ML19256F621

Final Deficiency Rept Re RCS Exceeding Heatup & Cooldown Rates.Physical Locations of Temp Elements Subject Them to Localized Transient Temp Changes Not Indicative of RCS as Whole.No Corrective Action Necessary

ML19256F621
Person / Time
Site:	Sequoyah
Issue date:	12/12/1979
From:	TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML19256F620	List: ML19256F619 ML19256F621
References
NCR-12P-&-13P, NUDOCS 7912190575
Download: ML19256F621 (2)

Text

- .

ENCLOSURE SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 REACTOR COOLANT SYSTEM EXCEEDED HEATUP AND C00LDOWN RATES NCR'S 12P AND 13P 10 CFR 50.55(e)

FINAL REPORT Description of Deficiency During hot functional testing of unit 1, temperature sensors in the loop 2 hot leg and in the lower portion of the pressurizer indicated temperature changes exceeding the rates in the proposed technical specifications. The occurrences coincide with formation and collapse of the bubble in the pres-surizer and fill and vent activities in the p.ressurizer.

The proposed technical specification maximum heatup and cooldown rates are 100 F/hr and 200 F/hr, respectively, for the pressurizer and 100 F/hr (heatup and cooldown) for the Reactor Coolant System (RCS). Temperature Element (TE) 68-24 in the loop 2 hot leg sensed temperature increases from 118 to 250 F in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and from 140 to 250 F in 8 minutes. TE68-2galsosysed temperature decreases from 255 to 129 F in 50 minutes, from 260 to 140 F in 25 minutes, and from 250 to 142 F in 12 minutes.

TE 68-319 in the pressurizer sensed temperature increases from 135 to 262 F in one hour and from 12g to 230 F in one hour. TE 68-319 sensed a temperature decrease from 432 to 180 F in a one-hour period.

The flow of fluid in and out of the pressurizer through the surge line when forming or collapsing the bubble in the pressurizer during heatup and

. cooldown is a normal operating occurrence. Similarly, the addition of cooler water to the pressurizer during fill and vent is a normal occur-rence. The physical locations of TE 68-24 and TE 68-319 make them subj ect to the resulting localized transient temperature changes which are not indicat.ive of the RCS and pressurizer as a whole. The technical specifi-cations do not make allowance for the special operating situations.

Safety Implications The accelerated heating and cooling of small local regions of the loop 2 hot leg and the pressurizer induces thermal stresses in the piping and pressurizer wall. Westinghouse has reviewed this deficiency and has concluded that safe operation of unit 1 will not be jeopardized. The reactor coolant loop piping of Sequoyah was analyzed according to the rules of B31.1 Code. The code required evaluation of the worst case thermal expansion and comparison with the appropriate allowable stress eq 33 1624 W 7m219e W f

A intensity. Since the heatup and cooldown temperatures in these non-conformances stayed well below worst case values, there is no effect on the piping stress analysis.

Corrective Action .

No corrective action is necessary.

Means Taken To Prevent Recurrence The startup procedure is being changed to commence heatup of the pressurizer with an approximate normal operating level, rather than filled. This reduces the volume of water expelled from the pressurizer through the surge line ints the loop 2 hot leg during the establishment of a pressurizer bubble. The new procedure will be in accordance with the latest Westinghoose recommendations from this phase of plant operation.

This action should prevent the RCS heatup rate limits from being exceeded and reduce thermal transients on the surge line and loop 2 hot leg.

An additional precaution will be added to the cooldown procedure to alert the operator that rapid filling of the pressurizer during cooldown will result in a surge of cooler RCS water into the pressurizer. This change to procedures will prevent the RCS cooldown rate limits from being exceeded as indicated on the pressurizer liquid space temperature indicator.

e 9 O Q J l624 4'