april 20th, 2011 – jnes assessment of spent fuel pool at fukushima daiichi unit 4 - pages from...

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From:Sent:

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Attachments:

RST01 Hoc

Wednesday, April 20, 2011 2:34 PM

(b)(6)

Nichols, Paul A (GE Power Water)

FW: Excitement group meeting

110419-JNES-1F4SFP.pdf

Here is another copy of the Assessment of the Spent Fuel Pool of Fukushima Daiichi Unit 4

Ibelieve this was sent out yesterday. Feel free to delete it if you already have a copy.

Mike

Mike Brown

Reactor Safety Team

---- Original Message-----

From: Garchow, Steve

Sent: Wednesday, April 20, 2011 12:45 AM

To: RST01 Hoc

Subject: FW: Excitement group meeting



Subject: Excitement group meeting

Dear Garchow

Thank you for your support for our challenges of Fukushima events.

Attached please find the electric file for 1F4 SFP analysis conducted by JNES.

Best regards,

Toshi

Toshiyuki OSHIMA

NISA, Japan



t JN SJapan /ir'J~ulear -nergy Saet rgnzto

OUFFIC lL

.- •OLf

Assessment of the Spent Fuel Pool

of Fukushima Daiichi Unit 4

April 19, 201.1 Excite Meeting



j N S Japa Nucea Enrg Saet Organizato

Contents

1. Possible scenarios

2. Assessment of scenarios

3. Conclusion



JN S IJpa Nucea Enegy Saet Organiztio

Measured data and assessment approach

Aerial photographs

- Water observed on March 15

Mass of feed water

- From pump trucks to SFP

Water level

- Skimmer surge tank level

- NWL - 5 m (sipping on April 12)

Temperature

- Existent thermometer: near the surface of NW L

- 900C (sipping on April 12)

Asesmn of caus

of explosio

/Asssmn of mass

an hea balance

Radioactive dose

- 87mSv/h (sipping on April 12)

- 134Cs: 88Bq/cm 3, 137 Cs: 93Bq/cm 3, 1311: 200Bq/cm 3

Asssmn of dose

ons qun



S.JNES Jaa ulerEeg Safet Organizato

Chronology

Date Description Injected mass Water type

3/11 15:42 The earthquake occurredLoss of all alternating current power

Loss of ultimate heat sink

3/14 04:08 (2.52d) SFP temperature I 84 0C3/15 06:14 (3.61d) Huge crash bang

R/B was broken

3/15 06:50 583.7pSv/h at main gate

3/16 05:45 (4.59d) Fire at R/B

3/16 14:00 (4.93d) Taking photos of water at SFP from helicopter

3/20 08:21-09:40 Water truck of SDF ca. 90 ton Fresh water



3/21 06:38-08:41 Water truck of TEPCO ca. 2.2 ton Fresh water

3/22 17:17-20:32 Concrete pump truck (spray) ca. 150 ton Sea water


3/24 2:30 SFP temperature : 100°C



3/25 06:05-10:20 Fire engine to FPC piping ca. 21 ton Sea water


3/30 14:04-18:33 Concrete pump truck (spray) ca. 140 ton Fresh water



4/4 09:30 Water level of FPC skimmer surge-tank: 5000mm



4/9 17:07-19-24 Concrete pump truck (spray) ca. 90 ton Fresh water

4/12 Sipping at 1F4/SFP




cjg~NESI Japan~ -uc eanrg aft Orgniato -

Logic tree - pyramid structure -



S N S J a N u l a E n r g S a f e t O r a i z t o I

Possible scenarios

" Scenario 1: Crack

- SFP was cracked due to the earthquake and resulted in leakage

Scenario 2: Flashing

- Depressurized boiling occurred and half of water spilled over

Scenario 3: Hydrogen from 1F3

- Hydrogen came from Unit 3 to Unit 4 via piping or duct

Scenario 4: Soot from MG-set lubricant

- Lubricant of MG-set caused explosion



c ýJNESIg Jaa Nula Enrg Saft raization

Assessment of mass and heat balance

Mass and heat balance calculation was conducted- Decay heat: 1.88MW (TEPCO information)

- Initial water level: 10.8m (NWL - 1.0m)

- TAF: 4.5m

- Level of H2 explosion: 4.Om

- Initial SFP temperature: 300C

- Feed water temperature: 150C

- Leakage rate: in proportion to square root of water level difference

- Plant model: I&



JNES JapaNulea Energy Saft raization

Scenario 1: Crack (1/2)

Crack at bottom, with broken pool gate

Assuming fuel exposure and hydrogen generation by fuel

cladding oxidation before March 15, pool would be empty after a

month

j0~I-o0

0

00~

0

100

90

80

70

60

50

40

30

20

10

0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

time (day)

Water level (m)

0 1 2 3 4 5 6 7 8 9 1 1112131415161718192 2122232425

time (day)

Temperature (°C)



JN S Japan Nucea Enrg Saet Oraizto

Scenario 1: Crack (2/2)

Crack at mid-level, with broken pool gate

- Even assuming fuel exposure before March 15, pool could

possibly keep the water level

- However, if hydrogen was generated from fuel cladding at SFP

of Unit 4, cesium dose would be high and iodine low compared

with measured data12

SFP

11 WELL -

TAF10 H2 -

9

8

7

_ 6

.~5

4

3

2

00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 192021 2223 24 25

time (day)

Water level (m)



•JN S Japa Nula Eeg Saft Organizatio

Scenario 2: Flashing (1/4)

* Static head of water continued to decrease withwater temperature increasing

Flashing started immediately when watertemperature reached the saturation temperature

Atmospheric pressure

Head

Spilled water

V

Flashing mechanism

Temperature increasing

IWater volume increasing

Liquid level increasing (overflow)

High temperaturewater>1000cPIPE6

Fuel

Bundle

Head decreasing

Saturation temperaturedecreasing

Flashing

RELAP5/MOD3.3 model 1F-4 spent fuel pool Overflow



SXJN S I Japa -uceanrg aety Oraizto


Flashing phenomenon caused swelling of the two-phasemixture level and accelerated the overflow

As a result, the pool liquid level dropped largely for very short

time of about 6 seconds

More than half water of the pool overflowed during the flashing

phenomena continued

12

10

8

6

4

---- I

Water level (m)

:-6s

---------------------------------------------------------

The water

level dropped

quickly near

the top of the

bundles2

0 I

20 4 6

time (day)

8 10



jg>jNES JapNan Nucea Enrg Saft Organization


" Flashing phenomenon accelerated the overflow of the pool water, and

thereby shortened the initiation time to the fuel temperature increasing

* The amount of the overflow due to flashing was not strongly

influenced by decay heat

Decay heat at March 11th 12 Decay heat at April 11thI Z

10

8

6

4

2

0

10

8

6

4

2

0

-Waterevel i

0

12

1

8

6

4

2

0

2 4 6 8

time (day)

Rod surface temperature__°C)

------------------ - -- - - - - - - - - - - - - - -

10

- - - - - - -

2 4 6 8 10

1200

1000

800

600

400

200

0

time (day)

Rod surface temperature . 0 )

I I

0 2 8 10 6

time (day)0 2 4 6

time (day)

8 10



c• N S Japa Nucea Enegy Saet Organzatio


* Flashing, with broken pool gate, no crack- Consistent with mass balance

- Not consistent with dose on April 12

j0)

0

Q.

100

90

80

70

60

50

40

30

20

10

00 1 2 3 4 5 6 7 8 9 1 1112131415161718192 2122232425

time (day)

Water level (m)

0 1 2 3 4 5 6 7 8 9 1 1112131415161718192 2122232425

time (day)

Temperature (°C)



cýJNESI6 Jaa Nula Enrg aft Organiatio

Scenario 3: Hydrogen from 1F3 (1/3)

Possibility of H2 transportvia piping or duct

- This picture shows that the --•7

space between Unit 3 and Unit -'

4 was also exploded

- This indicates the possibility of

spreading of hydrogen

generated in the core of Unit 3

- In addition, result of sampling

water, i.e. dose of cesium and ,

iodine, seems not to comefrom fuel at 1F4/SFP .............. ,..



V>JNES Japa Nucea Enrg Saet O rganzatio

Scenario 3: Hydrogen from 1F3 (2/3)

1H came from Unit 3, with intact pool gate, no crack

- Ifthis hypothesis were correct, the figure below shows the

possibility that rapture of fuel cladding might occur quite recently

- Another possibility is that sea water injected during March 22 to

27 might have included radioactive materials

Mj

0

E

20

15

10

5

0

-5

-10

-15

-20

mdotp

mdot leak

mdotvap -

mdot wp -

mdot ject

L t

. . . . . . . . . . . . .

0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223242526272829303132333435

time (day)

Water level (m)

0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223242526272829303132333435

time (day)

Mass flow rate (kg/s)



c• N S Jaa Nua Enrg Saet Oraizto

Scenario 4: MG-set lubricant

State of broken panel at 1F4

2

1=.X-

:1 ~

- ~ .~

=;~-~~i. - -



j JN S Japa Nucea -nergSaet Oraization

Scenario 4: MG-set lubricant

North

Distribution of broken panelat 1F4 shows that the floorthe MG-set located in isbroken widely

Plenty of lubricant oil is

included in the MG-set room

The oil mist generated by the

temperature increase and thecease of circulation fan

operation might be thesource of explosion

Li

L2

L3

L4

L5

L6 A B C D E

South

E D C B A

East

6 5 4 3 2

West

11 2 3 4 5 6

* L1-L6: Floor No. See

* 1-6: Panel No. (North - South: See)

0 A-E: Panel No. (East - West)

Fig.1 Distribution of Broken Panels at 1F4



JcwJNESI Japan Nuclear Energy. SaeyOgnz to I

Conclusion

Several assessments based on possible scenarioshave been made

- Assumption will be modified as new information would be obtained

At present,cause of explosion is not clear

- A hypothesis that huge oxidation of cladding at SFP was not

occurred is conceivable

- Still, there is a possibility that fuel rod rapture might occur at 1F4

- Sea water injection as well as 1F2 explosion could affect the dose

of the 1F4/SFP

Important thing is not to expose fuel to atmosphere

- Belief in SFP being full based on skimmer surge tank level was not

very good

april 20th, 2011 – jnes assessment of spent fuel pool at fukushima daiichi unit 4 - pages from...

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