Fukushima Nuclear Accidents Investigation Report

643 Pages·2013·28.19 MB·English

Fukushima Nuclear Accidents
Investigation Report

Attachment
Summary of Fukushima Daiichi Nuclear Power Station
Unit 6
Main gate
Unit 5
Unit 1
Unit 2
Service hall
Unit 3
Unit 4
Site area: Approx. 3,500,000 m2
Start of Output Main
Address Unit Type Status when the earthquake struck
operation contractor
(x 10,000 kW)
Unit 1 March 1971 BWR3 46.0 GE In rated output operation
Unit 2 July 1974 BWR4 78.4 GE/Toshiba
In rated power operation
Okuma
Unit 3 March 1976 BWR4 78.4 Toshiba
Town
All fuel removed, pool gate
Unit 4 October 1978 BWR4 78.4 Hitachi closed (core shroud
replacement work under way) R
Outage e
f
e
Unit 5 April 1978 BWR4 78.4 Toshiba r
Futaba Reactor pressure vessel top e
n
c
Town Unit 6 October 1979 BWR5 110 GE/Toshiba lid closed e

2
-
1
Summary of Fukushima Daini Nuclear Power Station
Unit 4
Unit 3
Unit 2
Unit 1
Site area: Approx. 1,500,000 m2
Start of Output Status when the
Address Unit Type Main contractor
operation (x 10,000 kW) earthquake struck
Unit 1 April 1982 Toshiba
Naraha
Town
Unit 2 February 1984 Hitachi
In rated power
BWR5 110
Unit 3 June 1985 Toshiba operation R
Tomioka
e
f
e
Town Unit 4 August 1987 Hitachi re
n
c
e

2
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2
Shape of Primary Containment Vessel of Fukushima Daiichi and
Fukushima Daini Nuclear Power Stations
Type BWR3 BWR4 BWR5 BWR5
Fukushima Daiichi Fukushima Daiichi Fukushima Daiichi Unit 6 Fukushima Daini
Plant
Unit 1 Unit 2 to 5 Fukushima Daini Unit 1 Unit 2 - 4
Electrical
460,000 kW 784,000 kW 1,100,000kW 1,100,000kW
output
Mark I type Mark I type Mark II type Mark II Advanced
(Flask type) (Flask type) (Cylinder type) (Bell type)
Containment
type
R
e
f
e
r
e
n
c
e

2
-
3

(
Source: NRC website 1
Fukushima Daini Unit 1 Fukushima Daini Unit 3 )
Attachment 2-3 (2)
Design of the Mark I Primary Containment Vessel

1. Difference between Mark I and Mark II primary containment vessel (PCV) capacity
・ In a boiling water reactor (BWR), the pressure suppression type PCV is used,
which is designed to restrain pressure build-up by passing the steam escaping
into the PCV, when a piping rupture occurs through the suppression chamber
(S/C) water pool, where it is condensed and pressure is relieved. There is no
problem here.
・ Both Mark I and Mark II PCVs are the pressure suppression type, and are
designed in such a way that the larger the power output, the larger the PCV
capacity.
・ Taking a look at the capacity-to-output comparison, which is a suitable indicator
in comparing the size, the Mark I and Mark II are very nearly the same, and thus
Mark I is not especially small.
Table: comparison of PCV capacity to reactor output
reactor 1F-1 1F-2~5 1F-6,2F-1 2F-2~4 KK-6/7 (ref)
Mark II
PCV Mark I Mark I Mark II RCCV
Improved
comparison of
approx. approx. approx.
capacity to approx. 4.3 approx. 3.4
4.4 3.1 3.0
output※1,※2
※1 ratio of PCV capacity [m3] to reactor thermal power [MW t]
※2 Reactor thermal power according to Application for Establishing Permit documents.
PCV capacity according to Establishing Permit document attachment No. 8 dry well (D/W)
capacity (including vent pipe) plus suppression chamber empty space capacity.

2. Anti-explosion measures when hydrogen is produced inside the suppression chamber
due to an accident
・ By controlling the oxygen level to within a fixed limited value by enclosing
nitrogen inside the PCV, hydrogen burn-up or explosion inside the PCV is
prevented even if a large volume of hydrogen is produced.
・ A flammability control system (FCS) installed inside the reactor building (R/B)
has a heating recombination design so as to control the level of hydrogen and
oxygen density inside the PCV after an accident occurs.

3. Increased load on the pressure suppression chamber (S/C) when accidents occur
・ When the Mark III PCV was being developed in the United States, necessary
measures were taken (installation of facility to mitigate the load transfer: facility
(quencher) that spews steam out evenly in four directions rather than in only one
direction)) in answer to the problem of the load created when high pressure
steam is transferred to the S/C when piping ruptures occur.
Attachment 2-3 (2)
・ Similar measures based on the measures taken in the US have been
implemented in Japan. In regard to the investigation of load, the Nuclear
Safety Commission (NSC) compiled the guideline entitled “BWR. Mark I type
PCV Pressure-Suppression System Evaluation Guidelines on Added Load
Transfer.” (Similar guidelines have been worked out for the Mark II)

4. Improvement of Mark I PCV efficiency (vent)
・ The Nuclear Regulatory Commission (NRC) of the United States established
that installing a PCV hardened vent on the Mark I PCV reduced the risks of
reactor core damage. Investigation through probabilistic safety assessment
carried out in Japan confirmed the viability of this PCV hardened vent facility as
being effective in preventing reactor core damage and impact mitigation, and the
PCV hardened vent is also installed on the Mark II PCV.
End
Overview of the Tohoku-Chihou-Taiheiyou-Oki Earthquake
Date/Time: Friday, March 11, 2011 at 2:46 p.m.
Location: Offshore Sanriku (latitude 38 degrees, 06.2 minutes, longitude 142 degrees, 51.6 minutes), depth of hypocenter 24 km
Scale : magnitude 9.0
Intensity around Japan : Intensity 7：Miyagi Prefecture: Kurihara City
Intensity 6 (upper) Fukushima Prefecture: Naraha Town,TomiokaTown,Okuma Town, FutabaTown
Intensity 6 (lower) Miyagi Prefecture: Ishinomaki City, Onagawa Town, Ibaraki Prefecture: Tokai-mura
Intensity 5 (lower) Niigata Prefecture: Kariwa-mura
Intensity 4: Aomori Prefecture: Rokkasho-mura, Higashidori-mura, Mutsu City, Oma-machi,
Niigata Prefecture: Kashiwazaki City
Hypocenter
coseismic slip
震源
NPS [m]
原子力発電所
a
Wave source of tsunami tt
Distribution of earthquake intensity Local area of earthquake a
c
(source: TEPCO) h
(source: Earthquake Research m
e
Institute of the University of Tokyo) n
t

3
-
The scale of the tsunami-earthquake was the fourth largest ever observed in the world. 1
Attachment 3-2 (1/3)
Comparison between the seismic observation records and
the design seismic motion at the Fukushima Daiichi Nuclear Power Station

Comparison of the observation records at Fukushima Daiichi NPS from the Tohoku-
Chihou-Taiheiyo-Oki Earthquake and the response spectrum against design basis seismic
ground motion (DBSGM) Ss
Observation records maximum acceleration
Observation response against DBSGM Ss
Maximum acceleration (Gal)
point (R/B base (Gal)
mat) NS EW UD NS EW UD
direction direction direction direction direction direction
Unit 1 460 447 258 487 489 412
Unit 2 348 550 302 441 438 420
Fuku-
Unit 3 322 507 231 449 441 429
shima
Unit 4 281 319 200 447 445 422
Daiichi
Unit 5 311 548 256 452 452 427
Unit 6 298 444 244 445 448 415
Legend: NS: North-South, EW: East-West, UD: Up-Down

Due north ≒ plant north (P.N.)
Magnetic north
Unit6* Unit5 Unit1 Unit2 Unit3 Unit4
Free base / seismic observation
room (north side)
Free base / seismic observation
room (south side)
Seismic observationpoint
*In the case of Unit 6, observations were carried out at
the ground in the vicinity of the building as well.
Locations of Fukushima Daiichi NPS seismic observation points

Figures 1-1 through 1-6 show the acceleration transient wave forms observed
Attachment 3-2 (2/3)
above the base mat of all reactor buildings at Fukushima Daiichi NPS Unit 1
through Unit 6 and Figures 2-1 through 2-6 show the observed spectrum with
the response spectrum calculated by inputting the DBSGM Ss.
Figures 2-1 through 2-6 show that a portion of the observed response spectrum
exceeds the DBSGM Ss response spectrum, but for the most part they are
roughly the same.
(h=0.05)
3000
O bservation record
加速度(Gal)eration (Gals) 1-5500000000 447 ( cceleration (Gals)m加速度加速度(Ｇal) /s2 )12000000 DDDBBBSSSGGGMMM SSSsss ---1 23
el Ac
c
c -1000
A 0 50 100 150 200 250
0
Time (seconds) 0.02 0.05 0.1 0.2 0.5 1 2 5
時間(秒) Period周 ( 期se(秒c)onds)
Figure 1-1 : Acceleration transient wave form (EW direction) at R/B Figure 2-1 : Response spectrum (EW direction) at
base mat of Fukushima Daiichi Unit 1 R/B base mat of Fukushima Daiichi Unit 1

(h=0.05)
3000

加速度(Gal)eration (Gals) 1-5500000000 550 (cceleration (Gals)m加速度(Ｇal) 加速度 /s2 )12000000 ODDDBBBbsSSSeGGGrvMMMa tSSSiosssn ---r1 e23 c ord
el Ac
cc -1000
A 0 50 100 150 200 250
0
Time (seconds) 0.02 0.05 0.1 0.2 0.5 1 2 5
時間(秒) Period周 ( 期se(秒c)onds)
Figure 1-2 : Acceleration transient wave form (EW direction) at R/B Figure 2-2 : Response spectrum (EW direction) at
base mat of Fukushima Daiichi Unit 2 R/B base mat of Fukushima Daiichi Unit 2

(h=0.05)
3000

eration (Gals)加速度(Gal) 1-5500000000 507 (celeration (Gals)cm加速度(Ｇal) 加速度 /s2 )12000000 ODDDBBBbsSSSeGGGrvMMMa tSSSiosssn ---r1 e23 c ord
ccel -1000 Ac
A 0 50 100 150 200 250
0
Time時 (s間e(c秒on)ds) 0.02 0.05 0P.1erio0d.2周 ( s 期e(c秒o0).n5ds) 1 2 5

Figure 1-3 : Acceleration transient wave form (EW direction) Figure 2-3 : Response spectrum (EW direction) at R/B

at R/B base mat of Fukushima Daiichi Unit 3 base mat of Fukushima Daiichi Unit 3

*The table illustrates examples of the larger direction on the horizontal plane (Fukushima Daiichi : EW direction).
Attachment 3-2 (3/3)
(h=0.05)
3000

加速度(Gal)eration (Gals) 1-5500000000 319 (celeration (Gals)cm加速度(Ｇal) 加速度 /s2 )12000000 ODDDBBBbsSSSeGGGrvMMMa tSSSiosssn ---r1 e23 c ord
el Ac
cc -1000
A 0 50 100 150 200 250
0
Time時 (s間e(c秒on)ds) 0.02 0.05 0.P1erio0.d2周 ( s期e(秒co0).5nds) 1 2 5
Figure 1-4: Acceleration transient wave form (EW direction)
Figure 2-4: Response spectrum (EW direction) at R/B base
at R/B base mat of Fukushima Daiichi Unit 4
mat of Fukushima Daiichi Unit 4

(h=0.05)
3000

eration (Gals)加速度(Gal) 1-5500000000 548 (cceleration (Gals)m加速度(Ｇal) 加速度 /s2 )12000000 ODDDBBBbsSSSeGGGrvMMMa tSSSiosssn ---r1 e23 c ord
ccel -1000 Ac
A 0 50 100 150 200 250
Time (seconds) 00.02 0.05 0.1 0.2 0.5 1 2 5
Figure 1-5: Acceleration tr時an間s(i秒en)t wave form (EW direction) Perio周d (期s(e秒c)onds)
Figure 2-5: Response spectrum (EW direction) at R/B base
at R/B base mat of Fukushima Daiichi Unit 5
mat of Fukushima Daiichi Unit 5

Gals) 1000 444 O観bs測erv記atio録n ①rec ord(1) OODBbbssSeeGrrvvMaa ttSiioosnn -rr1ee ccoorrdd ((12))
eleration (加速度(Gal) -5500000 3000 DDBBSSGGMM SSss --23 (h=0.05)
c
c
A -1000 s)
0 50 100 150 200 250 al
eleration (Gals)加速度（Gal） 1-5500000000 時間(秒43)1 O観bs測erv記atio録n r②eco rd (2) (cAcceleration (Gm加速度加速度(Ｇal) /s2 )12000000
c
c
A -1000 0
0 50 100 150 200 250 0.02 0.05 0.1 0.2 0.5 1 2 5
Time (seconds) Period周 ( 期se(秒c)onds)
時間（秒）
Figure 1-6: Acceleration transient wave form (EW direction) at R/B Figure 2-6: Response spectrum (EW direction) at R/B
base mat of Fukushima Daiichi Unit 6 base mat of Fukushima Daiichi Unit 6

* The table illustrates examples of the larger direction on the horizontal plane (Fukushima Daiichi : EW
direction).