ML20058C636
| ML20058C636 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 11/19/1993 |
| From: | Hebert J Maine Yankee |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| REF-GTECI-A-46, REF-GTECI-SY, TASK-A-46, TASK-OR JRH-93-237, MN-93-105, NUDOCS 9312020516 | |
| Download: ML20058C636 (6) | |
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MaineYankee MLLA BLLE LE cT R(CL11Sific[ 1972 r
EDISON DRIVE
- AUGUSTA, MAINE 04330 + (20M 622 4868 l
November 19, 1993 MN-93-105 JRH-93-237 j
UNITED STATES NUCLEAR REGULATORY COMMISSION Attention: Document Control Desk Washington, DC 20555
References:
(a) License No. DPR-36 (Docket No."50-309) i (b) USNRC Letter to MYAPCo dated September 17, 1993 - Review of l
Maine Yankee Response to NRC. Comparison Between Seismic Margin _
Assessment and USI A-46 Seismic Verification (TAC No. M76659)
(c) Maine Yankee Letter to USNRC dated June 15, 1993 - Comparison of l
the NRC SDMP to A-46 (d) USNRC Letter ~to MYAPCo dated April _ 29,.1993-Results of.
Comparison-MYAPS Seismic Design Margin-Program: Versus Requirements of USI A-46
Subject:
Comparison of the NRC SDMP'to A-46 l
Gentlemen-
-t i
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This letter is in response to your letter of September 17, 1993 which discussed'-
l the review by the staff of Maine Yankee's response, Reference (c), to'nine issues identified in Reference (d). You have indicated that issues._1, 2, 4, 5, and 6 were i
resolved and you requested further information on the four remaining' issues.
The attachment to this letter provides Maine Yankee's response to the four l
remaining issues.
We trust this information is satisfactory. Please feel free to-l l
contact us if you have any questions or require additional information.
i Very truly yours, j
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' James R. Hebert, Manager Licensing & Engineering Support Department.
JDM/jdm Attachment 1
c:
Mr. Thomas T. Martin Mr. J. T. Yerokun-Mr. E. H. Trottier
[
Mr. P. J. Dostie b
9312O20516 931119 PDR ADOCK 05000309 i
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ATTACHMENT l
l MAINE YANKEE RESPONSE TO ISSUES RAISED IN NRC LETTER DATED SEPTEMBER 17, 1993, REGARDING SEISMIC MARGINS AND A-46 Issue 3 - Omission of Relay and Breaker Chatter
.i Staff Comment:
In its response to this issue, MYAPCo indicated that it now has four engineers formally trained in the SOUG relay review methods (EPRI NP-7148) and is planning to conduct relay reviews with the remaining tasks to fulfill its commitment for completion of the IPE/EE by mid-1995. However, HtAWo's response I
was not specific with regard to the procedure that will be used for performing l
the relay seismic review, and the earthquake level that will constitute the basis for the seismic demand. As stated in its correspondence dated April 29,1993, the staff considers the licensee's commitment to use the S'US GIP, Revision 2, for performing the USI A-46 relay seismic adequacy reviews utilizing an earthquake level consistent with the NUREG/CR-0098 50th percentile spectrum. anchored at 0.189, an adequate basis for resolving this issue. However, if MYAPCo does not -
intend to make such a commitment, it should clearly identify for staff i
evaluation, the criteria and procedures that will be used in performing the relay i
seismic adequacy review.
MYAPCo Response:
Maine Yankee has committed to completion of a relay chatter review as an aspect of the NRC Seismic Margins review program and the IPE/EE. This ' work will be performed in accordance with our integrated schedule for the IPE/EE and in accordance with approved procedures.
As noted in our previous letter, Maine l
Yankee has several engineers trained by. SQUG in experienced based reviews l
l performing this work.
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Consistent with Maine Yankee's implementation of the NRC Margins Program,
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the relay assessments will be based upon a review level earthquake of 0.3g NUREG/CR-0098. The criteria and procedures to be used in performing the relay i
review will be provided by mid-1994. Our evaluation of potential cost effective i
upgrades that may be identified through these reviews will be provided to the.
i staff in mid-1995, in accordance with Maine Yankee's schedule for. submittal of the IPE/EE.
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Issue 7 - Loss of Offsite Power (LOOP)
Staff Comment:
In response to this issue, MYAPCo focused on the potential for certain 1
additional spurious actuation of relays if offsite power were to remain available. However, as stated in the staff's correspondence of April 29, 1993, there is additional equipment available during shutdown whose failure during an earthquake could impact essential equipment in the safe shutdown path. Some of the additional equipment was not examined as part of the Maine Yankee SMA, because the LOOP was assumed to occur. Therefore, to fully resolve this issue, the seismic adequacy of this sub-set of equipment, in the safe shutdown path, should be established considering the possibility of not losing offsite power.
MYAPCo Response:
In a telecon on 11/1/93 the staff clarified this issue to be a request that l
Maine Yankee assure that failures of equipment normally in operation with off-site power, would not affect the transition to the equipment qualified to achieve Hot Safe Shut Down (HSSD) (which does not rely on off site power), nor could such equipment fail in such a way as to compromise the HSSD path.
The Staff letter of April 29, 1993 gives limited guidance concerning the definition of " additional equipment available during shutdown whose failure during an earthquake could impact essential equipment in the safe shutdown path...considering the possibility of not losing off-site power." However, the staff seems to differentiate between safe shutdown equipment which is operable with a LOOP and a "sub-set" of safe shutdown equipment which is operable only if off-site power is available.
The Maine Yankee design powers all safe shutdown equipment with off-site power or, if LOOP occurs, with the emergency diesel generator (EDG) or seismic battery backed systems. There is no sub-set of non-emergency powered safe shutdown components in the Maine Yankee design.
Furthermore, Maine Yankee is a single unit station which eliminates any complex interaction with " swing" or commonly shared equipment. Emergency Diesel Generator (EDG) systems for example are totally redundant and exclusively dedicated to their respective busses. These systems are also independent of, and diverse from, the fast transfer capability between non-seismic off-site power systems.
Seismically induced failures of non-seismic equipment, which could physically impact safe shutdown equipment, were included in the scope of the NRC sponsored SDMP walkdowns. Equipment examined was identified on the basis of its physical proximity to safe shutdown equipment and the potential for physical interaction.
Operability or power source of the non-seismic equipment was not a criteria for examination of its potential interaction with safe shutdown equipment.
Block walls and ceiling structures, which were subsequently modified, are examples of proximity driven relationships which were identified.
Undesirable system interactions have historically been evaluated as separate l
issues.
GIP, page 3-7, section 3.2.5, excludes LOCA, HELB, fire, flooding, external events, etc. from the scope of the A-46 review.
This exclusion recognizes the work done to identify and eliminate undesirable ' interactions between equipment regardless of plant operating status at the time of the event.
As have others, Maine Yankee has participated in regulatory reviews as well as self-assessments of the design adequacy of the plant considering each of these issues.
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For example, Maine Yankee has experienced, since the SMA, a Safety Systems Functional Inspection (SSFI) on the Component Cooling Water and Service Water i
Systems and an Electrical Distribution System Functional Inspection (EDSFI) which examined in detail the seismic capability, functional capability, and potential undesirable system interactions with non-safety related systems.
These inspections are of particular note because they examined those safe shutdown systems which physically and functionally have significant interaction with non-seismic equipment.
Finally, Maine Yankee has instituted procedures (A0P 2-41) consistent with EPRI recomnendations, that assist the operator in transitioning from systems normally in operation to the HSSD systems for both " forced" and " voluntary" transitions.
Based on the above, it is Maine Yankee's position that there is no impact on the adequacy of the safe shutdown systems to perform their intended function should a LOOP r.ot be assumed.
Issue 8 - Lono Term Heat Removal Staff Comment:
MYAPCo stated that an additional 100,000 gallons of water from the seismically-qualified Condensata Storage Tank (CST), not considered in the SMA and NRC study, is available. According to the NRC's simplified calculations (which the licensee agreed with, "with small differences"), this additional inventory would still be insufficient (a shortfall of about 100,000 gallons) to meet the 72-hour guideline. MYAPCo further indicated that by using a combination of steaming and feed and bleed, a sufficient inventory would be available I
considering the extra CST volume of 100,000 gallons. It is not clear to the staff l
how this combination of core cooling methods, using the available inventory, could extend the shutdown condition and achieve the 72-hour guideline. In order j
to resolve this issue, MYAPCo should (1) demonstrate by calculations the validity
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of the proposed decay heat removal capability, (2) identify the operating procedures that are in place for removal of decay heat by employing a combination of the proposed core cooling methods, and (3) demonstrate that the seismic adequacy of the CST satisfies the SQUG GIP, revision 2, provisions for tank evaluation utilizing an A-46 earthquake level (0.189 NUREG/CR-0098 spectrum) or j
equivalent.
1 The other alternative suggested in the Maine Yankee response is the use of water from the fire system to replenish the Demineralized Water Storage Tank (DWST) using seismically-qualified equipment. The staff agrees this could be a valid approach. However, it needs to be demonstrated by calculations that the fire l
system can provide the necessary demand (both flow and total capacity), with the i
loss of offsite power, and that the critical equipment in the fire system is seismically qualified to an A-46 earthquake level (0.18g NUREG\\CR-0098 spectrum) or equivalent.
MYAPCo Response:
l The Maine Yankee response identified two methods for extending the decay heat l
removal following the depletion of the DWST, PWST and CST to meet the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> guideline.
One method involved injecting the RWST into the RCS in-a feed and l
bleed approach and the other involved continuing the use of the steam generators by replenishing the DWST from the fire system.
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4 The preferred method for removing core decay heat at Maine Yankee for the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> guideline, is by continuously feeding and steaming the steam generators. Per the staff's request, Maine Yankee has reconfirmed the capability of the fire system i
to provide adequate flow to refill the DWST and to maintain hot shut down heat removal capability per the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> guideline.
Less than 100 gpm is necessary following the depletion of the DWST (100,000) and PWST (150,000).
The fire system can provide several times that flow capability. Regarding capacity, the fire pond normally contains over 3 million gallons. The use of the fire system to refill secondary side coolant tanks is controlled by our abnormal-operating procedures (A0P's) and remains available following loss of offsite power.
J The fire pumps and their power sources, are seismic by design. Flow is supplied either by a direct drive diesel driven pump or by an electric pump powered from a safety bus. The fire system received only a limited Seismic Margins review as this system was not needed to achieve the objectives of the SDMP.
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Based upon subsequent field assessments, we believe that with certain additional walkdowns and analysis, the function of replenishing the DWST by utilizing the f
fire system can be assured following a major seismic event. Maine Yankee plans to complete these reviews by the end of the second quarter of 1994.
The alternative method of extending the decay heat removal utilizing the feed and bleed, while proceduralized and capable, by analysis, of removing decay heat for j
an extended period, is complex.
We also agree that this approach may fall several hours short of the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> guideline.
1 Issue 9 - Seismic Fraaility/ Capacity Estimates and Walkdown Staff Comment:
l The concern in this issue is not, as stated by Maine Yankee, the tradeoff l
between the use of nationally-accredited seismic experts to perform plant seismic reviews and the sole use of utility staff engineers. The issue is whether the undesirable experiences from certain earthquakes and equipment testing (collectively identified as " caveats" in SQUG GIP, Revision 2, dated February 14, 1992) have been properly addressed for equipment installed at Maine Yankee Atomic Power Station (MYAPS). The GIP developed by SQUG is a final product of the industry, SQUG, and the NRC staff and its consultant's efforts. The NRC has 2
contributed significantly to the GIP's final criteria and procedure through
'l research and collections of experience data.
Many equipment " caveats" were developed based on these experience data and vendor-supplied information after the Maine Yankee SMA effort was completed, and i
might not have been available to those experts and consulting engineers at the i
time of the plant-walkdown. Therefore, we are concerned that all the earthquake and test experience " caveats" may not have been addressed for safe shutdown equipment installed at MYAPS. This is the reason that the staff, in its April 29, 1993 letter, concluded that, as a minimum, a sample walkdown be performed by the staff, of selected equipment, to verify w' nether, in spite of the differences i
I between these two methods, the Maine Yankee SMA was.sufficiently adequate to resolve the USI A-46 issue at MYAPS, or whether additional action.is required to satisfy the USI A-46 resolution.
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W In its June 15, 1993 letter, MYAPCo stated that the consulting engineers and senior managers (identified in Attachment 4 to the June 15, 1993 letter) who performed the Maine Yankee review and walkdowns literally wrote the book for today's plant seismic review programs, both A-46 and IPE/EE. It has also stated its belief that the performance of the walkdowns using seismic experts without detailed procedures is equivalent to the performance of walkdowns by non-expert engineers with detailed procedures. MYAPCo further stated that performing the review again using procedures written by the same individuals who performed the plant review would not result in a substantial increase in the overall protection of the public health and safety.
The staff acknowledges the seismic expertise of the consulting engineers that performed the Maine Yankee SMA review and walkdowns and would accept a confirmatory letter from MYAPCo as an adequate basis for addressing the seismic fragility \\ capacity issue at the facility. The letter should confirm that the earthquake and test experience " caveats" (GIP, Revision 2, dated February 14, 1992) have been adequately addressed in the safe shutdown equipment installed at MYAPs and that the equipment in the safe shutdown path is seismically adequate to perform their intended function for an earthquake with the NUREG/CR-0098 50th percentile spectrum anchored at 0.189 MYAPCo Response:
i Maine Yankee has four SQUG trained Seismic Capability Engineers (SCEs). Three of the four are registered professional engineers with advanced degrees in structural engineering. All have 10-20+ years of seismic design experience.
Maine Yankee plans to use its SCEs to perform additional walkdowns as the basis for the statement requested by the staff that the " caveats" have been addressed for the safe shutdown equipment. The assessments and conclusions of our staff will be independently reviewed by a recognized expert seismic consultant familiar with the Maine Yankee plant.
The caveat reviews and the expert consultant peer review will be completed within the first half of 1994.
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