AECM-85-0333, Forwards Application for Amend to License NPF-29 Revising Tech Specs to Allow Insp of Low Pressure Turbine Discs at Insp Interval Not to Exceed 50,000 H of Operation
| ML20138B851 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 11/01/1985 |
| From: | Kingsley O MISSISSIPPI POWER & LIGHT CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20138B837 | List: |
| References | |
| AECM-85-0333, AECM-85-333, TAC-60085, NUDOCS 8512120395 | |
| Download: ML20138B851 (3) | |
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MISSISSIPPI POWER & LIGHT COMPANY Helping Build Mississippi WhhMiddB F. O. B O X 16 4 0, J A C K S O N, MISSISSIPPI 39215-1640 November 1, 1985
- o. D. KINGSLEY, JR.
tnCE PRESIDENT - NUCLE AR OPE R ATION$
U. S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Washington, D. C.
20555 Attention:
Mr. Harold R. Denton, Director
Dear Mr. Denton:
SUBJECT:
Grand Gulf Nuclear Station Unit 1 Docket No. 50-416 License No. NPF-29 File:
0260/0840/L-860.0 Proposed Amendment to the Operating License (PCOL-85/19)
AECM-85/0333 On July 29, 1985, a meeting was held at the Grand Gulf Nuclear Station (GGNS) between members of the NRC Staff and Mississippi Power 6 Light (MP&L) to review and discuss plans for both the Fall '85 outage and t'te first refueling outage. At this meeting the deferral of selected items past the first refueling outage was discussed. One item discussed was the ultrasonic inspection of the low pressure (LP) turbine discs required by License Condition 2.C.(26).
In accordance with the provisions of 10 CFR 50.59 and 10 CFR 50.90, MP&L requests an amendment to License NPF-29, for Grand Gulf Nuclear Station (GGNS) Unit I to allow for the inspection of the LP turbine discs on an inspection interval not to exceed 50,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> of operation.
License Condition 2.C.(26) was imposed because of a history of corrosion crack initiation associated with LP turbine discs manufactured by certain domestic turbine / generator vendors. The turbine / generator system at the Grand Gulf Nuclear Station (GGNS) was manufactured by Kraftwerk Union (KWU) in West Germany. However, the NRC Staff in Supplemental Safety Evaluation Report (SSER) Number 2, Section 10.2.1 states that an interim conservative approach has been taken by assuming that the propensity for disc cracking in the GCNS
' turbine is the same as that for Westinghouse turbines. The design of the KWU turbine is significantly different than that of the domestic designs which have shown a history of corrosion crack initiation.
Cec l
581 MP&L believes that adequate technical justification exists to demonstrate gg that the requirement to inspect the LP turbines at each refueling outage in C2o accordance with License Condition 2.C.(26) is unnecessarily conservative and og would impose undue hardship on MP6L in the form of prolonged outage time,
$8 increased outage direct cost and increased power replacement cost. The 00 inspection of the LP turbines is contrary to the turbine / generator maintenance g
[IT program as recommended by the vendor Kraftwerk Union (KWU).
In addition, such inspection would prolong the first refueling outage by as much as 11 weeks no idO c c. c.
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J16AECM85101101 - 1 Member Middle South Utilities System
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AECM-85/0333 Page 2 resulting in a refueling outage of approximately 24 weeks.
It has also been estimated that any future refueling outage which included the inspection of all three LP turbines in its work scope could be substantially extended. The KWU maintenance program recommends a high pressure (HP) turbine and generator /
exciter disassembly and inspection during the first refueling outage. As discussed in the attachment to this letter, these component inspections during the first refueling outage are essential to prevent potential problems and ensure reliable operation of the turbine / generator system. All three LP turbines are then to be inspected by completion of the fourth refueling outage.
Subsequently, all five components are reinspected on a four refueling outage cycle.
The KWU LP turbine disc is designed so as to minimize stress in the keyway area in order to be less susceptible to stress corrosion cracking as compared to other designs. To date several KWU turbines have undergone complete ultrasonic inspections with no cracking having been found.
This includes turbines which have accumulated up to 80,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> of service.
In addition to the steps taken in the design of the turbines to lessen the susceptibility to stress corrosion cracking, MP&L maintains high reactor o
feedwater quality by strict compliance with reactor vendor water quality criteria, fuel warranty requirements, and other industry recognized recommendations. However, in the unlikely event that a cracked disc resulted in a missile, the KWU turbine casing has been designed to internally contain all missiles generated at speeds of less than 160% of rated speed. The probability of this occurring is extremely small.
In fact, the probability of the turbine generator experiencing an overspeed event of greater than 120% of rated speed has been calculated to be 1.6E-7 per unit year.
Through the use of an apparent crack growth rate model developed by the Electric Power Research Institute, MP&L has projected for the end of cycle I a maximum crack size of less than 11% of the calculated critical crack size.
This demonstrates that at the end of cycle 1 even the maximum crack sizes predicted would not be of sufficient size to present a problem with the continued operation of the LP turbines. This is especially true considering that in using the model the worst case cycle 1 conditions of 100% plant availability (13,140 hours0.00162 days <br />0.0389 hours <br />2.314815e-4 weeks <br />5.327e-5 months <br /> of operation) and the occurrence of a 120%
overspeed event were assumed.
In addition, the ciodel assumes that the turbine disc cracks immediately upon the unit's initial start-up and then continues to
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grow throughout the life of the unit. MP&L helieves that the results from this
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model are extremely conservative.
The first refueling outage is now scheduled to commence no later than June of 1986. Since the inspection of the LP turbines requires the development of inspection procedures and the procurement of inspection equipment, both of which are long lead time items, it is requested that the NRC provide MP&L with a decision on this proposed license amendment by January 6,.1986.
This should allow adequate time for final planning and scheduling of the first refueling outage.
J16AECM85101101 - 2
AECM-85/0333 Page 3 In accordance with the provisions of 10 CFR 50.30, three (3) signed originals and forty (40) copies of the requested amendment are enclosed. The attachment provides the complete technical justification and discussion to support the requested amendment. This amendment has been reviewed and accepted by the Plant Safety Review Committee (PSRC) and the Safety Review Committee (SRC).
Based on the guidelines presented in 10 CFR 50.92, it is the opinion of MP&L that this proposed amendment involves no significant hazards considerations.
Based on the guidance provided in 10 CFR 170.21, we have determined that the application fee is $150. A remittance of $150 is attached to this letter.
As a matter of good operating practice, MP&L will maintain frequent contact with your staff during the review period to ensure that the date of issuance of this change supports the completion of the first refueling outage schedules.
Yours ruly,
/
ODK:bms Attachments: GGNS PCOL-85/19
/
cc:
Mr. T. H. Cloninger (w/a)
Mr. R. B. McGehee (w/a)
Mr. N. S. Reynolds (w/a)
Mr. H. L. Thomas (w/o)
Mr. R. C. Butcher (w/a)
Mr. James M. Taylor, Director (w/a)
Office of Inspection & Enforcement U. S. Nuclear Regulatory Commission Washington, D. C.
20555 Dr.'J. Nelson Grace, Regional Administrator (w/a)
U. S. Nuclear Regulatory Commission Region II 101 Marietta St., N. W., Suite 2900 Atlanta, Georgia 30323 Dr. Alton B. Cobb (w/a)
State Health Officer State Board of Health Box 1700 Jackson, Mississippi 39205 J16AECM85101101 - 3