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UNITED STATES
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NUCLEAR REGULATORY COMMISSION g '/
E WASHINGTON, D. C. 20$$5 March 8, 1984
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.n Docket No.: 50-416 MEMORANDUM FOR:
Frank J. Miraglia, Assistant Director for Safety Assessment Division of Licensing Lester R. Rubenstein, Assistant Director for Core & Plant Systems Division of Systems Integration Frank Rowsome, Assistant Director for Technology Division of Safety Technology R. W. Houston, Assistant Director for Reactor Safety Division of Systems Integration FROM:
Thomas M. Novak, Assistant Director for Licensing Division of Licensing
SUBJECT:
eitEVIEW d'0'5 SITE /0FFSITE. POWER.ENHANCEMENLPROGRAMD JDRJmm Ell OUNIT7 In regard to our letter dated February 24, 1984, to MP&L (Attachment 1),
we have indicated that our review of MP&L's submittal on the electrical power enhancement program for Grand Gulf 'Jnit I would be completed in about a month from the time of the formal submittal. The details of the MP&L program were discussed at a meeting on February 21, 1984. MP&L's formal submittal on the subject is dated February 26, 1984 (Attachment 2).
Your review and evaluation of the MP&L proposal for Grand Gulf Unit 1 is requested toibelcompleted'by: March;30 p1984p In addition to those review branches represented at the February 21, 1984, meeting, the Auxiliary Systems Branch and the Reactor Systems Branch should evaluate MP&L's listing of Essential AC Loads in Table VI-I of the formal submittal. A written safety evaluation will be required. Table 1 provides a listing of the subject matter described..the licensee's February 26, 1984 submittal with an identification of the NRR management assigned lead responsibility for the review of the specific section.
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. Table 1 Report Section Assignments Section (Lead Responsibility)
II. Offsite Power Supply Reliability (AD for Core & Plant Systems)
III. Standby Diesel Generator Reliability (AD for Safety Assessment)
IV. Plant Performance Under Loss of AC Power Event (AD for Reactor Safety)
V.
Additional means of Onsite Power Supply - Gas Turbines (AD for Core &
Plant Systems)
VI. HPCS Diesel Generator Application (AD for Core & Plant Systems)
VII. Long Term Risk Assessment (AD for Safety Technology)
The responsible A/D should solicit reviews outside his organization as his needs require. Any requests for additional information should be promptly brought to the attention of Dean Houston, Grand Gulf Project Manager. Staff time for this review should be charged to TACS #54222, PA #1111 entitled
" Grand Gulf Unit 1 - Onsite/Offsite Power Reliability".
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g, hrDinas M. Novak, Assistant Director for Licensing Division of Licensing Attachments:
As stated cc:
D. Eisenhut R. Mattson T. Speis
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NUCLEAR REGULATORY COMMISSION T.
j WASHINGTON, O. C. 20555 k., *.. s /
February 24,' 1984
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Docket No. 50-416 Mr. J. 8. Richard Senior Vice President - Nuclear Mississippi Power & Light Company P. O. Box 1640 Jackson, Mississippi 39205
Dear Mr. Richard:
Subject:
Grand Gulf Nuclear Station, Unit 1 - Issuance of Facility Operating License The U. S. Nuclear Regulatory Connission on June 16, 1982 issued Facility Operating License No. NPF-13 to Mississippi Power and Light Company, Middle South Energy, Inc., and South Mississippi Electric Power Association for the Grand Gulf Nuclear Station, Unit 1 Iocated in Claiborne County, Mississippi.
License No. NPF-13 authorizes operation of the Grand Gulf Nuclear Station, Unit I at five percent power (191 megawatts thermal). Authorization to operate beyond five percent is still under consideration by the NRC.
As you are aware, since the date of issuance of License No. NPF-13, serious deficiencies have been discovered in Delaval emergency diesel generators.
Your facility has such equipment for both Division I and II emergency busses. In your submittal dated February 20, 1984, you discussed these deficiencies and concluded that the specific corrective actions, engineering evaluations and testing that have been completed, enhance the reliability of the DGs and provide assurance, with a reasonable level of confidence, that the Grand Gulf Nuclear Station TDI enginis will adequately perform their required l
safety function. Further, you have met with the staff on February 21, 1984 to j
discuss measures to enhance onsite/offsite power supplies.
In regard to the TDI diesel generator reliability issue, the NRC staff l
relying on the results from the TDI Owners' Group program will determine whether acceptable bases exist to demonstrate adequate reliability of the TDI units as proposed for use in nuclear facilities.
It is expected that our evaluation of the generic Owners' Group program will be completed by about a month after the submittal of the last required detailed program information.
. Consideration of plant-specific actions including specific proposed TDI enhancement programs will follow from that.
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Mr. J. B. Richard (
With regard to the enhancement program discussed at the February 21, 1984 meeting, you should provide a written submittal giving the details of the program and your basis for how it justifies interim operation. The staff will require on the order of a month to review that submittal. We will not recommend operation at power levels in excess of that currently authorized until our evaluation is completed.
I would be pleased to discuss this matter with you further at your convenience.
Sincerely,
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Darrell G. Eisenhut, Director Division of Licensing Office of Nuclear Reactor Regulation cc: See next page
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P. O. B OX 164 0, J A C K S O N. MIS SIS SIP PI 3 92 0 5 February 26, 1984
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- U. S. Nuclear Regulatory Commission 0 fice of Nuclear Reactor Regulation Vashington, D. C. 20555 Attention: Mr. Harold R. Denton, Director
Dear Mr. Denton:
SUBJECT:
Grand Gulf Nuclear Station Unit 1 Docket No. 50-416 License No. NPF-13 File 0260/L-860.0 Onsite/Offsite Power Supply Reliability AECM-84/0113 This letter confirms discussions and commitments made by Mississippi Power & Light (MP&L) in our meeting with your staff on February 21, 1984 In the preparation of this report, MP&L has attempted to be responsive to your staff's comments in that meeting. All suitable quantitative information available at this time has been incorporated into the attached document.
Overall, MP&L wishes to emphasize the substantial evaluation, inspection, maintenance, and testing efforts already. accomplished to address known problems and to verify the reliability of the Transamerica Delaval, Inc. (TDI) diesel generators installed at Grand Gulf Nuclear Station (GGNS). These efforts were most recently discussed in our letter to you, AECM-84/0103, dated February 20, 1984. MP&L has actively participated in the formation and activities of the TDI Diesel Generator (D/G) Owners Group. Based on an evaluation of nuclear and non-nuclear experience with TDI diesel engines, the owners group identified sixteen potentially significant issues which must be addressed by each TDI owner. In our above referenced letter to you, MP&L reported the evaluations and corrective actions taken at GGNS to address these issues. In addition to physical inspection and maintenance activities on the TDI D/Gs at GGNS, MP&L has reviewed records of quality assurance / control activities at TDI during diesel fabrication and reported these results in MP&L letter, AECM-83/0724, dated November 15, 1983. In that all significant known issues have been aggressively acted upon and that substantial TDI D/G testing has been accomplished at the GGNS site, MP&L concludes that the subject D/Gs are reliable sources of emergency power.
Y#_ _ h_
Member Middle South Utilities System 7
AECM-84/0113 MISSISSIFFI PONER & LIGHT COMPANY
- E' MP&L is strongly committed to the goals of the TDI owners group and will provide all necessary resources to support that effort. The group effort to review design and revalidate quality will be a valuable contribution toward verifying the TDI product reliability. Furthermore, the effort is considered confirmatory in nature in support of conclusions already demonstrated by MP&L.
In response to continuing concerns regarding the thoroughness of evaluations of TDI D/Gs to date, MP&L recognizes the necessity for an integrated approach to the demonstration of an adequate, reliable onsite/
offsite AC power supply network. The purpose of the February 21, 1984 meeting i
with your staff and of this submittal is to present an integrated approach for your review. The attached report discusses features of the existing design that contribute to relisole performance and capability in supplying power to GGNS. In addition to the already existing features and performance information discussed in the attachment, MP&L hereby commits to certain additional measures to enhance the network reliability.
Specifically, MP&L has taken steps to install an additional power supply i
to further strengthen the onsite power supply system. This additional power supply consists of three diesel fueled gas turbines which have a total capacity sufficient to operate the safe shutdown loads of one safety related division. The gas turbines will operate independent of the current onsite/offsite AC network, with the exception of the connection of its generated output to the plant. All appropriate interaction / interface parameters will be included in the safety evaluation associated with this temporary design change. The gas turbine units will be onsite and operable until the owners group final report on the GGNS TDI D/Gs has been submitted and approved by your staff, i
Activities associated with the gas turbine implementation include turbine installation and testing. procedure development, and operator training. These activities are currently scheduled to be completed by mid-March, 1984 In the interim, MP&L proposes to increase the plant's reliance on offsite power supplies by implementing an administrative control which is more conservative than the current ifmiting condition for operation. This more restrictive measure would conservatively lead to a plant shutdown when any one of the three (3) offsite power supplies are lost. This measure is described in the attachment.
In addition, procedures will be developed to allow the application of the third, safety grade, GGNS D/G (not a TDI unit) to allow the operation of selected, safety related systems. Providing that certain ongoing feasibility evaluations are favorable, the application of this safety grade D/G in this manner will provide an additional means of assuring long term decay heat l
removal capability. This consideration is discussed further in the attachment.
To further verify and confirm these actions as an effective means to enhance reliability of the onsite/offsite network, MP&L commits to a limited risk assessment of all significant aspects discussed here. The scope and additional details of this longer term effort are discussed in the attachment.
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AECM-84/0113 Page 3 MISSISSIPPI PC'7W LIC*. i COMPANY, In summary, MP&L proposes that the above discussed design features, corrective actions, performance information, and commitments to future actions implement a " defense-in-depth" concept in providing reliable power to GGNS.
MP&L considers those actions to be appropriate and adequate and, therefore, proposes that full power operation with the TDI D/G owners group evaluations ongoing is justified and constitutes no undue risks to the public health and safety. As always, our staff is ready to meet with you to further discuss any aspect of this position. The cooperation of your office and your staff is greatly appreciated in this matter.
Yours truly,
/
Q JPM: sad Attachment cc:
Mr. J. B. Richard (w/a)
Mr. R. B. McGehee (w/o)
Mr. T. B. Conner (w/o)
Mr. G. B. Taylor (w/o)
Mr. Richard C. DeYoung, Director (w/o)
Office of Inspection & Enforcement U. S. Nuclear Regulatory Connaission Washington, D. C.
20555 Mr. J. P. O'Reilly, Regional Administrator (w/o)
U.S. Nuclear Regulatory Commission Region II 101 Marietta St.,
N.W., Suite 2900 Atlanta, Georgia 30303
Attachment to AECM-84/Oll3 ONSITE/0FFSITE POWER SUPPLY RELIABILITY I.
INTRODUCTION II.
bFFSITEPOWERSUPPLYRELIABILITY III. STANDBY DIESEL GENERATOR RELIABILITY IV.
PLANT PERFORMANCE UNDER LOSS OF AC POWER EVENT V.
ADDITIONAL MEANS OF ONSITE POWER SUPPLY - GAS TURBINES VI.
HPCS DIESEL GENERATOR APPLICATION VII. LONG TERM RISK ASSESSMENT J118sdl
I.
INTRODUCTION The Grand Gulf Nuclear Station (GGNS) has an AC power system of diverse design. Offsite power is provided by two 500KV transmission lines which provide power to the plant through a failure resistant switchyard and a 115KV transmission line which provides power directly to an ESF transformer (thereby bypassing the switchyard). Onsite power is provided by two diesels manufactured by Transamerica Delaval. Inc. (TDI) and a third diesel manufactured by the Electro-Motive Division (EMD) of General Motors. Mississippi Power & Light Company (MP&L) believes that this system is a highly reliable system which fully meets and exceeds the regulatory requirements for such systems.
Questions have been raised regarding the adequacy of the TDI diesels.
Although MP&L believes these questions have been resolved, further enhancements and evaluations are being implemented to provide interim assurance of the reliability of the GGNS AC power supplies, thus allowing power ascension testing to resume.
l Section II and III of this attachment discuss the reliability of the existing offsite and onsite power system at GGNS.Section IV discusses a preliminary evaluation of the GGNS capability tc withstand a station blackout. The duration of greater than six hours provides substantial time for actions to be taken to restore power and, in particular, to make use of power system enhancements described below.
MP&L has initiated action to install three gas turbines on site which have a total capacity sufficient to operate essential electrical loads in the event that both offsite power and the IDI diesels are unavailable. This provides an extra level of in depth protection against the loss of all AC power. Procedures are being developed which will enable the gas turbines to be energized and available for use within a short time following a loss of other AC power sources. Until the gas turbines are installed and operable, an additional administrative control which is more conservative than the current limiting condition for operation is being proposed.
These factors are discussed in Section V.
As a last resort, it is also possible to make use of the HPCS diesel (manufactured by EMD) to provide certain essential heat removal loads and substantially extend the duration prior to threatening the health and safety of the public. This is discussed in Section VI.
MP&L also proposes a confirmatory risk assessment to be conducted during the early period of resumed power ascension testing to provide a quantitative evaluation of onsite/offsite power supply reliability. The proposed risk assessment is discussed in Section VII.
The original system plus the hardware, procedural and administrative enhancement provides a defense in depth which assures that the GGNS AC power system is sufficiently reliable to allow resumption of power ascension testing.
J118sdl3 I
II.
OFFSITE POWER SUPPLY RELIABILITY A.
Introduction As discussed with the NRC Staff in the meeting held on February 21, 1984, MP&L offers several parameters for consideration regarding the reliability of the offsite power supply to Grand Gulf Nuclear Station (GGNS). The factors described below are: system and switchyard design, system outage data, and stability evaluations.
These features and measures of performance are considerations which contribute to a highly reliable offsite power supply network.
B.
System Design
As illustrated in Figure 11-1 the immediate grid network associated with GGNS provides three power supplies to the nuclear plant. There are two 500KV transmission lines, one generally north to Baxter Wilson generating station and one generally south to the Franklin substation. The third supply to GGNS is the 115KV line from Port Gibson, in the east. This system provides GGNS with an additional power supply not required by 10CFR50 General Design Criteria (GDC) 17 and by Technical Specifications, Sections 3/4 8.1.1 and 8.1.2.
It should also be noted that while the offsite supplies do intersect at several locations, they are not on common rights of way, exceeding the requirements of GDC 17.
The two 500KV lines terminate at the GGNS switchyard, immediately east of the plant. See FSAR Figure 8.2-3 (Attached as Figure II-2).
The 115KV line from Port Gibson approaches the switchyard from the east and is buried as it crosses beneath the Franklin 500KV line.
After crossing the Franklin line, the 115KV line resurface's and runs overhead to its respective Engineered Safety Feature (ESF) transformer (# XFMR.12), as illustrated in FSAR Figure 8.2-3 (Attached as Figure II-2).
By this configuration the 115KV supply to the plant is independent of the 500KV switchyard and, therefore, exceeds the requirements of GDC 17 which allows a common switchyard.
It should be noted that the tornado that inflicted damage to the GGNS construction site on April 17, 1978, did result in significant damage to the 500KV switchyard. At the time, construction power was supplied via the 115KV line from Port Gibson. Service from the 115KV line to the plant site was not lost during the subject tornado. While the subject line is not buried the full extent of its run adjacent to the switchyard, this feature does provide an additional measure of protection from the total loss of power to the plant.
C.
Switchyard Design A simplified schematic of the GGNS switchyard and the relationship to the ESF, divisional power supplies is shown in Figure II-3.
Note that there are 3 ESF transformers, each of which has the capability to supply any of the safety related, divisional busses. Two of the three ESF transformers are supplied from the 500KV switchyard. The remaining ESF transformer is supplied from the 115KV switchyard.
(See Figure II-3.)
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The switchyard arrangement is designed for. connecting both GGNS unit generators to the system grid. The switchyard is referred to as a
" breaker and one-half" arrangement providing the capability to isolate a switchyard fault or problem and still maintain the capability to provide a path from the source to the load. For example if any single breaker failed open, an alternate route is available in the switchyard to provide power from the grid to the subject ESF transformer.
2 As discussed earlier, in addition to the flexibility provided by the 500KV switchyard, the third ESF transformer, supplied by the Port Gibson 115KV line, is independent of the 500KV switchyard and provides another route to the divisional busses (Class 1E). Along with the diesel generator, each divisional bus has four power supplies.
An additional feature of the switchyard design contributing to favorable performance involves an improvement in the method of supplying startup and normal plant loads. A commonly used alignment places startup loads on a startup transformer and eventually places loads on the plant generator following startup. In the case of j
GCNS, normal plant loads are supplied from the 500KV switchyard, thus eliminating the need to shift from a startup transformer to the plant generator. In addition, plants of earlier designs generally experience an immediate loss of power when the station turbine generator trips. Since the GGNS plant loads are always supplied i;
from the switchyard, the plant scram and/or turbine trip does not interrupt power to those loads necessary to place the plant in a IJ safe condition. The favorable GCNS design reduces the plant's exposure to switching and other events which are significant contributors to incidents involving the total loss of offsite power.
4 D.
Stability Analyses The standard stability analyses and load flow studies for the offsite grid network associated with GGNS vere accomplished in support of.the FSAR review process. The majority of the work was reported in 1980 and can be found in Section 8.2 of the FSAR.
Updating analyses are performed periodically to account for. system changes and confirm the FSAR reported results. The latest confirmatory work was accomplished by MP&L in July,1983. The original FSAR load flow studies and the most recent evaluations indicate that the grid system is stable and can withstand emergency line outages and redistribute the loads without de-energizing other 2
lines in the system.
E.
Outage Information Outage data on the 500KV and 115KV transmission lines associated with GGNS is presented belcw. This data is updated from that presented in FSAR Table 8.2-1 and includes performance information through February, 1984 I
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J118sd9
IABLE II-1 115KV 500KV Years of data 11 123 total outages 8
39 Outages lasting over 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> 0
14 1 Data presented for 115KV network supplying GGNS; Baxter Wilson to Natchez, including Port Gibson to GGNS.
2 Data presented for entire 500KV network in MP&L portion of MSU 3 system.
Includes switchyard damage from April, 1978 tornado.
The 500KV transmission system, the preferred source of offsite power, has been a dependable distribution network since its introduction into the MP&L system. The total outages listed above translate to an average outage rate of under 1.0 outage / year /100 miles of 500KV transmission line.
The 115KV supply to GGNS, while exhibiting a slightly higher outage rate (due to shorter total length of transmission line) is considered to have performed in dependable fashion as well.
Regarding the 115KV outage data, it should be noted that only one of the eight emergency outages in 11 years of operation lasted over one hour.
There has not been a total loss of offsite power to GGNS since two or more supplies serviced the plant.
F.
Conclusion - Grid Reliability The offsite power supply system provides three (3) reliable sources of power to GGNS. Standard stability studies, updated periodically, confirm that the offsite network performs in a stable, reliable manner in response to systeu perturbations. Outage data on the offsite network lends confidence to the expectation that at least one offsite power supply will b'e available to the plant. The plant switchyard, in concert with the ESF onsite distribution, is considered to be an advanced design, providing significant flexibility in the methods of supplying pcwer to the plant and exhibits several features which enhance its performance and reliability.
Overall, MP&L considers the offsite power supply to be reliable both in its design and performance. The parameters and aspects discussed in this section will be treated in a more quantitative fashion in the risk assessment discussed later in this attachment. This longer term effort is expected to confirm those conclusions presented here.
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III. STANDBY DIESEL GENERATOR (D/C) RELIABILITY MP&L has undertaken a comprehensive program to enhance and verify the reliability and performance of the two Transamerica Delaval, Inc. (TDI)
D/Gs installed at GGNS. A description of this program was provided to the NRC in the MP&L letter, AECM-84/0103, dated February 20, 1984 The concern over the design adequacy of the TDI D/Gs was prompted by a crankshaft failure that occurred at Shoreham with their TDI supplied D/Gs. This led the NRC to issue IE Information Notice 83-58 which identified GGNS as having possible crankshaft design deficiencies. MP&L began an aggressive series of inspections, tests, maintenance activities and evaluations related to TDI D/G reliability. The major areas of concern which were addressed included piston inspection and replacement, crankshaft inspection, and an independent design verification of the l
crankshaft. Included in the comprehensive program was a review of GGNS D/G operating data thru February 1, 1984 The result of this review j
indicated a start reliability in excess of 99% for the two TDI D/Gs at 4
GGNS.
j In letter, AECM-83/0811, dated December 23, 1983, MP&L formally notified the NRC of the formation of a TDI D/G Owners Group. MP&L, as an active 4
member, will support and participate fully in the group's Design Review /
i Quality Revalidation (DRQR) program. MP&L is committed to implementing i
the group's recommendations, as they apply to GGNS, unless exceptions are fully justified.
In the TDI Owners Group meeting with the NRC on January 26, 1984, the Owners Group identified sixteen (16) potentially significant problems related to TDI D/Gs. In letter AECM-84/0103, MP&L presented details of these concerns, their applicability to GGNS, and corrective actions taken, if required, for each concern.
l As part of the GGNS D/G reliability program, MP&L is performing additional surveillances to verify engine reliability. These are listed as follows:
(1) A monthly operational test will be conducted for a four i
hour duration (instead of one hour). This monthly surveillance will be conducted such that one diesel is tested every two weeks.
(2) A monthly surveillance will be run utilizing vibration monitoring.
(3) A visual i
valkdown will be conducted weekly.
(4) An engine air roll will be performed eight hours after shutdown to check for water leakage into cylinders.
4 As an added precaution, MP&L is co--itted to starting and running at least one standby diesel generatt. ia the event that a tornado warning is in effect for the GGNS site area.
Overall, MP&L considers that the substantial evaluation, inspection, maintenance, and testing effort put forth to date establishes the GCNS l
standby D/Gs as reliable emergency power supplies. This effort along l
with MP&L's active participation in the TDI D/G Owners Group and our j
aggressive action to provide additional reliability enhancements demonstrate our intentions to be fully cooperative and responsive to your staff in this matter and our commitment to the safe operation of GGNS.
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I IV.
PLANT PERFORMANCE UNDER A LOSS OF AC POWER EVENT A preliminary evaluation of GCNS to withstand a station blackout (SBO),
i.e., a total loss of AC power except that provided by battery driven inverters, has been performed. The effects would be dependent on the operating state of the plant at the time of the event. The bounding operating state would be that of full power operation with an equilibrium core which maximizes decay heat generation simultaneously with the reduced availability of mitigating systems. Such a conservative assumption is not appropriate for this preliminary evaluation, instead it is assumed that an initial clean core undergoes power ascension testing and that the postulated loss of AC power occurs at 75% power. Other assumptions used in this evaluation are conservative. The immediate plant response would be similar to that which occurs during a loss of offsite power transient:
main generator load rejection and turbine trip reactor scram MSIV closure (due to loss of solenoid power) reactor recirculation pumps trip Under station blackout conditions, all systems and equipment not powered by the station batteries would be lost. The most significant losses would involve the systems for drywell cooling, suppression pool cooling I
and cooling for areas such as the RCIC equipment room and the control room.
The systems which would be available to maintain the reactor in a safe 4
condition following an SB0 include:
1.
Safety grade instrumentation to provide the operator with necessary information relative to reactor and containment status.
2.
Reactor Core Isolation Cooling System - This system provides necessary coolant injection to maintain coolaat inventory. The RCIC pump is a turbine driven component utilizing steam from the reactor pressure vessel. Monitoring and control instrumentation ~
power is provided by the 1-E DC power supply system.
3.
1-E DC Power Supply System - This system of batteries provides the required power for emergency lighting, control relays and the de-powered components of the RCIC system.
4.
Safety / Relief Valves and Automatic Depressurization System -
These valves provide a means of depressurizing the reactor vessel and maintaining it within safe limits. The safety / relief valves have both a relief valve capability until their air accumulator is emptied and a safety valve capability. The valves in the ADS have similar capabilities;-however, upon loss of the air compressor following an SBO, the ADS has the capacity to provide P73rgl 3
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two actuations of each valve and then hold each valve open for five days. For longer periods of time, the system can be recharged by connecting compressed air cylinders to a seismic Category I air supply line external to the containment.
Replacement of these external cylinders can be accomplished as required per the station blackout emergency procedure.
5.' Diesel-Driven Fire Pump and Fire Protection System Water Supply -
This pump and water supply can be aligned to supply additional
. water to the containment to provide additional heat sink capacity.
The capacities of these systems have been reviewed to determine their capabilities to ensore adequate protection following an SBO. This review has identified:
the-Condensate Storage Tank can provide cold water to the reactor pressure vessel (RPV) through the RCIC system for six and one-half hours the 1-E batteries can supply the necessary power for more than six hours assuming nonessential loads are removed as required by the emergency procedure the air supply for ADS operation can be readily replaced and thus ADS unavailability need not be considered a limiting factor in mitigating the consequences of an SBO.
Area cooling following an Soo event is lost as the fans and cooling water supply are AC-powered. In the control room, sensible heat stored in the equipment and the thermal load of the operators occupying the room would be the major heat' loads following an SBO. All of the AC-powered control room equipment will be unavailable and the use of equipment powered by the batteries or uninterruptible power sources will be minimized to conserve battery capacity. The room temperature would be expected to rise slowly. No peak temperature for the control room has been calculated following an SBO. The peak temperature which develops within the first ten hours of the SB0 event would not be expected to adversely affect equipment operation. Instead, the higher temperature would accelerate the aging of the component and its qualified life would be subject to evaluation following such an event.
The_RCIC equipment room temperature is expected to rise only slowly and the equipment should be capable of extended operation under the anticipated conditions. Violation of the room temperature limit would not result in immediate loss of equipment. In addition, the plant can still be maintained in a safe condition should RCIC be temporarily shut off due to equipment room temperatures. Both the existing RPV water inventory, which is sufficient to maintain fuel integrity for a significant period of time, and the availability of the Fire Protection i
Water Supply System as a backup source of makeup water serve to minimize the limiting influence of any RCIC room temperature concerns.
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In addition to reviewing the capabilities of the systems which can maintain the reactor in a safe condition, an analysis was undertaken to determine if the containment response would be limiting.
Based on a combination of conservative and realistic assumptions, it was found that Grand Gulf could sustain the postulated event for a minimum of six hours without exceeding containment design pressure.
(The containment has significant structural margin and could sustain higher pressures than design without losing it's functional capability.)
The postulated total loss of AC power includes the loss of all diesels with the consequential loss of all containment heat removal capability and the loss of all electrically operated pumps which can be used for core injection or spray leaving only the RCIC system to fill this need.
Because the primary concern at GGNS has been the reliability of the TDI diesels, it could be postulated that the Division III diesel which is dedicated to operation of the HPCS system is still available. In its designed operational mode, if it is assumed that all other AC power has been lost, this system would provide essentially the same function as the RCIC system. This has not been explicitly evaluated in this analysis since there is still no automatic capability to remove heat from the containment and containment factors are still limiting.
The suppression pool and containment air temperature was conservatively evaluated by performing a mass energy balance. The FSAR reactor vessel sensible energy, feedwater energy, and blowdown energy were added to the suppression pool along with the decay heat energy determined in accordance with ANS 5.1 (assuring a 75% initial reactor power). The upper pool dump was not considered since the suppression pool makeup system uses an AC-powered motor operated valve. Containment heat sinks were included in the evaluation.
Once the total loss of AC power has been identified, it is assumed the operator takes action to depressurize the reactor pressure vessel to about 200 to 300 psi at the rate of 100*F per hour.
(This pressure is needed to run the RCIC turbine.) The depressurization minimizes the impact on drywell temperatures and prevents the drywell from exceeding design temperatures.
The RCIC suction is assumed to be switched to condensate storage within one hour of the transient. This transfer is desirable since suction water temperatures of approximately 175*F become limiting for RCIC operation due to NPSH and lube oil temperature limitations.
With no RHR cooling, the suppression pool and containment air space temperatures continue to rise slowly. The containment design pressure is not reached in the six hour period after the event.
An important consideration in the assumptions of core cooling systems operation is the availability of the transmitters located within containment that provided RPV water level and pressure indication.
Although their environmental qualification level is about 185'F, their capability is judged to be about 225*F.
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temperatures are calculated to be less than 225'F for at least seven hours; hence, they are not considered limiting. These transmitters are powered from DC sources, and it is aisumed that the necessary control room meters and/or recorders have available DC power.
One important conservative assumption made in this evaluation was that of not using the upper pool dump. Had the upper pool dump been incorporated in the analysis, the minimum time before the containment design pressure is exceeded would increase to 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.
It is concluded that GGNS can conservatively withstand an SB0 for in excess of six hours during power ascension up to 75% power. It is believed that a more detailed analysis would clearly indicate a longer duration, but six hours is far in excess of the time required to take other mitigating actions as discussed elsewhere in this submittal.
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1 V.
ADDITIONAL MEANS OF ONSITE POWER SUPPLY - GAS TURBINES l
MP&L is presently installing three Allison Division, General Motors Model 501 liquid fueled gas turbines. These turbines drive Allis Chalmers type ABW synchronous generators capable of producing a combined output of 6200 kilowatts of three phase, 60 hertz, 4160 volt power. The units are provided in totally enclosed trailer mounted assemblies. The assemblies are self contained and includes all necessary controls for reliable power generation.
The gas turbines are presently being installed at Grand Gulf near the l
Unit 2 diesel fuel oil storage tanks as shown on Figure V-1.
This site l
was chosen to ensure that potential damage to the Unit 1 safety related equipment and structures will not occur due to turbine missiles or fire.
The location will preclude environmental concerns such as control room ventilation intake of gas turbine exhaust gases and will prevent unavailability of the gas turbines due to flooding and normal standing water conditions. This location will also provide an advantageous electrical connection to the non-Class IE portion of the Unit 1 plant distribution system.
(See Figure V-2.)
The gas turbines will be available to supply additional power to GGNS Unit I to shutdown the plant in the unlikely event of a total loss of off-site power and the unavailability of both standby emergency diesel generators. The gas turbine generator system is a non-safety related, non-seismic category I, non-Class lE system and is non-single failure proof. The power will be supplied through a locked-open breaker under the administrative control of the Unit I control room operators as shown in Figure V-2.
Procedures are being developed for the emergency operation of the gas turbines in the event they would be called upon to support the safe shutdown of Unit 1.
All personnel required to implement these procedures will be trained as necessary to ensure proper connection and operation of these units. These procedures will be demonstrated to ensure correct and timely operation of the gas turbines for safe shutdown of Unit 1.
MP&L will continuously maintain personnel trained to operate these units for the duration of this commitment.
Operating procedures pertaining to the use of the gas turbines will require that the turbines are manually started and made ready for loading when two or more offsite power supplies to GGNS are lost. This approach will assure that the turbines are ready to support the plant in the unlikely event that both standby diesel generators fail to respond at the loss of all offsite power.
In the event of the loss of offsite power and the subsequent failure of the standby D/Gs to start and supply power to their respective divisional busses, the gas turbine generator output breaker will be closed onto the de-energized Division 1 or 2 ESF bus. The gas turbines will supply power to that bus until a normal onsite or offsite source is restored.
MP&L has taken steps to help ensure these power units will not require significant maintenance in the forthcoming six months. Two units (2000KW each) have less than 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> of operation since their last overhaul.
The third unit (2200KW) has approximately 500 total hours of operation.
Jll8sd5
l Other factors such as fire protection, missile protection, security, site flooding characteristics, OSHA noise restrictions, communications, and emission restrictions are also being considered for the utilization of these turbines. A program of monthly testin,g for the gas turbines will be implemented to verify operability.
MP&L commits to maintain the gas turbines for Unit i use until the acceptable resolution of this issue by the NRC, based on the final report of the TDI D/G Owners Group for GCNS.
Prior to the gas turbines being demonstrated operable, MP&L proposes to implement the following additional administrative controls:
With one of three offsite power supplies inoperable, attempt to a.
restore inoperable supply within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
b.
If unsuccessful, place plant in Hot Shutdown within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and in Cold Shutdown within the following 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
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VI.
HPCS DIESEL GENERATOR APPLICATION The primary NRC concern has been with reliability of the two TDI diesels which provide emergency standby power for all essential systems except the HPCS system which is powered by a separate dedicated diesel generator. This third diesel generator is a 3300 KW capacity set manufactured by EMD. As noted earlier in this report, the availability of the HPCS diesel would not significantly affect the capability of GGNS to withstand a loss of all other AC power if it were used in a normal alignment.
If, however, all other sources of AC power were lost (including the gas turbines), it is possible to manually connect the HPCS diesel to provide power to loads normally served by the TDI diesels.
A detailed evaluation of this mode of operation is in progress. The HPCS diesel does not have sufficient capacity to operate all Division I and II loads identified in FSAR Tables 8.3-1 and 8.3-2, but certain essential loads which would enable GGNS to withstand such a partial SB0 (loss of all AC power except the HPCS diesel) for an extended period of time.
These loads are identified on Table VI-I and should be noted to include:
- HPCS diesel auxiliaries
- one RRR pump and all associated auxiliaries and support systems needed to operate one train of shutdown decay heat removal
- battery chargers
- drywell cooling
- instrument air compressor The total load required for such operations is 2931 KW which is within the operating capacity of the diesel generator.
Such an unusual alignment and operating mode would be used only as a last resort and should be considered a very remote event due to the total reliability of the GGNS AC power system (including the enhancements, i.e., the gas turbines). A more comprehensive evaluation of this use of the HPCS diesel is in progress including starting loads, safety implications, and exact methods for making the manual connections. If the safety and feasibility are demonstrated (as is now anticipated), then appropriate precedures will be implemented to allow this mode of operation if it is ever needed.
l Operation in this mode would use power from a diecel which is diverse in design and manufacture from the TDI diesels to significantly extend the conservative minimum capability of six hours discusred earlier for an essentisily indefinite period of time, thus assuring the safety and health of the public even if all other AC power sources are lost.
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TABLE VI-I ESSENTIAL AC LOADS ITEM LOAD (KW)
RHR~ Pump 803 SSW Pump 639 Motor Operated Valves 185 Control Room Emergency Fan 20 IE Battery Charger 110 Drywell Coolers 120 Fuel Pool Cooling and Recirculation Pump 124 SSW Pump 0/A Fan 40 Control Room Air Conditioning and Fan 120 SSW Cooling Tower Fans 244 ESF Electrical Room Cooler Fan 12 Instrument Air Compressor 230 Safeguard Switchgear and Battery Room Fans 122 ECCS Pump Room Cooler 8
HPCS D/G Accessories (Cooling Water Pump, Supply Fan and Auxiliaries) 154 TOTAL 2,931 J118sd12
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VII. RISK ASSESSMENT OF EVENTS INVOLVING A LOSS OF AC POWER l
A.
INTRODUCTION As discussed elsewhere in this submittal, a major concern of the Nuclear Regulatory Commission (NRC ) staff is the adequacy of the Division I and II diesel generators. Mississippi Power & Light (MP&L) believes that the diesels are adequate but has conducted substantial evaluation of the adequacy of the overall AC power system and has proposed substantial measures to enhance the adequacy of the overall AC power system.
At the February 21, 1984, meeting between MP&L and NRC staff I
members, the possibility of conducting a risk assessment for loss of AC power at the Grand Gulf Nuclear Station (GGNS) was discussed. It was suggested by the NRC that such an assessment could serve as i
confirmation of the adequacy of the GGNS offsite and onsite AC power supplies.
MP&L intends to conduct such a risk assessment beginning immediately and proceeding simultaneously with power ascension and associated testing on a schedule consistent with confirming the adequacy of the GGNS AC power systems within approximately 90 days following receipt of a full power license.
B.
. GOALS AND OBJECTIVES The primary goal of the proposed risk assessment is to provide confirmatory support to demonstrate adequacy of the GGNS overall AC power system. The central objective which will be used to meet this goal is the performance of an assessment of core melt frequency associated with loss of AC power events.
In order to carry out the central objective, a two phase assessment of diesel generator reliability will be performed: first, a direct assessment of diesel generator reliability (especially the Transamerica DeLaval. Inc. machines) which will also provide useful long term information to MP&L and the NRC for addressing Unresolved Safety Issue B-56 " Diesel Generator Reliability" and second, an assessment of the reliability required to meet a numerical goal of core melt frequency based upon appropriate sensitivity studies.
In order to provide meaningful analytical information for the assessment of core melt frequency, an assessment of the capability of GGNS to withstand a loss of all AC power, i.e., a Station Blackout (SBO), is needed and will be performed. In addition to providing the capability information needed for the risk assessment, the information will be useful to MP&L and the NRC in addressing Unresolved Safety Issue A-44 " Station Blackout." It will also be used by MP&L as a part of the information needed to respond completely to Generic Letter 83-24 This risk assessment will bc initiated immediately and conducted in parallel with resumed power ascension testing. The results are to be submitted to the NRC within approximately 90 days following issuance of a full power license.
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ASSESSMENT OF CORE MELT FREQUENCY The calculation of core melt frequency will be based on probability calculation using event trees in which a loss of AC power is a dominant factor in leading to core melt. Because of the tight schedule, event trees will be adapted from existing risk assessments to the extent feasible. In addition, to the extent feasible, system level data will be used where feasible rather than new fault tree
-construction. Where fault trees are required, existing work will be 4
i adopted as appropriate. The NRC sponsored RSSMAP study is being j
considered for use in this regard. Certain neu and additional work will be required especially in the area of assessing offsite power and diesel reliability. In these cases, fault trees'or other probabilistic methods will be used as needed. This is discussed in more detail in later sections of this attachment.
In addition to the basic calculation of core melt frequency, studies will be conducted to determine the sensitivity of the results to varying reliabilities of components of the GGNS overall AC power system. One component of the sensitivity study will determine the required diesel reliability for the TDI diesels to allow meeting a numerical goal for core melt frequency.
D.
STATION BLACKOUT CAPABILITY A major support element to the risk assessment is an assessment of the capability of GGNS to withstand an SBO. This is particularly important for assessing component or system repair probabilities and the time available for other operator intervention.
To the extent needed for ths risk assessment, a more detailed evaluation will be performed of the capability of GGNS to withstand an SBO, i.e., of the allowed duration of an SB0 prior to substantial core damage.
l This evaluation will consider at a minimum such possible limiting i
factors as:
I containment temperature drywell temperature suppression pool temperature j
pump seal temperature limits instrumentation requirements and associated temperature limits control room and remote shutdown panel temperatures battery life pump room temperatures To the extent necessary for a meaningful analysis, this evaluation will include a variation of'the time after shutdown that the SBO' occurs.
4 The core history and initial power level used in the analysis will
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be' consistent with confirming the adequacy of the GGNS AC power system to allow continued power ascension testing.
4 4
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l E.
RELIABILITY ASSESSMEN1 0F AC POWER SYSTEMS Reliability assessments will be made of the GGNS AC Power System consisting of multiple offsite transmission lines including one buried line which bypasses the switchyard and which provides a tornado resistant offsite power supply, three emergency standby die'sels (of two diverse types), and three gas turbines.
The basic assessment of the offsite power reliability will consider the transmission lines providing power to the site, their outage data, the reliability of the power supplied to the transmission system and the effects of external events.
The reliability of the onsite emergency standby diesels will be evaluated based on overall industry data and the GGNS history of operation. Both starting reliability and operating reliability will be considered. Special emphasis will be placed on the TDI diesels where an assessment of recent changes will be included.
The additional gas turbine AC power sources will also be assessed for reliability based on industry and plant specific operating data.
Consideration of gas turbine life will be included.
.The ability to manually connect the HPCS diesel to assume certain Division I and II loads and thereby provide a final source of power which can be used for containment heat removal thereby providing relatively long term maintenance of the plant in a safe condition despite loss of all other AC power sources will be considered.
F.
SUMMARY
In order to confirm the adequacy of the GGNS AC power system, a risk assessment will be conducted of events involving a loss of AC power.
This will be done by assessing core melt frequency. In order to support this confirmatory trork, comprehensive reliability studies of the offsite and onsite AC power systems will be conducted. A more detailed assessment of the GGNS SB0 capability will also be conducted in support of this effort. These efforts will be initiated immediately and scheduled for completion approximately 90 days following issuance of the GGNS full power license.
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