ML14342A196
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McGuire Units 1 and 2 B 3.8.8-1 Revision No. 115 InvertersShutdown B 3.8.8 B 3.8 ELECTRICAL POWER SYSTEMS B 3.8.8 InvertersShutdown BASES BACKGROUND A description of the inverters is provided in the Bases for LCO 3.8.7, "InvertersOperating."
APPLICABLE The initial conditions of Design Basis Accident (DBA) and transient SAFETY ANALYSES analyses in the UFSAR, Chapter 6 (Ref. 1) and Chapter 15 (Ref. 2),
assume Engineered Safety Feature systems are OPERABLE. The DC to AC inverters are designed to provide the required capacity, capability, redundancy, and reliability to ensure the availability of necessary power to the Reactor Protective System and Engineered Safety Features Actuation System instrumentation and controls so that the fuel, Reactor Coolant System, and containment design limits are not exceeded.
The OPERABILITY of the inverters is consistent with the initial assumptions of the accident analyses and the requirements for the supported systems' OPERABILITY.
The OPERABILITY of the minimum inverters to each AC vital bus during MODES 5 and 6 ensures that:
- a.
The unit can be maintained in the shutdown or refueling condition for extended periods;
- b.
Sufficient instrumentation and control capability is available for monitoring and maintaining the unit status; and
- c.
Adequate power is available to mitigate events postulated during shutdown, such as a fuel handling accident.
The inverters were previously identified as part of the distribution system and, as such, satisfy Criterion 3 of 10 CFR 50.36 (Ref. 3).
LCO The inverters ensure the availability of electrical power for the instrumentation for systems required to shut down the reactor and maintain it in a safe condition after an anticipated operational occurrence or a postulated DBA. At least two AC vital buses on one train energized by their associated battery powered inverters provide uninterruptible supply of AC electrical power to associated loads even if the 4.16 kV
Inverters - Shutdown B 3.8.8 BASES McGuire Units 1 and 2 B 3.8.8-2 Revision No. 115 LCO (continued) safety buses are de-energized. OPERABILITY of the inverters requires that the AC vital bus be powered by the inverter. When the redundant train of class 1E AC vital bus electrical power distribution subsystem is required by LCO 3.8.10, the power source for these AC vital buses may consist of 1) the associated inverter powered by its associated battery; or 2) the regulated voltage transformer. This ensures the availability of sufficient power sources to operate the unit in a safe manner and to mitigate the consequences of postulated events during shutdown (e.g., fuel handling accidents).
APPLICABILITY The inverters required to be OPERABLE in MODES 5 and 6 and during movement of irradiated fuel assemblies provide assurance that:
- a.
Systems to provide adequate coolant inventory makeup are available for the irradiated fuel in the core;
- b.
Systems needed to mitigate a fuel handling accident are available;
- c.
Systems necessary to mitigate the effects of events that can lead to core damage during shutdown are available; and
- d.
Instrumentation and control capability is available for monitoring and maintaining the unit in a cold shutdown condition or refueling condition.
Inverter requirements for MODES 1, 2, 3, and 4 are covered in LCO 3.8.7.
ACTIONS A.1, A.2.1, A.2.2, A.2.3, and A.2.4 If two trains are required by LCO 3.8.10, "Distribution Systems Shutdown," the remaining OPERABLE Inverters may be capable of supporting sufficient required features to allow continuation of CORE ALTERATIONS, fuel movement, and operations with a potential for positive reactivity additions. By the allowance of the option to declare required features inoperable with the associated inverter(s) inoperable, appropriate restrictions will be implemented in accordance with the affected required features LCOs' Required Actions. In many instances, this option may involve undesired administrative efforts. Therefore, the allowance for sufficiently conservative actions is made (i.e., to suspend CORE ALTERATIONS, movement of irradiated fuel assemblies, and operations involving positive reactivity additions), that could result in loss of required SDM (Mode 5) or required boron concentration (Mode 6).
Suspending positive reactivity additions that could result in failure to meet the minimum SDM or boron concentration limits is required to assure continued safe operation. Introduction of coolant inventory must be from
Inverters - Shutdown B 3.8.8 BASES McGuire Units 1 and 2 B 3.8.8-3 Revision No. 115 ACTIONS (continued) sources that have a boron concentration greater than that what would be required in the RCS for minimum SDM or refueling boron concentration.
This may result in an overall reduction in RCS boron concentration, but provides acceptable margin to maintaining subcritical operation.
Introduction of temperature changes including temperature increases when operating with a positive MTC must also be evaluated to ensure they do not result in a loss of required SDM.
Suspension of these activities shall not preclude completion of actions to establish a safe conservative condition. These actions minimize the probability of the occurrence of postulated events. It is further required to immediately initiate action to restore the required inverters and to continue this action until restoration is accomplished in order to provide the necessary inverter power to the unit safety systems.
The Completion Time of immediately is consistent with the required times for actions requiring prompt attention. The restoration of the required inverters should be completed as quickly as possible in order to minimize the time the unit safety systems may be without power or powered from a regulated voltage transformer.
SURVEILLANCE SR 3.8.8.1 REQUIREMENTS This Surveillance verifies that the power sources are functioning properly with all required circuit breakers closed and AC vital buses energized from the required power source. The verification of proper voltage ensures that the required power is readily available for the instrumentation connected to the AC vital buses. The Surveillance Frequency is based on operating experience, equipment reliability, and plant risk and is controlled under the Surveillance Frequency Control Program.
REFERENCES
- 1.
UFSAR, Chapter 6.
- 2.
UFSAR, Chapter 15.
- 3.
10 CFR 50.36, Technical Specifications, (c)(2)(ii).