RE: Errors in NRC TMI Factsheet

["Dukelow, James S Jr" <jim.dukelow@PNL.GOV>]

I tried to send this message about 12 hours ago, but one of our managers had mailbombed by mailbox with a 23 Mbyte email message (!!!) and the system admin responded by freezing my mailbox until I got back under the limit.



Norm Cohen, Jim Dukelow, and Doug Aitken wrote:

-----Original Message-----

From:	Doug Aitken [mailto:daitken@sugar-land.oilfield.slb.com]

Sent:	Tue 3/9/2004 8:24 AM

To:	Dukelow, James S Jr; Norm Cohen; radsafe@list.vanderbilt.edu

Cc:	

Subject:	RE: Errors in NRC TMI Factsheet

Norm Cohen Quoted;

"It was only by luck that the reactor walls were not breached. The industry

conjectured that voids in the coolant prevented molten fuel from burning

through the reactor walls. It is not known if these voids will form to

prevent a total meltdown in future accidents. "



In Reply, Dukelow, James S Jr wrote:

<<It was actually not luck, but a previously unanalyzed aspect of heat 

transfer during the accident.



   <snip long-winded discussion of corium behavior>



IMHO, The difference between "Luck" and "a previously unanalyzed aspect of 

heat transfer during the accident" is somewhat slim!



While the "after-the-fact" analysis of what happened shows a fortuitous 

combination of circumstances prevented a major disaster, there is no way 

that the professional community should clad this event in an aura of 

"science" (or obfuscation?). This is the sort of thing that can alienate 

the layman!



So in this instance, I am afraid that the honest answer would be "Yes, we 

got lucky. But we understand what happened and can incorporate this into 

future design to improve overall safety."



<Just a comment from a non-professional in the nuclear field, but a fair 

experience in safety management>

Doug

Doug Aitken		Schlumberger Drilling and Measurements QHSE 

Advisor

Phone (Sugarland):   	281 285-8009

Phone (Home office): 	713 797-0919	

Phone (Cell): 		713 562-8585

Principal E-mail: jdaitken@earthlink.net

Schlumberger E-mail: daitken@sugar-land.oilfield.slb.com

Mail: 	300 Schlumberger Drive MD2, Room 111

	Sugar Land, TX 77478



==================



Doug Aitken makes a good point.  We certainly shouldn't rely on unexpected magical features of the real world to keep us safe in situations where our safety analysis suggests we are not safe.



There is another feature of the situation that I did not comment on.  Since the early years of reactor licensing and regulatory safety analyses, the Nuclear Regulatory Commission has prescribed how safety analyses were to be performed -- what kinds of accidents were to be considered, what reliability to assume for engineered safety features and what kinds of real-world mitigating features the analyst could credit.



Sometimes, these prescriptions went astray, as with the focus on instantaneous, and physically unrealistic, breaks in large coolant pipes.  The first probabilistic risk assessments suggested and most nuclear safety analysts now believe that other types of accidents -- small breaks (as at TMI) and full station blackout accidents -- are responsible for more of the risk of operation of nuclear reactors.



On the other hand, the NRC imposed some conservatisms on the analysis that seem to have resulted in serious over-estimates of the risk in certain areas.  In the TMI accident, almost all of the radio-iodine released from the core ended up chemically bound in the reactor coolant water in the bottom of containment, with the end result that of a million and a half curies of radio-iodine released (if memory serves), only 15 curies were released to the environment.  This is a phenomenon that was predicted, but which the NRC did not let analysts credit.



I am unaware if anyone had predicted before the TMI accident the sort of mitigating heat transfer through the vessel to water in the bottom of contaiment that I described, although I should be able to check that once I find the relevant files in my well-distributed archives.



Best regards.



Jim Dukelow

Pacific Northwest National Laboratory

Richland, WA

jim.dukelow@pnl.gov



These comments are mine and have not been reviewed and/or approved by my management or by the U.S. Department of Energy.







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