SimplyInfo: Unit 1 Earthquake Radiation Spikes, Meltdown Sequence

see http://www.simplyinfo.org/?p=5855 for complete article

Simplyinfo crowd-sourced analysis is that earthquakes caused Unit 1 to leak even more radiation in spikes, and that Unit 1 had problems requiring shutting of Isolation Condensor within minutes of automatic activation, radiation was released and detected almost immediately when tsunami waves struck, showing major leakage of radiation BEFORE losing diesel geneators, and complete loss of wather within hour of power loss.

Fukushima Unit1 Group Findings

Unit 1 Group Findings

(They believe that earthquakes caused radiation spikes by breaking crust on melted fuel / corium) 

April 23rd, 2012 

Earthquake And Corium Issues:

We found an ongoing trend where significant earthquakes of 6.0 or higher that occurred near Fukushima Daiichi caused significant changes in unit 1. On July 31, 2011 there was a 6.4 earthquake. The radiation readings at Drywell B in unit 1 had been below 300 sV/h until the earthquake. After the earthquake radiation readings jumped to 356 sV/h. A 56 sV/h or greater jump.

Conclusion:

Other changes were noted along with the radiation increases including temperature and pressure changes at various reactors. These did not have the clear constant pattern that the unit 1 drywell radiation did.   The conclusion on the radiation Drywell B spikes at unit 1 are that corium forms a crust as it cools. Our conclusion is something that has not been covered by any known analysis for post core meltdown accidents. Significant earthquakes or major after shocks cause the crust formed over the corium to break open and release radiation which were then sensed by the radiation monitors.

UNIT  1 Started Melting in Only 17 Minutes

Unit 1 Rapid Meltdown Issues:We have looked into the issue surrounding unit 1′s rapid meltdown at length. Unit 1′s core became uncovered (without water) after only 17 minutes where units 2 and 3 took 337 minutes and 315 minutes respectively. What issues went into unit 1′s rapid and unique demise may go back to it’s older design and human intervention that inadvertently made things worse.

• The quake hit at 14:46 on March 11, 2011. Unit 1 successfully went into a seismic SCRAM to put the reactor into emergency shut down.
• NHK reports that at 14:56 the IC (isolation condenser) was manually shut down by workers at unit 1. (10 minutes after scram) 
• At 15:27 the tsunami hits.
• At 15:29 the radiation monitor 1 mile from unit 1 detects high levels of radiation. (only 2 minutes after tsunami hits)
• 15:41 the second diesel generator fails causing complete loss of A/C power.(from flooding)
• 16:36 the IC at unit 1 had boiled dry. (less than one hour after power loss)

At a point within all of these events as all power and cooling were lost, fuel at unit 1 began to be uncovered as water levels dropped. This was when the melt down process began. In less than one hour fuel melt began at unit 1. In less than 2.5 hours fuel would have slumped to the bottom of the reactor. Differences at unit 1 show a rapid melt down that did not happen at units 2 and 3. Reports indicated that diesel generators only lasted 19 minutes post quake at unit 1.


** These are estimates based on known conditions and observed data **

Note:  Initial Condition Assumed at Reactor SCRAM + 10 minutes to Station Blackout
All times are in minutes.
SCRAM = Emergency shut down of a nuclear reactor.
HPCI =  High Pressure Coolant Injection
RCIC = Reactor Core Isolation Cooling
SORV = Safety Operated Relief Valve

5/17/2011                ACCIDENT PROGRESSION IN MINUTES
Event	Case 1	Case2	Case3
	Station Blackout	Station Blackout	Station Blackout
	No HPCI/RCIC	Manual HPCI/RCIC	Normal HPCI/RCIC
	NO SORV	Manual SORV	Normal SORV
Core uncovered	17	337	315
Start core melt	57	396	388
Corium slumps to bottom head	78	453	419
RPV bottom head fails	142	543	515
Corium starts boil off of water @ concrete containment floor	142.5	543.5	515.5
Corium starts melting containment floor	162	544	580
Containment failure and leakage starts	185	596	601
Drywell and Wetwell electric penetrations start to leak at T=204C – 400F
Drywell and Wetwell electric penetrations decompose and blow out of containment at T=260C – 500

Table 1 Accident Progression Timeline