ML20082E429
| ML20082E429 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 04/04/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20082E426 | List: |
| References | |
| NUDOCS 9504110223 | |
| Download: ML20082E429 (5) | |
Text
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[$puta k UNITED STATES NUCLEAR REGULATORY COM..
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WASHINGTON, D.C. 2056M1001 j
%..... / SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMEllDMENT NO. 196 TO FACILITY OPERATING LICENSE NO. DPR-77 AND AMENDMENT NO.187 TO FACILITY OPERATING LICENSE NO. DPR-79 TENNESSEE VALLEY AUTHORITY SEOUOYAH NUCLEAR PLANT. UNITS I AND 2 QQ QET NOS. 50-327 AND 50-328 l.0 INTRODUCTION By letter dated December 16, 1994, which was supplemented by letter dated February 10, 1995, the Tennessee Valley Authority (the licensee) proposed an amendment to the Technical Specifications (TS) for Sequoyah Nuclear Plant (SQN) Units 1 and 2.
The requested changes would reduce the maximum allowed power levels and more clearly specify the plant conditions allowed by the TS for operation with one or more main steam safety valves (MSSVs) inoperable.
This would be accomplished by lowering the maximum allowable power range neutron flux setpoints corresponding to the number of inoperable MSSVs.
In addition, the Bases would be revised to reflect these changes and incorporate i
the revised methodology used to establish the neutron flux setpoints.
2.0 EVALUATION j
i The MSSVs are located in the steam line between the outlet of the steam generators and the main steam isolation valves. There are five MSSVs per i
steam generator with a combined capacity, according to the SQN Final Safety l
Analysis Report, corresponding to the calculated flow capacity of one steam generator. Their purpose is to provide emergency pressure relief for the steam generators in the event that steam generation exceeds steam consumption.
They provide 100 percent relieving capacity to ensure that the system pressure in the associated steam generator will be limited to 110 percent of the main steam system design pressure during the most severe anticipated system operational transients.
Westinghouse Electric Corporation has identified a potential problem with the allowable rated thermal power (RTP) levels when one or more of the MSSVs are inoperable.
In Nuclear Safety Advisory Letter 94-001 dated January 20, 1994, i
Westinghouse reported their determination that the relationship between the available MSSV relief capacity and allowable RTP level may not be linear under all plant conditions.
Because the current TS assumes linearity, Westinghouse has recommended that either the plant specific loss-of-load turbine trip transient be reanalyzed to determine the maximum allowable power levels (which may validate RTP levels in the current TS), or the TS be revised to reduce the ENCLOSURE 3 9504110223 950404 PDR ADOCK 05000327 P
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i maximum power levels allowed with inoperable MSSVs to a level below the heat removal capability of the operable MSSVs. Westinghouse supplied a calculational method for determining this power level _ using site-specific
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information.
SQN has chosen the latter approach.
l To ensure that the' secondary side pressures do not exceed 110 percent of the system design pressure during the most severe anticipated transient, the licensee has proposed new values in TS Table 3.7-1 that will specify power levels that are calculated to be below the heat removal capability of the remaining operable MSSVs.
For example, if one MSSV is inoperable for one steam generator, the relief capacity of that steam generator has been reduced.
To maintain the ability of the remaining MSSVs to protect the main steam system from overpressure, the energy transfer to that steam generator must be reduced by the same amount. This is accomplished by reducing the thermal power trip setpoint, which has the conservative effect of limiting the energy transfer to all steam generators to a value equal to the relief capacity of the steam generator with the inoperable MSSV. A proposed change to TS Bases 3/4.7.1.1 would reflect the calculation method recommended by Westinghouse to determine the maximum power level. This method, with adjustments for plant-specific instrumentation and channel uncertainties, has been used by SQN' to determine the new maximum. allowable power range neutron flux high setpoints.
(percent of rated thermal power) in Table 3.7-1 for operation with one, two, or three inoperable MSSVs on any operating steam generator. As a result, the setpoints have been reduced from 87, 65, and 43 percent to 63,'45, and 28 percent for operation with one, two, and three inoperable MSSVs respectively.
Exceeding these setpoints 4111 cause a reactor trip.
The staff has found that the revised method of determining the maximum power level setpoints ensures that operation with inoperable MSSVs will be below the heat-removing capability of the operable MSSVs. This will ensure that the
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secondary system steam pressure will not exceed 100 percent of its design valve.
In addition,.the new setpoints are more conservative than the existing setpoints. Therefore, the staff finds the proposed changes to TS Table 3.7-1 and the Bases changes that describe this method acceptable.
The licensee has also proposed combining the action statements in TS 3.7.1.1.a and TS 3.7.1.1.b.
TS 3.7.1.1.a allows 4-loop operation in Modes 1, 2, or 3 with one or more MSSVs inoperable provided that the neutron high flux setpoint is reduced per Table 3.7-1 within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. Otherwise, the unit must be placed' in hot standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in cold shutdown in the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. TS 3.7.1.1.b allows 3-loop operation in Mode 3 with one or more MSSVs inoperable in the operable loop, with the same restrictions.
- However, TS 3.4.1 already requires that all reactor coolant loops be in operation for Modes 1 and 2, or the unit be in at least hot standby (Mode 3) within I hour.
The purpose of the proposed change, then, is to simplify the specifications by eliminating this conflict and separating the reactor coolant loop operating requirements and the MSSV requirements. The proposed change would allow operation with one or more MSSVs inoperable for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> provided that the j
neutron flux high setpoint is reduced per Table 3.7-1.
If this cannot be accomplished, or if one or more steam generators have less than two MSSVs operable, the unit must be in hot standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in hot shutdown in the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. These, and the administrative changes
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I proposed by the licensee to TS 3.7.1.1, are consistent with NUREG-1431, i%stinghouse Standard Technical Specifications. The staff has-reviewed the proposed changes and finds them acceptable.-
The licensee has also proposed removal of the present Table 3.7-2, " Maximum Allowable Power Range Neutron Flux High Setpoint with Inoperable Steam Line Safety Valves During 3 Loop Operation." The table specifies that for 1, 2, and 3 inoperable MSSVs on any operating steam generator, the power level setpoints must be*less than 60, 45, and 30 percent. However, as pointed out above, TS 3.4.1 already requires that all 4 reactor coolant loops be in operation for Modes 1 and 2, or the unit be in at least hot standby (Mode 3) within I hour. Therefore, 3-loop operation is severely limited, making it unnecessary to specify a maximum power level if MSSVs are inoperable when the unit would be required to be in Mode 3 within I hour.
In addition, the licensee has proposed changing the title of Table 3.7-1 to remove its applicability to 4-loop operation. As a result, the maximum power level setpoints specified for the number of inoperable MSSVs will be applicable for 3- (as well as.4-) loop operation. The proposed change is, therefore, acceptable. As a result of this change, the existing Table 3.7-3 (TS page 3/4 7-4) will be redesignated Table 3.7-2 (page 3/4 7-3).
The licensee has proposed administrative and Bases changes corresponding to these changes. The staff finds them acceptable.
The supplemental information supplied by letter dated February 10, 1995, proposed modifying the original submittal-regarding TS 3.7.1.1.
This proposed TS change would add an asterisk to Mode 3 Applicability that would reference a note that would state:
"With the reactor trip system breakers in the closed position." As a result, when in Mode 3 with inoperable MSSVs, the maximum high neutron flux setpoints would be limited to the values shown in Table 3.7-2 only when the reactor trip breakers (RTBs) are closed..The staff j
finds this change acceptable since it is the purpose of the high flux trip to open the RTBs if the setpoint is reached. Therefore, reducing the trip setpoint with the RTBs already open (as they would be under certain conditions in Mode 3), provides no safety benefit.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Tennessee State official was notified of the proposed issuance of the amendment. The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement 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 amendment involves 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 m
exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no P
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public comment on such finding (60 FR 11140). Accordingly, the amendment meets 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 amendment.
5.0 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 tne Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: David E. LaBarge Dated: April 4, 1995 a
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-Mr. Oliver D.'Kingsley, Jr.
SEQU0YAH NUCLEAR PLANT Tennessee Valley Authority-cc:
Mr. 0.'J. Zeringue, Sr. Vice President TVA Representative Nuclear Operations Tennessee Valley Authority Tennessee Valley Authority 11921 Rockville Pike 38 Lookout Place.
Suite.402 1101 Market Street Rockville, MD 20852 Chattanooga, TN 37402-2801 Regional Administrator Dr. Mark O. Medford, Vice President U.S. Nuclear Regulatory Commission Engineering & Technical Services Region II Tennessee Valley Authority 101 Marietta Street, NW., Suite 2900 3B Lookout Place Atlanta, GA 30323 1101 Market Street Chattanooga, TN 37402-2801-Mr. William E. Holland Senior Resident Inspector Mr. D. E. Nunn, Vice President Sequoyah Nuclear Plant New Plant Completion U.S. Nuclear Regulatory Cummission Tennessee Valley Authority 2600 Igou Ferry Road 3B Lookout P1 ace Soddy Daisy, TN 37379 1101 Market Street Chattanooga, TN 37402-2801 Mr. Michael H. Mobley, Director Division of Radiological Health :
Site Vice President 3rd Floor, L and C ' Annex Sequoyah Nuclear Plant 401 Church Street Tennessee Valley Authority Nashville,.TN 37243-1532 P.O. Box 2000 Soddy Daisy, TN 37379 County Judge Hamilton County Courthouse General Counsel Chattanooga, TN 37402-2801 Tennessee Valley Authority ET 11H l
400 West Summit Hill Drive Knoxville, TN 37902 Mr. P. P. Carier, Manager Corporate Licensing Tennessee Valley Authority i
4G Blue Ridge 1101 Market Street Chattanooga, TN 37402-2801 Mr. Ralph H. Shell Site Licensing Manager Sequoyah Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Soddy Daisy, TN 37379 t