ML19344F407
| ML19344F407 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 09/08/1980 |
| From: | Plesset M Advisory Committee on Reactor Safeguards |
| To: | Ahearne J NRC COMMISSION (OCM) |
| References | |
| ACRS-R-0895, ACRS-R-895, NUDOCS 8009150238 | |
| Download: ML19344F407 (3) | |
Text
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NUCLEAR REGULATORY COMMISSION I-ADVISORY COMMITTEE ON REACTOR sATCGUARDS g,
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September 8,1980 I
Honorable John F. Ahearne Chairman Nuclear Regulatory Commission Washington, D.C. 20555
Dear Dr. Ahearne:
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SUBJECT:
SEQUOYAH NUCLEAR POWER PLANT, UNITS 1 AND 2 In connection with the Committee's review of the Sequoyah Nuclear Plant, Commissioner Gilinsky has addressed specific questions to the ACRS regard-ing ice condenser containments.
This is in response to your request for the Committee's' comments on the questions raised by Commissioner Gilinsky in his letter of August 7, 1980.
- 1). "Does the Committee believe additional hydrogen control measures are necessary for ice condenser containments?"
An intensive review of the capability of the Sequoyah containment has recently been completed.
Independent estimates have been made ' by the Applicant, the NRC Staff, various consultants, and the ACRS Subcommittee on. Structural Engi neering. ' As a result,. it has been concluded that the Sequoyah contain-ment is capable of sustaining a pressure of at least-45 psig.without struc-tural failure.
On this basis, the containment structure could tolerate burning' of all the hydrogen evolved from the oxidation of 20%, or so, of the zirconium in the reactor, assuming the hydrogen was. uniformly distributed in the containment atmosphere..
Hence, there is a range of accidents, involving severe core damage - for which additional hydrogen control measures are not necessary.
Of course, it would also' be necessary to ascertain that all the essential equipment in the containment could withstand such an event. TVA has stated that they are conducting a thorough raview of this matter.
For a full scale core meltdown there is ' no assurance that -failure of the o
containment could be avoided merely by the use of hydrogen control measures.
For events involving more than about 30% oxidation of the zirconium, hydrogen control measures may be necessary to avoid containment: failure.
JA similar situation, though not identical in" detail, would be expected to Japply-to ice condenser plants other than Sequoyah.
LThel Committee believes that it would be prudent to provide additional ' hydrogen control measures'for ice-condenser containments, and that studies to demon-strate. the leffectiveness, reliability, and absence of significant adverse effects of candidate measures should be pursued actively on a time scale that woulde permit their application before more than a few additional reactor 80.0 9.150 ASI f-
Honorable John F. Ahearne September 8,1980 years of operation of ice condenser containment plants have elapsed.
As stated in our Sequoyah Report of July 15, 1980, in the Committee's opinion, there is no need to delay the issuance of a full power operating license for Sequoyah until these studies have been completed.
2)
"Is the Committee reasonably persuaded of the effectiveness of distrib-uted igniters in ice condenser containments?
Can such igniters be coun-ted on to keep pressure increases caused by hydrogen burns at suitably low values -- which I would define as design pressures -- during acci-dent sequences involving TMI-like quaritities of hydrogen?"
On the basis of the preliminary information available, it appears that a distributed ignition system of the type considered for Sequoyab may provide a good capability of controlling the burning of a large amount of hydrogen.
It is yet to be established at just what hydrogen concentration a particular style of igniter will provide ignition with high reliability under the con-ditions anticipated.
With the assumption that it can be shown that this concentration is little, if any, higher than the average when the burn oc-curred at TMI-2, the pressure levels induced by iterated ignition would be well within the 45 psig capability of the Sequoyah containment.
There is no present basis for assurance that the pressure increases can be held below the design pressure -- nor would there seem to be any need to do so under the circumstances considered.
The hoped for, and expected, performance would be capable of disposing of all the hydrogen that might present itself, up to the point (about 800 kg burned) at which the oxygen level in the containment atmosphere should drop to about 5%, after which no further hydrogen could burn.
This, of course, would depend on the continuing operation of the containment heat removal systems.
The action of the igniters will probably reduce the risk, since there will be at least as many ignition events with them in use as if only unintended ignition sources were present.
The average amount of hydrogen per burning event should therefore be smaller, and the chance that a large pocket of ignitable or detonable hydrogen could survive without ignition (while waiting for a random source to act) will be reduced.
The results of the present testing program will, of course, be necessary before concluding that the ignition system being studied meets all the neces-sary objectives.
Sincerely, Milton S. Plesset Chai rman
c Honorable John F. Ahearne September 8, 1980 References 1.
U.S. Nuclear Regulatory Commission, " Safety Evaluation Report Related to the Operation of Sequoyah Nuclear Plant, Units 1 and 2," USNRC Report NUREG-0011, Supplenent No. 2, August 1980 2.
U.S. Nuclear Regulatory Commission, " Safety' Evaluation Report Related to the Operation of Sequoyah Nuclear Plant, Units 1 and 2," USNRC Report NUREG-0011, Supplement No. 3 September 1980 3.
Letter from Commissioner V. Gilinsky to M. Plesset, Chairman, Advf;ory Conmittee on Reactor Safeguards, dated August 7,1980 l
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