ML20198N376

Forwards Written Rept on Snp 971011 Event That Caused Total Residual Chlorine Excursion.Rept Follows Up 971017 Telcon Re Subj Matter

ML20198N376
Person / Time
Site:	Sequoyah
Issue date:	10/17/1997
From:	Bodine D TENNESSEE VALLEY AUTHORITY
To:	Stewart P, Whalen T TENNESSEE, STATE OF
References
NUDOCS 9711040102
Download: ML20198N376 (3)

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i Termessee Valley Authority, Post offico Box r000. Soddy Daisy. Tennessee 37379 2000 October 17,1997 Mr. Phil Stewart Chattanooga Environmental Field Office State Office Building, Suite 550 540 McCallie Avenue Chattanooga, Tennessee 37402 Attention: Mr. Terry Whalen DIFFUSER POND DISCHARGE, SEQUOYAH NUCLEAR PLANT, NPDES PERMIT TN0026450 s

Pleaso find enclosed the written report on the Sequoyah Nuclear Plant event that cau'.,ed a total residual chlorine excursion (TRC) on October 11,1997. This written report follows up on my conversation with you this morning regarding this matter.

Please contact me at (423) 8'43-6700 or pager 1-800-323-4853,70343, if you have any questions regarding this matter.

Sincerely, A< 51 Debb Bodine -

Environmental Supervisor Signatory Authority 4 '

for Masoud Bajestani b6;-

Vice President Sequoyah Nuclear Plant Enclosure cc (Enclosure):

U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555

( n 3 t'" 3 9 lllllllll$llllllll1lllll 9711040102 971017 PDR ADOCK 05000327

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- e Sequoyah Nuclear Plant (SdN)- Event Relating to Diffuser Discharge, Outfall 101 NPDES Permit No. TN0026450, pigdpligApfylscharg; Outfall 101, Diffuser Pono Discharge - the calculated total residual chlorine (TRC) in the Diffuser Pond discharge (Outfall 101) was in excess of 0.058 mg/L during the event cf October 11,1997.

Qsuse and Period of Even_ti ne TRC level in the water from the High Pressure Fire Protection (HPFP) system expedenced a temporary excursion due to problems with the chemicalinjection pumps. A calculated TRC of 0.076 mg/L at the Diffuser Pond Discharge was obtained. He actual discharge concentration may have been within the 0.058mg/L NPDES Permit limit but cannot be vedf.'ed by analytical measurement. Control limhs are set for each chlorinated system to ensure compliance with the NPDES Permit limit at the Diffuser Pond discharge.

The chlodnation of HPFP, as required by the Sequoyah Fire Protection Plan, was being conducted at the time of the excursion. A problem with the chemical injection pumps was the cause of the increased TRC.

Problems with the injection pumps were causing the HPFP system TRC values to fall below the required level that ensures proper chlorination of the system. One HPFP chemical injection pump was out of s service due to motor problems. The other pump was not injecting an adequate amount of hypochlorite into the HPFP system.

At 1900 hours0.022 days <br />0.528 hours <br />0.00314 weeks <br />7.2295e-4 months <br /> on October 10,1997, following maintenance on the pump, Operations personnel increased the pump stroke until a visual deficction of the hypochlorite in the gauge was observed. This deflection allowed Operations to verify that the chemical was being injected into the system. At 0345 hours0.00399 days <br />0.0958 hours <br />5.704365e-4 weeks <br />1.312725e-4 months <br /> on October 11,1997 Chemistry personnel performed TRC checks of plant systems being chlo-inated using an NPDES approved method. He TRC in the HPFP system had increased to a value excet , .ig the system control index used to monitor TRC in the pond discharge. A maximum of 2,060 gpm was flowing through the HPFP system rather than the normal 4,000 gpm due to the inoperability of one HPFP pump.

De eleymd level in the HPFP system coupled with a reduction in plant dilution flow to approximately one-half of the normal value (due to the outage of one unit), resulted in a calculated TRC of 0.076 mg/L at the DiiTuser Pond Discharge. Four grab samples were taken at the Diffuser Pond Discharge. The method detection limit (MDL) is 0.10 mg/L. Each sample result was below the MDL.

The HPFP system sample is taken pdor to flouing through the system. This is the most conservative (highest TRC) point that has a discharge pathway (into the CCW system). The HPFP system TRC is then eniculated by multiplying measured concentration by the total system flow. The calculated Diffuser Pond Discharge TRC is then calculated by summing the point of chemical injection HPFP TRC value with the system TRC multiplied by the system flow of all other chlorinated systems and dividing the total plant system TRC contribution by the totc.1 flow of plant systems to the Tenrassee River. Actually, approximately 450 gpm from the HPFP system was flushing from hydrants and across a gravel area before discharging through concrete drains to the Diffuser Pond, approximately 200 gpm from the HPFP system was not being chlorinated but, was providing Raw Service Water to various buildings for heating, cooling, etc. The remaining HPFP ilow was providing some chlorination to the CCW system before its discharge to the Diffuser Pond.

Part IA, footnote 5. of NPDES Permit TN0026450 allows the results of field tests to be used for compliance when the CCW system is chlodnated. The chlorinated portion of the HPFP system flow not being used for system flushes or as water supply to the make-up water treatment system discharges into the CCW system. This kind of direct discharge was occuning at the time of the TRC excursion, resulting in the chlorination of the CCW system. In view of this circumstance, TVA believes that it would be appropdate to use the field tests for compliance in lieu of calculated TRC level in the dischar';e. As mentlotied above, each field test sample showed the TRC to be below the MDL of 0.1 mg/L. i

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Mtasures Taken 19_ Correct Prg.idgni Chemistry personnel notified Operations to reduce the injection pump stroke. A second analysis of IIPFP was performed at 0530 using an NPDES approved method. The TRC in the liPFP had then decreased sufficiently to bring the calculated TRC value down to 0.056 mg/L.

Grab sampics were taken at the Diffuser Pond discharge at 0730,0920,1128 and 1328. He analytical result of these analyses werc <0.100 mg/L which is the MDL. Tne transport time for the flow of a plant discharge across the Diffuser Pond is several hours. The area of the Tennessee River in the vicinity of the Diffuscr Pond discharge was observed to ensure there had been no apparent effect on aquatic life.

EisetTak nJ2JIiminatJtand t Prevent Recurrence of the Excursion Sequoyah is in the process of upgrading the IIPFP system, including the water supply for the ifPFP system from raw water to potable water supplied by filxson Utility. Tids change will climinaic the need for cidorination of the 11PFP system. Implementation is scheduled to be completed by December 31, 1997. The current Fire Protection Plan requirement for chlorination of the llPFP to prevent occlusion by s macmphyte invertebrates will be removed when this change is complete. Dere will be some discharge of potable water from the new IIPFP supply dae to testing, required flushes and actuations. Ilowever, there is no planned addition of blocide other than the TRC residual in potable water supply. This TRC has historically been <1 mg/L at the point of connection of the filxson Utility main line to Sequoyah Nuclear Plant. As discussed with Steve LeTendre, Robert IIaley, and Larry Bunting of your office, the TRC in the potable water discharged from the IIPFP will be measured and added to the daily TRC calculation. A recurrence of t! is kind of problem that caused the TRC excursion will be prevented upon completion of the system change. In the interim period, chemical injection will be periodically monitored Lnd carefully controlled.

Sequoyah has la place procedures limiting the TRC feed rate to chlorinated systems that are designed to maintain the DhNet Discharge TRC below the calculated 0.058 mg/L NPDES permit limit. In this instance, an unexpectedly clevated rate of injection from a pump that had been experiencing problems resulted in the calculated TRC excursion. liowever, even during the excursion, field tests showed TRC levels to be below the MDL, which is the governing standard at times when the CCW system is chlorinated.

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