ML16161A306
| ML16161A306 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 11/12/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML16161A305 | List: |
| References | |
| NUDOCS 9811160291 | |
| Download: ML16161A306 (6) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.
233' TO FACILITY OPERATING LICENSE DPR-38 AMENDMENT NO.
233 TO FACILITY OPERATING LICENSE DPR-47 AND AMENDMENT NO. 232 TO FACILITY OPERATING LICENSE DPR-55 DUKE ENERGY CORPORATION OCONEE NUCLEAR STATION, UNITS 1. 2. AND 3 DOCKET NOS. 50-269, 50-270, AND 50-287
1.0 INTRODUCTION
By letter dated September 17, 1998, as supplemented October 15, 1998, Duke Energy Corporation (Duke or the licensee) submitted a request for changes to the Oconee Nuclear Station (Oconee), Units 1, 2, and 3, Updated Final Safety Analysis Report (UFSAR) for staff review. The October 15, 1998, letter provided clarifying information that did not change the initial proposed no significant hazards consideration determination.
The change to the UFSAR would add a brief discussion of an additional test (Keowee Emergency Power - Engineered Safeguards Functional Test) that is scheduled to be performed during the 1998 Oconee Unit 3 refueling outage. The scope of the test is in support of Nuclear Station Modification (NSM) ON-53014.
In its September 17, 1998, letter, Duke stated that a modification is planned that will add voltage and frequency protection for Oconee loads when they are powered from a Keowee hydro unit. The protection will separate Oconee loads from a Keowee unit if that unit's voltage or frequency becomes greater than 110 percent or less than 90 percent of rated value at any time after loading. The planned design will delay the loading of Oconee loads on the underground power path until the Keowee unit reaches greater than 90 percent voltage and frequency. The existing design allows early loading of the underground path Keowee unit at approximately 60 percent voltage.
Duke stated that during the design phase of this modification, considering the frequency overshoot the Keowee units experience on emergency start, questions arose concerning whether the preferred loading design for the emergency power system is 60 percent loading or 90 percent loading. For this reason, the Keowee Emergency Power and Engineered Safeguards Functional Test is planned. The test, scheduled during the Oconee Unit 3 refueling outage, will be performed on the Keowee underground path and will consist of two parts. One test will load the Keowee unit at its present design of approximately 60 percent rated voltage and frequency and a second test using the same loads will load the Keowee unit at 9811160291 981112 PDR ADOCK 05000269 P
-2 approximately 90 percent rated voltage and frequency. Test data will be collected throughout the Oconee emergency power system during each test. Duke will review the test data to determine whether it is prudent to implement the delayed loading modification. Regardless of the loading scheme design chosen, Duke stated that out-of-tolerance voltage and frequency protection will be installed.
In its submittal, the licensee indicated it has determined that this test involves an unreviewed safety question (USQ), which, therefore, requires NRC approval prior to performing the test.
Duke indicated that, in the extremely unlikely (2E-9) event that a real loss-of-coolant accident (LOCA) with loss of offsite power (LOOP) were to occur on either of the other two operating Oconee units simultaneously with test initiation on Oconee Unit 3, the Oconee emergency power system (EPS) could be placed in a condition outside the design basis. Additionally, Duke indicated that the requirements of Selected Licensee Commitment 16.5.5, "Shutdown Cooling Requirements ([reactor coolant system] RCS loops not full and fuel transfer canal is not full),"
will not be met during each test when power is intentionally interrupted to the low pressure injection pumps (LPI) during the simulated LOOP, and again during the dead bus transfer back to the unit startup transformer. Duke has, therefore, submitted for staff approval, the amendment to the Oconee UFSAR that identifies the subject test as a USQ.
By letter dated October 21, 1998, the licensee also requested an exemption from 10 CFR 50.46 for the test. This is being evaluated against the requirements of 10 CFR 50.12 separately from this evaluation and must be approved prior to conducting the tests.
2.0 EVALUATION 2.1 Electrical Considerations Because the tests will be performed with fuel in the vessel, and because the capability of the Keowee units to pick up the Oconee loads at 90 percent voltage and frequency has not been tested before, the staff asked Duke to describe what work has been done to verify to a reasonable degree that equipment will operate properly during the test. The staff also asked that Duke provide CYME computer model results that show the expected motor response characteristics against their overload protection, and the associated Keowee response. The staff was aware that Duke uses the CYME model to analyze the Oconee EPS.
In a letter dated October 15, 1998, Duke responded that they do not have the capability in CYME to model loading at reduced voltage and frequency (either 60 percent or 90 percent).
A previously performed 60 percent loading test (integrated tests performed in January 1997) was modeled using the CYME model with the frequency initially at 60 hertz, and simulated the overshoot of Keowee similar to that seen during the test by performing a CYME load rejection.
Duke stated that the predicted motor start results from the modeling correlated well with the test data. Duke concluded, therefore, that the January 1997 test gives the most valuable information regarding successfully completing the tests currently planned.
Duke determined from the results of the January 1997 test that both of the planned current tests (60 percent and 90 percent) can be successfully completed because the system is being challenged to a lesser degree. Duke indicated that in the previous test, the LOCA loads of
-3 Oconee Unit 3 were started simultaneously with the LOOP loads of Oconee Unit 1. For the current tests, only Oconee Uhit 3 LOCA loads will be started. Duke stated that it is, therefore, confident that both the 60 percent and 90 percent tests scheduled for this present outage will be successful.
The staff has previously reviewed the test results from the integrated test performed in January 1997. The results included the motor overload trip information and showed that satisfactory margin exists between the motor starting currents and the relay trip curves. On the basis of Duke's statements that the CYME modeling performed initially at 60 hertz correlated well with the January 1997 test, and because there is a smaller load demand for the current tests, the staff finds that there is sufficient confidence that the current tests will be successful and the motors will start satisfactorily. The staff also notes that in response to a staff question, Duke has indicated that a complement of equipment separate from the tests' electrical transients is available that can provide reactor coolant system (RCS) forced circulation, decay heat removal (DHR), heat sink, inventory replenishment, and spent fuel pool (SFP) cooling capability.
An additional concern in a test of this type is that the EPS (Keowee) will fail to power the safety equipment during the test as expected, and an alternate power source will not be available to power DHR equipment. In this regard, Duke has indicated that throughout the entire test, even during transfers, alternating current power will be available either automatically or with minor operator action from all of the following sources:
- 1. Switchyard to Unit 3 main feeder buses via the normal source (backcharged main auxiliary transformer).
- 2. Switchyard to all units' main feeder buses via the startup transformer (CT-1, CT-2, CT-3).
- 3. Keowee to all units' main feeder buses via the startup transformer (CT-1, CT-2, CT-3).
- 4. Keowee to all units' main feeder buses via the standby transformer (CT-4) and the standby buses.
- 5. Lee Gas Turbine to all units' main feeder buses via a dedicated 100kV line and the standby buses. A Lee Gas Turbine will be running in standby during each part of the emergency power engineered safeguards functional test.
The staff finds these provisions to be acceptable.
With regard to the USQ, Duke has stated that in the extremely unlikely event that a real LOCA/LOOP were to occur on either of the operating units (Oconee Unit 1 or 2) during this test (simulated LOCA/LOOP) on Oconee Unit 3, the Oconee EPS could be placed in a condition outside the design basis. The EPS may not be capable of handling the electrical loading of two instantaneous LOCA/LOOP events without some safety-related equipment being adversely affected; i.e., tripping off, experiencing low voltage, etc. However, the EPS would be able to handle the electrical loading if the two events are offset in time by approximately 10 seconds to allow the first unit's load to reach a steady-state condition prior to starting of the second unit's emergency loads. Therefore, this 10-second window of vulnerability causes an infinitesimally
-4 small, but non-zero, increase in the probability of a malfunction of equipment important to safety and the potential consequendes of a LOCA/LOOP event during the performance of the test.
Duke has stated that there are two key factors that reduce the risk for the tests. First, the planned testing is of limited duration. Second, the likelihood of a coincident LOCA and LOOP is very low. Duke indicates that, even in the event the test has to be repeated for data gathering, the probability of a coincident LOCA/LOOP on another unit has been evaluated and found to be acceptably small. Duke has concluded, therefore, that the likelihood of a LOCA/LOOP sequence at Oconee on either of the two operating units while this Keowee test is being performed during the Unit 3 outage is extremely low, approximately 2E-9. The staff agrees that the likelihood of this scenario is acceptably low, and the test is, therefore, acceptable in this regard.
The licensee has indicated that during the test, no other work will be allowed on the ES or engineered safeguards system of any unit. This practice minimizes the likelihood of a plant-centered LOOP occurring during the test period. Additionally, the planned LOOPs on Oconee Unit 3 are not expected to propagate to the operating units. Therefore, the likelihood of two LOCA/LOOP events occurring within approximately 10 seconds of each other (one event being the LOCA/LOOP test at Unit 3 and the second event actually occurring at Oconee Unit 1 or 2) is low during the postulated period of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> duration of the test.
2.2 Systems Considerations The one-time, two-part electrical test will be conducted with Unit 3 shut down. Neither test part, the 90 percent nor the 60 percent load test, will be conducted more than three times without NRC approval. The unit will be refueled following a refueling outage with approximately one-third of the core being new unirradiated fuel. As a result, there will be relatively little decay heat. However, DHR will be interrupted for a short time for each test because power will be removed from Unit 3 for 12-15 seconds. The primary system will be vented by the pressurizer through a removed code-safety relief valve and with the steam generator hand holes removed to prevent an overpressure event.
Oconee Units 1 and 2 will be at power during the test while Oconee Unit 3 is shut down.
Oconee Units 1 and 2 will not be affected by the test; however, there will be a very short period of time for each test (approximately 10 seconds) while the Oconee Unit 3 emergency core cooling system loads are being loaded to the Keowee generator when equipment for Oconee Unit 1 or 2 could be damaged if a simultaneous LOCA/LOOP were to occur (at one of the two operating units). The likelihood of a LOCA/LOOP occurring in any 10-second window is very remote and allowing this for a one-time test is acceptable. However, for the 10-second window following the initiation of the Oconee Unit 3 test, Oconee Units 1 and 2 may not be able to mitigate the design basis LOCA/LOOP. Therefore, an exemption to Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Section 50.46 for Oconee Units 1 and 2 was requested and is being reviewed under a separate action.
For Oconee Unit 3, the shutdown unit, the licensee has applied a defense in depth concept and has indicated that the operators would be prepared and trained for the test, including the use of contingency plan procedures. Because the test will result in an electrical transient to the loads
-5 (or the safety equipment) for pconee Unit 3, the licensee has Verified that the important safety functions of adding inventory, DHR and SFP cooling can be accomplished with equipment that will not be affected by the electrical transient. The licensee has calculated that if a total loss of DHR were to occur, there would be approximately 89 minutes for the operators to respond with equipment not affected by the test before boiling would occur in the core. If SFP cooling were lost, the licensee has calculated that there would be approximately 34 hours3.935185e-4 days <br />0.00944 hours <br />5.621693e-5 weeks <br />1.2937e-5 months <br /> for the operators to respond before boiling would occur. The licensee has verified that there will be a number of power sources available during the test, including the Lee gas turbine running in standby and energizing CT 5, ready to supply the Oconee safety buses.
The licensee has indicated that there will be no credible leakage paths that would remove inventory or divert flow from the RCS in excess of the Technical Specification limit of 2 gallons per hour and the operators will be able to gravity feed the RCS from the borated water storage tank if inventory is being lost or an LPI pump not affected by the test is being used. The licensee addressed the potential for a criticality excursion and determined that because the high pressure injection pumps will be injecting from the borated water storage tank and the LPI and building spray pumps will be recirculating water from the RCS, there are no boron dilution concerns. The licensee has verified that the containment equipment hatch will be maintained closed for the duration of the test.
3.0
SUMMARY
The staff has reviewed the license amendment application and the supporting technical justification and concludes that the proposed one-time test is acceptable. The amendments are acceptable because the two operating units will not be affected by the test, the licensee has addressed the potential for loss of RCS inventory and DHR, the containment, the potential for a reactivity excursion, and the SFP cooling. The licensee has also verified that there will be a number of available offsite power supplies during and after the test and that sufficient operator training will be conducted. As a result, the staff concludes that the test will be conducted safely and the proposed change to the UFSAR is acceptable, which resolves the USQ.
Since the tests will be completed and this authorization will expire prior to the next scheduled annual UFSAR update, there is no need to submit an update to the UFSAR, pursuant to 10 CFR 50.51(e), to reflect this change.
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the South Carolina State official was notified of the proposed issuance of the amendments. The State official had no comments.
-6
5.0 ENVIRONMENTAL CONSIDERATION
The amendments change requirements with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (63 FR 52304 dated September 30, 1998). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributors: James Lazevnick Daniel O'Neal Christopher Jackson Date: November 12, 1998