ML20063P185

Ro:On 820814,normal Shutdown Initiated to Investigate Higher than Normal Difterential Pressure Readings in Emergency Svc Water Sys.Caused by Debris Blockage Consisting of Live & Dead Animal Matter.Organisms Removed & Tubes Cleaned

ML20063P185
Person / Time
Site:	Oyster Creek
Issue date:	09/22/1982
From:	Fiedler P GENERAL PUBLIC UTILITIES CORP.
To:	Haynes R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
NUDOCS 8210130167
Download: ML20063P185 (4)

Text

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,, a .o GPU Nuclear g g7 P.O. Box 388 Forked River, New Jersey 08731 609-693-6000 Writer's Direct Dial Number:

September 22, 1982 Mr. Ronald C. Hayneo, Administrator Region I U.S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406 rear Mr. Haynes:

Subj ect: Oyster Creek Nuclear Generating Station Docket No. 50-219 Item of Interest Biofouling of Containment Spray Heat Exchangers On Saturday, August 14, 1982, a normal reactor shutdown commenced at the Oyster Creek Station. The shutdown was initiated to investigate higher than normal differential pressure readings in the Emergency Service Water System (ESW) which provides cooling water to the Containment Spray Heat Exchangers. Upon removal of the Containment Spray Heat Exchanger waterbox heads, blockege of the tube sheet inlets was discovered. The debris comprising the blockage was primarily composed af live and dead animal matter.

The first indications of a problem were higher than normal differential pressure measured acmss the ESW pamps and a decrease in ESW flow rates found during performance of a monthly surveillance test on Friday, August 13, 1982.

The ESW pumps provide cooling water, vis the intake canal from Barnegat Bay, to the Containment Spray Heat Exchangers. Since all four ESW pumps showed high

> differential pressure, it was surmised that t? a reason for this was increased system resistance, which resulted in decreased flow rates, caused by piping or heat exchanger flow blockage. A retest of the ESW pumps indicated a decrease in differential pressure initially measured. The results, however, had not returned to values considered to be normal; end, based upon available data, the i decision was made to shutdown.

All Containment Spray Heat Exchanger waterbor heads were removed and the tube sheets inspected. Samples of the fouling organisms were obtained and analyzed. The fouling organisms were Soncentrated on tube sheet inlets, ra ther  ;

than on the surfaces of the tubes or the tubesheet outlets.

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• Mr. Ronald C. Haynes ' Page' 2 September 22, 1982 The types of organisms found, their relative abundance, and condition are indicated on Attachment 1. Plants accounted for only two (2) . percent of the

!- sample and consisted primarily of small fragments. The remainder.of the i organisms have four characteristics in common which enable them to become established and thrive in the heat exchanger:

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. 1. Their larval stages are extremely small allowing them to disperse into any ama where Barnegat Bay water flows.

l 2. They possess some means of attachirg to substrates such as adhesive

threads or glue-like substances. This allows them to remain in place

during high flow rate conditions.

f i_ 3 They-feed by removing food particles frota the water. High flow rates, therefore, provide good feeding conditions.

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!- 4 They are aile to "close up" unGer edverse conditions and can therefore avoid biocides in the surrounding water for considerable j periods of time.

It can be concluded that most, if not all of these organisms, entered the l'

heat exchangers as larvae, settled on the exchanger surfaces, and grew in

. place. They did not enter the system as adults. This conclusion is supported i by the fact that most of the mussel shells, barnacles and tunicates were too ,

large to pass through the thms-eighths (3/8) inch mesh of the intake structure

< traveling screens. Furthermore, the adult forms of most of these animals are j- unable to reattach once dislodged from the substrate they settled upon as

larvae.

The colonial Bryozoans and Hydroids (grass-like organisms) and Hydroides (worms in white calcereous tubes) appear to be the major problem organisms. -

These animals were found attached directly to the tube sheets indicating that 4

they were the first to become established. They provide a large amount of j surface area which acts as a filtsr for any debris in the water and serve as a point of attachment for additional organisms.

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! The Containment Spray Hoat Exchangers are the straight-tube, four-pass type with two top end (inlet / outlet side) baffles and one bottom end baffle.

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-Increased differential pressure across the top end baffles resulted in top end

. baffle deformation in all heat exchangers. Braces were installed to inhibit further deformation until a permanent repair can be made during the next -

j' . refueling outage, now scheduled for January 1983 I

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• Mr. Ronald C. Haynes Page 3 September 22, 1982 Analysis of measured flow rstes and the extent of the biofouling-and baf fle deformation determined that the heat exchangers' performance had been reduced, but the ability to perform their intended function, if called upon, was not compromised; .however, it is not known how long this condition would have prevailed.

The fibrous-like mat of fouling organisms was removed from the tube sheets. The tubes were cleaned by means of a water-jetting process. Also, additional local pressure gauges were installed to determine baffle plate differential pressures. Prior to restart, a satisfactory surveillance was performed on the Emergency Service Water System.

In order to avoid the biofouling problem in the future, a chlorination system will be put into operation. An optimized schedule for chlorination will be developed dependent upon the seasonal abundance patterns of these fouling organisms. ,

The ability of the Inservice Test (IST) program to detect degrading performance of the heat exchangers will be enhanced by the installation of additional local pressure indication to measure baf fle differential pressures, to ensure that an instance of this type can be detected before major fouling occurs which might render a heat exchanger inoperable.

Very truly yours, b

J E r Jcr) - J Pet 6r'HT"Fiedler <

Vice President and Director Oyster Creek PBF:lse Attachment ec: Mr. Leo Modenos Institute of Nuclear Power Operations 1820 Water Place Atlanta, Georgia 30339 i NRC Resident Inspector Oyster Creek Nuclear Generating Station t Forked River, NJ 08731 l l

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i i ATTACEMENT I  !

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j Results of Analysis of Biofouling Sample i Obtained from Containment Spray Heat Exchanger 1-2  !

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j ~ Relative Abundance Type of Organism (By Volume) Condition i

Colonial Hydroids and Bryozoans 56% Live }

i (" Grass like" organisms) j l l j Blue Mussels

• 21% Dead i i

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Amphipod Tubes 7% Dead  !

l (" Shrimp like" organisms) (

l l Hydroides 7% Live i i (Worms in white calcereous tubes)  !

! l harnacles 5% Dead l i

l Tunicates 3% Live f

.t l' Plant Fragments 2% Dead f

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l *Shell lengths ranged from 1.2-2.6 cm.

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