Science and Technology of Nuclear Installations / 2012 / Article / Tab 2

Review Article

The Fukushima Event: The Outline and the Technological Background

Table 2

(a) Cornerstone events during Fukushima accident, Reactor Core, Vessel and Containment, Units 1 to 3. (b) Cornerstone events during Fukushima accident, Spent Fuel Pool in Units 1 to 4.
(a)

No.EventUnit 1Unit 2Unit 3Notes

1Earthquake hits the NPPtime “0” 14.46 March 11, 2011.
2Reactor scramWithin a few seconds after the time Stop of fission reaction. RP trip. Possible LOCA. Isolation of RPV and of CO.
3SBO eventSame as aboveDBA conditions (expected).
4Tsunami hits the NPP55 minutesPresumed failure of all DG.
5SBO becomes LOOP(1–N) hours, where “N” can be between a few and a few dozen.Following “presumed” attempts to restart DG. SA starts. Mitigation measures needed.
6Venting to the stack directly from D/W of CO24 hrs.**, **High pressure in RPV****, **High pressure in RPV***To protect containment.*mitigation measures started.**RCIC started.***most of the time.
7Explosion (I) of RB25 hrs.15.36 March 12. Possible H2 explosion.
8Venting to the stack directly from CO.66 hrs.*11.36 March 12. RCIC lost, HPCI initiated at 12.35 and lost at 02.42 on March 13. 09.20 March 13. CO venting
9Explosion (II) of RB68 hrs.11.01 March 14. H2 flame.
10Venting to CO from RPV.80 hrs.13.25 March 14 RCIC lost detected. 16.34 SRV1 opened, depressurization CO from RPV.
11Explosion (III) of CO86 hrs.06.10 March 15. PSP damage.
12Electricity restored in the Control Room250–350 hrs.*March 22–26 period. *CO venting to the stack for Unit 1.
13Stable conditions reached for core cooling~300 hrs.March 25–26 period. Continued water injection into the vessel.
14End of CO leakage620 hrs.April 6.Unit 2. Breakage not repaired yet.
15Core statusDamaged*End-of-the-Accident. *(20 to 80) % core destroyed. **continued steam release. ***less in the case of Unit 2.
16Containment status **UndamagedRepaired **Undamaged
17Reactor Building statusDamaged***

(b)

No.EventUnits 1 to 3Unit 4Notes

1Earthquake hits the NPPtime “0”14.46 March 11, 2011.
2Occurrence of LOOP “N” hrs.See Table 2(a). Mitigation measures.
3Fire and Explosion (IV) occurred in RB89 hrs.09.38 March 15. H2 production and radioactivity to environment. SA starts.
4Injection of water in the SFP * 200 hrs. *Started March 31st, 20th, and 17th, for Units 1, 2, and 3, respectively. Various attempts after this time.
5Electricity restored in the Control Room * ~ 430 hrs.March 29. *see Table 2(a). Connected with stable cooling conditions in SFP.
6SFP statusCooling recovered with damaged fuel*End-of-the-Accident. *presumed: majority of fuel bundles affected. **see Table 2(a).
7Reactor Building status ** Damaged

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