ML19316A394
| ML19316A394 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 10/31/1978 |
| From: | Stello V Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUDOCS 7912110654 | |
| Download: ML19316A394 (10) | |
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twu:/.n nrnutA rOHY Cr? " *+ :oN R I n'Fani v.mm./ntcu.oc ~ as CctcN;r 31, 1973 Ocd et f jo. : E%209 Dod.cting and Service Sett'on CF.:o of the Couchry of the Commission GUBJEC T:
OCN1E !.UOJf2 SLYiIO:! !!.:IT
- 0. 1 Tv.o sgned orig'nal:, of the F>: 10. al R, tu N,t:r a id-nh!W! La'o e,.re cric W :d f;r pur tr..nu lial to the O ! ice of the Fed.;r:d Rcpt ar for pt Ucation. Ad 1,Unnain..formcd cepes ( 12 )of t'v 'P.N::e are encbsed 'or your use.
O Notice of Receipt of App':caron for Construction Penn:t(s) mnd Operating if nse(s).
O Notice of Receipt of Partial App!ication for Construction Pe.mit(s) and Faci lity Ucu.r2(s):
Time for Submission of Views on Antitrust f. tatters.
0 NoSce of Availibuity of Ar;'" cant's Environmental Report.
O Not'ce of Proposed issuance of Amendment to FacD;ty Operating i iconse O Not co of Receipt of Appfcation for Faci lity Uconseg); Notice of Avai'ab!iity of App!? cant's En.ironmental Report; and Notice of Considerafan of issuance of Fachity License (s) and Notice of npportunity for Hearing.
O Notice of Availability of NRC Draft. Final Environmental Statement.
s O Notice of Limited Work Authorization.
0 Notice of Availability of Safety Evafuation Report.
O Notice of issuance of Construction Permit (s).
O Notice of issuance of Facility Operating License (s) or Amendment (s).
O Other:._Excration dtd. 10/23/73 i
Referenced docu ents have been provided PDR.
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Division of Operating Pecciors, C D 4l Edm Office of Nuc! car Reacbr Regu'a';on As Stated ORB #4: DOR.
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7590-01 e
UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION In the Matter of
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Duke Power Company
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DOCKET NO. 50-269
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Oconee Nuclear Station Unit No. 1
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EXEMPTION I.
Duke Power Company ('Se licensee) is the holder of Facility Operating License No. DPR 38 which authorizes the operation of the nuclear peaer reactor known as Oconee Nuclear Station, Unit No.1 (the facility), at steady reactor power levels not in excess of 2563 negawatts thernal (rated power).
The facility consists of a Babcock & Wilcox (B&W) designed pressurized water reactor (PWR) located at the licensee's site in Oconee County, South Carolina.
II.
In accordance with the requirements of the Cornission's Emergency Core Cooling System (ECCS) Acceptance Criteria,10 CFR 50.46, the licensee submitted on July 9, 1975 an ECCS evaluation for the facility.
The ECCS performance sub-mitted by the licensee was based upon an ECCS Evaluation Model developed by Bt.U, the designer of the Nuclear Steam Supply System for this facility.
The B&W ECCS Evaluation Model had been previously found to conform to the requirements of the Commission's ECCS Acceptance Criteria,10 CFR Part 50.46, and Appendix K.
The evaluation indicated that with the limits set forth in L
7590-01
. the f acility's Technical Specifications, the ECCS cooling performance for the facility would confonn with the criteria contained in 10 CFR 50.46(b) which govern calculated peak clad temperature, maximum cladding oxidation, maximum hydrogen generation, coolable geometry and long-term cooling.
On April 12, 1978, B&W informed the fiRC that it had determined that in the event of a small break Loss of Coolant Accident (LOCA) on the discharge side of a reactor coolant pump, high pressure injection (HPI) flow to the core could be reduced somewhat.
Subsequent calculations indicated that in such a case the calculated peak clad temperature might exceed 2200 F.
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Previous small break analyses for B&W 177 fuel assembly (FA) lowered loop plants had identified the liniting small break to be in the suction,line of the reactor coolant pump.
Recent analyses have shown that the discharge line break is more limiting than the suction line break.
The Oconee fluclear Station Unit tio. I has an ECCS configuration which consists of two HPI trains which are supplied by three HPI pumps.
Each train injects into two of the four reactor coolant system (RCS) cold legs on the discharge side of the RCS pump.
The two parallel HPI trains are connected but are kept isolated by manual valves (known as the cross-over valves) that are nonnally closed.
1 Duke Power has proposed by letter dated April 21, 1978, to raintain all three pumps in an operable status.
The Oconee emergency power system is designed with sufficient capacity for this mode of operation.
Upon receiving a safety l
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7590-01 injection signal the liPI pumps are started and valves in the injection lines are opened.
Assuming loss of offsite power and the worst single failure (the liPI pump C or the liPI valve lip 26), two HPI pumps would still be available and only one of the two injection valves would fail to open.
l If a small break is postulated to occur in the RCS piping between the RCS pump discharge and the reactor vessel, the high pressure injection flow injected into this line (about 50% of the output of two high pressure pumps) could flow out the break. Therefore, for the worst combination of break location and single failure, 50% of the flow rate of two high pressure ECCS pumps would contribute to maintaining the coolant inventory in the reactor vessel.
This situation had not been previously analyzed and B&W had indicated that the limits specified in 10 CFR 50.46 may be exceeded.
B&W has stated that they have analyzed a spectrum of small breaks in the pump discharge line and have determined that to meet the limits of 10 CFR 50.46(b), operator action is required to open the two ranual operated crossover valves and to manually align the motor driven isolation valve which had failed to open.
This would allow the flow from the two HPI pumps to feed all four reactor coolant legs.
B&W has assumed that 30% of the flow would be lost through the break and 70% would enter the core.
The licensee has coninitted to provide for the necessary operator actions within the required time frame. That is, in the event of a small break and a limiting single failure, manual action will be taken to begin opening these valves within five minutes and have them fully opened and an adequate flow split obtained within the 1
following 10 minutes. The analyses perfonned by B&W assumed that the flow 1
7590-01
. split was established at 650 seconds by operator action.
We conclude that the analyses are a reasonable approximation of the operator action that actually
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will be taken, provided specific procedures are prepared and followed tc assure such action.
B&W has prepared a summary entitled " Analysis of Small Breaks in the Reactor Coolant pump Discharge Piping for the B&W Lowered Loop 177 FA Plants," April 24,1978 (the B&W Surrary), which describes the methods used and the results obtained in the above analysis.
The analysis nodels operator action by assuming a step increase in flow to the reactor vessel (with balanced flow in the three intact loops) ten minutes after the LOCA reactor protection system trip signal occurs.
On April 26, 1978, the Conmission issued an Order for tbdification of License which amended the license for Oconee Unit 1 requiring (1) sub-mission of a reevaluation of the emergency core cooling system cal-culated in accordance with the B&W Evaluation lbdel for operation with operating procedures described in the licensee's letter of April 21,1978 and (2) operation in accordance with the procedures described in the licensee's letter of April 21, 1978.
7590-01 By letter dated May 16, 1978, the licensee submitted a copy of the B&W Surrary for our review.
In their submittai the licensee stated that the analysis indicates that the ECCS cooling performance calculated in accordance with the B&W Evaluation Model for operation of Oconee units at the rated core therral power of 2568 Mwt with operating procedures described in their letter of April 21, 1978, is wholly in confornance with the provisions of 10 CFR 50.46.
We have reviewed the B&W Summary and find that the methods of analysis meet the requirenents of 10 CFR Part 50.46.
By letter dated April 20, 1978 and as supplemented on April 27, 1978, the licensee submitted proposed Technical Specifications to imple-ment the operating procedures and maintenance of all three HPI pumps in an operable status as described in the licensee's April 21, 1978 letter.
We are issuing these Technical Specifications in the license arendment accompar. jing this Exemption.
On August 21, 1978, the licensee requested an exemption from the provisions of 50.46.
In the licensee's submittal of June 8,1978, it was stated that to meet the limits of 10 CFR 50.46, operator action at the valve
7590-01
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locations is required to open High Pressure Injection (HPI) Pump B-C discharge header cross over valves (ItP-ll6 and itP-117) and the llPI injection line A en,gineering safeguards valve (llP-26) within 10 minutes.
Reliance on local operation of valves this soon after the onset of a loss-of-coolant accident is not desirable on a permanent basis.
The licensee has requested an exemption from the requirements of 10 CFR 50.46 for operation at Oconee 1 during Cycle 5 until such time as a perranent solution to this problem can be implemented.
The original concern derived from an unexpected but nevertheless inadequate assessment of a spectrum of breaks. This deviation from 10 CFR 50.46 has been ameliorated on a temporary basis by the actions discussed herein.
However, combined reliance on prompt operator action to perform the required steps to assure plant safety over a period of years into the future is undesirable and should be replaced as promptly as possible by returning the system to autoratic or control room actuation.
To this extent, the original defect still remains until the modifications are made to climinate the reliance on prompt operator actions.
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7590-01 i
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We have reviewed the effects of changes made to the facility during the current refueling outage and have concluded that operation of Oconee Unit 1 at power levels of up to 2568 Nt and in accordance j
with the Technical Spec,ifications will assure that the 4
ECCS system will conform to the performance criteria of 10 CFR 50.46.
Accordingly, until modifications are completed to achieve full compliance i
3 with 10 CFR 50.46, operation of the facility at power levels up to 2568 Nt with appropriate operating procedures will not endanger life or 7
t property or the comon defense and security.
i Uhile Oconce Unit No.1 does not comply with our requirements for j
ECCS, appropriate actions, as previously described, have been taken to mitigate the consequences of any accidents at this plant.
The I
Technical Specifications will provide protection against the subject small break LOCA and will bring plant operation wholly in conformance i
with 10 CFR 50.46.
These Technical Specifications will be in force only for the brief interval of time until the proposed modifications l
of the ECCS are completed.
The public interest is served in that by i
issuing this exemption for Unit No.1 a significant power reduction i
with no concomitant increase in safety is avoided.
Such a power reduction could affect system reliability, cause unemployment and increase consumer power costs in the area.
III.
Copies of the following documents are available for inspection at the Commission's public Document Room at 1717 H Street, Washington, D.C.
i 20555, and are being placed in the Comission's local public document room at the Oconee County Library, 201 South Spring, Walhalla, South Carolina.
21, 1978, and The application for exemption dated August (1)
This Exemption in the ratter of Duke Poaer Conpany, Oconee (2) fluclear Station, Unit flo.1.
IV.
h 1.HEREf0RE, in accordance with the Cor:aission's regulations in 10 CFR 50.12, the licensee is hereby granted an exemption fro liith respect to the provisions of 10 CFR Part 50, Paragraph 50.45(a).
this exemption supersedes the conditions of the Cte. mis Oconee Unit 1 26, 1978, and is conditioned Order for liodification of License dated April t
as folloas:
The licensee has submitted the plans and schedules to (1) modify the facility to eliminate reliance on prompt opera-Additional guidance in these tor action described herein.
f Septcmber 26, 1978 areas has been provided by the I;RC letter o to Duke Power Company.
Upon approval by the staff the licer.see shall undcrtake (2) such r.odifications in accordance with the approved schedule.
This exemption shall be tenainated upon completion of the (3) modifications in accordance with this exemption or upon shutdown for the next scheduled refueling outage, whichever occurs first.
FOR iliE IlVCLETR REGULATORY CC
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Vis or Ste#Qo,1 r7,/P' rector Division of Operati g heactors A
Office of !!uclear Reactor Regulction Dated at Bethesda, Maryland, this 23rd day of October 1978.