ML20236G079
| ML20236G079 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 07/30/1987 |
| From: | VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | |
| Shared Package | |
| ML20236G070 | List: |
| References | |
| NUDOCS 8708040123 | |
| Download: ML20236G079 (8) | |
Text
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' ATTACHMENT _1_ ,
I PROPOSED TECHNICAL SPECIFICATIONS CHANGES NORTII ANNA POWER STATION UNIT 2-
-i Virginia Electric and Power Company
-PDR 8708040123 870730 P ADOCM 05000339 4
pg
g PLANT SYSTEMS .
TURBINE OVERSPEED LIMITING CONDITION FOR OPERATION 3.7.1.7 At least one turbine overspeed system sha.11 be OPERABLE.
APPLICABILITY: MODE 1, 2 and 3 ACTION: With the above required turbine overspeed protection system inoperable, within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> either restore the system to OPERABLE status or isolate the turbine from the steam supply.
SURVEILLANCE REQUIREMENT 4.7.1.7.1 The provisions of Specification 4.0.4 are not applicable.
4.7.1.7.2 The above required turbine overspeed protection system shall be demonstrated OPERABLE:
- a. At least once per 31 days by cycling each of the following valves through one complete cycle.
- 1. 4 Turbine Throttle valves
- 2. 4 Turbine Governor valves *
- 3. 4 Turbine Reheat Stop valves
- 4. 4 Turbine Reheat Intercept valves i
- b. At least once per 31 days by direct observation of the movement of each of the above valves through one complete cycle.*
- c. At least once per 18 months, by performance of CHANNEL CALIBRATION on the turbine overspeed protection instruments,
- d. At least once per 40 months, by disassembly of at least one of each' of the above valves and performing a visual and surface inspection of all valve seats, disks and stems and verifying no unacceptable flaws or corrosion.
- For cycle 5 only, further testing of the turbine governor valves may be suspended during power coastdown operation between 196 and 835 MWe.
NORTH ANNA - UNIT 2 3/4 7-12 l
f 4 e ATTACHMENT 2 i
SAFETY EVALUATION i
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Virginia Electric and Power Company '
DISCUSSION OF PROPOSED EMERGENCY TECHNICAL SPECIFICATION CHANGE Presently, North Anna Unit No. 2 Technical Specification 4.7.1.7.2.a requires that at least once per 31 days the four turbine throttle valves, four turbine gove rnor valves , four turbine reheat stop valves, and four turbine reheat intercept valves be cycled through one complete cycle. The proposed emergency Technical Specification change would permit a one-time exemption for cycling the turbine governor valves. The turbine valve freedom test for the other turbine valves (throttle, reheat stop, and reheat intercept valves) will be performed to satisfy the Technical Specification surveillance requirements.
By the next scheduled performance of the turbine valve freedom test, the turbine should be operating with only two governor valves open and would continue to be operated in this configuration throughout the remainder of the power coastdown. As a result, the concern to verify proper overspeed protection is reduced from four to two governor valves. It should be noted that the operability of the turbine governor valves can be demonstrated on an ongoing basis (i.e., every few days) as turbine load is periodically adjusted downward to match reactor power during the power coastdown. This can be confirmed by monitoring the changes in governor valve position as turbine power is adjusted. The possibility of either of the two open governor valves failing to close upon demand is extremely remote based on the reliability of these valves as demonstrated during previous testing and operation during the power coastdown. Prior to 1984, the turbine valves on both units were tested weekly Since that time, the turbine valves have been tested monthly without any failures to close. In addition, the valves have not failed to close in response 'o turbine trip demand. This high level of reliability is also assured, in part, by the all volatile chemical treatment of the feedwater system which essentially eliminates valve failure due to scale buildup on the .
valve surfaces.
In the event either of the two open turbine governor valves failed to close following a turbine trip demand, the turbine throttle valves, which will continue to be verified operable per Technical Specification surveillance requirements, would serve as a backup means to isolate steam from the turbine
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in this case. It should be noted that the turbine throttle valves are the )
valves taken credit for in the Reactor Protection System for tripping the j turbine. The operator can take other manual actions to isolate steam from the j turbine, and, in fact, is provided the necessary guidance by a Emergency i Operating Procedure (EOP) to ensure the turbine is tripped.
In the event that the turbine did not trip on a valid signal, the E0P (EP-1, Revision 1) provides specific actions to be taken. These actions include manually closing the main steam trip valves (MSTVs) to isolate the turbine.
The North Anna Unit No. 2 turbines are of the heavy hub design which reduces the probability that turbine generated missiles from disk failure that could potentially result from an overspending of the turbine would be produced before the turbine could be isolated. Additionally, we have performed regular i ultrasonic inspections of the turbine blading and disks. These considerations I provide assurance that the structural integrity of the turbine rotors is maintained, with adequate margin, at a safe level.
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North Anna Unit No. 2 is at end of cycle with zero boron and in a power coastdown. To preclude the possibility of damaging the turbine's first stage blading, Westinghouse recommends that the governor valvec not be cycled at the current power level. Only if power is reduced to less than approximately 196 MWe or increased to approximately 835 MWe could the governor valves be cycled without subjecting the turbine blading to excessive. loading. To enable Unit 2 to return to power after performing such a test at low power, control rods would have to be used to lower power. This condition would induce a xenon transient in the core because of the lack of excess reactivity in the core and could affect core stability. Core peaking factors would also be adversely.
affected by the Xenon redistribution. A decision to perform the test at the lower power level would also result in an extended reduction in power in order-to minimize the. effects of any transient on the core and to ensure the secondary plant performance is controlled and monitored closely. Not only would the power reduction result in lost generation, but it would also subject the plant to increased risk of a severe transient such as a reactor trip. I J
Rather than subject the unit to a potentially severe transient, justification exists to request a one-time exemption from cycling the turbine governor valves for the remainder of Cycle 5 operation. The operability of the other-turbine v-1ves will be verified, and the demonstrated high reliability of the governor valves and the monitoring of the governor valve position changes during the coastdown provide assurance that the turbine overspeed protection system will operate as designed, if needed, until the Unit 2 refueling outage which is currently scheduled to begin on September 7, 1987.
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10 CFR 50.59 EVALUATION The granting of an emergency Technical Specification change for one-time relief from having to the cycle governor valves will not result in an unreviewed safety question as defined in 10 CFR.50.59. The basis for this determination is summarized below:
- 1. The probability of occurrence or the consequences of an accident or malfunction of equipment important to safety previously evaluated in the safccy analysis is not increased. The testing of the turbine governor valves performed to date has demonstrated the reliability of these valves. The operability of the turbine governor valves will be demonstrated on an ongoing basis as turbine load is periodically adjusted to match reactor power during the power coastdown. This can be confirmed by monitoring 'the changes in governor valve position as turbine power is adjusted. A one-time exemption from testing only the governor valves for the remainder of Cycle 5 operation will not degrade the reliability of the turbine overspeed protection system. The design of the turbine rotors and the existence of procedures to manually backup automatic initiation of the turbine trip provide further assurance that the probability of the generation of destructive missiles remains minimal.
- 2. The possibility for an accident or malfunction of a different . type than any evaluated in the safety analysis is not created since the design and operation of the turbine protection and control systems are not being changed.
- 3. The margin of safety as defined in the Bases for any Technical Specification is not reduced since the design and operation of the turbine prutection and control system is not being changed and the ;
operability of the turbine governor valves will be demonstrated on l an ongoing basis as turbine load is periodically adjusted as discussed previously. Further, past testing of the , turbine governor valves has shown the valves to be highly reliable.
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i 10 CFR 50.92 SIGNIFICANT HAZARDS CONSIDERATION ANALYSIS The proposed change does not involve a significant hazards consideration as defined in 10 CFR 50.92 since the change does not:
- 1. Involve a significant increase in the probability or consequences of an accident previously evaluated in the safety analysis. The testing of the turbine governor valves performed to date has demonstrated the reliability of these valves. The operability of the turbine governor valves will be demonstrated on an ongoing basis as turbine load is periodically adjusted to match reactor power during the power coastdown. This can be confirmed by monitoring the changes in governor valve position as turbine power is adjusted. A one-time exemption from testing only the governor valves for the remainder of Cycle 5 operation will not degrade the reliability of the turbine overspeed protection system. The design of the turbine rotors and the existence of procedures to manually backup automatic initiation of the turbine trip provide further assurance that the probability of the generation of destructive missiles remains minimal.
- 2. Create the possibility of a new or different type of accident previously evaluated in the safety analysis is not created since design and operation of the turbine protection and control systems are not being changed.
- 3. Involve a significant reduction in the margin of safety since the design and operation of the turbine protection and control system is not being changed and the operability of the turbine governor valves will be demonstrated on an ongoing basis as turbine load is periodically adjusted as discussed previously. Further, past testing of the turbine governor valves has shown the valves to be hfghly reliable.
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COMMONWEALTH OF VIRGINIA )
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CITY OF RICHMOND )
The foregoing document was acknowledged before me, in and-for the City and Commonwealth aforesaid, today by W. L. Stewart who is Vice President - Nuclear Operations, of Virginia Electric and Power Company. He is duly authorized'to execute and file the aforegoing document in behalf of that _ Company, and the statements in the document are true to the best of his knowledge and belief.
Acknowledged before me this 3 8 day of d , 19D.
My Commission expires:t- / //Ago f 19,Qp.'
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Notary P6b11c- - ~'
I (SEAL) l
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