ML19098B459
| ML19098B459 | |
| Person / Time | |
|---|---|
| Site: | Surry  (DPR-032, DPR-037) |
| Issue date: | 07/29/1977 |
| From: | Stallings C Virginia Electric & Power Co (VEPCO) |
| To: | Case E, Reid R Office of Nuclear Reactor Regulation |
| References | |
| Serial No. 325 | |
| Download: ML19098B459 (3) | |
Text
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VIRGINIA ELECTRIC AND POWER COMPANY RIOHMOND, V:lRGINIA 2 3 2 61 July 29, 1.977, '.
Hleguiatory Docket file Mr. Edson G. Case, Acting Director Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C.
20555 Attn:
Mr. Robert W. Reid, Chief Operating Reactors Branch 4
Dear Mr. Case:
Serial No. 325 PO&M/ALH:das~..---..
Docket Nos.<itt 759;,
50-281 License Nos. DPR-32 DPR-37 The purpose of this letter is to request approval for continued operation of Surry Unit No. 2 until September 15, 1977. This extended operation is neces-sary to permit Unit No. 2 to operate through an expected peak demand period un-til refueling.
We have reviewed the safety aspects of this and have determined that continued operation of Surry Unit No. 2 will not endanger the health and safety of the public provided that the requirements of the April 1, 1977 NRC order are applied.
The Safety Evaluation Report that accompanied the Aprill,. 1977 order stat-es: "For the case of a postulated main steamline break, we estimate, using con-servative assumptions (table 1), that steam generator tube leak rates as high as 250 GPM may be tolerated without exceeding a 2-hour dose to the thyroid of 150 rem at the site boundary."
Therefore, it can be said that a leak rate in the order of 500 GPM is.required before the 10CFRlOO thyroid limit of 300 rem is ap-proached.
As was thoroughly discussed in our submittal of March 25, 1977 serial no. 031B/011977, the source of steam generator tube leaks during a steam line break (SLB) are those tubes which leak prior to the accident and those tubes which leak as a result of the accident.
In our March 25 submittal we showed that a pre-existing.3 GPM tube leak would reach a maximum flow rate of.078 lb/sec.
(. 78GPM) during a SLB accident.
We also presented information predicting that 15 partially cracked tubes with 85%-100% through wall flaws would leak during a SLB accident at.005 lb/sec (.05 GPM) *each.
This resulted in a maximum total primary to secondary leak rate during the SLB of.78 GPM + 15(.05 GPM) =:=.1.53 GPM.
If we continue to operate with the requirements of the April 1, 1977 order, until Sept-ember 15, 1977; the only possible change in the consequences of a SLB would be the occurrence of more than 15 tube leaks from partially cracked tubes with 85%-
100% through wall flaws. We estimate that approximately 5000 partially cracked tubes would have to exist with 85%-100% through wall flaws before the primary to secondary leakage during SLB would exceed 250 GPM.
Approximately 10000 partially cracked tubes would have to start leaking during the SLB before the 10CFRlOO thy-roid dose limit of 300 rem is reached.
These figures assume that a pre-existing
.3 GPM leak "opens up" to a.78 GPM constant leak and the remaining leaks from partially cracked tubes remain constant at*. 05 GPM each.*
e VIR01NIA ELECTRIC AND POWER COMPANY TO Mr. Edson*. G. Case Page No. 2
.It is intuitively obvious that neither conditionis credible during a SLB "upstream" of the main steam trip valves since there are less than 3388 tubes in service in each unit 2 steam.generator.
Therefore, we judge that 10CFRlOO limits would not be exceeded during a SLB *
. We believe that our evaluation adequately addresses the potential safety hazards associated with continued operation of. Surry Unit No *. 2.
We would appreciate your prompt response to this request.
cc:
Mr. Norman.C. Moseley Vice and Very truly yours,
- ','t<c,,(~c--
- c. M. Stallings
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President-Power Supply Production Operations
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