Progression of Accident at Fukushima Daiichi Nuclear Power Station and the Lessons Learned ...

125 Pages·2012·3.36 MB·English

Attachment - 1
Progression of Accident at Fukushima Daiichi
Nuclear Power Station and the Lessons
Learned
＆
Measures based on
the Fukushima Daiichi accident
Confidential Information. No unintended use, reproduction, or disclosure. TEPCO Att1 - 1
Use other than purposes/copy/disclosure are prohibited Tokyo Electric Power Co.,Inc.
Attachment - 1
I. Progression of Accident at Fukushima Daiichi
Nuclear Power Station and the Lessons Learned
Confidential Information. No unintended use, reproduction, or disclosure. TEPCO Att1 - 2
Use other than purposes/copy/disclosure are prohibited Tokyo Electric Power Co.,Inc.
Accident at Fukushima Units 1~3
Course of Accident Progression Flow at 1F-1
Attachment - 1
Date Time RPV control PCV control
March
11,2011 14:46 Reactor scram signal transmitted due to earthquake
•Reactor automatically shutdown
14:47 EDG automatically started up (automatic scram)
•Turbine & generator shut down
14:52 IC automatically started up Determined that the reactor •MSIV closed
coolant cooling rate of •Off-site power source lost
15:03 IC was manually shutdown → 5p5ro℃ce/dhu, raess s, tcipanunlaotte db ei n the
15:10 Standby maintained S/C cooling commenced
Controlled reader pressure at around 6-7MPa, as
※
stipulated in procedure, with IC system A
1st wave15:27
2nd wave15:35 Reactor could not be cooled because Tsunami arrival
the isolation valve 3A of return line of
IC system A was closed.
15:37 EDGA and B were tripped → Station black out (SBO)
15:42 Determined to be an event corresponding to Article 10 of the Nuclear Disaster Act (SBO)
•DC power sources were lost
•SBO causes loss of function for
•Isolated due to loss of DC power source removing residual heat from PCV
(control power source) IC function was
lost due to a false signal (inferred)
Determined to be an event corresponding to Article 15 of the Nuclear Disaster Act (the loss of
ECCS injection source)
16:36 Reactor water level dropped
•March 12, Around 0:00
It is prepared for
D/W pressure may have
reshuffling parallel to fresh
March 4:00頃 Fresh water injection was water injectionto seawater exceeded 600KPa
PCV venting •March 12, 9:04
12,2011 commenced using ithneje fcrteioshn wtoa bteer loimf tihteed f iinre (D/Wpressure Work commenced for PCV
14:30 fire brigade vehicle prevention water tank decline was venting
•March 12, 9:15
confirmed） ・Venting line MO valve 25%
15:36 Hydrogen explosion n・ot AbeO o vpaelrvaete idn mthaen fuiaellldy cionu hldig h
radiation dose environment
・Temporary air compressor set
19:04 Seawater injection was commenced using fire engine up to operate AO valve and
venting operation performed
※Weshow the arrival time to tide gaugeat the arrival time of the tsunami(Following page too) Att1 - 3
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Accident at Fukushima Units 1~3
Plant Status Immediately After Earthquake Struck (Unit 1)
Attachment - 1
IImmmmeeddiiaatteellyy aafftteerr The earthquake interrupted off-site power and the condensate & feed water pumps were shut down.
eeaarrtthhqquuaakkee The emergency diesel generators started up and all emergency functions worked properly.
Main-steam safety
S
t relief valve
a
c Isolation Generator Regular power source
k Batteries
Condenser
system Turbine Off-site power
p C/B B1F
r
e Main steam isolation valve
s
Motor-operated suR Condenser Circulating water pump
vent valve Dry well re
vent valve Standby liquid e veacto Feepdiwpeater
control system sr
s
pump e
l
Sea
Feedwater
pump
Suppression
chamber vent Primary Condensate pump Operational
valve containment
vessel
Main equipment unit inundated
Seawater cooling lost
Control rod Emergency AC power lost
H PCV cooling drive hydraulic
Core sppuramyp system eat ex system pump sCtoornadgeen psaotoel DC power lost
c
h
a Normal AC power lost
n High-pressure coolant
g Make-up water
e injection system pump
r condensate system pump
Power
C/B B1F panels Filtered
water
R/B：Reactor building
tank
Seawater pump T/B：Turbine building
Diesel generator
Sea Diesel-driven fire C/B：Control building
T/B B1F protection system pump
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Accident at Fukushima Units 1~3
Plant Status After Tsunami Arrival (Unit 1)
Attachment - 1
The seawater pump shut down and the emergency diesel generators shut down.
AAfftteerr ttssuunnaammii
The tsunami inundated the building interiors, and battery and power panel function was also lost.
iinnuunnddaattiioonn All instrument displays, operational function and lightening were lost.
S
t Main-steam safety relief valve]
a
ck Isolatiosyns cteomndenser Batteries Generator Regular power source
Turbine Off-site power
R C/B B1F
ve Main steam isolation valve
ea
Mveontto vra-olvpeerated Dry well vent ssecto Condenser Circulating water pump
valve Standby l (Rr pr Feepdiwpeater
liquid Pe
control Vs
system )su
pump r
e Sea

Feedwate
rpump
Suppression Primary
chamber containment Condensate pump Operational
vent valve
vessel
Main equipment unit inundated
Seawater cooling lost
Control rod Emergency AC power lost
H PCV cooling drive hydraulic
Core spray system ea system pump Condensate DC power lost
pump t e storage pool
x
c
h Normal AC power lost
a High-pressure coolant
n Make-up water
ge injection system pump condensate system
r Power pump
panels
C/B B1F Filtered
water
R/B：Reactor building
Seawater pump Diesel generator tank T/B：Turbine building
Diesel-driven fire
Sea
protection system C/B：Control building
T/B B1F pump
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Accident at Fukushima Units 1~3
Progression of Accident at Unit 1 and Necessary Measures
Attachment - 1
【3/11 14:46 Earthquake occurs】 【3/11 15:35 Tsunami arrives 】
Isolation condenser system (IC)
There are no facilities capable of injecting cooling
Tsunami caused loss of power for
automatically started up and water
water when the reactor is in a high pressure state.
operating valves, and closed valves no
level was maintained
↓
longer opened.
In 2~3 hours, the water level drops to reactor core
Reactor pressure vessel (RPV)
S h utd o w n
Tsunami arrival Water level falls ※
IC
Confusion when first
tsunami wave, Not able to ascertain
surpassing assumptions, condition of reactor
arrives
【Tangible measure】 【Intangible measure】 【Tangible measure 】 【Intangible measure 】 【Tangible measure 】
Enhance seismic performance Accident assumptions, Tsunami countermeasures, Information sharing Strengthen high-pressure cooling
of off-site power source response to multiple unit accident reinforcing power sources water injection function
【3/11 ~18:18 】 【3/11 20:00 〜3/12 in the morning】 【3/12 15:36】
vTahlvee o spteartuatso irn dopiceant otrh ela vmaplv eli tb uecpa, ubsuet tthhee Reactor core Wcaoterre ldeavmel afgaell sp fruorgtrheesrs easn d PCV damaged, and Hydrogbeuni ledxinpglosion at
damage begins
After short operator closed the valve again because Primary containment vessel hydrogen leaks into
time, steam steam generation from IC stopped. (hydrogen generated) pressure rises reactor building
stopped Difficult to perform venting (R/B)
Fuel exposed and
damaged, and
hydrogen generated Damage progresses
※
IC
Water level falls
Shortage of machinery,
materials(personal
【Tangible measure 】 dosimeters, etc.)
Strengthen low-pressure cooling Contamination spreads
Not able to ascertain
water injection function 【Intangible measure 】
condition of reactor 【Tangible measure 】
Transport of materials
Hydrogen countermeasures
【Intangible measure 】 【Tangible measure 】 and equipment
PCV damage countermeasures
Information sharing Strengthen venting function Strengthen radiation
control framework
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Accident at Fukushima Units 1~3
State of SSCs after the earthquake struck (1F-1)
Attachment - 1
Reactor pressure analysis and visual confirmation were conducted to confirm effects of the earthquake for Unit 1
Reactor pressure analysis
Technical findings for hearing opinion of NISA
Technical findings about Fukushima Daiichi for hearing opinion of NISA reported that if less than 0.3 cm2 crack occurred, it is not
clear RPV pressure difference to check the leakage of coolant. On the other hand, if there is ca, 0.3 cm2 crack, it effects the accident
progression so that amount of 10 ton water leaks from RPV
The RPV pressure analysis was conducted under the
PCV pressure
conditions of occurring 0.3 cm2 crack as to these findings
The safety regulations requires that the coolant leak rate to PCV is within 0.23
m3/h.Following figure shows that the result of 0.23m3/h crack occurs
Earthquake Result of RPV pressure (correspond to 8mm2@vapor condition, 2mm2@liquid condition )
/ SCRAM
IC automatically start up
This analysis show that
analytical value and s]
b
measured value did not a,a 8mm2(vopor condition)
make significant deference. P
g] M
MPa, IsCta rmt uanpu/ astlo p Pressure gauge ure [ 2mm2(liquid condition)
ure [ IC manual stop press
ss V
V pre PC Observed value
Analytical value (vapor dome)
P No leakage condition
R measured value (transient record device)
measured value (record chart)
Reference：JNES Time
The observed value (red line) is under analytical values
(green, blue line)
Time
Reference：JNES
Judging from PCV pressure trend, it is less likely to effect the accident progression
even if some cracks occur.
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Accident at Fukushima Units 1~3
State of SSCs after the earthquake struck (1F-1)
Attachment - 1
Ex. visual confirmation (IC, Unit 1)
There was no definite evidence leading LOCA at outside of PCV result of visual confirmations
Othet visual
confirmation
check points
Unit 5,6 : R/B, T/B
Unit 1,2,3 : T/B
Unit 2 : R/B
Level Unit 1,2,3,4
gauge
IC : outside installations
IC (B) condensate water return pipe line IC entrance vapor pipe line
MO-
1301-2
MO-
1301-10
Note: These valves drown by this figure are in
MO-
1301-1 stand-by state.
原原原
MO- 子子子
1301-4 炉炉炉
V圧圧圧
RP力容力容力容
器器器
MO-
1301-3
2FL
PPLLRR--AA PPLLRR--BB
IC (A) condensate water return pipe line
The result of visual confirmations and seismic response analysis for unit 1,2 and 3 using observed
records shows that SSCs would sustain these requisite functions after the earthquake.
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Accident at Fukushima Units 1~3
IC operating condition and indication of water level gauge (1F-1)
Attachment - 1
The presumed RPVwater level by a MAAP analysis result.
①【3/11 14:46 Earthquake occurs】②【3/11 15:35 Tsunami arrives 】 ③ 【3/11 ~18:18 】 ④ 【3/11 20:00 〜3/12 【3/12 15:36】
in the morning】
Isolation condenser system (IC)
Tsunami caused loss of power The operator open the valve because Water level falls further and core Hydrogen
automatically started up and water for operating valves, and closed the valve status indicator lamp lit up, damage progresses explosion at
level was maintained valves no longer opened. agbaiunt btheec aoupseer astteoarm cl goesende rtahtei ovna lfvreo m Primarpyr ceosnsutarien rmiseenst vessel building
Primary containment vessel IC stopped. Difficult to perform venting
Reactor pressure vessel (RPV)
S h utd o w n
Isolation Tsunami arrival Water Water Damage
condenser level falls level falls progresses
Recognition of those days ② ③ ④
① Tsunami caused became Since the vapor efflux of IC Since preparation of a ICwas completed, the
The cold shutdown
impossible to check stopped, failure of IC is operation which opens IC valve was carried out
procedure of training is
parameters, such as RPV considered and it stops. and started at 21:30.
carried out.
water level.
① ②
MCR indicated value
Earthquake
Tsunami It was recognized as the ability of the reactor
Core damage
5000 L-8（4643mm） presumed core to be cooled by that the water gauge of
m] 4000 NWL（4370mm） 21:19 showed more than TAF, and operation of
m D/D FPand IC.
[ 3000

el
v 2000 L-L（1950mm）
e However, ...
l 1000
ater 0 TAF ③
w It is presumed around 21:00 that reactor
or -1000 L-0（-1405mm） ④ water levels were few, cooling by IC is not
t -2000
c
a carried out, and core damage had already
e -3000
R 3/11 3/11 3/11 3/11 3/11 3/11 3/11 3/11 3/11 3/11 3/11 3/11 3/12 3/12 3/12 advanced.
12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 0:00 1:00 2:00
 As for the reactor water gauge of 21:19, the surface of the water established outside of RPV evaporated by a temperature rise by the core
damage and was not able to measure exact differential pressure.It was thought that this showed the high water level on appearance, and it was
convinced that a reactor core is normal till time (3/11 23:50) for a D/W pressure gauge to restore the persons concerned those days.
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Accident at F福u島ku第sh一im１a 〜U３ni号ts 機1~の3事故
About a Water level gauge
Attachment - 1
The water level in the RPV measures it by the at the water head in the RPV and the difference in
pressure of the adjacent datum level device.
Normal case The state after the point in time when a water level
gauge showed a constant value in the unit 1.(Estimate)
Base level vessel
PCV All the water in D/W
D/W lost it in evaporation by
the core damage.
Accident
Base water
level
Base water level
decreased by Water level
evaporation by the (Calculated value)
Reference
core damage.
water head TAF
TAF
Difference pressure −1853mm
(ΔP) becomes small
BAF
and overestimates
ΔP
water level.
Fluctuate
water head ΔP A water level higher Differential
A water level is measured from pressure than an original pressure
difference (ΔP). Differential gauge
water level is shown.
A high water level is shown, so that pressure
pressure difference is small. gauge
]
m ・When the water of instrumentation piping in
m
[
PCV is lost, if a water level calculates, it will be
el
v
e about TAF-1853 mm.
l
r
e
t
wa ・This value is almost the same as the steady

or value which is directing the water gauge of Unit 1
t
c
a on and after 3/12.
e
R
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