ML20086C530

Proposed Tech Spec Limiting Condition for Operation 4.2.15 Re Pcrv Cooling Water Sys Temps

ML20086C530
Person / Time
Site:	Fort Saint Vrain
Issue date:	11/15/1991
From:	PUBLIC SERVICE CO. OF COLORADO
To:
Shared Package
ML20086C529	List: ML20086C527 ML20086C530
References
NUDOCS 9111220287
Download: ML20086C530 (4)

Text

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. Fort St. Vrain #1 Technical Specifications Amendment No.

Page 4.2-17 top' casing. In this case, the local temperature in the concrete would be less than 250*F, an allowable and acceptable concrete temperature.

(FSAR Section 5.4.5.3).

Specification LCO 4.2.15 - PCRV Coolina Water System Temperatures, Limitino conditions for Operatiqn The limiting conditions for the PCRV cooling water system 1 temperatures utilize the following water temperature definitions:

Inlet Water Temperature - is the water temperature measured-at the common PCRV cooling water heat exchanger outlet in.

each loop.

Outlet Water Temperature - is the water temperature measured at the common PCRV cooling water discharge from'the Core Support Floor,. Lower Barrel Section, and Upper Barrel

-Section-and Top Head in each loop.

l- With the reactor. shut down, the temperature of the PCRV cooling .

f water system shall be maintained within the limits stated belows a) The maximum temperature difference between the outlet water temperature of the PCRV cooling water system, and the PCRV external concrete surface temperature, averaged over 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, shall not exceed 50*F.

4 The maximum outlet water temperature of the PCRV cooling water system shall not exceed 105*F.

c) The maximum temperature difference between the outlet water temperature and the inlet water temperature of the PCRV.

cooling water system shall not exceed 20*F.

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.' i Fort St. Vrain #1 Technical Specifications

, Amendment No. -4 Page 4.2-18 d) The maximum rate of change of the PCRV concrete temperature shall not exceed 14'F per week, as indicated by the weekly average outlet water temperature of the PCRV cooling water system.

e) The minimum average of the inlet and outlet cooling water

. temperatures shall be greater than or equal to 85'F.

Basis for Specification LCO 4.2.15 The PCRV concrete may experience non-uniform temperature-l distribution since the PCRV liner will generally be at temperatures l greater than Reactor Building ambient temperatures. Those non-uniform temperatures result in thermal stresses in the self-strained structure, but these stresses tend to relax due to creep and other inelastic effects, particularly in areas of local stress concentration.

Therefore, only the bulk temperature of the PCRV concrete is considered in establishing the acceptable thermal lording of the PCRV.

In addition to temperature gradients through the walls, the concrete temperature-varies locally between cooling tubes; this, f- however, involves only a small amount of concrete. The original cooling system specification which applied during reactor power operation l

l ensured that the temperature of the concrete between cooling tubes was limited to 150*F. In certain cases, local concrete temperatures of

.250*F would be acceptable, if the affected area is small, since the resulting possible small loss in concrete strength can be tolerated.

The lOS*F limit on the maximum PCRV cooling water outlet temperature l =will also conservatively serve to ensure concrete temperature does not exceed 150'F.

f Due to the very large bulk of concrete, and the relatively long time-constant for response for temperaturo changes, short-term variations in the temperature of the air in contact with the vessel, or the PCRV liner, can be tolerated without development of undesirable

.1 l

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Fort St.'Vrain #1 Technical Specifications Amendment No.

Page 4.2-19 stresses. Similarly, significant changes in the bulk concrete temperature must be performed slowly such that the average bulk temperature changes at a rate no greater.than 14*F per week.

-l The 85*F minimum average PCRV cooling water temperature l restriction provides assurance that average fuel temperature cannot l decrease below 80*F, under conditions of interruption of all forced l circulation'(when primary coolant temperatures cannot be accurately f measured), with very low decay heat generation rates. The shutdown j margin assessments identified in LCO/SR 3/4.1.4 and 3/4.1.6, and l discussed in their bases, assume an average fuel temperature of 80*F in f determining the reactivity contribution due to the negative temperature l coef.ficient of reactivity. Maintaining the average PCRV liner f temperature anove 85'F will provide assurance that average fuel temperature remains above 80*F, even under conditions of interruption of l all forced circulation, so that the temperature assumption associated l with the shutdown margin assessment remains valid.

f FSAR Sections 5.7.2.2 and E.24.5 discuss the experimentally l determined nil ductility transition (NDT) tetaperatures of all heats of liner material-(including weldment material), before and following exposure to an integrated neutron dose of 2.3 EIS n/cm -2 (E > 1 MeV) .

This value represents the maximum dose to the most highly irradiated

( portion of the liner, at the top head, assuming a 30 year operational lifetime with an 80% capacity factor (24 effective full power years or l 8760 effective full power days - EF ).

l The reactor.was permanently shut down after having accumulated 890 EFPD, approximately one-tenth of the liner design lifetime. Therefore, l the NDT' temperatures of the liner and weldment materials would only increase approximately one-tenth of the range observed in the

.l experimental tests, whose results are documented in FSAR Table E.24-16.

L The end-of-life fracture transition elastic (FTE) temperature, l

j approximately equal te the end-of-life NDT + 60*F, is calculated to be l

i. f less than 15*F for both the liner and weldment materials.

+ r .

. ' Fort St. Vrain #1 Technical Specifications-Amendment No.

Page 4.2-19a l Maintaining the liner temperature above the FTE temperatures _of the liner and weldment materials ensures that crack propagation in the l

l liner at any tensile membrane stress up to yield stress would be incredible, and in this respect the liner meets the same criteria as are l prescribed for steel nuclear pressure vessels, but is more conservative l- since the liner is in general compression for all normal operation l modes.

Limiting.the average cooling water temperature to a minimum of l-85'F and the maximum inlet to outlet temperature difference to 20*F l

' ensures that the top head liner material average temperatures will be in excess of 85'F at all times.

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