ML20100G640

NPDES Noncompliance Notification:On 850107,11,18 & 31,temp Rise Limit & Rate of Temp Change Limit Exceeded at Diffuser Discharge Gate.Caused by Malfunctions of Equipment,Including Cooling Tower Lift Pumps

ML20100G640
Person / Time
Site:	Sequoyah
Issue date:	03/27/1985
From:	Rivers M TENNESSEE VALLEY AUTHORITY
To:	Marler J OHIO, STATE OF
References
NUDOCS 8504080335
Download: ML20100G640 (5)

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' TENNESSEE VALLEY AUTHORITY KNOXVILLE. TENNESSEE 37902 MAR 271985 Mr. John Marlar U.S. Environne al Protection Agency, Re on IV Water Man at Division

.345 Cou and Street, NE.

Atlan , Georgia 30365

Dear Mr. Marlar:

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Enclosed is a revised Notification of Noncompliance (NON) for Sequoyah Nuclear Plant (NPDES Permit No. TWOO26450, DSN 101) for January 1985. The January 31 noncompliance event, which was the date the cooling towers were e removed from service, was inadvertently omitted on the original NON. The figures submitted with the previous NON remain unchanged and are not being subaitted.

If you have questions, please call Nadonna Martin at FTS 856-6695 in  ;

Knoxville, Tennessee.

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!. Sincerely, GL tk Hartin E. Rivers, Director Environmental Quality i

Enclosure 4

cc (Enclosure):

Mr. Harold R. Denton. Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attention: Document Control Clerk.

Mr. D. Elmo Lunn. Director Tennessee Department of Public Health Division of Water Management

150 Ninth Avenue, North--TERRA Building i Nashv111e. Tennessee 37203-Mr. James P. O'Reilly, Director i Office of Inspection and Enforcement U.S., Nuclear Regulatory Cossaission l Region II - Suite 2900. '

! 101 Marietta Street NW.

Atlanta, Georgia ~30303 see page 2 f i

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/sh 8504080335 PDR- ADOCM O 8 b327327-S PDR ' f y\'

- Ari Equal Opportunity Employer

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o MAR 271985

-Mr. John Marlar cc: Tennessee Division of Water Management Environmental Health Services 2501 Milne Street Chattanooga, Tennessee 37406 1

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('* NOTIFICATION OF NONCOMPLIANCE WITH EFFLUENT LIMITATIONS - NPDES PERMIT NO.

TN0026450 - SEQUOYAH NUCLEAR PLANT (SQN)

Description of the discharge--Discharge No.101 - Diffuser discharge gate. During January the temperature rise limit (5.40F or 3.000) and rate of temperature change limit (+3.60F or +2.000) were exceeded.

Since-there were several occurrence's, these a're detailed in the next section.

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Cause and period of the noncompliance--Unprecedented cold temperatures during January 1985 created a large demand on the TVA power system. In January, SQN operated at full two-unit load for the first time during severe cold weather. Lack of rainfall in November through January caused I low flow conditions and reservoir storage below normal levels. Hydro plants were scheduled to peak during periods of high demand and hold back flow during the morning hours. Figure 1 shows the major plant features and the location of instream temperature monitors.

4 Five separate noncompliances with the temperature rise limit occurred on January 7, 11, 18, and 31. Problems associated with malfunctioning equipment (cooling tower lift pumps) were responsible for four of the

- noncompliances. . Computed compliance model results were not valid from January 20-31 when a diffuser gate was closed, causing bad input to the model. Backup instream temperature monitors showed no further temperature 4

rise noncompliances during January 20-31. However, there were times when the rate of temperature change limit was exceeded in the instream temperature monitor data during that period. These occurrences were due to cooling tower lift pump problems which caused large changes in the pond temperature before discharge. The plant was on full closed mode (two-tower operation) between January 20-31. The following paragraphs detail the events, starting on January 7, which led to the thermal noncompliances at SQN. Plant operating loads, cooling tower use, and air temperatures are shown in Figure 2. Figure 3 shows the temperature rise and river flow data. Figure 4 shows rate of temperature change data and discharge pond temperatures.

The first noncompliance occurred on January 7, at 0545 CST. The maximum temperature rise (delta T) was 5.6 degrees F. Temperature rises exceeded 1 the thermal limit for 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. SQN was operating at full power. - River I

, flow, scheduled for hydro peaking operation, fell to 14,700 cubic feet per l second (cfs) at 0645 CST. River flows increased immediately after the i

limit was exceeded. One cooling tower was placed in service at 2030 CST, anticipating further high temperature rises during the next morning's low-flow period.

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.v The scheduling model used to determine the effects of river flo:' on the thermal' limits at SQN showed partial cooling tower operation was needed to ,

. meet the thermal limits. The plant has experienced problems with the cooling tower' lift pumps and plant operators were concerned about and reluctant to use partial cooling tower operation because of extremely cold weather.- Last year. partial usage lead to severe icing damage which cost 1 approximately one half million dollars to repair. For these reasons, full tower ~ operations were not commenced immediately r,esulting in the noncompliance. ,

The second noncompliance occurred on January 11 at 0030 CST. The maximum 1 temperature rise was 5.6 degrees F. Temperature rises were above the limit for 1.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. River flow at SQN was as low as 14,300 cfs during this i period. A third noncompliance occurred at 0445 CST, reached a maximum of 5.7 degrees F and lasted 1.0 hour0 days <br />0 hours <br />0 weeks <br />0 months <br />. River flow had increased for a period

' of two hoars but then decreased .to 21,900 ofs causing the added temperature rise problems. SQN was operating one tower, open/ helper mode, anticipating low-flow induced temperature rise problems. The cooling tower placed in -

operation on January 10 at 2300 CST was started too late to prevent these l noncompliances.

The fourth noncompliance occurred on January 18 starting at 1615 CST. The I maximum temperature rise was 5.6 degrees F. Total duration above 5.4 degrees F was one hour. SQN operated at full two-unit operation with one cooling tower in service (helper mode). River flow dropped to 7,700 cfs and was not enough flow for operation of only one tower. The secord tower was placed in service at 1800 (helper mode).

I The 'fifth noncompliance occurred on January 31 starting at 1315 CST, during the transition from closed mode (beginning at 1020 CST) to helper mode (1225 CST) to open mode (1428). The maximum temperature rise was Total duration above 5.40F was 2.25 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br />. The cooling towers

! 6.40F.

' were taken out of service in order to assess icing damage.

l On January 20, SQN went to full closed mode operation to prevent further t

icing which was first observed early that morning. While on closed mode, a 1 diffuser' gate was closed routing all flow through one diffuser leg. The computed compliance model had been previously changed to.use only two

, diffuser leg operation. The computed discharge flow is based on the difference between elevation in the diffuser pond and the river. The-i closed diffuser gate caused the model to receive false diffuser flowrate information and produced invalid results. This continued through January 31' at 1020 CST when the diffuser gate was opened during transition

• to open mode operation. Backup temperature monitors in the river from

' January 20-31 (figure 3), show temperature rises below the limit during the closed mode operation. Procedures at the plant will be changed to leave both diffuser gates open during all plant operations. Discharge flow measurements will also be calibrated under low flow and closed mode operation.

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During January 20-31, there were times when the river monitored data were outside the rate of temperature change limit. 'igure 4 shows this data

- along with the discharge pond temperatures. Measured values exceeding the limit coincide with large changes in discharge pond temperature. The plant had problems with the cooling tower lift pumps during most of closed mode operation. 'When a lift pump failed, the heated water it was pumping had to be discharged into the diffuser discharge pond. All exceedances of the J rate of temperature change limits were an hour or less. A list of these occurrences is shown in Table 1 which provides starting times, maximum values, and durations. Lift pump maintenance will be improved to provide better operation during cooling tower use.

I Steps taken to reduce, eliminate, and prevent recurrence of the noncomplying discharge--TVA is currently assessing cooling tower damage and procedures to be followed when cooling tower icing is expected. During periods of possible icing, full cooling (as opposed to partial) tower operation will be implemented when the scheduling model indicates that the thernal limits cannot be met in open mode. Plant procedures will be changed to keep diffuser gates oren during all plant operation. The 1 computer model for verification cf compliance with the thermal limits will 4 be calibrated for closed mode operation. Cooling tower lift pumps will be repaired, and maintained and tested on a periodic basis to be ready for future cooling tower operation.

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