CNS-16-046, Technical Specification Bases Changes, B 3.7 Plant Systems

Technical Specification Bases Changes, B 3.7 Plant Systems

ML16168A029
Person / Time
Site:	Catawba
Issue date:	06/14/2016
From:	Henderson K Duke Energy Carolinas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
CNS-16-046
Download: ML16168A029 (7)

Text

.

Kelvin Henderson

~-,DUKE Vice President

~ ENERGYm Catawba Nuclear Station Duke Energy CN01VP I 4800 Concord Road York, SC 29745 o: 803. 701.4251 f: 803.701.3221 CNS-16-046 June 14, 2016 U.S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555-0001 .

Subject:

Duke Energy Carolinas, LLC Catawba Nuclear Station, Units 1 and 2 Docket Nos. 50-413 and 50-414 Technical Specification Bases Changes Pursuant to 10CFR 50.4, please find attached changes to the Catawba Nuclear Station Technical Specification Bases. These Bases changes were made according to the provisions of Technical Specification 5.5.14, "Technical Specifications (TS) Bases Control Program."

Any questions regarding this information should be directed to Larry Rudy, Regulatory Affairs, at (803) 701-3084.

I certify that I am a duly authorized officer of Duke Energy Carolinas, LLC, and that the information contained herein accurately represents changes made to the Technical Specification Bases since the previous submittal.

Kelvin Henderson Vice President, Catawba Nuclear Station Attachment

Catawba Nuclear Station Technical Specifications Manual Amendments June 14, 2016 Page 2 xc: C. Haney, Regional Administrator U.S. Nuclear Regulatory Commission, Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, GA 30303-1257 M. D. Orenak NRC Project Manager (CNS)

U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 8 G9A .

11555 Rockville Pike Rockville, MD 20852-27 46 G. A. Hutto, Senior Resident Inspector Catawba Nuclear Station

MSSVs B 3.7.1 B 3. 7 PLANT SYSTEMS B 3. 7 .1 Main Steam Safety Valves (MSSVs)

BASES BACKGROUND The primary purpose of the MSSVs is to provide overpressure protection for the secondary system. The MSSVs also provide protection against overpressurizing the reactor coolant pressure boundary (RCPB) by providing a heat sink for the removal of energy from the Reactor Coolant System (RCS) if the preferred heat sink, provided by the Condenser and Circulating Water System, is not available.

Five MSSVs are located on each main steam header, outside containment, upstream of the main steam isolation valves, as described in the UFSAR, Section 10.3.1 (Ref. 1). The MSSV capacity criteria is 110% of rated steam flow at 110% of the steam generator design pressure. This meets the requirements of the ASME Code, Section Ill (Ref. 2). The MSSV design includes staggered setpoints, according to Table 3.7.1-2 int.he accompanying LCO, so that only the needed valves will actuate. Each valve is orificed to a size of 14.18 square inches.

Staggered setpoints reduce the potential for valve chattering that is due to steam pressure insufficient to fully open all valves following a turbine reactor trip.

APPLICABLE The design basis for the MSSVs comes from Reference 2 and its SAFETY ANALYSES purpose is to limit the secondary system pressure to :::;; 110% of design pressure when passing 100% of design steam flow. This. design basis is sufficient to cope with any anticipated operational occurrence (AOO) or accident considered in the Design Basis Accident (OBA) and transient analysis.

The events that challenge the relieving capacity of the MSSVs, and thus RCS pressure, are those characterized as decreased heat removal events, which are presented in the UFSAR, Section 15.2 (Ref. 3). Of these, the full power turbine trip without steam dump is the limiting AOO.

The transient response for turbine trip without a direct reactor trip presents no hazard to the integrity of the RCS or the Main Steam System.

Catawba Units 1 and 2 B 3.7.1-1 Revision No. 2

MSSVs B 3.7.1 BASES

• APPLICABLE SAFETY ANALYSES (continued)

For the peak secondary pressure case, the reactor is tripped on overtemperature L1T. Pressurizer relief valves and MSSVs are activated and prevent overpressurization in the primary and secondary systems.

The MSSVs satisfy Criterion 3 of 10 CFR 50.36 (Ref. 4).

LCO The accident analysis assumes five MSSVs per steam generator to provide overpressure protection for design basis transients occurring at 3479 MWt. An MSSV will be considered inoperable if it fails to open on demand. The LCO requires that five MSSVs be OPERABLE in compliance with Reference 2, even though this is not a requirement of the OBA analysis. This is because operation with less than the full number of MSSVs requires limitations on allowable THERMAL POWER (to meet ASME Code requirements). These limitations are according to Table 3.7.1-1 in the accompanying LCO, and Required Action A.1 and A.2.

The OPERABILITY of the MSSVs is defined as the ability to open within the setpoint tolerances, relieve steam generator overpressure, and reseat when pressure has been reduced. The OPERABILITY of the MSSVs is determined by periodic surveillance testing in accordance with the lnservice Testing Program.

The lift settings, according to Table 3.7.1-2 in the accompanying LCO, correspond to ambient conditions of the valve at nominal operating temperature and pressure.

This LCO provides assurance that the MSSVs will perform their designed safety functions to mitigate the consequences of accidents that could result in a challenge to the RCPB.

APPLICABILITY In MODE 1, the number of MSSVs per steam generator required to be OPERABLE must be according to Table 3.7.1-1 in the accompanying LCO. In MODES 2 and 3, only two MSSVs per steam generator are required to be OPERABLE.

In MODES 4 and 5, there are no credible transients requiring the MSSVs.

The steam generators are not normally used for heat removal in MODES 5 and 6, and thus cannot be overpressurized; there is no requirement for the MSSVs to be OPERABLE in these MODES.

Catawba Units 1 and 2 B 3.7.1-2 Revision No. 2

MSSVs B 3.7.1 BASES

• ACTIONS The ACTIONS table is modified by a Note indicating that separate Condition entry is allowed for each MSSV.

A.1 and A.2 With one or more MSSVs inoperable, reduce power so that the available MSSV relieving capacity meets Reference 2 requirements for the applicable THERMAL POWER.

Operation with less than all five MSSVs OPERABLE for each steam generator is permissible, if THERMAL POWER is proportionally limited to the relief capacity of the remaining MSSVs. This is accomplished by restricting THERMAL POWER so that the energy transfer to the most limiting steam generator is not greater than the available relief capacity in that steam generator. For example, if one MSSV is inoperable in one steam generator, the relief capacity of that steam generator is reduced by approximately 20%. To offset this reduction in relief capacity, energy transfer to that steam generator must be similarly reduced. This is accomplished by reducing THERMAL POWER by the necessary amount to conservatively limit the energy transfer to all steam generators, consistent with the relief capacity of the most limiting steam generator.

• The maximum power level specified for the power range neutron flux high trip setpoint with inoperable MSSVs must ensure that power is limited to less than the heat removal capacity of the remaining OPERABLE MSSVs. The reduced high flux trip setpoint also ensures that the reactor trip occurs early enough in the loss of load/turbine trip event to limit primary to secondary heat transfer and preclude overpressurization of the primary and secondary systems. To calculate this power level, the governing equation is the relationship q = m L-.h, where q is the heat input from the primary side, m is the steam flow rate and L-.h is the heat of vaporization at the steam relief pressure (assuming no subcooled feedwater). The algorithm use is consistent with th_e recommendations of the Westinghouse Nuclear Safety Advisory Letter, NSAL-94-001, dated January 20, 1994 (Ref. 5). Additionally, the calculated values are reduced by 4.2% to account for instrument and channel uncertainties.

The allowed Completion Time of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> provides an acceptable time to reach the required power level from full power operation without allowing the plant to remain in an unacceptable condition for an extended period of time and provides sufficient time to reduce the trip setpoints. The adjustment of the trip setpoints is a sensitive operation that may inadvertently trip the Reactor Protection System.

Catawba Units 1 and 2 B 3.7.1-3 Revision No. 2

MSSVs B 3.7.1 BASES

• ACTIONS (continued)

B.1 and B.2 If the MSSVs cannot be restored to OPERABLE status within the associated Completion Time, or i.f one or more steam generators have less than two MSSVs OPERABLE, the unit must be placed in a MODE in which the LCO does not apply. To achievethis status, the unit must be placed in at least MODE 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, and in MODE 4 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The allowed Completion Times are reasonable, based on operating experience, to reach the required unit conditions from full power conditions in an orderly manner and without challenging unit systems.

SURVEILLANCE SR 3.7.1.1 REQUIREMENTS This SR verifies the OPERABILITY of the MSSVs by the verification of each MSSV lift setpoint in accordance with the lnservice Testing Program. The ASME Code (Ref. 6), requires that safety and relief valve tests be performed. According to Reference 6, the following tests are required:

• a.

b.

c.

Visual examination; Seat tightness determination; Setpoint pressure determination (lift setting);

d. Compliance with seat tightness criteria; and

e. Verification of the balancing device integrity on balanced valves.

All valves are required to be tested every 5 years, and a minimum of 20%

of the valves are required to be tested every 24 months. The ASME Code specifies the activities and frequencies necessary to satisfy the requirements. Table 3. 7 .1-2 allows a+/-. 3% setpoint tol.erance for OPERABILITY; however, the valves are reset to +/-. 1% during the Surveillance to allow for drift.

This SR is modified by a Note that allows entry into and operation in MODE 3 prior to performing the SR. The MSSVs may be either bench tested or tested in situ at hot conditions using an assist device to simulate lift pressure. If the MSSVs are not tested at hot conditions, the lift setting pressure shall be corrected to ambient conditions of the valve at operating temperature and pressure.

Catawba Units 1 and 2 B 3.7.1-4 Revision No. 2

MSSVs B 3.7.1 BASES

• REFERENCES 1.

2.

UFSAR, Section 10.3.1.

ASME, Boiler and Pressure Vessel Code, Section Ill, Article NC-7000, Class 2 Components.

3. UFSAR, Section 15.2.

4. 10 CFR 50.36, Technical Specifications, (c)(2)(ii).

5. Westinghouse Nuclear Safety Advisory Letter, NSAL-94-001, dated January 20, 1994.

6. ASME Code for Operation and Maintenance of Nuclear Power Plants .

Catawba Units 1 and 2 B 3.7.1-5 Revision No. 2