ML032190026

Technical Specification Pages for Amendment 277

ML032190026
Person / Time
Site:	Sequoyah
Issue date:	07/31/2003
From:	NRC/NRR/DLPM
To:
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Download: ML032190026 (10)

Text

CURVES APPLICABLE FOR HEATUP RATES UP TO 60 °FIHR FOR THE SERVICE PERIOD UP TO 32 EFPY. MARGINS OF 60 PSIG I AND 100 F ARE INCLUDED FOR POSSIBLE INSTRUMENT ERRORS.

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FIGURE 3.4-2 SEQUOYAH UNIT 2 REACTOR COOLANT SYSTEM HEATUP LIMITATIONS APPLICABLE UP TO 32 EFPY I SEQUOYAH - UNIT 2 314 4-29 Amendment No. 138, 148, 264,277

CURVES APPLICABLE FOR COOLDOWN RATES UP TO 10 0 FIHR FOR THE SERVICE PERIOD UP TO 32 .EFPY. MARGINS OF 60 PSIG I AND 10rF ARE INCLUDED FOR POSSIBLE INSTRUMENT ERRORS.

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0 50 100 150 200 250 300 350 400 45D 500 550 Moderator Temperature (Dog. F)

FIGURE 3.4-3 SEQUOYAH UNIT 2 REACTOR COOLANT SYSTEM COOLDOWN LIMITATIONS APPLICABLE UP TO 32 EFPY I SEQUOYAH - UNIT 2 3/4 4-30 Amendment No. 138, 148, 264. 277

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O' 4-0 50 100 150 200 250 300 Q 400 40Q 5W TEMPERATRE. *OF PORV NOMINAL LIFT SETTINGS - APPLICABLE UP TO 32 EFPY I FIGURE 3.4-4 SEQUOYAH - UNIT 2 314 4-35 Amendment No. 147, 264, 277

REACTOR COOLANT SYSTEM BASES SPECIFIC ACTIVITY (Continued)

Reducing Tg,, to less than 500W F prevents the release of activity should a steam generator tube rupture since the saturation pressure of the primary coolant is below the lift pressure of the atmospheric steam relief valves. The surveillance requirements provide adequate assurance that excessive specific activity levels In the primary coolant will be detected In sufficient time to take corrective action.

Information obtained on iodine spiking will be used to assess the parameters associated with spiking phenomena. A reduction In frequency of Isotopic analyses following power changes may be permissible if justified by the data obtained.

3/4.4.9 PRESSURE/TEMPERATURE LIMITS The temperature and pressure changes during heatup and cooldown are limited to be consistent with the requirements given In the ASME Boiler and Pressure Vessel Code,Section XI, Appendix G.

1) The reactor coolant temperature and pressure and system heatup and cooldown rates (with the exception of the pressurizer) shall be limited in accordance with Figures 3.4-2 and 3.4-3 for the first full-power service period.

a) Allowable combinations of pressure and temperature for specific temperature change rates are below and to the right of the limit lines shown. Umit lines for cooldown rates between those presented may be obtained by interpolation.

b) Figures 3.4-2 and 3.4-3 define limits to assure prevention of non-ductile failure only. For normal operation, other inherent plant characteristics, e.g., pump heat addition and pressurizer heater capacity, may limit the heatup and cooldown rates that can be achieved over certain pressure-temperature ranges.

2) These limit lines shall be calculated periodically using methods provided below.

3) The secondary side of the steam generator must not be pressurized above 200 psig if the temperature of the steam generator is below 700°F.

4) The pressurizer heatup and cooldown rates shall not exceed 1000F/ hr and 2000/hr respectively.

The spray shall not be used If the temperature difference between the pressurizer and the spray fluid Is greater than 5600F.

SEQUOYAH - UNIT 2 B 3/4 4-6 Amendment No. 32,277

REACTOR COOLANT SYSTEM BASES PRESSUREITEMPERATURE LIMITS (Continued)

5) System preservice hydrotests and in-service leak and hydrotests shall be performed at pressures in accordance with the requirements of ASME Boiler and Pressure Vessel Code, Section Xl.

10 CFR 50, Appendix G, addresses metal temperature of the closure head flange and vessel regions. Appendix G states that the minimum metal temperature of the closure flange region should be at least 120 degrees Fahrenheit (F) higher than the limiting RTNDT for this region when the pressure exceeds 20 percent of the preservice hydrostatic test pressure (561 pounds per square Inch gauge (psig) for Westinghouse Electric Corporation plants). For SQN, Unit 2, the minimum temperature of the closure flange and vessel flange regions is 117 degrees F since the limiting Initial RTNDT for the closure head flange Is -13 degrees F (see Table B 3/4.4-1). These numbers (561 psig and 117 degrees F) include a margin for Instrumentation error of 10 degrees F and 60 psig.

Heatup and cooldown limit curves are calculated using the most limiting value of the nil-ductility reference temperature, RTNDT at the end of 32 effective full power years of service life. The 32 EFPY service life period Is chosen such that the limiting RTNDT at the 1/4T location in the core region is greater than the RTNDT of the limiting unirradiated material. The selection of such a limiting RTNDT assures that all components In the Reactor Coolant System will be operated conservatively in accordance with applicable Code requirements.

The reactor vessel materials have been tested to determine their Initial RTNDT; the results of these tests are shown in Table B 3/4.4-1. Reactor operation and resultant fast neutron (E greater than 1 MEV) irradiation can cause an Increase in the RTNDT. Therefore, an adjusted reference temperature, based upon the fluence of the material In question, has been predicted using Regulatory Guide 1.99, Revision 2 and a peak surface fluence of 1.82 x 10 19 n/cm2 for 32 effective full power years (reference WCAP-1 5321, Revision 1, 'Sequoyah Unit 2 Heatup and Cooldown Umit Curves for Normal Operation and PTLR Support Documentation," April 2001). The heatup and cooldown limit curves of Figures 3.4-2 and 3.4-3 include predicted adjustments for this shift in RTNDT at the end of 32 EFPYs, as well as adjustments for possible errors In the pressure and temperature sensing instruments. The heatup and cooldown limits In WCAP-15321, Revision 1 were based on a core thermal power of 3411 MWt. The curves have been evaluated In WCAP-1 5725 to be still effective for operation through the end of 32 EFPYs for the uprated core thermal power of 3455 MWt.

SEQUOYAH - UNIT 2 B 3/4 4-7 Amendment No. 148, 264, 277

REACTOR COOLANT SYSTEM BASES PRESSUREITEMPERATURE LIMITS (Continued)

Allowable pressure-temperature relationships for various heatup and cooldown rates are calculated using methods derived from the Summer 1996 Addenda of Appendix G in Section Xi of the ASME Boiler and Pressure Vessel Code as required by Appendix G to 10 CFR Part 50.

The general method for calculating heatup and cooldown limit curves is based upon the principles of the linear elastic fracture mechanics (LEFM) technology. In the calculation procedures a semi-elliptical surface defect with a depth of one-quarter of the wall thickness, T. and a length of 312T is assumed to exist at the inside of the vessel wall as well as at the outside of the vessel wall. The dimenstions of this postulated crack, referred to in Appendix G of ASME Xl as the reference flaw, amply exceed the current capabilities of inservice inspection techniques. Therefore, the reactor operation limit curves developed for this reference crack are conservative and provide sufficient safety margins for protection against non-ductile failure. To assure that the radiation embrittlement effects are accounted for in the calculation of the limit curves, the most limiting value of the nil ductility reference temperature, RTNDT, is used and this includes the radiation induced shift, ARTNDT, corresponding to the end of the period for which heatup and cooldown curves are generated.

SEQUOYAH - UNIT 2 B 3/44-8 Amendment Nos. 147, 148, 277

REACTOR COOLANT SYSTEM BASES PRESSURE/TEMPERATURE LIMITS (Continued)

The ASME approach for calculating the allowable limit curves for various heatup and cooldown rates specifies that the total stress intensity factor, K1, for the combined thermal and pressure stresses at any time during heatup or cooldown cannot be greater than the reference stress Intensity factor, KIc, for the metal temperature at that time. Kic Is obtained from the reference fracture toughness curve, defined In Code Case N-640, OAlternative Reference Fracture Toughness for Development of PT Limit Curves for Section XlI [I &t2 of the ASME Appendix G to Section Xi. The Kic curve Is given by the following equation:

KIc = 32.2 + 20.734 exp E0.02(T-RTNDT)] (1) where Kic is the reference stress Intensity factor as a function of the metal temperature T and the metal nill ductility reference temperature RTNDT. Thus, the governing equation for the heatup-cooldown analysis is defined In Appendix G of the ASME Code as follows:

C KIM + KR : KIc (2)

Where, KM is the stress Intensity factor caused by membrane (pressure) stress.

K1 is the stress intensity factor caused by the thermal gradients.

KIc Is provided by the code as a function of temperature relative to the RTNDT of the material.

C = 2.0 for level A and B service limits, and C = 1.5 for Inservice hydrostatic and leak test operations.

SEQUOYAH - UNIT 2 B 314 4-11 Amendment No. 277

REACTOR COOLANT SYSTEM BASES PRESSURE/TEMPERATURE LIMITS (Continued)

At any time during the heautp or cooldown transient, Kic Is determined by the metal temperature at the tip of the postulated flaw, the appropriate value for RTNDT, and the reference fracture toughness curve.

The thermal stresses resulting from temperature gradients through the vessel wall are calculated and then the corresponding (thermal) stress intensity factors, Krr, for the reference flaw are computed. From Equation (2) the pressure stress intensity factors are obtained and from these the allowable pressures are calculated.

COOLDOWN For the calculation of the allowable pressure versus coolant temperature during cooldown, the Code reference flaw is assumed to exist at the inside of the vessel wall. During cooldown, the controlling location of the flaw is always at the inside of the wall because the thermal gradients produce tensile stresses at the Inside, which increase with increasing cooldown rates. Allowable pressure-temperature relations are generated for both steady-state and finite cooldown rate situations. From these relations composite limit curves are constructed for each cooldown rate of Interest.

The use of the composite curve in the cooldown analysis is necessary because control of the cooldown procedure is based on measurement of reactor coolant temperature, whereas the limiting pressure Is actually dependent on the material temperature at the tip of the assumed flaw. During cooldown, the 1/4T vessel location Is at a higher temperature than the fluid adjacent to the vessel ID. This condition, of course, is not true for the steady-state situation. It follows that at any given reactor coolant temperature, the delta T developed during cooldown results in a higher value of Kic at the 114T location for finite cooldown rates than for steady-state operation. Furthermore, if conditions exist such that the increase in KIc exceeds Kgr, the calculated allowable pressure during cooldown will be greater than the steady-state value.

SEQUOYAH - UNIT 2 B 3/4 4-12 Amendment No.277

REACTOR COOLANT SYSTEM BASES PRESSURE/TEMPERATURE LIMITS (Continued)

The above procedures are needed because there Is no direct control on temperature at the 114T location; therefore, allowable pressures may unknowingly be violated if the rate of cooling is decreased at various intervals along a cooldown ramp. The use of the composite curve eliminates this problem and assures conservative operation of the system for the entire cooldown period.

HEATUP Three separate calculations are required to determine the limit curves for finite heatup rates. As is done in the cooldown analysis, allowable pressure-temperature relationships are developed for steady-state conditions as well as finite heatup rate conditions assuming the presence of a 1/4T defect at the Inside of the vessel wall. The thermal gradients during heatup produce compressive stresses at the Inside of the wall that alleviate the tensile stresses produced by Internal pressure. The metal temperature at the crack tip lags the coolant temperature; therefore, the K~c for the 114T crack during heatup Is lower than the Kic for the 1/4T crack during steady-state conditions at the same coolant temperature. During heatup, especially at the end of the transient, conditions may exist such that the effects of compressive thermal stresses and different Kc's for steady-state and finite heatup rates do not offset each other and the pressure-temperature curve based on steady-state conditions no longer represents a lower bound of all similar curves for finite heatup rates when the 114T flaw is considered. Therefore, both cases have to be analyzed In order to assure that at any coolant temperature the lower value of the allowable pressure calculated for steady-state and finite heatup rates is obtained.

The second portion of the heatup analysis concerns the calculation of pressure-temperature limitations for the case In which a 1/4T deep outside surface flaw is assumed. Unlike the situation at the vessel inside surface, the thermal gradients established at the outside surface during heatup produce stresses which are tensile in nature and thus tend to reinforce any pressure stresses present. These thermal stresses, of course, are dependent on both the rate of heatup and the time (or coolant temperature) along the heatup ramp. Furthermore, since the thermal stresses, at the outside are tensile and increase with increasing heatup rate, a lower bound curve cannot be defined. Rather, each heatup rate of Interest must be analyzed on an Individual basis.

SEQUOYAH - UNIT 2 B 3/4 4-13 Amendmet No. 277

REACTOR COOLANT SYSTEM BASES PRESSUREITEMPERATURE LIMITS (Continued)

Following the generation of pressure-temperature curves for both the steady-state and finite heatup rate situations, the final limit curves are produced as follows. A composite curve Is constructed based on a point-by-point comparison of the steady-state and finite heatup rate data. At any given temperature, the allowable pressure is taken to be the lesser of the three values taken from the curves under consideration.

The use of the composite curve is necessary to set conservative heatup limitations because it is possible for conditions to exist such that over the course of the heatup ramp the controlling condition switches from the inside to the outside and the pressure limit must at all times be based on analysis of the most critical criterion.

The leak test limit curve shown on Figure 3.4-2 represents the minimum temperature requirements at the leak test pressure specified by applicable codes. The leak test limit curve was determined by methods of Branch Technical Position MTEB 5-2 and 10 CFR 50, Appendix G.

The criticality limit curve shown in Figure 3.4-2 specifies pressure-temperature limits for core operation to provide additional margin during actual power production. The pressure-temperature limits for core operation (except for low power physics tests) require the reactor vessel to be at a temperature equal to or higher than the minimum temperature required for the in-service hydrostatic test, and at least 40 degrees F higher than the minimum pressure-temperature curve for heatup and cooldown. The maximum temperature for the in-service hydrostatic test for the SQN Unit 2 reactor vessel is 214 degrees F.

A vertical line at 214 degrees F on the pressure-temperature curve, intersecting a curve 40 degrees F higher than the pressure-temperature limit curve, constitutes the limit for core operation for the reactor vessel.

Finally, the composite curves for the heatup rate data and the cooldown rate data are adjusted for possible errors in the pressure and temperature sensing instruments by the values Indicated on the respective curves.

Although the pressurizer operates In temperature ranges above those for which there is reason for concern of non-ductile failure, operating limits are provided to assure compatibility of operation with the fatigue analysis performed in accordance with the ASME Code requirements.

314.4.10 DELETED SEQUOYAH - UNIT 2 B 3/4 4-14 Amendment No. 148, 198, 277