March 18th 2011 – It might be good to know the effects of salt deposition on cooling of BWR fuel assemblies

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From: “Per F. Peterson” [[email protected]]
Sent: 03/18/2011 09:22 AM MST
To: “Lyons, Peter” ; “Kelly, John E (NE)”

Cc: SCHU ; “Adams, Ian” ; “Aoki, Steven”
; Bob Budnitz ; Brian Sheron
; “DAgostino, Thomas” ; Dick Garwin
; Dick Garwin ; John Grossenbacher; “Hurlbut, Brandon”
; John Holdren ; “Koonin, Steven”
; Harold McFarlane; “Owens, Missy” ;
Per Peterson ; Phillip Finck; “Poneman, Daniel”
; Ronaldo Szilard; Steve Fetter
Subject: Effects of salt deposition on cooling of BWR fuel assemblies

Pete and John,

It could be helpful to have someone at Sandia address the question of the impact of salt deposition on the coolability of BWR fuel assemblies by air and steam after they are uncovered by pool boil off or leakage, and get their response out to the group. A quick expert opinion from someone who has done these calculations and is familiar with the available experimental data could be helpful in reducing our uncertainty about the risks posed by salt in the Unit 3 pool.

My intuition is that the heat generation rates for fuel that is over one year past removal from the core are much lower than for freshly discharged fuel, which is the usual focus for analysis experiments.

Because all of the fuel in the Unit 3 pool is old, it is possible that air cooling of the outside of the shrouds around the assemblies may be able to prevent heating of pins in the center of the assembly to the temperature needed to initiate zirconium oxidation. If so, then salt is probably less of a problem because the flow area between the assembly and the rack, for low density racking, is pretty large, so it is more difficult to generate flow
blockage with salt.

Some expert judgement on whether this could be the case could be very helpful. This said, I think that we can buy significant risk reduction if we can expedite the transition to use of fresh water for spray cooling of the pool in Unit 3, where there is significant evidence that the pool may have a leak. Bringing in ship-based desalination capability thus merits serious consideration.


Per F. Peterson
Professor and Chair
Department of Nuclear Engineering
University of California
4153 Etcheverry Hall
Berkeley, California 94720-1730
[email protected]
Office: (510) 643-7749 Fax: (510) 643-9685

From: Lee, Richard [mailto: Richard. [email protected]]
Sent: Friday, March 18, 2011 2:02 PM
To: Powers, Dana A
Dear Dana:
More stuff.
TO: Distribution
FROM: Bob Budnitz, LBNL

I was worried in yesterday’s meeting, and remain worried, about the effect on core cooling of the salt in the reactor vessel(s). Let us suppose that some of the upper fuel in a given vessel is damaged, has melted, has slumped, has partially oxidized, or some combination, but the remaining lower fuel is still roughly intact in its correct geometrical configuration, namely fuel assemblies. (This assumption of partial core melting but partial core still intact is probably a correct description for all 3 of the damaged cores, Units 1, 2, and 3.) It is a major objective that this lower fuel not melt and slump! And I am worried that dense, briny, salt water down there could impede heat transfer, possibly gum up the channels, and interfere with what we call the “coolable geometry” that keeps a core assembly intact. I think that the chemistry of the brine is not necessarily that of NaC1, although it is mostly NaCl, but even minor other constituents in sea water could be a problem with coating the fuel cladding surfaces, etc.

In my view, DOE and NRC together ought to be able to identify the experts on fuel behavior and water chemistry who might know what the issues are. I could suggest starting with DON OLANDER, UC-Berkeley professor of nuclear engineering emeritus. Per Peterson is his colleague. Don at home in Berkeley is at 510- 526-2418. I know of no more knowledgeable fuels person in the US, frankly. But DOE at INL has some really top people too! Ditto elsewhere, like at Argonne and Oak Ridge and Sandia.

I am also worried a lot about the coolability of whatever fuel has slumped down to the bottom of the vessel. Cooling it through its upper surface, or cooling it as it contacts the lower metal vessel, is another major objective, because lower head vessel integrity is vital. (The BWRs also have a problem of all those control-rodrive penetrations through the lower head which are locations of weakness. These were studied 3 decades ago, after TMI, in the NRC and IDCOR-industry programs of that time.) I’d ask Bob Henry or Hans Fauske of Fauske and Associates on that melted-core-coolability issue — the best we have on that subject, 630-323-8750. Or Dana Powers at Sandia, a member of the NRC’s ACRS.

Bob Budnitz

On 3/18/2011 11:15 AM, Per F. Peterson wrote:

Also, if the pool is leaking, switching to fresh water spray can flush away any salt that has accumulated.

This is pretty urgent, in my assessment. Do any of the Navy ships have sufficient desalination capacity to support the Unit 3 and 4 pool spray effort? They will get contaminated, but this is sufficiently urgent that this could be a warranted impact. Alternatively any commercial ships with desalination capacity.

I would think that this warrants prompt action. Salt deposition is much more problematic for disable passive
cooling by air than it is for water, so much less salt deposition is needed to cause problems.

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