ML20127N951
| ML20127N951 | |
| Person / Time | |
|---|---|
| Issue date: | 03/15/1985 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| REF-GTECI-A-44, REF-GTECI-EL, TASK-A-44, TASK-OR AB38-1-104, ACRS-2287, NUDOCS 8505230659 | |
| Download: ML20127N951 (6) | |
Text
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kC. M - 3 &O 5 DATE ISSUED: 3/15/85 h 7DR 6S \3 8 d j MEETING MINUTES FOR THE ,
3f3fffS FEBRUARY 26, 1985 ELECTRICAL SYSTEMS SUBCOMMITTEE MEETING t
' The ACRS Subcomittee on Electrical Systems met on February 26, 1985 at 1717 H-Street, N.W., Washington, D.C. in Room 1046. The purpose of this meeting was to discuss the status of the NRC and Industry work on USI A-44, " Station Blackout" and recent operating experience with failure of AC/DC power systems. The Subcommittee heard presentations from NRR, RES, I&E, EPRI, and the Nuclear Utility Group on Station Blackout. The f
l meeting was begun at 8:30 a.m. and was adjourned at 4:00 p.m. and was held in open session. The principle attendees were:
l W. Kerr, Subcommittee Chairman J. Ebersole, ACRS Member l J. C. Mark, ACRS Member ,
M. El-Zeftawy, ACRS Staff R.' Savio, ACRS Staff A. Rubin, hRC P. Baranowsky, NRC E. Rossi, NRC H. Wyckoff, EPRI C. Poindexter, Nuclear Utility Group on Station Blackout Highlights (1) The NRC Staff briefed the Subcommittee on the status of the ongoing work on USI A-44, " Station Blackout." The ACRS had last reported on this topic in July 1983, (See Attachment A). The proposed .
resolution has since been reviewed by the CRGR and has been mod-ified to account for improved data on the frequency of loss-of-off::ite power (LOOP). It is the NRC Staff's intent to L . . v.au.D CMCINAI, 8505230659 850315 ACRS Certiflod Py /3 g
Electrical Systems Meeting Minutes 2/26/85 implement the resolution of USI A-44, via a rule requiring a demonstration of the plants ability to withstand station blackout.
The basic approach which the NRC Staff was following in July 1983, has not changed. A brief chronology of what the NRC Staff has accomplished since July 1983, is given on Figure 1.
(2) The NRC Staff was proposing in July 1983, that operating plants be placed into categories of " station blackout vulnerability." Deter-ministic and performance based criteria (LOOP frequency, diesel generator configuration, diesel generator failure rates) were to be used to establish what plants went into what categories and, depending on the frequency of extended station blackout associated with each category, a demonstration of the capability to withstand station blackout for a particular length of time would be required.
In July, 1983, the NRC Staff anticipated that the categorization of operating plants would be such that 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, and 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> of demonstrated station blackout duration capability would be -
required. The demonstration would be by way of analysis and, as required, limited testing. In the NRC Staff's current proposal 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> and 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> of demonstration station blackout capability would be required. The NRC Staff expects that 90% to 85% of the operating plants will fall in the "4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />" category. The current ,
proposal for station blackout categories and requirements are displayed on Figure 2. It appears that the implementation of the proposal will result in something close to a uniform requirement for demonstrating that plants will withstand 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of station blackout conditions.
Electrical Systems Meeting Minutes 2/26/85 (3) The NRC Staff, in developing the resolution of USI A-44, has spon-sored work at Sandia and ORNL on accident sequence analysis, LOOP frequency, and diesel generator reliability. In summary, some of i
l the principle results are as follows:
l l
(a) LOOP frequency was (via analysis of existing experience, uncorrected for any changes which occurred over the 15 year data base) estimated to be 0.1 site / year (average) with a range over the existing nuclear power plant sites of 0. to 0.4 site / year.
(b) The median time to resolving offsite power after a LOOP is about i hour based on the current experience base. The longest time to restore offsite power was 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />, with power being restored for 90% of the events within 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />.
(c) The emergency diesel generator reliability (auto-start) per demand is 0.98 (average) with a range of 0.9 to 1.0 (See Figure 3). Median repair time has been 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> for the conditions under which the failures have occurred.
(d) The estimated range of emergency AC power systems unavail-ability is 10-4 to 10-2 per demand and the estimated range of ,
station blackout frequency is 10-5 to 10-3 per reactor year.
(e) The estimated range of core damage frequency caused by station
Electrical Systems M:eting Minutes 2/26/85 blackout is 10-6 to 10-4 per reactor year.
(4) LOOP events have occurred for a variety of reasons. The NRC Staff a concluded that through 1983, there have been 46 events with a duration of greater than i hr and 8 shorter duration events. (The total number of site years in this data base is 533). In the 46 events, 6 have involved severe weather conditions, 10 have been caused by failure of equipment in the grid, and 30 have been caused by plant equipment failures (See Figure 4). Improvements have been made in good configuration and plant equipment which would be l expected to reduce the frequency of LOOP events. Shrinking reserve l
margins, if they occur, would tend to increase LOOP frequency.
(5) The NRC Staff has concluded that recent diesel generator failures have been from a variety of hardware failures (some of which are human error related) and that no single diesel generator system dominates (See Figure 5). There is some evidence that diesel generator performance is improving (See Figure 6). The NRC Staff stated that, while there were still some diesel generators at some plants which still had a poor performance record, they saw no reason why all diesel generators could not perform at the general level of the best ones (unavailability in the range of 0.02 to 0.01 perdemand). The available data indicates that comon cause -
failure becomes important when diesel generator unavailability becomes lower than 0.04 to 0.03.
o .
Electrical Systems Meeting Minutes 2/26/85 4
(6) The NRC Staff has evaluated a number of plants for dominant station blackout core damage accident sequences. These plants are thought to be representative of all but the oldest of the operating plants. li-The results are summarized as Figure 7. The parameters which most affect the plants ability to withstand a station blackout are summarized on Figure 8.
(7) EPRI has also evaluated the LOOP experience. They noted that the reporting procedures were of a nature that would increase the perceived frequency and duration of LOOP events. EPRI, in addition, believes that grid and plant improvements have greatly reduced the potential for LOOP events. EPRI has concluded that prior to 1982 (431 site years) that there have been 22 LOOP event (with a duration longer than 30 minutes and 21 events which were shorter than 30 minutes. These conclusions, as to an average frequency for a LOOP longer than i hour, are different than what was obtained in the NRC's work by about a factor of two. During the 1982 through 1984 time period, (157 site years), there have been 2 LOOP events with a duration longer than 30 minutes and 5 events shorter than 30 minutes. This is about a factor of 5 less than what would be learned by multiplying the average frequency for .-
the pre-1984 period by 3 years. This, even in view of the small number of LOOP events involved, would support the contentions that the steps would have been taken to reduce the frequency and duration of LOOP events have been effective. l l
Electrical Systems M;eting Minutes 2/26/85 (8) The Nuclear Utility Group on Station Backout made a short presenta-tion. It is this Owner's Group opinion that station blackout does not present a level of risk large enough to warrant a rule based requirement for the demonstration of a plant ability to withstand I
station blackout. The Owner's Group believes that NRC and Industry efforts have greatly reduced the occurrence of LOOP events and the likelihood of station blackout.
NOTE: Additional meeting details can be obtained from a transcript of this meeting available in the NRC Public Document Room,1717-H Street, N.W., Washington, D.C., or can be purchased from ACE-Federal Reporters, 444 North Capitol Street, Washington, D.C.,
20001,(202)347-3700.
fWTo W N &
- 'o UNITED $TATEs NUCLEAR REGULATORY COMMISSION
,k ADVISORY COMMITTEE ON REACTOR SAFEGUARDS W ASHtNGTON, D. C. 20565
[
-C0C0 July 13, 1993 .
Mr. William J. Dircks .
Executive Director .for Operations -
U. S. Nuclear Regulatory Commission Washington, DC 20555
Dear Mr. Dircks:
SUBJECT:
ACRS COMMENTS ON THE NRC STAFF PROPOSAL FOR RESOLUTION OF USI A-44, "STATIUN BLACKOUT" During its 279th meeting, July 7-9, 1983, the Advisory Committee on Reactor Safegtjards discussed the NRC Staff's proposal for the resolution of USI A-44,
" Station Blackout." The NRC Staff's recent activities in this area were also discussed during Subcomittee meetings held on March 30, May 10, and Septem-ber 8,1982 and during the 264th ACRS meeting, April 1-2,1982 and 270th ACRS meeting, October 7-9, 1982. l The proposed NRC Staff position has been developed over the past three years I
and has the benefit of studies which were performed at Oak Ridge National ,
A recommen. .- I
\ Laboratory and Sandia National Laboratory (References 1 and 2).
dation as to the acceptability of this proposal has not yet been made by the'
\ j Comittee to Review Generic Requirements.
The NRC work has identified five plant- and site-related character.istics as the main contributors to risk from station blackout. These are: (1) the number and the capacity of the diesel generators. (2) the diesel generator reliability (3) the number of AC-independent decay heat removal systems. (4) .g the frequency of loss of offsite power, and (5) the duration of less of of fsite power.
Under the NRC Staff's proposal for the resolution of USI A-44, a plant should be able to withstand a station blackout for a length of time that depends on l the configuration of the plant with respect tohaving Plants the five theplant- most and site-favorable l related characteristics listed above. I configuration in this respect would be required to be capable ofless withstanding favorable a station blackout for at least For 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, and plants with only a few plants, a period of 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> may 8 configurations, for 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.
be required. The plant's ability to withstand station blackout would typf-cally be established by analysis supported by component, subsystem, and -
.l system testing. The implementation of the NRC Staff recommendations would be ~
via a rulemaking action.
( 9M7 nA e i
auly 13, 1983 William J..Dircks j The approach proposed by the 'NRC Staff is to . establish performance This approach allows thecriteria based on an evaluation of individ'ual plant risk.
licensees to use a variety of design, test, and procedural methods to meet the specified performance criteria and, when backfitting is necessary, to use
' the most cost-effective methods which they are able to devise.
We believe that this proposal for the resolution of USI A-44 would result in significant improvements onlyWe forbelieve those plants that the that have an will approach unusual resultvulnera-in a
~ bility to station blackout. plants and believe this is a
- cost-effective upgrading of the higher riskWe note, however, that marty foreign necessary and worthwhile interim goal. -
l LWR plants, which are generally quite similar to those used in the Unitedfeatures w States, either have features 'or are planning backfit markedly reduce plant vulnerability to station blackout beyond the measures
' which would be required by the proposed resolution of USI A-44.
The NRC. Staff has performed a value/ impact analysis for operating plants to determine thgt cost-effective fixes could reduce the probabil melt below 10-
.value/ impact ratio less than $1000 per man-rem should be implemented as backfits. However, the Committee disagrees with the probabilistic accept-( ance criteria proposed by the NRC Staff in the draft analysis of USI A-44.
(1) that the maximum estisaated proba-In particular, the Staff recommende'd:
' bility of core melt from station blykout perfor reactor plants currently year in operation (for a best estimate or under construction should be 10-and (2) that the maximum estimated probability for new plants should value)4 per reactor year. Since extended station ' blackout can result in be .10 core melt and a loss of containment integrity, without the benefit of having mitigation features such as containment spray in operation, In a our large release view, of radioactive material may be associated with such an event. '
e acceptance criteria for this or single 10' sourry should be smaller than the pr bilities mentioned above (10-factor of ten.
For these reasons, though the Committee believes that ,the changes which may be required to meet the proposed resolution of USI A-44 are desirable, the NRC position should be that. On a long-term basis and with the probabilistic criteria referred to above, those changes do not provide an acceptable ultimate phase.
solution and further improvements may be required coordinated with recommendattuns which may emerge from the ongoing work on .
resolving USI A-45, " Shutdown Decay Heat Removal Requirements " and consid ,
eration should also be given to actions taken in this aret by foreign regu- -
latory authoritias.
(
__m_ ,
July 13, 1983 h William J. Dircks We understand that the NRC Staff is generally -inclined to delay requiring .
major, expensive backfits (such as additional diesel generators) to resolve station blackout concerns for plants for which resolution of USI A-45 would
.. With the understand.
also reduce risk of core melt due to station blackout.
ing that exceptions may be peded for pl~ ants. subject to an unacceptably high likelihood of core. melt due to station blackout, we endorse this policy.
Further, we urge that the resolution of USI A-45 be accelerated.
In addition to USI A-45, the NRC Staff is currently developing resolutions to Generic Safety Issues B-56, " Diesel Reliability," and A-30, " Adequacy of Safety-Related DC Power Supplies," both of which deal with issues closely related to those being considered in USI A-44. 'The ACRS recommends that the ,
work in these areas be closely coordinated so as to assure the most effec- !
- tive combined resolution of these safety issues.
In summary, subject to the coments made above, the Advisory Comittee on Reactor Sa feguards supports the proposed approach for the resolution of U$1 A-44 on an interim basis.
Sincerely, W2 J. J. Ray Chairman
References:
- 1. " Reliability of Emergency AC Power Supplies at Nuclear Power Plants,"
NUREG/CR-2981, undated draft (currently in publication).
- 2. " Station B1ackout Accident Analysis," NUREG/CR-3226, dated May 1983.
e-9
/4
M: :
.l S~ s1- USI A-44 CHRONOLOGY ,
ISSUE FOR' PUBLIC COMMENT
,' TECHNICAL RESOLUTION TO CRGR
- FOR DIVISION COMMENT ,
l CRGR FINAL RESOLUT10
" ! NUREG-1032 Review NUREG-1032 PROPOSE 0 RULE
1st DRAFT Completed REVISED DRAFT TO COMMISSION ACRS LETTER ISSUE July
\ FINAL-Oct May oce l
83 84 84 84 _ _ _ _, _ _ _ _
, _ E July Nov Feb Mar Jan Feb Mar 3
83 83 84 84 85 85 85 ANS 58.12 DRAFT STANDARD I LOSP NUREG/CR-2989 LETTER REPORT NUREG/CR-3992 NUREG/CR-3992 AND DRAFT LOSP REPORT MANUSCRIPT t
W/ UPDATED DATA COMPLETED NUREG/CR-3226
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l Table C.I. Summary of Potentially Ocminant Core Damage '
Ac:idcat Sequent s l i
- o. Genui; C*G System /Co ponent AC .'!acc ime P1:nt Secuence Contributors to .tvoid ' N mage PWR TMLj Bj Steam driven AFWS unavailable 1-2 ;
(all)
TML 822 DC power or condensate exhausted 4-15 *.-;rs TMQ 822 RCS pump seal leak 4-16 hours
- SWR THUjtj Isolation condenser unavailable 1-2 hours -
w/ Isolation Condenser TMQ3 8) ,
Stuck open relief valve ,
1-2 hours
(
TMQ23 2 RCS pump seal leak 4-16 hours SWR TMUjtj HPCI/RCIC Unavailable 1-2 hours w/HPCI-RCIC TMU 8 22 DC power or condensate exhausted. 4-16 hours component operability Italts
, exceeded (HPCI/RCIC)
BWR TMujBj HPCS/RCIC unavailable 1-2 hours w/HPCS-
.RCIC ,
TMU228 HPCS unavailable, DC power or 4-16 hours condensate exhausted, component .
operability limits exceeded ,
(RCIC) .
Y%3 .
NUREG-1032 Appendix C C-2
Table 6.2. Possible Factors Limiting the Ability to Cope wt:h a Statica Blackcut PWR~ 3'.iR 2/3 2 1 1/5/6 RC .7 seal leakage X X R:. . :d::wn/ makeup & water X X
... :stry control lines Stuck cpen relief valve X ,
X DC battery capacity (I&C) ' X X X Compressed air (valve control) X X X DHR water supply X X X (condensate, firewater) -
Operating environment (temperature)
I control room (ISC) ,
X X X, containment X (suppression pool, wetwell, drywell) auxiliary building X X (AFWSroom) (HPCI/RCIC room) l l
i i
s
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Nh ,
O NUREG-1032 /t
-_ __ _ _ . - . - .