ML19312C832
| ML19312C832 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 07/06/1978 |
| From: | Stello V Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19312C830 | List: |
| References | |
| NUDOCS 8001100746 | |
| Download: ML19312C832 (9) | |
Text
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7590-01
.O UNITED STATES OF AMERICA fl0 CLEAR REGULATORY COMMISSION In the Matter of
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Duke r'ower Company
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DOCKET NO. 50-287
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Oconee Nuclear Station Unit No. 3
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EXEMPTION I
1.
k Duke Power Company (the licensee) is the holder of Facili.ty Operating License No. DPR-55 which authorizes the operation of the nuclear power reactor known as Oconee Nuclear Station, Unit No. 3 (the facility), at steady reactor power levels not in excess of 2568 megawatts thermal (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.
j In accordance with the requirements of the Commission'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 the B&W, the designe'r 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 4
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. the facility's Technical Specifications, the ECCS cooling performance for the facility would conform 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 tooling.
On April 12, 1978, B&W informed the NRC 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.
Previous small break analyses for B&W 177 fuel assembly (FA) lowered loop plants had identified the limiting 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 t!.a suction line break.
The Oconee Nuclear Station Unit No. 3 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 normally closed.
Duke Power has proposed by letter dated April 21, 1978, to maintain all three pumps in an operable status.
The Oconee emergency power system is designed with srfficient capacity for this mode of operation. Upon receiving a safety
7590-01
. injection signal the HPI pumps are started and valves in the injection lines are opened. Assuming loss of offsite power and the worst single failure (the HPI pump C or the HPI valve HP26), two HPI pumps would still be available and only one of the two injection valves would fail to open.
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) 5 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 manual 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 coclant legs.
B&W has assumed that 30% of the flow would be 4
lost through the break and 70% would enter the core.
The licensee has committed 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, manua1 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 following 10 minutes.
The analyses performed by B&W assumed that the flow y
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i split was established at 650 seconde ey operator action. We conclude that the analyses are a reasonable appro'.1mation of the operator action that actually will be taken, providet specific procedures are prepared and followed to assure such action.
B&W has prepared a summary entitled " Analysis of Small Breaks in the Reactor Coolant Pump Discharge Pipir.g for the B&W Lowered Loop 177 FA Plants," April 24,1978 (the B&W Summary), which describes the methods used and the results obtained in the above analysis.
The analysis models operator action by assuming a step increase in flow I
to the reactor vessel (with balanced flow in the three intact loops) 1 l
ten minutes after the LOCA reactor protection system trip signal occurs.
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i On April 26, 1978, the Commission issued an Order for Modification of License which amended the license for Oconee Unit 3 requiring (1) sub-missim of a reevaluation of the emergency core cooling system cal-culated in accordance with the B&W Evaluation Model for operation with operating procedures described in the licensee's letter of l
April 21,1978 and (2) operation in accordance with the procedures 4
described in the licensee's letter of April 21, 1978.
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b By letter dated May 16, 1978, the licensee submitted a copy of the B&W Sunmary for our review.
In their submittal the licensee j
stated that the analysis indicates that the ECCS cooling performance calculated in accordance with the B&W Evaluation Model for operation l
of Oconee units at the rated core thermal power of 2568 Mnt with operating procedures described in their letter of April 21, 1978, is wholly in conformance with the provisions of 10 CFR 50.46.
We have reviewed the B&W Summary and find that the methods of analysis meet the requirements of 10 CFR Part 50.46, However, due to the Oconee Unit 3 ECCS not meeting the operator action requirements of 10 CFR 50.46 and because Oconee Unit 3 was i
to be shut down for refueling for Cycle 4 operation, the licensee
.was requested by telephone on June 8,1978, to either provide an acceptable ECCS for Oconee Unit 3 Cycle 4 operation or file a request for an exemption from the provisions of 10 CFR 50.46 and supporting justification to support the licensing of Oconee 3 for Cycle 4 operation.
On June 8,1978, the licensee requested an exemption from the provisions of 50.46.
On June 16, 1978, Oconee 3 w >s shutdown-for refueling.
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 s
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7590-01 locations is required to open High Pressure Injection (HPI) Pump B-C discharge header cross over valves (HP-ll6 and HP-ll7) and the HPI injection line A engineering safeguards valve (HP-26) within 10 minutes.
Reliance on local operation of valves this soon after the onset of a loss-of-coolant accident is not desir';1e on a permanent basis.
The licensee has requested an exemptior from the requirements of 10 CFR l
50.46 for operation at Oconee 3 during Cycle 4 until such time as a k
permanent 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 automatic or control room actuation.
To this extent, the original defect still remains until the modifications are made to eliminate the reliance on prompt operator actions, l
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t We have reviewed the effects of changes made to the facility during the current refueling outage and have concluded that operatic.i of Oconee Unit 3 at power levels of up to 2568 ikt and in accordance with the operating procedures of this Exemption, will assure that the ECCS system will conform to the performance criteria of 10 CFR 50.46.
Accordingly, until modifications are completed to achieve full compliance with 10 CFR 50.46, operation of the facility at power levels up to 2568 Mwt with appropriate operating procedures will not endanger life or property or the common defense and security.
In the absence of any safety problem associated with the facility during the period until the modifications for achieving full com-pliance with 10 CFR 50.46 are completed, there appears to be no public interest consideration favoring undue restriction of the operation of the captioned facility.
Accordingly, the Commission has determined that an exemption in accordance with 10 CFR 50.12 is appropriate.
The specific exemption is limited to the period of time necessary to complete modifications to the ECCS system.
III.
Copies of the following documents are available for inspection at the Commission's Public Document Room at 1717 H Street, Washington, D.C.
20555, and are being placed in the Commission's local public document room at the Oconee County Library, 201 South Spring, Walhalla, South Carolina.
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The application for exemption dated June 8,1978, and (1)
This Exemption in the matter of Duke Power Company, Ocone (2) fluclear Station, Unit tio. 3 IV.
t forth WHEREFORE, in accordance with the Commission's regulatio in 10 CFR 50.12, the licensee is hereby granted an exemp With respect to the provisions of 10 CFR Part 50, Paragraph 50.46(a).i i n's l
Oconee Unit 3, this exemption supersedes the conditions o 26, 1978, and is conditioned l
Order for Modification of License dated April as follows:
As soon as possible the licensee shall submit plans an (1) i on schedules to codify the facility to eliminate rel ance prompt operator action described herein.
Upon approvai by the staff the licensee shall undert (2) dl such modifications in accordance with the approved sc Until further authorization by the Commission, the licen (3) ibed in shall operate in accordance with the procedures descr its letter of April 21, 1978.
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This exemption shall be terminated upon completion of the (4) modifications in accordance with this exemption.
FOR THE NUCLEAR REGULATORY COMMIS d,,7f',
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Victor Stello, Jr., Director Division of Operating Reactors Office of Nuclear Reactor Regulation I
Dated at Bethesda, Ibryland, this 6th day of July 1978.
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