apdx_applicability_to_pwp.xls

Applicable
to PWR?

Events / Issues

Comparedwith otherplants

Cause

Team H2O

3/13

Comments○

All valves needed for TDAFWP operation
are outside of the containment vessel, andmanual operation is possible

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Lessons-Learned from the Research on BWR, and its Applicability to PWR

Extremely Confidential

Type

Measures / Lessons

High・ Fukushima Unit 1 hydrogen explosion
pressure
coolingfunction ②

・ 1F Unit 2: High pressure cooling system setup incomplete – repeated interruptions and damage to the water
injection line from the hydrogen explosion (3/12): Response unit completed the preparations for backup water
injection to the core, and connected the power supply vehicle to a working P/C, but the cables and the power
supply vehicle were destroyed when Unit 1 exploded on 3/12 and everything had to be setup from scratch again.

・ Review the risks involved in operating multiple
plants・ Absolute prevention of hydrogen explosion○○

・ Same as above. (Unit 3)

・ Same as above (3/14): The response unit was able set up a seawater injection line using fire trucks and hoses,
but the 3/14 hydrogen explosion in Unit 3 destroyed the fire trucks and hoses and everything had to be set up
from scratch again.

・ Review the risks involved in operating multiple
plants・ Absolute prevention of hydrogen explosion○

・ Frequent aftershocks

・ 1F Unit 2: Effect of aftershocks: In parallel with previous items, repeated aftershocks interrupted theinjection line set up, and as a result the response unit was not able to execute their procedures in time.

・ Necessity of AM design and training anticipating
overwhelmingly poor environment○

・ Insufficiency in the AM

・ 1F Unit 2: Effect of after quake: In parallel with previous items, repeated after quake interrupted the injection
line setup, and as result the response unit was not able to execute in time.

・Necessity of AM design and training anticipating
overlaying poor environment○

・ Maintain DC power・ Failed to secure alternative power source
during this period

・ 1Ｆ Unit 3: Importance of DC power and Effectiveness of RCIC: DC power (DC125V Main bus boards 3A
and 3B) survived the earthquake and tsunami, and it was used to power the high pressure system (RCIC or
HPCI). However, the plant wasn't able to secure backup power, and the DC power depleted 35 hours after
activation of RCIC. At this point, HPCI also was already on halt. Consequently, the plant failed to decrease thereactor's pressure and recover the water level. (We were able to verify that the batteries were depleted so ourtheory is that this is the reason the system stopped.)

・ Reaffirmed importance of DC power and RCIC・ Secure additional power sources; reinforce andconduct training○○

・ Use of car batteries
・ Activation of HPCI・ 1F Unit 3: Effectiveness of HPCI: The batteries depleted on 3/12, at 11:36, causing the RCIC to stop. HPCI
was activated on the same day at 12:35. During this period the core pressure dropped from 7.53MPa to
0.58MPa, but went back up to 7.4MPa on 3/13, 2:42, when the batteries for HPCI were depleteed (cause of
stoppage is believed to be depleteed batteries since the batteries were found and confirmed).

・ Same as above.

○・ Insufficient coverage in the AM (Secure
extra DC power and backup power)・ Same as above.(Devise countermeasures
to events when DC power is lost fromflood and batteries can't be charged.)・ 1F Unit 3: Insufficient coverage in the AM (Secure extra DC power supply or backup power supply): 1F
Unit 3 was the only reactor among Units 1 - 4 that retained its DC power supply. However, looking at thechronology, there is no evidence of additional backup power source being secured before the DC power supply
was consumed (used batteries from employees' cars and other sources when HPCI stopped). Additionally, there
is no trace of reserve DC power batteries stored in the reactor building or in the seismically designed building.
Storing of reserved batteries for emergency, such as in this case, may not have been specified in the AM (= itseems that they have no other measures than to restore the AC power within 8 hours (battery life) and then to
recharge DC batteries when AC power is restored). As a result, high pressure cooling systems such as the RCIC
and HPCI had to stop prematurely.
・ 1F Unit 3: Insufficiency in the AM (multiplex defense): This is related with the previous item. It seems that
AM provides only one solution for high pressure system (RCIC/HPCI) power recovery. It only states to “restore
AC power within 8 hours (the life span of DC batteries) and recharge the batteries with the AC power.” This
leads to the conclusion that the facility has weaknesses in its defense multiplexing.

・ Reserve extra DC batteries (multiplex - since
batteries can no longer be charged if flooded)○

・ Same as above.
・ Update AM and training to include responding toinstant loss of all DC power supplies from flood(batteries can't be recharged).

○○・ 1F Unit 3: AM ineffective (core reactor scram): Of all Units in 1F it is believed that only the event in Unit 3
was within the scope of the AM manual (earthquake, AC power outage, core reactor scram, DC power
utilization (8hrs)). However, Unit 3 was not able to achieve cold shutdown. Although they were able to prevent
damage to the core for 36 hrs by powering the high pressure cooling systems (RCIC and HPIC) with the DC
power supply, they were not able to "restore AC power, depressurize the core reactor, and make the transition
to low pressure cooling" as indicated in the AM.

・ Same as above.

○

Ventilation ・ Loss of all AC & DC powerfunction・ SR valve malfunction（Depressuri
zation via
SR valve）①

・ 1F Unit 1: SRV non-functional due to loss of DC power: The SRV (safety release valve) which is used by
the high pressure cooling system stopped functioning due to loss of all AC and DC power by the earthquake andtsunami. In Unit 1, the SRV didn't work at all. Because of this, they decided to reduce core pressure by using
IC. However, partially due to the adverse environment the IC didn't function as designed. At the end, site
workers failed in reducing the core's pressure, and it continued to build. (Regarding the decrease in the nuclear
reactor pressure, the SR valve may have been stuck, and steam may have leaked through the SRV flange section
gasket due to the rise in pressure vessel temperature. This may have reduced the pressure in the nuclear reactor,
but at this point these are just theories.)○

・ Loss of all AC & DC power
・ SR valve malfunction

・ 1F Unit 2: SRV non-functional due to loss of DC power: Same as above. (＝＞ P/C (2A, 2B, 2C, 2D) were
working, but like in Unit 1 the entire battery room, where the DC batteries were stored, was flooded. Without
power the SRV didn't function.) When the RCIC stopped, they decided to depressurize the nuclear reactor core
to perform lower pressure water injection, so workers used spare batteries to power the SRV for the
depressurization operation.

・ Multiplex DC power (extra batteries, and allow
charging from battery vehicles and AC power supply
vehicle)・ Improve water protection of DC power supplies(batteries) (safer storage location or water seal of thebatteries themselves).
・ Store spare batteries, and optimize installation time.
・ Increase number of response unit members andconduct training to achieve the above.
・ What about using a mechanism that doesn‘t rely on
DC power to operate the SRV?
・ Same as above.

・ Same as above.
・ Delay in ordering spare batteries.
・ Delay in setting up water injection line
for fire truck?

・ 1F Unit 3: Delay of depressurization (SRV) due to lack of batteries.: With DC power (3A, 3B) available,plant workers followed the manual and cut-off unnecessary power consumption to buy more time for
RCIC/HPCI to work. The batteries provided power for approximately 35 hours until the HPCI was tripped.
After the HPCI stopped working, workers attempted to depressurize the reactor to inject water via the fire truck
hose, but weren't able to operate the SRV because there was no power. So they collected the car batteries fromthe employees' cars, and at 9:08, 3/13, they were finally able to operate the SRV and depressurize the reactor(HPCI stopped at 2:42, 3/13; pressure relieved 6 hours after). Later at 9:25 the fire trucks arrived and started thealternative water injection (one truck from 1F 5 & 6, and one more from 2F).

・ Same as above.
・ Upgrade regular DC power supplies (extended
battery life).
・ Reduce the time spent for setting up water injection
line for fire trucks.

○○○

・ Insufficient coverage in the AM (Nomultiplex defense for DC power?)・ Restoration process under unexpected
field condition (not covered by AM)

apdx_applicability_to_pwp.xls

Applicable
to PWR?

Events / Issues

Highpressure
coolingfunction ③

Cause

Team H2O

4/13

Comments
Problems occurred even when plant was
stopped, so what are the risks of multiplesite locations?

TDAFWP at PWR can be operated even
without DC power.

TDAFWP at PWR can be operated even
without DC power.

○○○

Manual opening of the PWR main steam
release valve is possible, but reconstructionis planned for greater ease of use.

○

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Lessons-Learned from the Research on BWR, and its Applicability to PWR

Extremely Confidential

Type

Cause

Ventilation ・ Secured external powerfunction・ Secured DC power（Depressuri ・ RCIC was functioning
zation via ・ Set up line for low pressure cooling
SR valve）②
・ Failed to secure power・ Failed in high pressure cooling due tolack of power)
・ Failed to depressurize (SRV)

Applicable
to PWR?

Events / Issues

Measures / Lessons

・ 2F Unit 2: Success in pressure vessel depressurization with the SRV: 2F Unit 2 lost its emergency DG fromthe tsunami and its ultimate heat sink. However, the facility was able to receive external power supply, and thepower panels and DC power supplies were working. They were able to maintain the water level of the nuclear
reactor with RCIC, which bought time for setting up the line for the Make-up Water Condensate system(MUWC). After setting up MUWC, operators adjusted the SRV to depressurize the reactor as planned. After
that, they performed low pressure coolant injection and achieved cold shutdown => Importance of external andDC power.

・ Reconfirmed the importance of the following:－ External and DC power－ RCIC (with power)－ Low pressure cooling system (with power)○

・ 1F1～Unit 3: Limitation of AM (Especially with risks in failing high pressure cooling): Nuclear reactor
depressurization operation was performed on Units 1-3 after the high pressure cooling stopped working.
Workers weren't able to set up the transition to low pressure cooling while the high pressure cooling system wasrunning. It is believed that the delay was partially caused by the unprecedented adverse field conditions.

・ Same as above.
・ Revise AM (integrate unexpected incidents learned
from this event)・ Same as above (Provide judgment base fordetermining plausibility of cold shutdown with thestandard operating procedure. Also provide timeframe
as when to start setting up low pressure system.)・ In addition to the previous item, provide alternative
action guidelines (the guideline should aim to prevent
worst case scenario instead of aiming for perfection.
i.e. prevention of hydrogen explosion, venting reactor
building, seawater injection, rapid depressurization
using IC, etc)
・Maintain worker's ability to respond to emergency
situations with regular training.

○
○
○

○

・ 1F Unit 1: Delay in PCV operation: On 3/12 (00:06), orders were given to prepare for vent operation, when
they realized that D/W pressure may have exceeded 600k Pa abs. However, the actual vent operation was
performed at 14:30 that day. The operation started at 09:04 but took approx. five and a half hours to complete.
The reasons are:No power to the valve (no AC & DC power)
Complete darkness inside the building due to blackout (except for main control room)
Increasing dosage rates parallel with the progression of reactor core damage (especially basement 1)
Orders to stop field work due to frequent aftershocks
Work halted until evacuation of neighboring residents completed. Insufficient means of communication on
progress updates.
Lacking means of communication between main control room and field workers inspecting the vents
Failed in vent release due to lack of pressure from air compressor
Time consumed by arranging for temporary air compressor, delivering adaptors, and transport.
Although they were able to vent the containment vessel and confirm drop in pressure, the reactor building
exploded approximately an hour afterward.

・ Secure power (DC, AC and backup power
supplies)
・ Confirm availability of emergency lights (installed
in reactor building and portable lights for field work)
・ Secure emergency communication methods
・ Secure extra compressors and adaptors
・ Change the vent system. It should be operable evenin the event of SBO (system that allows vent executed
remotely with reserved power (manual release as lastresort)).

○
○
○
○
○

・ RD operation pressure

1F Unit 2: S/C vent failure due to high Rupture Disk (RD) operational pressure: In the initial attempt to vent the
S/C, the workers had to overcome an obstacle, in which the circuit board for energizing the solenoid valve cameoff in the explosion in Unit 3. On the same day around 21:00, workers had completed constructing all vent lines
except for the RD, but even with the D/W pressure exceeding its max capacity of 427 Pa gage (530k Pa abs),
the pressure in S/C was not enough to move the RD. At 23:35, they decided that the operation was a failure andhad no choice but to switch to D/W venting.

・ Review RD operational pressure.
・ Confirm reason for setting high pressure
configuration on vent operation(The operational pressure was set to a little under 2times the designed pressure value. This was done in
the hopes of preventing the release of radioactive
material as much as possible. But this action may
have contributed to the hydrogen density exceeding
4% when (generated due to fuel damage) it leaked out
from the containment vessel.)・ Consider replacing RDs with valve-operated ventsystem.

××

There is no rupture disk in PWR×・ Same as above.

1F Unit 2: D/W vent failure: On 3/15 (apprx. 00:02 ) after failing with the vent operation in the previous issue,
the attempt to open the D/W vent commenced. The preparation of the vent line was completed at 0:02, on 3/15.
Although the D/W pressure varied around 750k Pa abs, after a few minutes the vent was confirmed to be shut.
Around 6:00 - 6:10 the same day, it is estimated that severe damage to the PCV had occurred, judging from therecord that pressure of S/C was 0 k Pa.

・ Same as the above

×・ Insufficient pressure from aircompressor
・ Faulty solenoid valve
・ Delay in vent line setup

・ 1F Unit 2: Delay in vent line set up due to lack of pressure from air compressor and faulty solenoid valve:
After the Unit 3 explosion on March 14 (11:01), workers attempted to open the S/C vent valve (large AO valve)
but failed. The pressure from the air compressor was too low. It is postulated that the AO valve couldn't be
opened in processes with the same line up due to a faulty solenoid valve.

・ Consider a vent system that doesn't use airpressure (prepare temporary compressor, fieldenvironment management, line construction thatallows connection, change to valve that allows
manual operation.)×・ Complete darkness
・ Hot and humid work environment
・ Difficult vent line setup

・ 1F Unit 3: Slow W/W vent set up progress due to the dark, hot, and humid work environment: On March 12,
at approximately 4:50 (RCIC still running) after energizing the S/C vent solenoid valve with the main control
room's compact generator, the shift workers went to the torus room to confirm if the valve was opened.
However, they found that the room was in complete darkness, and the temperature and humidity were highbecause of heated steam coming out from the S/C vent SR valve. The work environment was tough and they
were making very slow progress. Also on March 13, around 11:00-12:00, workers once again entered the torus
room in an attempt to lock the S/C vent valve (AO valve), but weren't able to complete the task due to increased
temperature and vibration from SR valve.

・ Review and reconsider position of the valve

×

5/13

Comments○

Ventilation ・ AC & DC power outage
function・ Complete darkness inside the building（Depressuri ・ Increasing radiation dosage in thezation bybuilding with the progression of reactor
SR valve） core damage①
・ Frequent aftershocks (required
temporary evacuation)・ Lack of pressure from air compressor
・ Delay in arranging and transport ofequipment such as air compressor andadapters.
・ Delay in venting containment vessel

Ventilation
function(PCV vent)②

apdx_applicability_to_pwp.xls

Team H2O

There is no rupture disk in PWR

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Lessons-Learned from the Research on BWR, and its Applicability to PWR

Extremely Confidential

Type

Applicable
to PWR?

Events / Issues

Measures / Lessons

Ventilation ・ Delay in air cylinder replacement
function(PCV vent)③・ Reduced pressure of air cylinder due toleak・ 1F Unit 3: Delay due to air cylinder replacement: On march 12, approx. 5:23, workers attempted to open the
S/C vent (AO vent) but failed. Second attempt, after replacing the air cylinder, was successful.

・ Secure extra air cylinder for operating vent valve
・ Include replacing of air cylinder in the training.

×・ 1F Unit 3: Problem keeping the vent open due to defect in the air cylinder: On March 13, after venting was
successfully performed, the S/C vent valve (AO large vent) was closed again at approx. 11:17 due to leak in air
cylinder.

・ Secure extra air cylinder for operating vent valve
・ Include replacing of air cylinder in the training.

×・ Insufficient air pressure supplied to thelarge valve
・ Energizing of solenoid valve unstable

・ 1F Unit 3: Difficulty maintaining air pressure for operating the large valve and energizing the air supply line
solenoid valve: Although Unit 3 succeeded in venting, workers were having difficulty keeping it open (orfailed). The postulated reason is a problem with the air pressure used to operate the large valve, and a problem
with the air supply line solenoid valve (unable to energize consistently). This seemed to have occurred 5 times
after the explosion.

・ Review the entire vent system and reinforce thesystem to keep vent opened when needed. (Secure thereliability of the air supply line by developing a safety
sysytem, and its diversity.)

×・ Difficulties and delays in supplying
water via the fire truck
・ Trouble with the diesel-driven fire pump・ Damage to fire hydrant from earthquake
and tsunami, and filtered water was
gushing out
・ Time consumed searching for alternative
water source
・ Not enough fire trucks
・ Fire truck mobility issues due to adverse
environment
・ Delay in setting up water injection linefrom fire truck
・ Insufficient water injection capacity offire truck

・1F Unit 1: Difficulties in supplying water from fire truck, delay in commencing: As early as 17:12, on March
11, instructions to consider water injection from the fire line and fire trucks were given. However, the diesel
generated fire pump was having trouble, so the decision was made to inject water directly from the fire line,
instead of using the fire truck (March 12, 1:48). From the previous item, setting up water injection line from thefire truck (loading to fire truck, transport to reactor building, connecting with water protection system line) wastime consuming. The injection process started at 5:46 (3/12). The main reasons are as follow:

・ Reinforce and add more backup water sources(install large fire protection tank)・ Increase number of fire trucks and hoses
・ Review posting of fire trucks
・ Secure predetermined route for fire trucks (forsmooth transport during blackouts)
・ Secure backup power supplies and pumps; upgrade
fire truck; etc.
・ Investigate cause of the diesel-driven fire pumpproblem, and come up with a countermeasure.

○
○
○
○

・ 1F Unit 1: Inefficient water injection from the fire protection tank: Laps had to be made in loading fresh
water from the Unit 3 fire protection tank to and transporting it to Unit 1 fire protection tank. The fire protection
tanks only have one hose connection, so workers had no choice but to remove the injection hose and interrupt
the injection each time it needed to be refilled.

・ Review the design of the fire protection tank hoseconnection.

○

・ Delay in boric acid injection (SLC)・ 1F Unit 1: Delay in setting up boric acid injection (SLC): In concurrence with the water injection process(via fire truck), power restoration (via power supply vehicle) and Boric acid injection (SLC), pump restoration
processes were on going. Preparation for boric acid injection was completed on March 12 (15:36), but the plantbuilding exploded right after it was completed (15:36). SLC pump cables and the high pressure power supply
vehicle were destroyed.

・ Secure backup power supplies (high pressure
power supply vehicle)
・ Supply more cables and fire trucks○○

・ Same as above (due to explosion)・ 1F Unit 1: Delay in boric acid injection (SLC): After the explosion on March 12 (19:04), seawater injection
using the fire protection line fire truck commenced. Injection of seawater mixed with boric acid started later at
20:45.

・ Same as above○

Low
pressure
coolingfunction ①

Cause

Team H2O

Trouble with the diesel-driven fire pumpDamage to fire hydrant from earthquake and tsunami - filtered water was gushing out (valve closed manually tostop out-rushing water)
Time consumed searching for alternative water source (After surveying the site, they discovered that a fire
protection tank can be used)
Not enough fire trucks (of the 3 trucks, 1 was damaged by the tsunami, 1 was with Units 5 & 6 and was unable
to transfer.)
Trouble moving the fire trucks due to adverse environment (gasoline tank blocking the road, main gate stuck
due to blackout. Workers had to destroy the lock on the gate between Units 2 - 3 to create passage)
Delay in setting up water injection line from fire truck (ordering for fire trucks, transport to reactor building,connecting to fire protection system line)
Insufficient water injection capacity of fire truck (1000 liters per payload)

Comments○○

On March 12 filling of water to the reactor started at 5:46 and finished at 14:53 (total of 80 tons of water). At
first they were only able to fill 1000 liters at a time, but later were able to fill water continuously. Before thenthe fire truck had to make laps for refills. Fast-progressing events require a more efficient response.

Low
・ Problem with the fire protection tank's
pressure
designcooling・ Inefficient water injection
function ②

apdx_applicability_to_pwp.xls

6/13

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Lessons-Learned from the Research on BWR, and its Applicability to PWR

Extremely Confidential

Applicable
to PWR?

Type

Cause

Events / Issues

Measures / Lessons

Generallessons ①

・ Difficulties executing countermeasuresdue to overwhelming, unexpected events,and severe accidents

・ General AM: Overwhelming difficulties and delays in executing countermeasures: As part of accident
management the low pressure water injection was modified, and manuals have been distributed. The actual
environment of the work field was adverse, and it required time to restore power and perform low pressure
water injection. Workers were unable to contain the situation.

・ Improve the AM training to respond to more
specific situations, and continue the training on aregular basis (effects of the earthquake and tsunami ofthis event, setting of specific target completion times
for actions, confirm the time required, accrue knowhow)○

・ Difficulties executing countermeasuresdue to overwhelming, unexpected events,and severe accidents

・ AM: Anticipate night time / holiday events: The field response to this event was difficult and slow because of
the adverse field environment. Debris were scattered by the earthquake and tsunami, and lots of the work had tobe done during the night.

・ Practical training simulating power outage during
night / holiday
・ Improve and standardize night time visibility ofvalves and gauges (use of fluorescent paint, etc.).

○○

・ Risk of sharing water source andinjection line for multiple purposes

・ Water source & water line: Risk of sharing lines for multiple purposes: We learned the importance of the fire
protection system from the incident in Kashiwazaki-Kariwa Nuclear Power Plant when the transformer in Unit 3
caught fire during the Chuetsu offshore earthquake. As for this event, the M/C power panel in Onagawa
Nuclear Power Plant Unit 1 caught fire. There was no fire in the Fukshima Dai-Ichi Nuclear Power Plant, whichallowed them to use the power protection line and water source for lower pressure water injection. But if a fire
had occurred, it can't be denied that it could have caused greater problems to the plant water injection operation.

・ Consider segregating water sources・ (Multiplex) Increase number of water source for themost important ones (take into account water source
for fire response as well)○○・ Risk of positioning several nuclear
plants at the same place
・ Diffculty of controlling several plants
simultaneously during a severe accident
and failure to respond to all of them.

・ General AM: Risk of operating multiple plants in the same location: Nuclear Emergency Response
Headquarters of Fukushima Dai-Ichi Units 1 – 4 prioritized responding to Unit 1 because it wasn't able tomaintain in high pressure cooling with IC. Units 2 & 3 weren't given priority since RCIC high pressure coolingwas working. The decision was a right one to make at that time. However, looking at the fuel rod damage
chronology of Units 2 & 3, They would have been able to avoid the worst-case scenario if they had been able tosetup low pressure cooling system before the RCIC's DC power supply was depleted.

・ Organize the issues with the field response system
・ Organize the problems encountered due to severe
accidents simultaneously occurring at multiple plants
・ Reflect the previous two items in the manual andconduct training.

○○○・ Rupture disk pressure settings in DaiIchi Unit 2 were too high.

・ Dai-Ichi Unit 2: Difficulties venting R/D (required pressure was high) : Dai-Ichi Unit 1 and Unit 3 succeededin venting the containment vessel suppression chamber (S/C). However, the same vent in Unit 2 failed to open
even with the drywell pressure exceeding maximum capacity. The suppression chamber pressure wasn't enoughto move the rupture disk (R/D). After that, a system to release the drywell pressure was set up, but S/C wasdamaged and the venting process was once again unsuccessful.

・ Reconsider the pressure settings of the rupture
disk・ Regular inspection and replacement of rupture disk

××・ Relation between the containment
vessel vent and the hydrogen explosion
・ Hydrogen leak mechanism unclear

・ Dai-Ichi Units 1 & 3: Relation between the containment vessel vent and hydrogen explosion: Hydrogen
explosion occurred in Fukushima Unit 1 and Unit 3 one to two hours after successful venting of the containment
vessel. The hydrogen produced inside the reactor by molten fuel may have transferred and filled the containment
vessel when the SR valve was operated, and released steam to the suppression pool. The hydrogen thenprobably leaked to the reactor building through the containment vessel's routing and vent line, or back flowedfrom the SGTS line connected to the exhaust stack. And finally, when the hydrogen accumulation exceeded the
combustible limit, the explosion occurred. In this project we have taken into account the possibility that thehydrogen accumulation speeded up when the containment vessel was vented. Actual details and cause andeffect are still unclear, so we are hoping that it will be solved in the future.

・ Identify the leak path of hydrogen into the reactor
building
・ Devise countermeasures for hydrogen leaks
・ Review vent in post-core meltdown (nitrogensealing, operation pressure)・ Prevention of hydrogen accumulation in reactor
building and exhaust system○○
×・ Extended external power outage
・ Extended DC power outage

・ General: Risk of extended external and DC power outage: External power outage, emergency DG
malfunction, and seawater cooling system malfunctions occurred in Fukushima Dai-Ichi, Fukushima Dai-Ni,
Onagawa, and Tokai Dai-Ni. Only Fukushima Dai-Ichi lost its DC power. By securing external power, the plantis able to retain its high pressure cooling system, buying time to restore the low pressure cooling systemseawater pumps and motors, and deploy power supply vehicle. Prolonged station blackout depleted the DC
power, and meant loss of hope of restoring the plant. Without the seawater pump working the DG won'tfunction. This increases the urgency to restore external power for the seawater pump.

・ Increase number of temporary DC and AC power
supplies・ Prepare connection devices for alternative power
supplies
・ Reinforce training○○○

・ May not have considered the relation
between vent operation pressure andhydrogen explosion.
・ May have lack of understanding inhydrogen explosion risks, and lack ofcountermeasures in AM.

・ Fukushima Dai-Ichi (General): Relation between the mechanism of the hydrogen explosion and the vent
operation: Compared to other electric companies, TEPCO had configured a higher value for the vent operationpressure. They thought that this would further decrease the chance of releasing radioactive materials toneighboring residences. However, this decision may have been one of the main reasons the hydrogen explosion
occurred. It is postulated to have caused massive build up of hydrogen in the containment vessel. Regarding thehydrogen explosion, there is no record of a backup plan in the response chronology of Unit 1. We assume thatthat this accident was not expected by TEPCO.

・ Solve the mechanism of the hydrogen explosion(leakage path, accumulation path, ignition cause, etc.)
・ Prevent hydrogen accumulation (Detector, reactor
building vent, etc.)
・ Verify the relationship between the vent and thehydrogen explosion
・ Reflect in the corresponding manuals○○

・ Main control tower functions failed due
to SBO・ Fukushima Dai-Ichi (General): Effect of the incomplete main control room functions: The station blackout
disabled the instrumentation and took away the indicator monitoring tasks from the operators.. Without the
instruments, it's impossible to plan the next move. Further, when the Nuclear reactor is at high temperature, it's
doubtful whether the indications given by the instruments powered by the temporary power supply are accurate.
Without indicators the operators will succumb to fear, which affects their ability to make proper judgments.
Operators must be equipped in order to be able to make proper judgments.

・ Secure main control room lights, fieldenvironment, measuring instruments, etc. (power,
lights, work clothes, dosimeters, furniture)・ Reflect to AM and reinforce constant daily training
・ Apply remote measuring instruments○

・ Fukushima Dai-Ichi (General): Radiation leaked out to the environment when Units 1 – 4 exploded, causing
enormous damage to the local community. Today, there are many that suffer from the effects of land
contamination and radiation exposure. The spread of Cesium 137 (from the explosion) has a long-term effect,
and is an especially big problem. The most important things are to prevent a hydrogen explosion at all cost,prevent the spread of radioactive materials, or to minimize the effect.

・ Prevent Hydrogen explosions
・ Create countermeasures against leaks and releaseof radioactive materials(Consider installation of vent filter, etc.)○○

Generallesson ②

Generallesson ③

・ Hydrogen explosion
・ Leak of radioactive materials from
explosion

apdx_applicability_to_pwp.xls

Team H2O

7/13○

Comments

Exhaust procedure established to annulus air
cleaning fan by power supply from air
cooling type generator device

Hydrogen accumulation prevention
measures implemented to annulus as statedabove. However, concentration of hydrogenin containment vessel is extremely low
compared to BWR○○○

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Applicability of Safety Measures to PWR, and the Level of Implementation

Extremely Confidential

Valid also Implewith
mentedPWR?
orplanned?

Team H2O

Purpose Safety Measures（High Level）

Safety Measures(Detail)Securepower● Improve water seal and pressure resistance of switching stations.
● Switching stations should be located in elevated areas, or sea-walls should be built to protect the equipment from tsunami impact.

○
○

○
○

● Improve earthquake tolerance of switching stations in the plant and of the transmission lines. Include those improvements in the design
guideline as anti-seismic requirements.

○○● Multiply transmission lines from transformer substation (at least 2 lines), or connect each plant directly to the external power so as toprevent external power loss to such a substantial extent.

○○● Regarding the substation power transmission lines, switch from overhead wires to underground cable.

○

×● Remote control: Secure power transmission route and cables for remote supplying of power to the nuclear reactor from a power supply
vehicle. (Or is it possible to supply without wires?)○×● Improve earthquake resistance of substations and include it in the design requirements.

○

×● Apply anti-flooding countermeasures to the DG room's air inlet.

○○● Improve water protection and pressure resistance of the DG rooms.

○○● Store controlling equipments and power cables to allow power interchange between separate DG rooms.

○△

Added air cooling emergency DGs. Permanently-installed DG which
can be connected with either A/B systems is planned.

● Place DG equipment on elevated areas (DG, power panel, etc.).

○○

Plan to implement with the third power source.

● Improve DG power interchange function: Interconnect all DGs to allow sharing of power to all nuclear reactors (was able connect
power between Units 5 & 6 but not designed so with reactors 1 - 4).

○○

Other than Ooi Plant, power supply can be shared among all plants
through the secondary lines of backup transformer. (Procedure needs
to be defined). Regarding Ooi Plant, further construction is necessary.

● Plant should be designed to function even with minor flooding.

○×● The plant is vulnerable to disasters during regular inspection since the probability is high that the DGs is also stopped for inspection.
Install an additional DG to eliminate this risk. Place air-cooling DG in an elevated area together with the gas turbine. Air-cooling typedoesn't require seawater pumps and seawater circulation system. For fresh-water cooling DG, set it on an elevated area to avoid damage
from tsunami.

○○● Place diesel and gasoline tanks on an elevated area to avoid damage from tsunami.

○△

Already planned for countermeasures for sliding and floating of large
tank.

● Automatically activate a DG if scrammed during earthquakes.

××

Because activated DG is weaker than the one stopped (with more
effect of axis), automatic activation when external power has not been
lost is not recommended.

Secure external DC power
supplySame as above (Mid to longterm)

Secure emergency diesel
generators (DG)

Same as above (Mid to longterm)Same as above (Mid to longterm. Mitigation measures)

apdx_applicability_to_pwp.xls

8/13

Comments

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Applicability of Safety Measures to PWR, and the Level of Implementation

Extremely Confidential

Purpose Safety Measures（High Level）

Secure DC powerSame as above (Mid to longterm)

Secure AC powerSame as above (Mid to longterm)

SecureSecure functions of control
functions of room
controlroom

Comments● Relocate equipment indoors - into a pressure resistant and water-sealed building to avoid flooding by tsunami.

○○● Station mobile battery vehicles (DC125V, 24V, and 250V) with cables in case of accidents to the DC power supplies.

○△

There are two ways to supply power to the parameter-monitoring
panel, the one via the DC line and the other directly through the AC
panel. TD-AFWP can be activated manually even if the DC power islost. (DC is only 125v).

● Relocate DC power supplies to a higher position.

○△

Planned to either store portable batteries in the anti-seismic isolation
tower, or implement the permanently installed DG in a higher place.
Movement of facility is not being considered.

● Upgrade DC power supply capacity (from 8 hrs to 24 hrs or more).

○△×

Have AM procedure to extend battery life by limiting its use only totop priorities, and to bring in regular batteries. But it is difficult to lastfor 24hrs. The batteries can be re-charged by the air cooling DG.

● Improve water protection and pressure resistance of AC power supply equipment.

○○● Reinforce power supply vehicles:
・ Secure additional permanent units (secure necessary number of units based on the required load capacity). Review locations (i.e.
elevated areas).
・ Increase the type of power supply vehicles: DC, AC, combination of AC & DC, w/ generator, w/DG, etc.

○△

● Set multiple access points of power panels for power supply vehicles and ensure water protection.

○○● Increase number of backup power supplies besides the power supply vehicles.

○○● To hasten restoration of AC power, set up power supply cables and store tools for terminal handling in accessible areas for swift
response.

○○

Already set up the connection board and cable from air coolingemergency DG.

● Sharing of AC power distribution （Cross-connect all units to allow distribution of power through M/C and P/C）.

○△

Backup transformer's secondary side is connected to all plants. (In Ooi
reactor 3&4, it is also planned). The connection is through M/C, not
P/C.

● Utilize air transport of power supply vehicles and backup power source after the tsunami and earthquake have subsided.（Set helipad on
the roof/in the vicinity of the reactor building.）○○

Heliport is set on-site and near the site.

● Transfer the AC power supplies to a higher location.

○○

Air cooling emergency generators are installed in a higher place.

● Secure livable conditions and monitoring capabilities for operators△

×

In Fukushima Dai-ichi, it is estimated that operators in the control
room were exposed to radiation from fission product that flowed into
the room through the duct hoses for ventilation which were brought
into the room. As to the improvement of shielding, if it means toenhance the air seal by closing doors, it is also applicable to PWR.
However, the phrase of 'improvement of shielding effect' usuallymeans to lower the radiation level in the room by increasing the
thickness of concrete wall or ceiling. Revision of terminology may beappropriate.

・ Main control room has to function as a shelter during emergencies, so protection against radiation should be improved.

Other than the air cooling emergency DG (2 units at each plant), 2
power supply vehicles are placed at the plants. Those vehicles supply
power to the metal clad switching gear (6.6kv). Vehicles with various
voltages and back-up powers to P/C have not been deliberated (ifvoltage is lowered it is necessary to make the cable larger).

Same as above (Mid to longterm)

・ To ensure the vent and air conditioning systems in the main control room, emergency power systems such as gas turbines should beinstalled.

○○

Already introduced the measure to supply power from air coolingemergency DG to ventilation fan in the control room, and remove
fission products with filters.

Same as above （Mitigation
measures）

・ Store spare batteries in case meters and gauges stop working.

○△Is now considering to implement connection lines and devices forregular batteries. Will consider to utilize portable batteries.

・ Store sufficient quantities of protective gear, masks, dosimeters and other supplies. Since the situation in Fukushima lasted several days,
there should be adequate supplies stored for the duration.

○○

・ Due to power shut down, parameters such as the reactor's water level and pressure were no longer observable. Portable measuring
instruments and alternative measurements should be developed .

○○Same as above (Mitigation
measures. Mid to long term)

apdx_applicability_to_pwp.xls

Valid also Implewith
mentedPWR?
orplanned?

Safety Measures(Detail)Team H2O

9/13

Plan to examine this issue in the research project of the government,"research on parameter-monitoring systems for severe accidents(phase 1)".

Unauthorized copying or distribution of this file is prohibited. Copyright Team H2O Project all rights reserved

Applicability of Safety Measures to PWR, and the Level of Implementation

Extremely Confidential

Valid also Implewith
mentedPWR?
orplanned?

Team H2O

Purpose Safety Measures（High Level）

Safety Measures(Detail)Secure high Secure high pressure coolingpressuresystemcoolingsystem● The HPCI and RCIC are installed in the basement of the nuclear reactor plant. Although the reason it stopped working was due to thepower loss, it's still necessary to maintain the water seal and pressure resistance of the room to ensure the safety of the pumps and motors
inside.

○○For PWR, TD-AFWP and MD-AFWP are the high pressure coolingsystems. Sealing of the room with these systems for water protection
has been implemented to doors of the rooms. In the future, the doors
will be replaced with the water-proof ones.

● Since the nuclear reactor in a high pressure state can be cooled by SLC, CRD, and CUW water injection methods, it's important tosecure power supplies for these systems. It is necessary to consider storing temporary power supplies to ensure power for the systems
above.

○○

It is possible to supply power to MD-AFWP (2 units), which supply
water to SG in case TD-AFWP is lost, from air cooling emergency
DG. The DG can also supply power to a mid-to-high pressure pumpwhich is under planning.

Same as above （Mitigation
measures）● Night work progress was slow. There was a delay in restoring the high pressure cooling system, which caused the situation in the plant
to worsen, and delay the staging of the low-pressure cooling system. To improve efficiency of the field work, mark valves and machines thatneed to be operated with fluorescent paint for easy observation. Coating the temporary power cables with fluorescent paint will provide easy
direction to install.

○△Though not in the central control room, fluorescent paint was used in
NFB on the DC board, so as to easily lower the battery load during
SBO.

Same as above （Mitigation
measures. Mid to long term）● It takes too much time and causes delays in decision-making if operators are unable to access the site to confirm the state of the highpressure cooling system. We think that it will be effective to have multiple means to observe the site. This will require power but we suggest
installing ITV (for vision), sound monitors, and vibration sensors to allow remote monitoring of the status of the pumps, gauges, and valves.

○△

High performance cameras (approx 50 units) are installed for prompt
actions against fire. The cameras can be remotely controlled from thecentral control room and accident management room. It is possible tocheck the instrumental devices by some of those cameras. In order tomonitor inside of the containment vessel where operators cannot
easily access, ITV has been set up.

Secure containment vessel
ventilation functions（Mitigation measures）● Prepare items for setting up ventilation line (temporary power supplies, air tanks) beforehand for efficiency.

○○(As PWR does not have PCV ventilation function, we treat thefunctions of Main Steam Relief (MSR) valve to release heat of steam
outside of PCV as an equivalent to PCV ventilation in BWR).
For PWR, though the MSR valve can be operated manually even if
air-pressure pump is lost, it is planned to consider to store back-up
compressor to open the valve.

● Given that PCV ventilation operations failed in the reactor No.2, reconsider the vent's pressure requirements (reconsider the pressure
limit of the rupture disk).

＿＿

MSR valve can be opened/closed by hand.

●

Install a neutron sensor inside the containment vessel to observe the activities inside the core during meltdown.

○

×Plan to examine this issue in the research project of the government,"research on parameter-monitoring systems for severe accidents(phase 1)".

●

Multiplex the air pressure supply and vent line and classify them to the 'safety-system' class to ensure the reliability.

○○

Air compressor system for the MSR valve is doubled as a safetysystem. Further alternatives are being implemented.

● Too much time was consumed in the construction of the vent line. Consider placing the valve in an accessible area and allow manual
operation.

○○

Access to MSR valve is easy as it is outside of PCV.

● Given that ventilation with the rupture disk in reactor No.2 was unsuccessful, consider the use of a valve for ventilation without the
disk.

＿

＿

MSR valve can be opened/closed by hand.

Depressurization with SR valve
operation （Mitigation
measures）● Unable to perform depressurization operation using the SR valve due to DC power outage. Prepare batteries in the central control
room.

○

△

The MSR valve is operable without any power source. Portablebatteries are not prepared yet.

Same as above （Mitigation
measures. Mid to long term）●

Consider SR valve mechanism that doesn't rely solely on DC power○○

The MSR valve is operable without any power source.

●

Consider multiple methods for nuclear reactor depressurization○○

MSR valves are placed at each steam generator. For Ooi reactor No.3,
4 units were installed. Pumps to cool SG are TD-AFWP (1 unit), MDAFWP (2 units), mid-to-high pressure pump (1unit under planning),
and fire extinguishing pump.

Secureventilation
functions

Same as above （Mitigation
measures. Mid to long term）

apdx_applicability_to_pwp.xls

10/13

Comments

Unauthorized copying or distribution of this file is prohibited. Copyright Team H2O Project all rights reserved

Applicability of Safety Measures to PWR, and the Level of Implementation

Extremely Confidential

Valid also Implewith
mentedPWR?
orplanned?

Purpose Safety Measures（High Level）

Safety Measures(Detail)Secure low Secure low pressure coolingpressuresystemcoolingsystem● Place emergency core cooling pumps, used for low pressure cooling, at a higher location to avoid damage from tsunami; or, securewater protection and pressure resistance.

○○● Secure appropriate number of fire trucks and hoses, and station them on higher ground. Take into account the water source, water
injection range, and water injection capacity when selecting the fire trucks.

○○● Set multiple water injection points for fire trucks○○● Investigate why the diesel-driven fire pump lost its function and develop appropriate countermeasures.

○＿● Reinforce water sources: Need to supply water from multiple sources, such as a water tank, dam, reservoir, lake, river and/or sea. Also,
review whether the water supply methods and available capacity are sufficient. If the water supply will also be used as a coolant, consider
the following:○△

Same as above (Mid to long
term）

・

Design a mechanism that allows contaminated water in the reactor building to be used as coolant in the circulation system.

・

Prepare multiple routes for the coolant

Anti-seismic tank in an elevated place is being considered.

Intake to SG: Main water supply - 4 places, supplemental water supply- 4 places.

○○

Mid-to-high pressure pump, anti-seismic tank in an elevated place(injection to condensate tank by gravity).

● There was no means of monitoring the spent fuel pool in the field, so temperature and water level monitoring instruments (requires
power) need to be installed. As a backup plan in case instruments are not working, prepare portable contactless thermometers and waterlevel indicators.

○○

Monitoring camera, measuring scale for water level.

● Multiplex the cooling systems for the spent fuel pool.

○○

Recover CCW cooling by large volume pump, and recover SPF
cooling by SFP pump and cooler.

Same as above （Mitigation
measures. Mid to long term）● Secure the water source for low pressure water injection while taking into account its cross-use for fire fighting.

○○

Secure seawater cooling system● Need to prepare portable water pump and temporary power supply in case the seawater pumps malfunction from tsunami attack.

○○● The seawater pump in the building was flooded and malfunctioned. Aside from improving the water seal and pressure resistance of thebuilding, it is also important to completely shut the building doors when there is a tsunami warning.

○○● When adding or replacing emergency generators, secure the cooling line for the air-cool types as backup systems (not relying onseawater coolant).

○○

PWR has an ultimate heat sink that releases steam-heat to the air anddoes not rely on sea water cooling. An application of air fin cooler isbeing deliberated.

● Operate feed-and-bleed cooling with the wet well vent (secure heat sink until cold shutdown.).

－－

PWR has a method for low-heat shutdown by SG.

● Diversification of heat release methods for containment vessel when all AC power is lost○○

In addition to the method above, PWR has already planned toestablish a method for low-heat shutdown by using RHR and reactor
auxiliary cooling water system with large volume pump to use ocean
as an ultimate heat sink.

● Build sea-wall or breakwater○○● Introduce alternative core cooling systems (water source, power source, and water injection system)○○

Power is connected to a M/C panel from the air cooling emergency
DG while for water source a large volume pump is connected to sea
water pipeline.

Same as above （Mitigation
measures）● Equip the site with motor cleaning and winding equipment, and secure spare parts.

○○

A back-up motor for sea water pump has been stored.

Same as above （Mitigation
measures. Mid to long term）● Since the seawater pumps/motors malfunctioned due to the tsunami, consider using sealed type motors (reinforced pressure resistanceand water seal).

○○

A back-up motor for sea water pump has been stored.

Same as above (Mid to longterm）

apdx_applicability_to_pwp.xls

Whether boric acid can be poured inComments● Reinforcement of water supply paths: Confirm other means of water supply than by fire truck (i.e. air-lift or sea transport)

Same as above （Mitigation
measures）

Secureultimateheat sink・Team H2O

11/13

Large volume pump （to be placed in December, 2011）

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Applicability of Safety Measures to PWR, and the Level of Implementation

Extremely Confidential

Valid also Implewith
mentedPWR?
orplanned?

Team H2O

Purpose Safety Measures（High Level）

Safety Measures(Detail)Preventhydrogen
explosionandradiation
leakage● Install hydrogen ventilation systems in the nuclear reactor building to open before it's filled with hydrogen (vent system with remotecontrol + manual control + radioactive material filtering).

↓↓● Even if large quantities of hydrogen are generated and leak from the containment vessel, before hydrogen detonation occurs, should use
a hydrogen release method from the annulus. (PWR) (Release method to include suction filter to remove fission products.)○○● Reinforce air-seal of containment vessel: Review the materials in the seals of areas including the D/W flange, electric routing, hatches,
etc. Reinforce resistance against high temperature and pressure.

△＿● In case mass hydrogen build-up does occur, prevent it from accumulating in an enclosed space.

○○● Reconsider the shape of the upper area/ ceiling of the nuclear reactor, containment vessel, and reactor building so that the hydrogen
does not accumulate in one narrow space (i.e. slant ceiling to redirect the gas).

××● Capacity of the PWR containment vessel is large. Even if large quantities of hydrogen are generated, the concentration in thecontainment vessel will be small compared to BWR. The danger of hydrogen combusting is low, but from the viewpoint of loweringhydrogen concentration over the long term, install a hydrogen depressurizing facility, such as a static catalytic hydrogen recombining
device, in the containment vessel.

○○● Consider reinforcing the concrete or install a debris catcher to prevent debris from penetrating the containment vessel (prevent debris
concrete reaction in pedestal).

○△

Core-catcher is implemented. A water injection hole has been set in
the containment cavity (AM countermeasure).

● To prevent the rupture disk from failing, conduct regular inspections and replacement.

－－

PWR has no containment vessel ventilation or rupture disk.

● In Fukushima Dai-ichi, although they were apprehensive of radiation leakage in reactor No.1, they weren't anticipating a hydrogen
explosion. Add procedures for handling hydrogen explosions in the Accident Manual and conduct training to ensure accurate responses.

○○

In the PWR, in preparation for hydrogen leaks through PCV's
penetration, an AM procedure to supply power to annulus fan for
ventilation has been prepared. Trainings have been conducted.

● With the hydrogen explosion causing the spread of radioactive materials, evaluate the effectiveness of the wet well vent and consider
installing a vent filter.

－－

PWR can release its decay heat (steam) to the open air via SG even if
all the AC powers are lost. The pressure within the PCV are notassumed to rise very much.

Prevent hydrogen explosion

Comments

In PWR, if hydrogen leaks from various penetrations of containment
vessel, the annulus fan powered by alternative power source canexhaust the gas.

Damage of various seal in PCV penetrations was caused by theradiation heat due to core meltdown. Because the PWR containment
vessel is large, the effect is assumed to be small. Countermeasures are
realistically difficult.

・ Install hydrogen detectors in closed spaces (Transmit signals using own battery line or RF).
・ Perform preventive measures such as using a nitrogen seal inside the containment vessel when venting.

Same as above (Mid to longterm）Same as above （Mitigation
measures）

Prevent radiation leakage （Midto long term）

apdx_applicability_to_pwp.xls

12/13

In the PWR, in preparation for hydrogen leaks through PCV's
penetration, an AM procedure to supply power to annulus fan for
ventilation has been prepared.

Unauthorized copying or distribution of this file is prohibited. Copyright Team H2O Project all rights reserved

Applicability of Safety Measures to PWR, and the Level of Implementation

Extremely Confidential

Valid also Implewith
mentedPWR?
orplanned?

Team H2O

Purpose Safety Measures（High Level）

Safety Measures(Detail)

Disaster
responsemanual ・
Infrastructureetc.

● Redesigning AM: How many hours should the plant's water and power sources last? How to get reinforcement from outside?
Implement the following:○○・ Define the numerical requirements specifically as to the minimum number of hours in which coolant and power should last on-site, andadd to the operation manual.

○○・ In the logistics and accident manuals, specify how to bring in additional power, coolant, and other supplies from off-site before the onsite power and coolant are lost.

○○・ Reinforcement of training: Do not let the training end with the preparation phase. It's necessary to cover the actual processes (e.g. actual
connection of cable terminal) and reflect its mechanism in the training as well.

○○● Revise the power restoration manual: The manual originally gives guidelines in restoring short term power loss. Revise the manual toanticipate up to a few days of power loss.

○○● Since earthquake and tsunami can hit all of the reactor units in the power plant at the same time, there should be plant-wide training
with night and holiday scenarios as well.

○○● Revise the organization of the nuclear disaster emergency to handle concurrent accidents on multiple plants.

○○● Include risk assessment in regards to the power of a tsunami besides its height.

○○● Assess the risk of tsunami and earthquake more frequently on regular basis○○● Enforce quick assembly of operators to the plant in case of an earthquake (including at night and during holidays). Secure necessary
staff for the emergency response as well (e.g. Require assembly within X hours).

○○● Communication means among operators in a control room of each plant, accident response members in the field, on-site emergency
response headquarter, and the central control room were cut off, thus affecting timely reports. This slows down the emergency response, so
it's important to secure and distribute appropriate numbers of communication equipments (means of communication).

○○● Improve the environment of the emergency response headquarter on site by providing sleeping quarters and bedding.

○○● Improve the structure of the anti-seismic isolation tower against tsunami (Secure emergency power supplies as well).

○○● To improve the accessibility to the plant after earthquakes and tsunami:○○・ Secure sufficient numbers of heavy machineries and operators for clearing the debris○○

・ Bolt-down the gasoline tanks to avoid floating.

○○● Reinforce roads to the head quarters (including anti-liquefaction)○○

Strengthening of the roads on the grounds has been implemented● Ensure that the transport path remains after earthquakes and tsunami (Construct a path that won't crack or suffer liquefaction. No
manholes).
● Reinforce roads and bridges leading to the power plant.

○

×Transportation methods by sea and air have been enhanced.

○○

Bridges are planned to be strengthened.

● Secure safety of the workers: Consider responding remotely and with fewer staff. (e.g. Set up long distance hoses beforehand, allow
remote control of hoses as with a crane, etc.)○○

Enhance the emergency organization, power savings, and safetymeasures to easily connect emergency equipments are being
implemented.

Update disaster responsemanual (AM)

Review the methods ofearthquake and tsunami risk

Reinforce infrastructure

Same as above (Mid to longterm）

apdx_applicability_to_pwp.xls

13/13

Comments

Unauthorized copying or distribution of this file is prohibited. Copyright Team H2O Project all rights reserved