ML14342A404
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McGuire Units 1 and 2 B 3.9.2-1 Revision No. 115 Unborated Water Source Isolation Valves B 3.9.2 B 3.9 REFUELING OPERATIONS B 3.9.2 Unborated Water Source Isolation Valves BASES BACKGROUND During MODE 6 operations, all isolation valves for reactor makeup water sources containing unborated water that are connected to the Reactor Coolant System (RCS) must be closed to prevent unplanned boron dilution of the reactor coolant. The isolation valves must be secured in the closed position. One of the following groups of valves is required to be closed: 1) NV-250, or 2) NV-131, NV-140, NV-176, NV-468, NV-808, and either NV-132 or NV-1026 when it is necessary to makeup to the RWST during refueling operations.
The Chemical and Volume Control System is capable of supplying borated and unborated water to the RCS through various flow paths.
Since a positive reactivity addition, that could result in failure to meet the minimum SDM or boron concentration limits, is inappropriate during MODE 6, isolation of all unborated water sources prevents an unplanned boron dilution.
APPLICABLE The possibility of an inadvertent boron dilution event (Ref. 1) occurring SAFETY ANALYSES during MODE 6 refueling operations is precluded by adherence to this LCO, which requires that potential dilution sources be isolated. Closing the required valves during refueling operations prevents the flow of unborated water to the filled portion of the RCS. The valves are used to isolate unborated water sources. These valves have the potential to indirectly allow dilution of the RCS boron concentration in MODE 6. By isolating unborated water sources, a safety analysis for an uncontrolled boron dilution accident in accordance with the Standard Review Plan (Ref. 2) is not required for MODE 6.
The RCS boron concentration satisfies Criterion 2 of 10 CFR 50.36 (Ref.
3).
LCO This LCO requires that flow paths to the RCS from unborated water sources be isolated to prevent unplanned boron dilution during MODE 6 and thus avoid a reduction in SDM.
Unborated Water Source Isolation Valves B 3.9.2 BASES McGuire Units 1 and 2 B 3.9.2-2 Revision No. 115 APPLICABILITY In MODE 6, this LCO is applicable to prevent an inadvertent boron dilution event by ensuring isolation of all sources of unborated water to the RCS. For all other applicable MODES, the boron dilution accident was analyzed and was found to be capable of being mitigated.
ACTIONS The ACTIONS table has been modified by a Note that allows separate Condition entry for each unborated water source isolation valve.
A.1 Continuation of CORE ALTERATIONS is contingent upon maintaining the unit in compliance with this LCO. With any valve used to isolate unborated water sources not secured in the closed position, all operations involving CORE ALTERATIONS must be suspended immediately. The Completion Time of "immediately" for performance of Required Action A.1 shall not preclude completion of movement of a component to a safe position.
Condition A has been modified by a Note to require that Required Action A.3 be completed whenever Condition A is entered.
A.2 Preventing inadvertent dilution of the reactor coolant boron concentration is dependent on maintaining the unborated water isolation valves secured closed. Securing the valves in the closed position ensures that the valves cannot be inadvertently opened. The Completion Time of "immediately" requires an operator to initiate actions to close an open valve and secure the isolation valve in the closed position immediately. Once actions are initiated, they must be continued until the valves are secured in the closed position.
A.3 Due to the potential of having diluted the boron concentration of the reactor coolant, SR 3.9.1.1 (verification of boron concentration) must be performed whenever Condition A is entered to demonstrate that the required boron concentration exists. The Completion Time of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> is sufficient to obtain and analyze a reactor coolant sample for boron concentration.
Unborated Water Source Isolation Valves B 3.9.2 BASES McGuire Units 1 and 2 B 3.9.2-3 Revision No. 115 SURVEILLANCE SR 3.9.2.1 REQUIREMENTS These valves are to be secured closed to isolate possible dilution paths.
The likelihood of a significant reduction in the boron concentration during MODE 6 operations is remote due to the large mass of borated water in the refueling cavity and the fact that all unborated water sources are isolated, precluding a dilution. The boron concentration is checked every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> during MODE 6 under SR 3.9.1.1. This Surveillance demonstrates that the valves are closed through a system walkdown.
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, Section 15.4.6.
- 2.
NUREG-0800, Section 15.4.6.
- 3.
10 CFR 50.36, Technical Specifications, (c)(2)(ii).