ML14342A193
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McGuire Units 1 and 2 B 3.8.5-1 Revision No. 41 DC Sources - Shutdown B 3.8.5 B 3.8 ELECTRICAL POWER SYSTEMS B 3.8.5 DC SourcesShutdown BASES BACKGROUND A description of the DC sources is provided in the Bases for LCO 3.8.4, "DC SourcesOperating."
APPLICABLE The initial conditions of Design Basis Accident and transient analyses in SAFETY ANALYSES in the UFSAR, Chapter 6 (Ref. 1) and Chapter 15 (Ref. 2), assume that Engineered Safety Feature systems are OPERABLE. The DC electrical power system provides normal control and switching during all MODES of operation.
The OPERABILITY of the DC subsystems is consistent with the initial assumptions of the accident analyses and the requirements for the supported systems' OPERABILITY.
The OPERABILITY of the minimum DC electrical power sources during MODES 5 and 6 and during movement of irradiated fuel assemblies 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 DC electrical power is provided to mitigate events postulated during shutdown, such as a fuel handling accident.
The DC sources satisfy Criterion 3 of 10 CFR 50.36 (Ref. 3).
LCO The DC electrical power subsystems, with 1) at least one subsystem consisting of two channels of DC; and 2) when the redundant train of DC electrical power distribution subsystem is required by LCO 3.8.10, the other subsystem consisting of either a battery or a charger, and 3) the corresponding control equipment and interconnecting cabling within the channel, are required to be OPERABLE to support required channels of the distribution systems required OPERABLE by LCO 3.8.10, "Distribution
DC Sources - Shutdown B 3.8.5 BASES McGuire Units 1 and 2 B 3.8.5-2 Revision No. 41 LCO (continued)
SystemsShutdown." This ensures the availability of sufficient DC electrical 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 channel of DC sources required to be OPERABLE in MODES 5 and 6, and during movement of irradiated fuel assemblies, provide assurance that:
- a.
Required features to provide adequate coolant inventory makeup are available for the irradiated fuel assemblies in the core;
- b.
Required features needed to mitigate a fuel handling accident are available;
- c.
Required features 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.
The DC electrical power requirements for MODES 1, 2, 3, and 4 are covered in LCO 3.8.4.
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, the remaining train with DC power available may be capable of supporting sufficient systems to allow continuation of CORE ALTERATIONS and fuel movement. By allowing the option to declare required features inoperable with the associated DC power source(s) inoperable, appropriate restrictions will be implemented in accordance with the affected required features LCO 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, 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 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
DC Sources - Shutdown B 3.8.5 BASES McGuire Units 1 and 2 B 3.8.5-3 Revision No. 41 ACTIONS (continued) 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 probability of the occurrence of postulated events. It is further required to immediately initiate action to restore the required DC sources and to continue this action until restoration is accomplished in order to provide the necessary DC electrical 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 DC sources should be completed as quickly as possible in order to minimize the time during which the unit safety systems may be without sufficient power.
SURVEILLANCE SR 3.8.5.1 REQUIREMENTS SR 3.8.5.1 requires performance of all Surveillances required by SR 3.8.4.1 through SR 3.8.4.8. Therefore, see the corresponding Bases for LCO 3.8.4 for a discussion of each SR.
This SR is modified by a Note. The reason for the Note is to preclude requiring the OPERABLE DC sources from being discharged below their capability to provide the required power supply or otherwise rendered inoperable during the performance of SRs. It is the intent that these SRs must still be capable of being met, but actual performance is not required.
REFERENCES
- 1.
UFSAR, Chapter 6.
- 2.
UFSAR, Chapter 15.
- 3.
10 CFR 50.36, Technical Specifications, (c)(2)(ii).