ML20199C209
| ML20199C209 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 11/03/1997 |
| From: | Kim T NRC (Affiliation Not Assigned) |
| To: | Richard Anderson NORTHERN STATES POWER CO. |
| References | |
| GL-88-20, TAC-M83644, NUDOCS 9711190264 | |
| Download: ML20199C209 (10) | |
Text
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November 3, 1997 Mr. Roger 0. Anderson, Director Licensing and Management Issues Northern States Power Company
.414 Nicollet Mall Minneapolis, Minnesota 55401
SUBJECT:
MONTICELLO NUCLEAR GENERATING PLANT - REQUEST FOR ADDITIONAL INFCRMATION RELATED TO IPEEE REPORT (TAC NO. M83644) l
Dear Mr. Anderson:
Supplement 4 of Generic Letter (GL) 88-20. " Individual Plant Examination of External Events (IPEEE) for Severe Accident Vulnerabilities." was issued in
-June 1991.
The IPEEE is to specifically address seismic and internal fire events, and other external events such as high winds and floods.
Supplement 5 of GL 88 20 was issued in September 1995 providing the staff position i
regarding modified procedures for satisfying the intent of the seismic IPEEE.
The Northern States Power Company (NSP) submitted its IPEEE report on March 1.1995. addressing internal fires, high winds, floods and other credible events. On November 20, 1995, the NSP submitted Revision 1 of its IPEEE report.
The staff has reviewed the NSP's IPEEE report submittals and determined that additional information is needed to complete the staff's review.
The staff's request for additional information (RAl) is enclosed.
The staff requests that NSP respond by January 30. 1998.
if you have any questions or comments concerning the enclosed RAI and/or the requested response schedule, please contact me at (301) 415 1392.
Sincerely.
ORIGINAL SIGNED BY Tae Kim. Senior Project Manager Project Directorate 111-1 Division of Reactor Projects Ill/IV Docket No. 50-263
Enclosure:
As stated cc w/ encl:
See next page
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Mr. Roger O. Anderson, Director Monticello Nuclear Generr"ng Plant Northem States Power Company cc:
J. E. Silberg, Esquire Kris Sanda, Commissioner Shaw, Pittman, Potts and Trowbridge Department of Public Service 2300 N Street, N. W.
121 Seventh Place East Washington DC 20037 Suite 200 St. Paul, Minnesota 55101 2145 U.S. Nuclear Regulatory Commission Resident inspector's Office Adonis A. Nebiett 2807 W. County Road 75 Assistant Attomey General Monticello, Minnesota 55362 Office of the Attomey General 445 Minnesota Street -
Plant Manager Suite 900 Monticello Nuclear Generating Plant St. Paul, Minnesota 55101 2127 ATTN: Site Licensing Northem States Power Company 2807 West County Road 75 Monticello, Minnesota 55362 9637 Robert Nelson, President Minnesota Environmental Control Cit!zens Association (MECCA) 1051 South McKnight Road St. Paul, Minnesota 55119 Commissioner Minnesota Pollution Control Agency 520 Lafayette Road St. Paul, Minnesota 55119 Regional Adminisuator, Region lil U.S. Nuclear Regulatory Commission 801 Warrenville Road Lisle, Illinois 60532-4351 Commissioner of Health Minnesota Department of Health 717 Delaware Street, S. E.
Minneapolis, Minnesota 55440 Daria Groshens, Auditor / Treasurer Wright County Govemment Center 10 NW Second Street Buffalo, Minnesota 55313 a.nu y ms l
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l MONTICELLO IPEEE REPORT l
Request For Additional Information (RAI)
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l ADoendix A - Seismic Analysis 1.
NUREG 1407, " Procedural and Submittal Guidance for Individual Plant t
Examination of External Events (IPEEE) for Severe Accident i
Vulnerabilities." issued in May 1991. requested that screening criteria be applied with respect to nonseismic failures and human actions, t
Provide a list of all operator actions that are required to ensure integrity of the chosen success paths.
Include in this list any operator actions that may be required to recover from relay chatter.
For each human action. Indicate the timr. after the earthquake that the operator action is required, and its location.
Indicate also the human error probabilities, accounting for seismic effects on operator actions.
i Provide a list of the random failures (and their failure rates) having the most significant putential to compromise integrity of the success
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paths.
Indicate the screening criteria ap) lied to rates of random failures and operator errors, and report tie results of your screening i
evaluation.
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' 2.
Please provide a success path logic diagram (SPLD) that clearly
- identifies the plant success paths and delineates the preferred and
-alternate paths.
Indicate the train / division of equipment for which the (following the earthquake) provide a discussion of the durationfor which the success paths apply.
Also be available.
3.
There is no discussion in the IPEEE report pertaining to an evaluation of seismically induced floods, specifically-addressing failures of nonsdfe shutdown equipment list (SSEL) tanks and failures of piping other than fire water piping, Pleasc report the findinss-of your walkdown and resulting evaluation portaining to seismicolly induced floods that may be caused by non SSEL tank failures and non fire water piping failures.
L 4.
The submittal does not discuss walkdown findings related to the potential for seismically induced 1 M s of capability of fire suppression systems.
Examples of relevant items found in past studies include (but are not limited to):
tanks or bottles-Unanchored CO, doffs penetrating suspended ceilings Sprinkler stan Fire pumps unanchored-or on vibration isolation mounts
. Unrestrained batteries / rack for diesel driven fire pumps Block wall interactions-with fire pumps or batteries Use of cast iron fire mains to provide fire water to fire. pumps NUREG 1407 suggests a'walkdown as a means 'of identifying any such items.
Please identify equipment in fire suppression systems that may be
. damaged due to the review level earthquake and discuss your resolution Enclosure l
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of these items, if any.
Provide guidelines given to walkdown personnel for evaluating these issues (if they exist).
5.
For the following key components that were not screened out, please provide representative capacity calculations, completed walkdown work sheets, walkdown notes / checklists and photographs:
of IPEEE submittal)pacity) cases for masonry block walls (page A 37 Bounding-(lowest ca Bounding (lowest capacity) case for flat-bottomed tanks Bounding anchorage evaluations for generic mechanical equipment categories () age A 37 of 1PEEE submittal)
Bounding anc1orage evaluations for electrical equipment categories (page A 38 of IPEEE submittal)
Bounding anchorage evaluations for heating, ventilation, and air conditioning-(HVAC) ductwork (page A 38 of IPEEE submittal) 4.16 kV Buses 14 and 16 (Table A.2.5 1)
Motor Control Center (MCC) 42A/B and 43A/B (Table A.2.51)
Containment Spray (CS) Pumps P 208A/B (Table A.2.5-1)
Battery chargers 052. D53, D54. D70. 080.-090 (Table A.2.5 1)
MCC D311. D312 (Table A.2.5-1)
Residual Heat Removal (RHR) Pumas P 202A.B.C.D (Table A.2.51)
RHR Room B HVAC Unit Cooler (Ta)le A.2.5-1) 1 (Note: Where multiple components of a given class are listed above, and
-the walkdown findings for all such components are essentially identical.
relevant information need only be provided for one representative component of the class.)
6.
Please identify the key components that control the HCLPF [high confidence low probability failure) capacity of each of the selected success paths, report the HCLPF capacities for these components, and submit HCLPF calculations for components having an HCLPF capacity less than the 0.39 review level earthquake (RLE) recommended in NUREG-1407.
7.
Please identify any soil founded or buried components (e.g., piping and tanks) or soil structures (including onsite or offsite canals, dams, or embankments) that can affect plant response.
Evaluate their importance to plant rafety, evaluate the potential and effects of soil response / failure (including soil settlements /defor.T.ations, soil stresses, etc.) on their capacities, and report your related analyses and findings, 8.
Discuss the ability of the various shutdown paths to respond to medium and large loss-of-coolant accidents (LOCAs) resulting from stuck open safety-relief valves.
9.
Please provide a list of the comments made by peer reviewers of the seismic !PEEE and indicate how each review comment was resolved.
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3 Anoendix B - Internal Fires Analysis 1.
In Section D 21 and in Figure B.2.1.1 references are made to screening methods and acceptability of risk and core damage frequency It is not clear whether or not a method or criterion other than that prescribed in the EPRl's Fire Induced Vulnerabilities Evaluation (FIVE) Plant Screening Guide had been used for this fire analysis. Please provide a i
brief description of the screening methodology the criterion for risk ecceptance, and the criterion for screening based on core damage i
frequency.
i 2.
In Section B.2.1. in regards to the screening methodology. it is stated that the contents of a fire area were investigated, and it was verified l
if "the area contains no system credited in the internal events probabilistic risk assessment (PRA) or cables supporting those systems."
Generally, the PRA or the individual plant examination (IPE) model is more complicated, and addresses a larger number of core damage sequences, than the safe shutdown model typically developed for 10 CFR Part 50. Appendix R. compliance.
Therefore, when Appendix R related equipment and cables are used in fire analysis. it is assumed that all other equipment and cables are lost givan a fire. Otherwise, cable tracing is done in addition to that done for Appendix R compliance.
It is not clear how the differences between A)pendix R and IPE models were dealt with in this fire analysis. The a)ove stated assertion can be valid only if the two models (i.e..
Appendix R and IPE) are identical.
Please provide a discussion on how the differences between the two models were dealt with in the fire analysis.
Has credit been taken for non Appendix R equipment?
If so, which cables were traced in addition to those from the Appendix R effort? What additional assumptions had to be made to alleviate the impact of lack of knowledge of cable locations for certain equipment considered in the IPE model?
3.
Based on an analysis of the location of key transformers and power leads to essential switchgear it was concluded that no fire scenarios can lead to loss of offsite power.
Did the analysis include control room and cable spreading room fires? The control switches for the breakers feeding Class 1E buses are located in the control room, and therefore the associated cables are routed through the cable spreading room.
Often these switches are installed on the same panel. A fire inside that panel or in the cable spreading room may induce control circuit failures that would essentially simulate the effects of a loss of offsite power event.- How was this scenario considered in the fire analysis?1 Please provide some details regarding control circuit failures leading to loss of offsite power and separation of the associated circuits.
4.
Feedwater was assumed to be available for all reactor building fire scenarios.
It was further stated that "An investigation of feedwater system components located in the reactor building indicated that no single fire in the reactor building could cause feedwater system failure." Were cables and associated control and instrumentation l
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If not it should l
be noted that the integrated control system that controls balance of plant functions is often extremely complicated and requires a thorough analysis to ensure that all possible cascading events are identified that would not affect the availability of the main feedwater system.
Thus, the assurance that main feedwater can remain available during a fire in the reactor building may not be valid for areas and rooms where the functions of some of the cables within the area are not clearly identified.
Please justify the assumption that there are no control or instrumentation circuits in the reactor building that could potentially affect the availability of the main feedwater system.
5.
In Section B.2.2 of the submittal, it 1s stated that "LOCAs are not expected to be induced by a fire." A failure in the control circuit of the automatic depressurization system (ADS) can lead to rapid depressurization of the reactor into the supp?ression pool. How has this scenario been considered in the fire analysis Provide a discussion of the control circuit and cable failures that may lead to such an event and the fire areas and rooms where these cables are located.
6.
Regarding component fragilities, the submittal does riot specify the qualifications of the cables used for power. control, and instrumentation circuits.
In Section B.2.4.2.3, a reference is made to cable fire test results without providing specific information.
Please provide information on the specifics of the tests mentioned in Section B.2.4.2.3.
- Also, i
the cables at Monitcello. provide a discussion on the qualification of For example, the cable could be qualified per IEEE-383 test stan9 rd.
If the cables are not qualified per IEEE-383.
what damage threshold temperature was employed in the fire propagation analysis? Were the frequencies of fire occurrence adjusted to account for the possibility of self-ignited cable fires? Please explain.
7.
In Section B.2.4.2.3. it is stated that fire zones 16 and 17 (turbine building cable tunnels) were screened out hsed on engineering judgment and cable fire test results. The fret;uency of fire ignition in these two zones could be small.
However, if at least one of these fire zones includes a critical set of cables, a potential vulnerability may have been omitted.
Please provide further information regarding the contents of these two fire zones in terms of system trains present in each zone, and the conditional core damage probability associated with these fire zones, assuming that a fire has failed all the cables in each zone.
8.
In Section B.2.2. item #7. it is stated that horizontal fire spread is assumed to be limited to 7 feet.
For cable tunnels and corridors.
important fire vulnerability related information would be lost if the area screened in early stcges of the analysis was based on lack of fire propagation.
That is, the conditional core damage probability (CCDP) for these fire areas / compartments may be found to be large. indicating a potential source of vulnerability.
Were the cable tunnels and corridors examined for possible plant impact (i.e,. assuming loss of all cables and circuits within the fire area)?
If such an analysis was conducted.
please provide a list of cable tunnels and corridors and their corresponding CCDP.
If-such an analysis was not undertaken, please r
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The tests conducted at ferm1 National Accelerator Laboratory is mentioned as the basis for assuming that the horizontal fire spread on cables would be limited to 7 feet.
It should be noted that fire tests have proven to be sensitive to test settings.
The results of the Fermi Lab tests can be used for other settings only if the cables are of identical material. dimensions, and loading on the tray.
Also, the configuration should be similar to that in the test.
Please provide a discussion on the applicability of those tests to the cables at Monticello.
9.
The possibility of interfacing systems LOCA (i.e., the possibility of inadvertent opening of high/ low pressure interface isolation valves) has not been addressed in the submittal.
Please provide a description of the analysis as requested in NUREG 1407.
10.
For the cable spreading room, if the suppression system functions properly it was assumed that damaae will be limited to the feedwater system.
Please provide the basis for this assumption. One can envision a fire practically at any corner of the cable spreading room. Thus, all control and instrumentation circuits present in the cable spreading room are )rone to damage from a fire.
Since the supression system would not be a)le to prevent some damage and without a morough knowledge of the relative location of the circuits in this room, one cannot ascertain which cables would be damaged and which would rer ain functioning - one cannot conclude that only a specific set of components or system train.c would be damaged from a limited fire (i.e., a fire that is suppressed successfully) in the cable spreading room.
Please provide the basis for selecting feedwater as the most limiting failure.
11.
The suppression system unavailabilities that aro 3rovided in the FIVE documentation have been used for deriving the pro) ability of system failure to extinguish the fire in the cable spreading room.
This data is acceptable for systems that have been designed, instd led. and maintained in accordance with ap:)ropriate industry J ; Ccds. such as those published by the National ire Protection Association (NFPA).
Please provide the basis for using the suppression system unavailabilities in FIVE for the Monticello fire analysis.
12.
Outside the control room, credit was not given to the possibility of the fire brigade putting out a fire before critical damage.
This is certainly a conservative practice.
However. in the case of using fire hoses. a misdirected stream could potentially fail redundant equipment (if such equipment is within a short distance of the fire). It is argued that sufficient smcke removal and emergency lighting is available to provide adequate visibility for the fire fighters.
Without an analysis of possible failure scenarios for the fire fighters, it is optimistic to conclude that a misdirected fire hose stream cannot take place.
Please provide a discussior,on how the possibility of such errors was considered in the analysis. What were the ccnclusions regarding the possibility of misdirected hose streams and the impact of such events on redundant trains?
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j 13.
NUREG 1407. Appendix 0, identifies the effect of fire suppressants on
~ safety equipment as one of the safety issues identified in the Sandia i
fire rist scoping study [FRSS).
Subsequent to the issuance of NUREG 1407 and GL 88-20. Supplement 4. this issue was designated as part of GSI-172. " Multiple System Response Program (MSRP)-Issues." Fire suppression system actuation events can have an adverse effect on i
safety-related comncoents either through direct contact with suppression agents or through indirect interaction with nonsafety related components.
It is important to recognize that fire suppression can impact components outside the immediate area of the fire as a result of actuation of fire suppression systems due to transport of smoke, propagation of hot gas layers, or misdirected manual suppression.
efforts.
Please describe how the IPEEE fire analysis accounted for the i
impact on component and system availability arising from the actuation of fire suppression systems 'n areas not directly involved in a fire.
14.
The control room fire analysis included two probabilities: (1) the probability of failure to suppress the fire and limit its effects to one cabinet (0.01); and (2) the probability of failure to control the plant-from the alternate shutdown system (ASDS) panel (0.0034).- Both probabilities are deemed here to be optimistic.
There is not sufficient evidence in the industry to support such a small failure probability for manual fire suppression.
For ASDS failure probability, a value of 0.05 has been used in most other IPEEE submittals.
Furthermore, the analysts have assumed that there are no dependencies between the two failure i
probabilities.
If the o)erators fail to suppress the fire pro >erly and are forced to evacuate tle control room it is assumed that AS)S activities are not influenced by the first failure.
Please provide the detailed assumptions (including any frequency reduction factors, and the probability of abandonment) used in analyzing the MCR [ main control 3
room) and justifications for thesc assumptions, if the two failure probabilities are adjusted according to the above comments (e.g., SUP =
0.1 and ASDS 0.05). how would the conclusions regarding risk ranking-and potential vulnerabilities change?
15.
Related to the preceding RAI NUREG-1407. Section 4.2 and Ap>endix C.
and GL 88-20. Supplement 4. request that documentation be su)mitted with the IPEEE submittal with regard to the FRSS issues, including the basis and assumptions used to address these issues, and a discussion of the l
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 FRSS as aotential contributors-to fire-risk. This issue was later classified as Generic Safety Issue 147 (GSI.147). " Fire Induced Alternate-Shutdown / Control Room Panel Interactions." Subsequent to the issuance nf GL 88 20. Supplement 4 the NRC staff' determined 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 )lant-(e.g., the MCR) might lead to potential control systems vulnera)ilities.
Given a fire in the )lant.
- the likely sources.of-control systems interactions could happen 3etween
'the control room, the remote shutdown panel, and shutdewn systems.
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I Specific areas that have been identified as requiring _ attention in the resolution of this issue include:
(a) Electrical independence of the remote shutdown control systems: The I
primary concern of control systems interactions occurs at plants l
. that do not provide independent remote shutdown control systems, The electrical independence of the remote shutdown panel and the i
evaluation of the level of indication and con;rol of remote shutdown control and monitoring circuits need to be assessed.
i' (b) Loss of control equipment or power before transfer:
The potential for loss of control power for certain control circuits as a result of hot shorts and/or blown fuses before transferring control from the MCR to remote shutdown locations needs to be assessed.
1 (c) Spurious actuation of components leading to component damage, loss-of coolant accident (LOCA). or interfacing systems LOCA:
The related or safe shutdown-spurious actuation of one or more safety duced cable faults, hot r
related components as a' result-of. fire in i
shorts, or component failures leading to component damage, LOCA, or interfacing systems LOCA. prior to taking control from the remote shutdown Janel. needs to be assessed This assessment also needs to r
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include t1e spurious starting and spurious repositioning of valves.
l (d) Total loss of system function: The potential for totcl loss of system function as a result of fire-induced redundant comptnent 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 that can be taken from the remote panel (s),
Describe how your
)rocedures provide for transfer of control to the remote station (s).
)rovide 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 rist contribution of these types of failurcs (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 prior to taking control running of pumps as well as the-spurious repositioning of valves)g and from the remote shutdown panel (considering both spurious startin 16,'In Section B.2.1, the " virtual rooms" are defined as closed electrical cabinets and panels.
It is assumed that fires originating inside a closed electrical panel or cabinet cannot
. propagate to the outside and affect adjacent cabinets, cables or other equipment. This assumption is not supported by industry fire experience. For high-voltage cabinets an explosive breakdown of the electrical conductors may breach the integrity of the cabinet and allow fire to spread to combustibles located thove the cabinet.
For.
example, switchgear fires at Yankee-Rowe in 1984 and Oconee Unit 1 i
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8 in'1989 both resulted in fire damage outside the cubicles. Also, it is possible for a panel or_ cabinet door to be either left open for an extended time or for the door to be opened in order to fight the fire, and thereby allow the fire to propagate outside.
Please provide the basis for the assumption and a discussion on how the specific enclosures were analyzed to ascertain that the at. sum) tion is a)plicable to them. -Please >rovide an assessment of how tie i
IPEEE results would change if tie >otential for propagation from an I
electrical panel to other combusti>1es or targets is considered.
- 17. The submittal states that operators would remove the fuses of control circuits to prevent spurious actuation of containment isolation valves. This operator action may be optimistic, since-proper removal of the fuses, before a hot short opens a valve.
cannot be credited without a thorough analysis of the timings of
- control circuit failure, the core damage process, and operator -
actions.
It is-possible for hot shorts to occur within a short time l
following fire ignition.
Please provide an explanation of how it can be ensured that the operators can always remove these fuses t
prior to occurrence of the hot short, if this action is credited properly, how would this affect the results of the IPEEE7 Is there i
a procedure for these actions?
-18. The fire suppression model for the cable spreading room takes into account a non suppression probability.
This approach is acceptable if the critical set of components and cables are relatively far 1
a) art, and therefore it will take a long time for a fire to damage tlem. On the other hand, if the key cables and components are close i
together. critical damage may occur before successful suppression.
How did the IPEEE fire analysts confirm the relative location of critical cables in the cable spreading room? Please provide a r
discussion indicating whether or not the exact location of various cables within the cable spreading room were identified and used in the cable spreading room fire analysis.
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