ML20236L651
| ML20236L651 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 07/06/1998 |
| From: | Geoffrey Edwards PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 50-277-96-06, 50-277-96-07, 50-277-96-6, 50-277-96-7, 50-278-96-06, 50-278-96-07, 50-278-96-6, 50-278-96-7, TAC-MA0829, TAC-MA0830, TAC-MA829, TAC-MA830, NUDOCS 9807130111 | |
| Download: ML20236L651 (5) | |
Text
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10CFR 50.54(f) v PECO NUCLEAR nm mv -
Nuclear Group Headquarters h Uurr or PfCO futscy 965 Chesterbrook Boulevard Wayne, PA 19087-5691 July 6,1998 l
Docket Nos. 50-277 50-278 License Nos. DPR-44 DPR-ES U. S. Nuc' ear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
Subject:
Peach Bottom Atomic Power Station, Units 2 and 3, Request for Additional Information Regarding Station Blackout (SBO) Electrical Line Review (TAC Nos. MA0829 and MA0830)
References:
Letter from G. A. Hunger, Jr. to USNRC Document Control Desk dated April 25,1997.
Dear Sir / Madam:
The subject request for additional information (RAl) regarding the NRC's review of the Peach Bottom Atomic Power Station (PBAPS) Station Blackout Electrical Lina, dated May 14,1998, requested that PECO Energy Company (PECO Energy) respond within 45 days of the receipt of the letter with additional infonnation regarding the SBO electr.' cal tie line. This RAI was in response to previously submitted information regarding this subject as identified by NRC unresolved items 96-06-02 and 96-06-01 in NRC inspection reports 96-06 and 96-07 for PBAPS.
This letter provides the requested additional information. In Attachment 1 to this letter, the NRC request is restated, followed by the PECO Energy response.
If you have any questions, please do not hesitate to contact us.
I Very truly yours, b:^D Q
Garrett. D. Edwards Director-Licensing
Enclosures:
PECO Affidavit, Attachment 1 cc:
H. J. Miller, Administrator, Region I, USNRC A. C. McMurtray, USNRC Senior Resident inspector, PBAPS 9807130111 990706 PDR ADOCK 05000277 p
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COMMONWEALTH OF PENNSYLVANIA ::
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COUNTY OF CHESTER 1
J. B. Cotton, being first duly swom, deposes and says:
That he is Vice President of PECO Energy; the Ucensee herein; that he has read the
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enclosed response to the NRC Request for Additional Information Regarding the Station Blackout Line for Peach Bottom Atomic Power Station, Unit 2 and Unit 3, Facility Operating License Nos.
1 DPR-44 and DPR-56, and knows the contents thereof; and that the statements and matters set forth therein are true and correct to the best of his knowledge, information and belief.
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Vice President Subscribed and swom to before me thish day of 1998.
i Nota Public -
NOTARIAL SEAL l
CAROL A. WALTON. No'ary Pubbo CWy of Philadelphia, Phila. Cou My Comminoson Empires May 28.
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July 6,1998 DockM Nos. 50-277/278 RAI Response Regarding PBAPS Station Blackout Line Withstanding Likely Weather-Related Events 1.
The staff has additional questions related to withstanding likely weather-related events.
(3)
The August 6,1992, response by PECO stated all components of the station blackout (SBO) line would be capable of withstanding the effects of likely weather related events that may initiate a loss of offsite power event (reference NUMARC 87-00 item B.3).
However, a wooden utility pole is used at the Susquehanna Substation where the SBO line leaves the breaker and goes underground on the south side of route 1. Address how the use of a wooden pole is consistent with the stated design criteria on weather related events. Also, provided justification of how wooden utility poles and exposed conductors meet the requirements of NUMARC ltem B.3.
In Peach Bottom's response dated August 6,1992, it was stated that "all of these components are capable of withstanding likely weather-related events."
In order for the NRC staff to close this item more detailed information is required that will justify the conclusions reached in your August 1992 response. It is necessary to determine the design capabilities (i.e., ice loading capability, and wind loading capability) of the exposed structures and the most likely wthar-raicted events expected at Peach Bottom (some licensees have used probabilistic risk assessment (PRA) to determine the most likely weather-related events). It should be demonstrated that the design capabilities of the exposed structures can withstand the most likely weather-related events at Peach Bottom. Additionally, the most likely weather-related events should be supported by historical weather data.
Response
The installation of the wooden utility pole and exposed conductors utilized at the Susquehanna Substation have been verified to be capable of withstanding heavy weather-related loading conditions specified by the standard PECO Energy Company substation design and the PECO Energy High Voltage Transmission Line design. The weather conditions assumed in the design bound the actual weather conditions which have occurred in the local area.
The weather-related loading conditions for the standard PECO Er.ergy Company substation design is based on National Electrical Safety Code (NESC) Section 25 standards and the transmission system design is based on design criteria established by the Keystone Project companies during the construction of the original state of Pennsylvania 500 kV transmission system built in the 1960's. The ice and wind loads specified for these designs are:
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Steady wind of 40 mph with 0.5 inch radial ice (NESC Rule 250) 2.
Steady wind of 99 mph with no ice (Keystone Project) 3.
Steady wind of 56 mph with 1.0 inch radial ice (Keystone Project)
These weather conditions are based on historical national weather data applicable to the location of the Susquehanna Substation. Additionally, the standard substation design utilizes the American National Standard Specifications and Dimensions for Wood Poles (ANSI 05.1) to determine the maximum fiber stress for wooden utility poles. The most limiting weather related loading conditions has been determined to be the steady wind of SS mph with 1.0 inch radialice conditions which results in a horizontal stress of 5640 psi on the pole. The loads used for this calculation are ultimate loads including
. the applicable overload (safety) factors forwire tension and wind loads as set forth by the NESC. The calculated stress is below the maximum wood stress limit of 8000 psi. With the overload factor removed (i.e., actual working stress), the pole would be loaded to 32.4 percent of capacity during the most limiting
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Docket Nos. 50-277/278 Attachment Page 2 of 3 weather-related conditions. The pole's foundation is also over designed with the pole buried deeper than required for the shortened pole. The foundation has been determined to remain operable under the most limiting loading of the steady wind of 56 mpa with 1.0 inch radial ice conditions even though there will be some ground displacement at the base of the pole.
The conductor used for the aerial span from the wood pole to the substation take-off tower is aluminum conductor and meets the requirements of ASTM B 231,
- Standard Specification for Concentric-Lay.
Stranded Aluminum 1350 Conductors," with a rated strength of 9750 pounds force tension. The maximum loading from the heavy weather loading conditions from the steady wind of 56 mph with 1.0 inch radial ice has been calculated to be 513 pounds which is less than 6% of the rated strength. The associated insulators and hardware were selected to resist the maximum design tension for the class of construction with a factor of safety nf 2.0. The maximum tension used by PECO construction using this aluminum conductor is 2,200 pounds The insulators and hardware utilized in this installation are i
capable of resisting a minimum conductor tension of 5,000 pounds. With the calculated tension at the i
steady wind of 56 mph with 1.0 inch radialice conditions of 513 pounds, the insulators and hardware for the aerial span are stressed to 10.31 percent of capacity. Therefore, the conductor, insulator, and hardware are capable of withstanding the most limiting likely weather-related loads of the steady wind of 56 mph with 1.0 inch radial ice conditions.
The substation rigid bus conductors, supporting structures, and equipment are designed to meet the following two climatic requirements:
- 1. Steady wind of 40 mph with 0.50 inch radial ice
- 2. Steady wind of 88 mph with no ice An evaluation of the substation rigid bus conductors, supporting structures, circuit breakers, and associated equipment was performed which included an assessment of the stress load capabilities of the supporting structure (i.e., take-off tower). The evaluation concluded that all of the supporting structures and associated equipment was capable of withstanding the most limiting likely weather-related loads of
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the steady wind of 56 mph with 1.0 inch radial ice conditions.
Severe radial ice accumulation on wires is extremely rare in the PECO Energy service territory. Two climatic events in the last 40 years have resulted in significant ice and snow loading of the PECO transmission system. One event, in January,1994, was a series of ice storms that resulted in ice thicknesses from 0.50 to 0.75 inch on the transmission and distribution system equipment. A second event was a heavy, wet snowfall in March of 1958. Snow thicknesses of 4 inches and more on the transmission and distribution system equipment were recorded. Accumulation of these depths of snow on the conductors could not occur with greater than light wind conditions. Snow has highly variable density. A " wet" snow may have a 1:4 weight ratio to water equivalent. This would mean that 4 inches of radial wet snow would be equivalent to about 1 inch of ice with light winds. The Keystone criteria of steady wind of 56 mph with 1.0 inch radial ice has, to the best of our knowledge, never occurred in the PECO Energy service territory. There has been no weather-related damage to the offsite power transmission system that concurrently jeopardized all of the normal offsite power sources to PBAPS.
The meteorological information used in the original licensing of PBAPS Units 2 and 3 is provided in the Updated Final Safety Analysis Report (UFSAR) Section 2.3. The gener 9 wind flow in the sito area is moderate and the maximum steady wind experienced in the Philadelplj., area was 88 mph. Wind data from 1990 to 1997 indicates the maximum hourly average wind speed measured by the PBAPS meteorological instruments at elevation of 75 feet was 39.5 mph. These modest peak winds are to be expected, since the site is too far inland to be affected by the full force of the hurricanes, and the site is not usually influenced by other phenomena producing exceptional wind speeds. As stated in the UFSAR, the frequency of occurrence to the chance of a tomado affecting the site has a probability of 1 in 2,600 years. A severe ice storm is expected to occur one event in every three (3) years in the general area. A review of ice and snow storms that have occurred in the PECO Energy service territory concluded thet
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Dock;t Nos. 50-277/278 i
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the worst' storms'were less severe that the assumptions made in the Keystone Project. Additionally, the worst expected wind conditions is bounded by the worst ica and wind conditions assumed in the Keystone Project.
It is concluded that the severe weather assumptions made in the original design of the wooden utility pole and the exposed structures bounds the most likely weather-related events based on historical data and evaluations. Furthermore, it is concluded that the wooden utility pole and exposed conductors are capable of withstanding the likely weather-related events as previously stated.
I Hydro-Unit Reliability 2.
The staff has additional questions related to hydro-unit reliability.
(2) URI 96-06-02 states that the staff " expected" at least one Conowingo hydro unit would supply the SBO line loads normally and therefore could be considered an operating line.
However, with the possibility of no units operating, the system overall would be in standby and therefore, reliability should be monitored. Address measuring reliability given there are times when SBO generating units are off-line and how the NUMARC 87-00 guidance for reliability is being met?
i in your April 25,1997, response you stated that the availability is monitored under the Maintenance Rule and includes all equipment from the buses at Conowingo to the PBAPS switchgear.
Was there a PRA analysis completed for the attemate AC(AAC) power source to determino whether it was a low or high risk structure, system or component (SSC)? What was the result of your PRA analysis? If a PRA analysis was not done, was the AAC source determined to be a low or high risk SSC by some other method required by the maintenance rule. What was the
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result of that determination?
Response
The SBO Line was previously scoped into the Maintenance Rule program for PBAPS on October 30, 1996, and the system was considered to be risk significant based in part on the importance of the system during a SBO event. The expert panel reviewed this conclusion and concurred with the classification on October 30,1996. The PBAPS Probabilistic Safety Analysis (PSA) was updated in May 1997 to include a detailed component and train level model of the Conowingo SBO Line. Since all of the importance measures criteria defined in NUMARC 93-01 were met using the updated model, the SBO system was determined to be a risk significant system. Therefore, the SBO system is monitored as a " risk significant" system using the Maintenance Rule. Monitoring of the SBO system is being performed as documented in NRC Inspection Report 50-277/50-278 98-04, dated May 14,1998, which documented the closure of Unresolved liem (URI) 96-07-01 associated with this monitonng issue.
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