April 28th, 2011 – Mathcad analysis of Reactor 1 Lower Head Integrity

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From: Salay, Michael
Sent: Thursday, April 28, 2011 3:02 PM
To: Gauntt, Randall 0
Cc: Lee, Richard; Esmaili, Hossein; Marksberry, Don
Subject: integrity of U1 lower head

Randy,

We need some clarification on your Mathcad analysis of the U1 lower head integrity:

What we think we were hearing on the consortium call for the past few days was that, based on the analysis, vessel integrity would be maintained even if water injection was lost. This seemed to imply that containment flooding was not needed to maintain vessel integrity.

What we interpret from your analysis is that vessel integrity would be maintained even if water injection was lost if containment was flooded and skirt wall is cooled. This indicates that, based on the analysis, containment flooding would still be required to maintain vessel integrity.

We realize that this assumes that a high vessel-to-containment pressure differential does not develop.

Would you please let us know which was intended?

Thank you,
-Mike


From: M.T. Leonard [mailto:mtladycoda.coml
Sent: Monday, April 25, 2011 2:56 PM
To: Randy Gauntt (SNL); Jeff LaChance ([email protected])
Cc: Goldmann, Andrew S (asgoldmnsandia.gov)
Subject: Status of Fukushima calculations

Randy, et al.,

Attached is a summary of the current status of the three Fukushima calculations. Problems arose over the weekend in the calculations for Units 1 and 3, which have been at least partially addressed. In the 1F1 calculation, creep rupture of the main steam line occurred which permanently depressurized the RPV when debris relocated into the lower head.

There is no evidence this occurred and the model has been de-activated and the calculation restarted to re-run through this period of time. In the 1F3 calculation, seawater injection terminated before level recovery could be completed because the control volume used as the suction source went dry. This was corrected and the calculation was restarted at 42 hrs, which unfortunately is the slowest time frame for the calculation.

I will continue to babysit these calculations to completion, but there are at least two areas of major modeling improvements we should explore before embarking on any further work:

(1) Containment pressure response in Unit 1: A test calculation should be developed to examine the containment pressure response to SRV discharge to the containment atmosphere with no (or minimal) condensation in the pool. This would involve several model changes:

a. SRV discharge directly into the drywell atmosphere (J. Kelly seems rather insistent that none of the 1F1 SRVs discharge through tailpipes into the torus.)
b. Rupture of the torus ring header (or stuck-open WW-DW vacuum breaker(s)). This would prevent steam flow from the drywell entering the torus downcomers and reduce steam suppression to only the surface of the pool.
c. Stratify the control volume model for the torus to separate a thin layer of water on the surface of the pool from the bulk of the pool volume. This would represent poor thermal mixing in the pool and maximize the containment pressure response.

(2) The steam turbine models for RCIC and HPCI should be re-constructed to more accurately represent the steam flow through the turbines when the systems are throttled. This might improve the RPV pressure reponse while the systems operate.

Mark


From: M.T. Leonard rmailto:mtlbdycoda.com]
Sent: Monday, April 25, 2011 5:31 PM
To: Gauntt, Randall 0; Lachance, Jeffrey Lynn
Cc: Goldmann, Andrew S
Subject: RE: Status of Fukushima calculations

Randy et al.,

PLEASE DISCARD the earlier summary of the MELCOR calcs. The 1F1 calculation was so corrupted by the inadvertent MSL creep rupture that it should be ignored. ATTACHED is an updated summary of results, which corrects the 1F1 response to the debris relocation into the lower head. The creep rupture model was deactivated and the subsequent damage progression has been corrected.

Sorry for distributed the earlier flawed results.

Mark


From: Goldmann, Andrew S Fmailto:[email protected]]
Sent: Thursday, April 28, 2011 12:08 PM
To: Lee, Richard
Cc: Esmaili, Hossein
Subject: FW: Status of Fukushima calculations

Richard and Hossein,

Attached are the latest results I’ve received. The short email chain might also be useful.

Andrew


From: Lee, Richard
Sent: Thursday, April 28, 2011 12:17 PM
To: Salay, Michael; Marksberry, Don
Subject: FW: Status of Fukushima calculations

I spoke to Randy. The conclusion is not the same that I heard from RST this past two days. Randy is on his way to work.

Perhaps, we can chat with him later today.


From: Salay, Michael
Sent: Thursday, April 28, 2011 2:37 PM
To: Lee, Richard
Cc: Marksberry, Don; Esmaili, Hossein
Subject: RE: Status of Fukushima calculations

We notified the RST that the conclusion was not that the U1 lower head would not fail in the event of loss of cooling. I told them we would provide more detailed clarification via email.

-Mike


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