ML17193B369
| ML17193B369 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Quad Cities  |
| Issue date: | 04/14/1981 |
| From: | Ippolito T Office of Nuclear Reactor Regulation |
| To: | Abel J COMMONWEALTH EDISON CO. |
| References | |
| NUDOCS 8105060067 | |
| Download: ML17193B369 (5) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, 0. C. 20555 Docket Nos. 50-237, 50-249, 50-254, 50-265 Mr. J. S. Abel Director of Nuclear Licensing Commonwealth Edison Company P. 0. Box 767 Chicago, Illinois 60690
Dear Mr. Abel:
April 14, 1981 By letter dated February 9, 1981, you provided comments on our January 23, 1981 Supplement to our Generic Safety Evaluation Report -
Bl~R Scram Dis-charge System, issued December 1, 1980.
Your comments are for the most part, expressions of disagreement with much of the Supplement.
Your comments are, however, well defined.
Our response to them is contained in the enclosure to thiS 1 etter.
While we believe this response answers the points you have raised, we can discuss the matter further by telephone if you wish.
Enclosure:
NRC Response to Comments on Supplement 1 cc w/enclosure:
See next page
~ 105060 067 Sincerely,
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-~~~~-:if-Thomaf'*~~ Ippolito, Chief Oper-ating Reactors Branch #2 Division of Licensin~
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.e Mr. J. S. Abel cc:
Mr. *John W. Rowe
.lsham*, Lincoln & Beale
- Counselors at Law
- On~ First National Plaza, 42nd Floor Chi~ago~ Illinois _60603 Mr*. B. 6.. Stephenson *
- Plant Supe_rintendent
- Dresden Nuclear Power Station Rur.al Route fl
.* Mo.r~is; I1 l.inoi.s 60450 Morris*Public Library 604 Liberty Street Morris, Illinois* 60451 11 l; no is Department of Nuc1 ea*r Safety
- I 035 Outer Park Ori ve 5th F1 cor
~~~~r~:ield, Illinois 62704.
. Mr. Wi 11 i am Waters Chairr.;an, Board of S.uperviso.rs of Grundy County Grundy County Courthouse
- Morris, I11i.nois 60450 Director, Criteria and Standards Oivi sion Office of Radiation Programs (ANR-460)
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~- Environmental Protection Agency Washinoton, D. C.
20460 U. S. Environmental Protection Agency Federal Ac ti vi ti es Branch Reoi on V *Off-ice.
ATTN:* EIS COORDINATOR 230 So:.ith Dearborn Street Chicaoo, Illtnois 60604
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Susan N. Sekuler Assistant Attorney General Environmental Control Division 188 W. Rindolph Street Suite 231-S-Chi ca go, 111inais 60601 U. S. Nuclear Regulatory Corrrnission Resident Inspector's Office
- D'resden Station RR #1 *
- Morris, Illinois 60450
- ***John* F; Wolf, Esq.
3409 Shepherd Street Chevy Chase, Maryland 20015.
Dr. L.i.nda w:. Little
. SQQ Hermi ta,ge.Ori ve
- Raleigh, North: Carolina. 27612:
Dr. Forrest J. Remick 305 East Har.ii lton Avenue State College, Pennsylvania 168Pl
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UNITED STATES NUCLEAR REGULATORY COMMISSION
- W_ASHfNGTON, 0. C. 20555 tlRC RESPONSE TO CGr*iMON\\*IEAL TH EDISOtl COMPANY COMt1ENTS ON SUPPLEMENT 1 TO THE GENERIC SAFETY EVALUATION REPORT -
we have. reviewed Comtnonw~alth..Edison Company comments whi th* state thefr.
disagreement with s ev:e ra l pc;i i 11 ts ma.de in the supplement to the BWR $cram Oi.s*charge: System* SER dated December l, l9:SO.
Res.ponsi'E>le members 9.f the Division* of Systems* lhte.gration, Divfslon o.f Safety Technology and Divfsion
. of Human Factors Safety ha've contri Outed to tfl is response*..
Incorrect Basis for Concern The Commonwealth Edison statement that at elevated reactor pressure, full opening of the scram outl~t valve~ will cause control rod movement into the reactor core at the normal scram rate is not *disputed..
Commonweal th* Edi son missed the poi.-,t
- of the staff concern.
The SER supplement, as well as the SER of December 1, : 980*;
clearly states that the concern deals with an event where the control air sy:.tem depressurizes at a slow enoug_h rate~ to caus~ p:artial opening.of a numb.er of ::.cram.
outlet valves \\-1hile no *centrer rod m*ovemen't takes place. Tests have been pe1*-
formed tha.t show under this condition a rapid fi 11 of the scram discharge volume h~aders is possible before a reactor scram occurs.
Stattstical Evaluation The statistical di~cussion provided on pages 3 and 4 of the supplement was not meant to be used as the basis fo:r determining that a problem exi-sts.
Thi.s ~e.ter mination was bas*ed. in part upon human factors considerati:on listed on page 27 of the SER and in part upon the judgment that even though the. postulated event was unlikely,.the consequences could be severe if the operator was unable to manually scram the reactor before fill of the SDV headi:rs occurs.
We agree that the statistical evaluation presented on pa.ges 3 and 4* of the SER supplement is not rigorous or conclusive.
Its purpose ~1as to provide some insight regarding the suitability of granting an extension of time for the installation of the auto-m~tic air dump system.
It should be noted that the becember 1, 1980 SER re-quire.d that the system be installed within 2 months.
The SER supplement rec-ognized the large uncertainty associated vii th the cal cul ati on of a frequency of occurrence based upon a singl~ event and concludes that because of other
~ 2. -
actions listed on page 4 of the supplement, an extension of time is warranted in order to properly design, install and test the system.
It should be noted that approximately 20 loss of air events occurred at BWRs.
A fraction of these may have been similar to the Quad Cities event of 1977.
This additional un-known adds even greater impreciseness to any statistical evaluation, but any additional Quad Cities type events would make the frequency greater than what was assumed.
Operator Actions*.
The. third. point, ra'i sed' by. Commonwea 1th Edison was that operator response was timely in manually scrairrning the plant after recei:ving alarms for control rcid accumulator level/pressure trouble and control rod drifts. Out analysis does not argµe that it is not possibl~ for an operator to act in a timely manner.
The point. is that in the. Quad Cities event the operator came quite close to not. be.fog able to scr~m even tho.ugh he appears to have done everything right.
There is no assuranc;e that ev.ery operator, under unspecified circumstances, *
- will exhibit the same beh*avior.
This. is particularly difficu*lt to ima.gine
- if it i.s assumed* that no rod drift has occurred.
Commonwea 1th Ed:i son's cornme.nts that the source of water entering the SDV was.
- at least partly due to the control rods that were drifting when the scram o.ut-1et valves opened is not disputed.
However, there i~ good reason to assume that part of the water entering the SDV headers derived from those s.cram out-let valves that were only partially opened *s*ince the time for actuati.on of the S1V hi~h level alarm was considerably shorter than normal (20 se.conds vs.
It is likely that some of the scram outlet valves assoc-iated with control rods that did not drift (107 rods) were* leaking water into the SDV.
This leakage together with the *a*ccumul ated water caused by fully ope.ned scram outiet.valves, fndkates that only a short time remained after*
an ind.icatibn of rod drift (a matter of a minute or two) before the SDV could be completely filled. It fs s*peculative to assume that adequate operator action can be consistentlJ taken in thi~ short time span.
Human Factors Raising the issue of a varta-tion-petween plants on the location and number of annunciators assotiated with* a loss of air event was intended to point out that:
- a.
- b.
- c.
Considerable variatio~ exists between and within plants* i~ regard to the number and location of annunciators that could be associated with a loss of air event.
Some plants have more than one loss of air annunciator at different locations and set points.
Plant personnel could not predict the degree to which cither a~nunciators would be associated with a loss-of air event.
Q;
- c.
- d.
There was little consistency between operators in their anticipated response*
to a loss of air event and in their awaren~ss of loss of air annunciator set points.
The above items clearly indicate that the conditions identified will not "facilitate" an immediate manual scram with a loss of air event and we firmly believe that several aspects of the situation have the potential to hamper or delay operator response; specifically, the apparent lack of consistent direction to the operator, the un~
certainty of the situation, and the potential for competing sources of information..
Furthermore, it is o.u.r conservative judgement from data ava*ilable from simulato:r experiments that under the stress of an emergency, operator response time may
- increase.
Fina.lly, the Human Factors evaluatio.n does not suggest that tl:le use of a "unique and distinctly audfble alarm" wo.uld satisfy the stated concerns.
This was only suggested as a means of achieving greater assurance of timely operator response*
to a loss of air event.
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