ML20033C729
| ML20033C729 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 11/10/1981 |
| From: | Tedesco R Office of Nuclear Reactor Regulation |
| To: | Parris H TENNESSEE VALLEY AUTHORITY |
| References | |
| NUDOCS 8112040010 | |
| Download: ML20033C729 (5) | |
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DISTRIBUTION:
D cket Nos. 50-327/328 NOV 101981 LB #4 r/f DEisenhut Docket Nos: 50-327a EAdensam and 50-328 CStahle bcc: TERA MDuncan Local PDR SHanauer NRC PDR Hr. H. G. Parris RTedesco NSIC Manager of Power RVollmer TIC Tennessee Valley Authority
-T+ttrr1Ty j, N84HR. ACRS (16)
SOCI. Chestnut Street, Tower II RMattson Chattanooga, Tennessee 37401 RHartfield, MPA 0 ELD
Dear Mr. Patris:
OIE (3)
LRubenstein
Subject:
Tornado Missile Protection for Sequoyah Units In Supplement No. 5 to the Safety Evaluation Report for the Sequoyah facility we
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stated that further infornation was needed to determine the adequacy of protection for the 480-V transformers against tornado missile strikes.
On the basis cf your submittal of August 10, 1981, we conclude that the TVA design does not provide adequate tornado missile protection for the transforr.Trs.
Enclosed is our safety evaluation update which states that positive vent opening protection against one inch diameter steel tornado missile is required.
Your coments on our pcsition are requested by November 30, 1981.
Sincerely, 5
Robert L. Tedesco, Assistant Director for Licensing Division of Licensing
Enclosure:
As stated ix CC:
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.c SEQUOYAH Mr. H. G. Parris Manager of Power Tennessee Valley Authority 500A Chestnut Street, Tower II Chattanooga,. Tennessee 37401 cc: Herbert S. Sanger,. Jr., Esq.
General Counsel Tennessee Valley Authority 400 Commerce Avenue E 11B 33 Knoxville, Tennessee 37902 Mr. H. N. Culver Tennessee Valley Authority 400 Commerce Avenue, 249A HBB Knoxville, Tennessee 37902 Mr. Bob Faas Westinghouse Electric Corp.
P.O. Box 355 Pittsburgh, Pennsylvania 15230 Mr. Mark Burzynski Tennessde Valley Authority 400 Chestnut Street, Tower II Chattanooga, Tennessee 37401 Mr. J. F. Cox Tennessee Valley Authority 400 Commerce Avenue, W10C131C Knoxville, Tennessee 37902 Resident Inspector /Sequoyah NPS c/o U.S. NJclear Regulatory Connission 2600 Igou Ferry Road Soddy Daisy, Tennessee 37379 f
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SUPPLEt1 ENTAL SAFETY EVALUATION REPORT INPUT SEQUOYAH NUCLEAR PLANT -
In Section 3.5 of the Sequoyah Nuclear Plant Supplement Number 5 to the Safety Evaluation Report concern was expressed that tornado generated missiles might t
penetrate the ventilation openings in the roof of the auxiliary building and damage certain safety related 480 volt transformers. We requested that TVA provide information which assures that their design provides adequate protection for the 480 volt transformers against tornado missile strikes or propose ' additional protection for our review and approval.
TVA submitted an assessment of the potential for damage to the 480 volt shutdown transformers from tornado missiles in a letter dated August 10, 1981.
This assessment contains a derivation.of the total event probability of a vertical _
tornado missile impacting one of the intake or exhaust vents on.the roof of the auxiliary building.
The total event probability calculated by TVA is the product of the folicwing conditional probabilities:
P,P,P and'P,, wher.e s
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P is the probability of a tornado striking the plant;-
3 P is the probability of a missile striking a safety-related building i
given a tornado strike; and P is the probability of a vertical strike on.a horizontal roof surface
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y given a missile has impacted a safety-related building.
cm P is the probability of the missile striking that area.of the roof l
containing a vent, given that a tornado missile has hit the roof.
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-2 The product of P and P is taken from results contained in EPRI Report EPRI NP-768 3
n entitled " Tornado Missile Risk Analysis" dated May 1978.
In this report a com-puter simulation code is used to estimate the likelihood of tornado missile strikes. The basic approach relies on modeling techniques to describe each phase of the missile generation, transport and impact process.
The computer simulation code has the capability to mode? specific plant configurations, missile characteristics and origin zones, and regional tornado input data.
TVA used a P P value from EPRI NP-768 computed for an assumed two unit s
n plant site arrangement. The assumed plant site consists of a unit in operation and a unit under construction. A significant difference between the Sequoyah plant site and the assumed plant site in the study is that at Seciuoyah the tur-bine building, which is more than 30 feet higher than that portion of the auxiliary building roof containing the vent openings, is west of and immediately adjacent to the auxiliary building and has not been designeif for tornado winds.
More than half of the tornadoesin the area of the Sequoyah plant site originate from the southwest and travel in a northeasterly direction.
Therefore, tornadoes passing over or near the auxiliary building would be expected to' encounter the turbine building first.
In the EPRI study missiles originating from an elevation higher than the auxiliary
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building roof are considered, but these missiles are uniformly distributed over the area of the unit under construction. The two units in this study are separated by about 125 feet at their closest points and each unit has its own auxiliary and turbine building. At Sequbyah the plant layout is different in that a single auxiliary building and a single turbine building are shared between units.
For the Sequoyah site th,e turbine building is 30 feat higher T
t 3-l than the auxiliary building roof and thus represents a significant source of tornado misstles to the, auxiliary building roof.
Due to the close proximity of the turbine building to the vent openings and the sensitivity of missile strike probability to the distance between the original missile location and the target we believe that the EPRI results are not directly applicable to the Sequoyah plant site.
We therefor; conclude that the TVA design' does not provide adequate tornado missile protection for the 480 volt essential transformers.
It is our position, therefore, that TVA should provide positive protection against the one inch a
diameter steel rod tornado missiles for the vent openings on the auxiliary.
building roof.
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