ML20132D273
| ML20132D273 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 07/02/1985 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20132D270 | List: |
| References | |
| NUDOCS 8507170033 | |
| Download: ML20132D273 (3) | |
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I SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGtfLATION l
RELATED TO PROCEDURES FOR DEGRADED l
GRID VOLTAGE PROTECTION FOR CLASS 1E PNEP SYSTEMS FOR FACILITY OPERATING LICENSE NO. DPR-61 CONNECTICUT YANKEE ATOMIC POWER COMPANY' HADDAM NECK PLANT DOCKET MO. 50-?I3 INTRODUCTION The on-site alternating current (AC) safety class IE electric system is sup-plied power from either the off-site transmission grid or from the en-site standty emergency diesel generators. During nomal plant operating con-ditions, the class IE busses are supplied power from the transmission grid.
Should the grid voltage degrade and become low enough so that the voltage at the class IE equiprent is below its qualified operating voltage, equipment damage could occur.
The NRC requested that the licensee address this degraded voltage condition by responding to NRC Generic Letter dated June 3,1977. The generic letter re-quested the licensee to aralyze the class IE system to detemine the grid voltage at which damage could occur. As a result, the licensee made plans to install a voltage sensing device on the class IE busses with coincident logic and with the low voltage set point above a value where eaufprent damage could This voltage device would then cause the off-site grid supply to be occur.
disconnected from the class 1E system at voltages below this value. The class IE busses would then be supplied power from their respective emergency diesel generators.
New England licensees were concerned that significant degradation of the grid would result if automatic disconnection occurred as a result of the large number of nuclear plants in the New England area.
It was their view that autor!atic disconnection from the grid should only be required if a low grid voltage occurred at the same time as a loss of Coolant Accident (LOCA). They agreed that should their plant have a LOCA at the same time there was a degraded grid voltage condition, they veuld automatically disconnect from the off-site grid.. The emergency diesel generators would then supply power to the class 1E systems. However, if there was a degraded grid voltage condition without a LOCA the operator would take the necessary renual action to protect the class IE system.
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This proposal for the licensee has been reviewed and accepted by the t'PC and is documented in the f:RC Letter and Safety Evaluation Report of July 9,1982. The Sefety Evaluation report identified that the licensee should develop an operating procedure to provide the necessary operator guidance to protect the class IE system under degraded grid voltage conditions without a LOCA condi-tion. By letter dated February 14, 1985, the licensee submitted for staff review revised plant procedures to cover the required operator actions. This safety evaluation is for these procedures.
DISCUSSION By letter dated February 3,1983, the licensee submitted to NPC for review Abnomal Operating Procedure AOP 3-2-?5, Low Voltage on Emergency Busses. This procedure was desiqned to assure protection of class IE systems under degraded grid voltage conditions without a concurrent LOCA. The procedure was reviewed during an inspection conducted at the facility. During this review the staff reouested additional information to aid in the evaluation of the procedure.
These items were discussed in Irispection Report 50-213/84-19.
The information requests dealt with the following issues:
Basis for starting motors at low voltages Basis for the minimum bus voltage for satisfactory starter operation Basis for timing low voltage on the grid Clarification of diesel operability / availability Provisions to mininize the time the diesel generators operate in parallel with a degraded grid.
By letter to NRC dated February 14, 1985, the licensee submitted responses to the NRC infomation req' est and also submitted Revision 3 to AOP 3-2-25 dated u
January 25, 1985, which incorporated changes and clarifications as follows:
Procedure step 4.10.1 (now 4.13.1) has been revised to eliminate shifting / starting safety-related motor loads.
All affected motor starters required to operate at 386 volts will be tested.
If any fail to operate either AOP 3-2-25 will be revised or all of the starters will be replaced with units which will operate at 386 vol ts.
Procedure steps 4.3, 4.5, 4.8, and 4.10 have been modified to provide a basis for timing low voltage on the grid.
O Precedure steps 4.4 and 4.8 (now 4.10) have been modified to' clarify the diesel operability / availability tems.
Procedure step 4.6.4 has been revised to minimize the time diesels operate in parallel with a degraded grid by use of a five minute tirre limit.
EVALUATION The staff review of AOP 3-2-25, Revision 3 identified the following facts.
There are three levels of undervoltage protection alarms-level three at 3980 volts, level two at 3642 volts, and level one at 2870 volts. Operator actions are based on the liniting alarmed condition.
When a level three (3980 volt) alam sounds and if there is no LOCA, the opera-tor starts timing the duration of the low voltage and notifies CONVEX to see if the grid voltage can be restored.
If the grid voltage is not restored within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, the operator must bring the plant to hot standby within the next six hours.
If the voltage drops to 3850 volts, the diesel generators are manually started, imediately loaded in parallel with the grid and the emergency bus separated from the grid within five minutes.
When a level two (3642 volt) alarm sounds and there is no LOCA, the operator starts timing the duration of the low voltage and notifies CONVEX to see if the grid voltage can be restored.
If not restored, the operator must proceed to hot standby within four hours.
If the voltage drops to less than 3450 volts and cannot be restored within ten ninutes, the operator must proceed imediate-ly to hot standby and utilize the emergency diesel for, providing shutdown power to their respective busses.
When a level one trip signal occurs (2870 volts), offsite power is automati-cally tripped off and the busses are powered by onsite power.
CONCLUSION We have concluded, based on the considerations discussed above, that:
(1) Licensee procedure AOP 3-2-25 Revision 3 dated January 25, 1985 provides technically acceptable procedures covering operator actions required during degraded grid voltage conditions without concurrent LOCA conditions.
(2) There is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner.
ACKNOWLEDGEMENT This Safety Evaluation was prepared by Mr. Carl Woodard, Division Reactor Safety, Region I.
Dated: July 2,1985
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