ML20211Q165
| ML20211Q165 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 10/16/1997 |
| From: | Fields M NRC (Affiliation Not Assigned) |
| To: | Nunn D SOUTHERN CALIFORNIA EDISON CO. |
| References | |
| GL-88-20, NUDOCS 9710220141 | |
| Download: ML20211Q165 (8) | |
Text
October 16, 1997_
Mr. Dwight E. Nunn Vice President Southern California Edison Company San Onofre Nuclear Generating Station P. O. Box 128 San Clemente. California -92674-0128
^
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION ON THE SAN ONOFRE NUCLEAR GENERATING STATION. UNITS-2 AND 3 INDIVIDUAL PLANT EXAMINATION OF EXTERNAL EVENTS
Dear Mr,
Nunn:
Attached is a list of questions developed by the staff and its consultants based on an initial review of Southern California Edison's December 15. 1995.
.res)onse to Generic Letter 88 20. Supplement 4. Individual Plant Examination of External Events, for the San Onofre Nuclear Generating Station. Units 2 and 3.
In order to conform with the staff's review schedule, you are requested to provide your response to these questions within 60 days of the date of this letter.
If you have any questions, please call me at (301) 415-3062.
Sincerely.
Original Signed By Mel B. Fields. Project Manager Project Directorate IV-2 Division of Reactor Projects Ill/IV Office of Nuclear Reactor Regulation Docket Nos. 50-361
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Mr. Dwight E. Nunn October 16, 1997 cc w/ encl:
Mr. R. W. Krieger. Vice President Resident Inspector / San Onofre NPS Southern California Edison Company c/o U.S. Nuclear Regulatory Comission San Onofre Nuclear Generating Station Post Office Box 4329 P. O. Box 128 San Clemente. California 92674 San Clemente. California 92674-0128 Mayor Chairman. Board of Supervu ors City of San Clemente County of San Diego 100 Avenida Presidio 1600 Pacific Highway. Room 335 San Clemente. Californca 92672 San Diego. California 92101 Mr. Harold B. Ray Alan R. Watts. Esq.
Executive Vice President Woodruff. Spradlin & Smart Southern California Edison Company 701 S. b rker St. No. 7000 San Onofre Nuclear Generating Station Orange California 92668-4702 P.O. Box 128 San Clemente. California 92674 0128 Mr. Sherwin Harris Resource Project Manager Public Utilities Department City of Riverside 3900 Main Street Riverside. California 92522 Dr. Harvey Collins. Chief Division of Drinking Water and Environmental Management California Department of Health Services P. O. Box 942732 5
Sacramento. California 94234-7320
, Regional Administrator. Region IV U.S. Nuclear Regulatory Commission Harris Tower & Pavilion 611 Ryan Plaza Drive. Suite 400 Arlington. Texas 76011-8064 Mr. Terry Winter Manager Power 0)erations San Diego Gas & Electric Company P.O. Box 1831 San Diego California 92112-4150 Mr. Steve Hsu Radiologic Health Branch State Department of Health Services Post Office Box 942732 Sacramento. California 94234
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REQUEST FOR ADDITIONAL INFORMATION INDIVIDUAL PLANT EXAMINATION OF EXTERNAL EVENTS (IPEEE)
SAN ONOFRE NUCLEAR GENERATING STATION, UNITS 2 AND 3 SEISHIC ISSUES 1.
The December 15, 1995 IPEEE submittal indicated, as a result of an IPEEE sensitivity analysis, that the seismic core damage frequency (CDF) is sensitive to human error probabilities (HEPs) assigned to post-initiator seismic specific operator actions. This is a somewhat unusual finding, as compared to results obtained in IPEEEs for other plants.
It is observed that the performance shaping factors (PSFs) and/or the HEPs used in the seismic IPEEE are not necessarily conservative, particularly when compared to other IPEEE studies that have assumed HEPs of unity for operator actions required outside of the control room after severe ground shaking.
It is also noted that the HEPs do not increase with ground motion severity.
Furthermore, the sensitivity analysis provided in the submittal considers only the post-initiator seismic-specific operator actions, and does not examine the effects of HEPs for the post-initiator operator actions considered in the modified individual plant examination (IPE) portion of the seismic model From the SONGS seismic IPEEE, it is clear that effects of non seismic failures and human errors are highly important.
Consequently, please respond to the following:
For each post-initiator operator recovery action modeled in the seismic event tree (SET) and in the modified IPE event trees / fault trees, discuss the following: the required timing and location of the action: the nature of the required action, and the number of personnel it involves: the extent to which such action is addressed in plant procedures: the potential effect of seismically induced failures of buildings and other large structures on the-ability to implement such actions: the effects of shaking severity on operator stress levels and PSFs: and the potential for aftershocks to reduce the effectiveness of recovery.
In consideration of these and other important factors influencing operator error rates, please fully justify your PSF values.
A sensitivity study revealed that operator failure to recover from relay / process switch chatter in the diesel generator circuitry can increase the seismic CDF by an order of magnitude. This finding suggests that it would be cost beneficial to replace the relays.
Please address this issue and discuss why replacement of these relays should not considered.
For post-initiator actions considered in the IPE portion of the seismic model, evaluate and discuss the impact on seismic CDF if the HEPs are increased to unity.
l
r 2
2, The submittal states that the seismic screening walkdowns followed the guidance of EPRI NP 6041 SL.
Pleaseindicatewhichscreeningcriteria (e.g., the first, second, or third column of Tables 2 3 and 2 4) were employed. Was a consistent screening capacity level used for assessing all components? Justify the use of the chosen screening level (or levels) for application to a plant having a design basis peak ground acceleration of 0.67.
9 3.
Please prod de a list of (1) any masonry / block walls whose failure may adversely affect a component included in the seismic equipment list and (2) the fragility results or screening dispositions for each of these walls.
If not all of the block walls were screened out, please provide the screening evaluation work sheets and complete details of iregility calculations for (a) the block wall having lowest capacity, and (b) the block wall having the greatest risk significance.
4 Please provide ca>acity/ fragility calculations, completed screening evaluation work sleets, walkdown notes / checklists, and photographs (if any) for the following components:
Primary plant makeup tanks S21203MT055 and S21203MT056 Motor control centers 521805ESB D.E.H.J.0.RA.RB.S.Y.Z 480V switchgear S21805ESB04 and S21805ESB06 Auxiliary building CCW heat exchangers 521203ME001 and S21203ME0012 Emergency chiller units SA1513ME335 and SA1513ME336 Safety equipment building Condensate storage tanks (S21305MT120 and S21305MT121) and refueling water storage tanks (521204MT005 and 521204MT006)
Please also provide (a) representative calculations for relay chatter fragilities, and (b) screening evaluation work sheets and other walkdown notes / checklists for the 4kV emergency switchgear.
(Note: Where multiple components of a given class are listed above, and the walkdown findings and calculations for all such components are essentially identical, relevant information need only be provided for one representative component of the class.)
FIRE ISSUES 1.
Since only Appendix R equipment and cables are considered, several systems and components included in the IPE model may not have been considered in tie fire analysis.
Has the licensee assumed that all those IPE components and associated cables not included in the list of safe shutdown systems are failed (for all fire scenarios)? Furthermore, from a review of Sections 4.3.2 and 4.2.1.2 of the IPEEE submittal it is not clear what information was taken from the Ap>endix R effort and what non-Ap>endix R cable routing information was o)tained for IPEEE analysis.
- or example, the cable routing for main steam and main feedwater related items may not be straight forward. Many balance of i
3-plant related circuits have cascading effects that may eventually affect main feedwater and main steam availability.
Please provide a discussion on how non Appendix R components and cables have been accounted for in the fire core damage frequency computations.
2.
The cable spreading rooms and cable galleries have been screened out in Phase 11. These compartments may contain cables and equipment from redundant and diverse trains. The conditional core damage probability and probability of having a critical combustible loadin have been given in Table 4.3.1 without further details.g (Pect) values P
is the ect probability that given ignition the fire is of sufficient severity to fail the targets and includes the -)ossibility of automatic and manual su)pression.
Normally in fire risc studies, cable spreading room and ca)le galleries are found to be risk significant.
Please provide further details c.1 how the core damage frequencies for these compartments were estimated.
Please explain whether and how the effects of fire, other than failing cables and equipment in the compartment.
were taken into account (e.g., effect of smoke and other fire related phenomena on passages and on comunication methods).
For fires in cable s> reading rooms, one would expect the ability to control the plant from tie control room to be compromised, and that it would be necessary to control the plant from the remote shutdown panel.
Please explain how the possibility of using h emote shutdown panel was modeled and prov1rie the basis for the prWo111ty of failing to use this panel.
3.
Some of the HEPs reported in the submittal appear to be optimistic.
For example, the probability of operators failing to trip reactor coolant pumps when component cooling water is lost (presumably before seal failure) is reported as 5.2x10.
The probability of operators failing tostartadieselgeneratorfrog'thecontrolroom,givenafireinthe relay room. is reported as 3x10.
In these twc examples, given that the available time window can be as short as one-half hour, and that the fire analyst does not have sufficient knowledge of other failures (especially instrumentation failures), these probability Values seem to be optimistic.
It is important that the HEPs properly reflect the potential effects of fire (e.g., smoke, heat, loss of lighting), even if these effects do not directly cause equipment damage in the scenarios being analyzed.
If these effects are not treated, the HEPs may be optimistic.
Note that HEPs which are conservative with respect to an internal events analysis could be non-conservttive with respect to a fire risk analysis.
Please identify: (a) the scenarios screened out from furthtr analysis whose quantification involved one or more HEPs. (b) the HEP.s (descriptions and numerical values) for each of these scenarios, and (c) how the effects of the postulated fires were treated in quar tifying the HEPs.
A reanalysis may be requested if PSFs besides stress associ6ted with fires (e.g., smoke, loss of lighting, poor communication) are relevant and have not been considered.
4 4.
In the description of control room fire scenarios, the possible need for abandonment of the control room and controlling the plant from the remote shutdown panel has not been discussed explicitly.
Please provide the detailed assumptions used in analyzing fires in the main control room, and justification for these assumptions. Describe how the remote shutdown panel was modeled, and how the human errors associated with operating the plant from the remote shutdown panel were estimated.
include the probability, and its basis, for forced abandonment of the control room.
5.
Related to the preceding question, NUREG-1407, Section 4.2 and Appendix C, and GL 88 20. Supplement 4. request that documentation be submitted with the IPEEE submitte.: with regard to the Sandia fire risk scoping study issues. including the basis and assumptions used to address these issues, and a discussion of the findings and conclusions.
NUREG 1407 also requests that evaluation results and potential improvements be specifically highlighted.
Control system interactions involving a combination of fire-induced failures and high probability random equipment failures were identified in the Sandia fire risk scoping study issues as potential contributors to fire risk. This issue was later classified as Generic Safety Issue 147 (GSI-147), " Fire-Induced Alternate Shutdown / Control Room Panel Interactions." Subsecuent to the issuance of GL 88-20. Supplement 4. the NRC staff determinec that they will assess the extent to which GSI-147 is addressed in the IPEEE submittals.
The issue of control systems interactions is associated primarily with the potential that a fire in the plant (e.g., the main control room) might lead to potential control systems vulneraDilities.
Given a fire in the )lant, the likely sources of control systems interactions could happen >etween the control room, the remote shutdown panel, and shutdown systems.
Specific areas that have been identified as requiring attention in the resolution of this issue include:
(a)
Electrical indeoendence of the remote shutdown control systems The primary concern of control systems interactions occurs at plants that do not provide independent remote shutdown control systems. The electrical independence of the remote shutdown panel and the evaluation of the level of indication and control of remote shutdown control and monitoring circuits need to be assessed.
(b).
Loss of control eauioment or oower before transfer The potential for loss of cor. trol power for certain control circuits as a result of hot-shorts and/or blown fuses before transferring control from the main control room to remote shutdown locations needs to be assessed.
s 6 e (c)
SDurious actuation of comoonents leadino to comoonent damace.
loss-of-coo' ant accident (LOCA). or interfacina systems LOCA The spurious actuation of one or more safety related or safe-shutdown related components as a result of fire-induced cable faults hot shorts, or component failures leading to component damage. LOCA or interfacing systems LOCA prior to taking control from the remote shutdown panel, needs to be assessed. This assessment also needs to include the spurious starting and running of pumps as well as the spurious repositioning of valves.
(d)
Total loss of system function The potential for total loss of system function as a result of fire-induced redundant component failures or electrical distribution system (power source) failure needs to be addressed.
Please describe your remote shutdown capability including the nature and location of the shutdown station (s). as well as the types of control actions which can be taken from the remote panel (s).
Describe how your arocedures provide for transfer of control to the remote station (s).
Provide an evaluation of whether loss of control power due to hot shorts and/or blown fuses could occur prior to transferring control to the remote shutdown location and identify the risk contribution of these types of failures (if these failures are screened, please provide the basis for the screening).
Finally, provide an evaluation of whether spurious actuation of components as a result of fire-induced cable faults, hot shorts, or component failures could lead to component damage, a LOCA or an interfacing systems LOCA 3rior to taking control from the remote shutdown panel (considering bot 1 spurious starting and running of pumps as well as the spurious repositioning of valves).
6.
There are many differences between Appendix R and IPE models. One of the differences is in the initiating events considered as possible from a fire event. The submittal does not indicate whether or not all the initiating events considered in the IPE have been systematically analyzed for the possibility of occurrence from a fire event.
For example, loss of component cooling or service water are not mentioned in the submittal.
Please provide a discussion regarding the selection of initiating events in the fire analysis, and whether or not the Appendix R related analyses have addressed all those initiating events modeled in the IPE that can possibly be induced by a fire.
7.
On page 4-38 of the IPEEE submittal, it is stated that "An additional nine compartments screened due to the fact that they did not contain fixed ignition sources." - From this statement it can be inferred that it was assumed that there is no possibility for transient combustibles to be introduced into these compartments. It must be noted that it is the NRC' staff's position that administrative controls are an insufficient basis for eliminating transient combustible fires from consideration.
This can lead to the omission of a potential vulnerability if a compartment contains cables or equipment from redundant trains.
For
)
6-each compartment where transient fires have not been considered, please provide the justification for this conclusion and provide a discussion on compartment inventory in terms of system trains and associated components (i.e., cables and other equipment).
Please explain whether or not the conditional core damage probabilities, given damage to all cables and equipment in these compartments, are significant (i.e.,
cables from redundant trains are present),
If the conditional core damage probability for a compartment is considered significant, please provide justification for assigning a very low likelihood of occurrence f.o transient fuel fires for the compartment. If transients were
';onsidered, what would be the impact on the final results, including the fire core damage frequency and t1e list of dominant fire scenarios?
HIGH WINDS, FLOODS AND OTHER EXTERNAL EVENTS 1.
Section 5 of the IPEEE submittal concludes. in aart, that SONGS Units 2 and 3 meet the criteria of the 1975 Standard Review Plan.
For these specific events; high winds, floods and other external events, provide a detailed comparison of the SONGS Units 2 and 3 Updated Final Safety Analysis Report design criteria to the design criteria of the applicable Standard Review Plan sections.
2.
High winds are screened out on a qualitative basis (i.e., the 100-year return period maximum wind speed is less than the design wind speed).
Please provide justification (including, as a minimum, the wind-hazard analysis) to demonstrate that the CDF associated with high winds is less than 1x10/yr.
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