ML20003B816
| ML20003B816 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 02/09/1981 |
| From: | Berman M SANDIA NATIONAL LABORATORIES |
| To: | Murley T, Ross D Office of Nuclear Reactor Regulation, NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| References | |
| NUDOCS 8102250620 | |
| Download: ML20003B816 (5) | |
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Sandia National Laboratories mie. February 9, 1981 Atouquorcuo. No. us..,co en as to: Thomas E. Jiurley and Denwood F. D as United States Nuclear Regulatory Cnmmission O 44Au Gw from: ' Marshall Berman, 4441 sag a Deliberate Ignition in the Ice Condenser Upper Plenum Region of Sequoyah In reference 1, Sandia recommanded that the igniters located in the upper plenum of the ice condensers (IC) be removed for the Sequoyah Interim Distributed Ignition System (IDIS).
The justification for this suggestion was based on the following reasoning:
We felt that deliberate ignition in the lower com-partment (LC) was desirable, and that serious threats to
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containment would most likely arise from situations where LC ignition was prevented.
Lower compartment combustion would not occur if the LC was steam inerted or oxygen deprived.
Small break and large break calculations with the liARCH code shcwed very large and potentially inerting quantities of steam released at times close to the times of hydrogen release (PJ gs. IS, 20, 23, and 25 in Ref. 1).
LC inerting was, in fact, calculated to occur when the fans were inoperative.
Since the IDIS system is intended to burn lean hydrogen mixtures, and steam inerting in the II would produce the richest possible hydrogen mixture at the ice condenser outlets, we recommended that the igniters there be moved higher up in the upper compartment.
This veuld result in the burning of more dilute mixtures and would lessen the possibility of inadvertent local detonations occarring in the ice condanser upper plenum region.
Sandia has continued its investigation of hydrogen mitigation systems since the release of the Sequoyah draft (Ref. 1).
Three additional factors concerning igniter placement have been identified which tend to reinforce our earlier conclusions.
These include a re-examination of the assumptions and calculations reported in 'Ehe first Sandia Drafts, the " anomalous" steam inerting experiments performed by Lawrence Livermore Laboratory, and new detonation calculations with the Sandia CSQ computer code.
8 APPENDLX 0
1
.1 T. E. Murley & D.
P.
Ross 2.
1 February 9, 1981 Sequoyah, we modified our report to reflect PSAR dataBecause i
This meant that 2250 lbs of hydrogen,100% metal-water reaction would produce the draft.
ccmpared to 1950 lbs reported in hydrogen concentration for a given fraction of metal-This change water reaction.
the MARCH calculational results with more care than wasSandia a possible for the draft report.
Anomalous calculational
.. behavior has been observed; in particular, a numerical oscillation of cladding temperature from cycle to cycle has been noted. (an order of magnitude)
Also, some of the MARCH input assLT.ptions do not agree with the plant status as we know it.
For example, UHI accumulator injection appears to have been prevented in some runs, would be expected to occur under the prevailing pressure although it conditions.
Whether these problems would result or less conservatism in the results is not known. in more is known, however, is What Given that an abundance of steam is a necessary conditionthat the re for zirconium oxidation and hydrogen production, difficult to imagine any accident it is scenario in which hydrogen prcduction and release would not be accompanied by large quantities of steam.
This result is independent of MARCH calculations.
Since MARCH, however, also predicts large quantities of steam for much of the S,D and AB calculations, steam inarting of the lower compartment must be considered a possible, if not likely, occurrence.
Sandia also modified and improved its prediction of-l adiabatic, isochoric deflagration pressures.
These c resulted in the predictions of higher burn pressures.hanges has assum NRC pressure.gd that 45 psig would be a conservative " failure" Considering that burns in the Sequoyah upper l
compartment can approach adiabatic, isochoric conditions, it is prudent to keep those concentrations at or below St.
Lawrence Livermore Laboratories performed some combustion experiments for NRR.2 Two tests at high steam fractions led to anomalous (i.e., unexplained) results.
In one, an initial concentration of 12% H2 and 534 steam was not ignited by a continuously activated glow plug as the steam condensed.
perceptible ignition occurred even as low as No 231 steam frac-tion.
A second test was conducted where the glow plug was activated periodically at steam fractions from 50% down to 301.
No burns were evidenced at any time, even when the w
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i T. E. Murley & D. F. Ross 3.
February 9, 1981 fan was switched on before the final sampin.
plausible (although unsubstantiated)
We have a results based on our studies of fogs.gxplanation for these If a fog is composed of very fine droplets, it may vaporize within the flame front (about 1 mm wide and quench the flame.
Such o " cone.ansation fog" appears) to have existed in the LLL tank.
i Note that the MARCH S D calculations mimic this 2
test behavior in large scales i.e., an initially high steam fraction (almost 701 minutesto20% steam {. decreasing over a period of about 90 If a fog is generated in this procana, then lower campartment inorting becomes even mor i
likely.
(Sandia has e
ocheme in conjunction with deliberate ignition. recommended fogging as a mitigation cizes, however, would have to be large enough to pass Droplet through the flama front without quenching, but not so large that_they would not vaporize within the necessary time interval). _
since the ice condenser upper plenum region contains in the plant,the highest concentration of hydrogen to be found anywhere detonation occurring which might damage containment.we postulated the calculation was performed in which a 20% concentration of A CSQ hydrogen was This ring ignition is conservativecircumferential1y detonated in the u region.
in this region. unrealistic since TVA has placed a large num,ber of ignitersbut not wholly
- However, code, the artificial viscosity in the all combine to produce detonation pressures lower than theth oteady state Chapman-Jougust values.
FurtherdBrm, the rest of the upper compartment was assumed-to contain only air.
All of these latter assumptions tend to reduce the con-corvatism introduced by the cylindrical symmetry of the 1
ignition source.
toinment dome exceeded the conservative failure criterionCalculate i
for impulsive loading reported in Refs.
4 and 5.
Further cniculations are planned to investigate the effects of cymmetric versus point-source ignition.
All of our research to date indicates that upper com-pcrtment combustion of hydrogen mixtures above 84 l
plenum is possible and may be dangerous.bo avoided and that a de should the IC UP increase The igniters in without providing any significant safety benefit.the possibility of a local deton placed higher in the upper compartment should be able to Igniters burn lean mixtures below St.
The TVA and LLL exp hnve demonstrated this capability in small scale.griments if the igniters cannot burn such mixtures,
- Indeed,
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premise of deliberate ignition is questionable.then the basic be installed in the upper compartment for the interima more app Perhaps cystam.
inadvertent ignition i.n.The UC is a large, nearly empty region, and
- t. his.. r. egion may be, erp n1$En, 9; 6;g S
-. =,
T. E. Murley & D. F. Ross 4.
February 9, 1981 In the absence of hard data, several qualitative argu-ments can be made.
an UC deflagration occurs.The sprays may or may not be on when lean mixture deflagration to propagate back downSpray-induced turb cause a into the IC UP.
Although that is an outside possibility, we believe that the enhanced turbulence is more likely to result in more ef ficient i with reduced overpressures.gnition at lower concentrations Furthermore, this situation does not present an argument against removal of igniters in the IC UP, but rather a confirmation of the potential danger of ignition there.
Arguments have also been made that early burning is preferable to later, because uniform concentrations have not had time to build up.
Those argu-ments again ignore the experimental data on lean mixture ignition.
There are also important advantages to delaying ignition.
Allowing time for the hydrogen to mix will pro-duce more dilute mixtures and lessen the probability of high concentrations remaining in pockets.
may also result in the plating out of some Time delays radioactive aerosols; combustion might also be reignited in the lower compartment (an important question here would be the possibility of flame propagation through the ice con-densers and rasultant ignition in the UC mixture).
Jeveral improvements are possible for UC deliberate ignition.
The most obvious is the inclusion of hydrogen sensors and separate controls for igniters placed high in the UC.
These ignitors would be inactivated if the hydrogen concentration approached 8%.
is mechanical separation of regions, perhaps by screensAnother possibility These screens might prevent UC turbulent deflagrations from propagating dounward into the IC upper plenum.- Turbulence could also be significantly reduced (if that was shown to be desirable) if the spray systems were not activated prior to a burn are with respect to spray activation).(I do not know what TVA's present amarg In summary, we think that:
1.
The potential for hydrogen generation and combustion may be larger than previously estimated.
2.
The codes being amployed for accident analysis may be very inadequate for licensing decisions and should not be used to replace physical in-tuition and engineering judgement.
3.
The probability of lower compartment inerting during an accident may be higher because of ccmputational uncertainties and because of the possible existence of an additional physical mechanism for inerting (condensation fog).
4.
If a detona-tien were to occur in the IC upper plenum, calculations have shown that containment failure could not be conserva-tively precluded.
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T. E. Murley & D.
P.
Ross 5.
February 9, 1981 Deliberate ignition in the upper compartment is a difficult, quantitative problem.
Igniters placed high in the upper compartment will probably be beneficial most of the time, but circumstances can be postulated where they might be dangerous.
Igniters in the IC upper plenum appear to be justified only 11 one abandons the entire con-cept of lean mixture combustion, and replaces it with early, rapid, rich mixture, local combustion.
We think that such a concept is fraught with danger.
If you feel that we can be of further assistence to you, don' t hesitate to call on us.
Retferences 1.
M.
Berman et al.,
" Analysis of Hydrogen Hitigation for Degraded Core Accidents in the Sequoyah Nuclear Power Plant", SAND 80-2714, NUREG/CR-1762, December, 1980.
2.
W. lowry, " Preliminary Results of Thermal Igniter Experi-ments in H -Air-Steam Environments", UCRL-84167, presented 9
at the.WorRshop on the Impact of Hydrog_en on Water l
Reactor Safety, Albuquerque, New Mexico, January, 1981.
3.
L.
S. Rubenstein, " Input to Sequoyah SER on Igniter Systems."
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4.
R.
K.
Byers, "CSQ Calculations of H Detonations in y
Zion and Sequoyah", SAND 81-0361C, pTesented at the Workshop on the Impact of Hydrogen on Water Reactor i
I safety, Albuquerque, New Mexico, January, 1981.
5.
J. C. Mark, Memorandum for ACRS Members, " Notes on Hydrogen Burn with Igniters", December 4 1980.
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