ML19257F130
| ML19257F130 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear, Brunswick  |
| Issue date: | 09/30/1981 |
| From: | Giannelli J, Imbro E NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML19252B529 | List: |
| References | |
| NUDOCS 8110300056 | |
| Download: ML19257F130 (47) | |
Text
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REPORT ON SERVICE WATER SYSTEM FLOW BLOCKAGES BY BIVALVE MOLLUSKF AT ARKANSAS NUCLEAR ONE AND BRUNSWICK by the Office for Analysis and Evaluation of Operational Data September 1981 Prepared by:
Eugene V. Imbro Joan M. Giannelli NOTE: This report documents results of studies completed to date by the Office for Analysis and Evaluation of Operational Data with regard to particular operating events.
The findings and recommendations contained in this report are provided in support of other ongoing NRC activities concerning this event.
Since the studies are ongoing, the report is not necessarily final, and the findings and recommendations do not represent the position or requirenents of the responsible program office of the Nuclear Regul atory Conni ssion.
8110300056 811021 CF ADOCK 05000313 CF
-i-PREFACE The AEOD findings, recommendations, and conclusions in this report are based on information gathered through formal and informal communications between Arkansas Power and Light Company ( AP&L), Carolina Power and Light Company (CP&L) and the U. S. Nuclear Regulatory Commission Headquarters and Regional Of fi ces.
The findings and recommendations are broadly and generally applicable to all light water reactors (LWRs).
To the extent possible, the information used in this report has been verified by cross checking with other sources.
This report addresses the problem
.f service water flow blockage by bivalve mollusks.
Events that occurred at two plants are cited.
A description is provided of the principal types of bivalves infesting the systems, and the potential effects of fouling on plant operability are discussed.
TABLE OF CONTENTS Page No.
PREFACE..........................
1 EXECUTIVE
SUMMARY
I 1.
DESCRIPTION OF EVENTS.................
3 1.1 Arkansas Nuclear One...............
3 1.2 Brunswick....................
7 2.
BIOLOGICAL CHARACTERISTICS OF SOME FOULING ORGANISMS.......................
15 2.1 Asiatic Clams, Corbicula Species (sp.)......
16
- 2. 2 Bl ue Mus sel s, Myt11 us Eduli s...........
18
- 2. 3 American Oysters, Crassostrea Virginica.....
20 3.
POTENTIAL EFFECTS OF FOULING BY AQUATIC ORGANISMS ON THE OPERABILITY OF SYSTEMS AND COMPONENTS.........
22 4.
ACTIONS TAKEN BY OTHER OFFICES............
26 4.1 Office of Nuclear Reactor Regulation.......
26
- 4. 2 Of fice of Inspection and Enforcement.
28 5.
RESPONSES TO IE BULLETIN 81 -03............
28 6.
FINDINGS.......................
29 7.
RECOMMENDATIONS....................
31 8.
CONCLUSIONS......................
33 Tables Number 1
Chronology of Chlorinator Outage 2
Location of Fouling Found at Brunswick 3
Chronology of RHR Heat Exchanger Maintenance 4
Heat Exchanger Monitoring Program Figures Number 1
Location of Fouling at Brunswick 2
Chlorination System at Brunswick 3
Intake Structure at Brunswick 4
Chlorination and Flush Path for Nuclear and Conventional Headers 5
Plant Areas Not Cleaned 6
Plant Areas Cleaned 7
Clean RHR Heat Exchanger AP Test Results 8
RHR Heat Exchanger Baf fle Plate Deformation
EXECUTIVE
SUMMARY
On September 3,1980 Arkansas Nuclear One ( ANO), Unit 2, was shut down after failing to meet the technical specification requirements for mininum service water flow through the containment air coolers. After plant shutdown, Arkansas Power and Light Company, the licensee, determined that the inadequate flow was due to extensive plugging of the coolers by Asiatic clams (Corbicula species).
Brunswick 1, which was shutdown on April 17, 1981 to begin a scheduled maintenance outage experienced a total loss of residual heat removal (RHR) capability on April 25, when the batfle plate which divides the water box of RHR heat excnanger (HX) 1 A failed and allowed service water to bypass the HX tubes.
The damage was caused by excessive dif ferential pressure across the baffle plate due to the buildup of shells and shell fragments from marine organisms (principally oysters) which blocked the HX tubes.
The principal concern stenming from the growth of fouling organisms in service water systems is the potential for common cause failure of redundant components due to flow blockage.
The events previously described, that occurred at the ANO and Brunswick stations, although not serious in actual consequence, clearly are precursors to a possible common cause failure.
The nature of bivalve fouling in piping systems is such that it may go unnoticed, or not severely degrade system performance, until the system is called upon to function following an incident.
However, the periodic surveillance testing of components currently required by plant technical specifications may not uncover actual system flow blockages or the potential for flow blockages that can occur when the system is required to operate for extended periods of time following an incident.
Therefore, common cause
_2_
service water system failures affecting redundant systems can result from system fouling and flow blockages caused by the presence of fouling organisms, the accumulation of silt, or the buildup of corrosion products.
At sites where potentially troublesome fouling organisms are found in the supply or receiving waterbody, open cycle service water systems should be required by technical specifications to be inspected periodically, particularly the large diameter piping with normal low service water velocities, since these are conducive to the growth of fouling organ.sms.
In such piping, growth of organisms could be substantial before any flow blockage is noticed.
Additionally, cooling water flow supplied to each safety _related equipment cooler, room cooler, or heat exchanger should be required by technical specifications to be periodically verified to assure that the equipment will perform satisfactorily.
Finally, if licensees are aware that potentially troublesome fouling organisms are present in the supply or receiving waterbody at particular sites, control strategies can be developed to prevent organisms from accumulating to a large extent in plant piping.
With the awareness of the potential for fouling and implementation of effective control and surveillance strategies, plants can be safety operated even at sites where fouling organisms such as Asiatic clans abound in the supply or receiving waterbodies.
. ?.
DESCRIPTION OF EVENTS 1.1 Arkansas Nuclear One On September 3,1980, Arkansas Nuclear One (ANO), Unit 2, was shut down after failing to meet the technical specification requirements for minimum service water flow rate through the containment air coolers. After plant shutdown, Arkansas Power and Light Company, the licensee, $etermined that the inadequate flow was due to extensive plugging of the coolers by Asiatic clams (Corbicula species).
The Unit 2 containment air coolers are redundant to the containment spray system and function both during normal operation and following a LOCA to remove heat from the containment. The coolers have two separate sets of cooling coil s.
During normal operation chilled cooling water is pumped through one of the sets of coils with the other set isolated.
On an engineered safety features actuation signal (ESFAS), the chilled cooling water is isolated and service water is pumped throuch the second set of cooling coil s.
In order to determine the cause for the low service water flow in the containment coolers, the licensee disassembled the service water piping on the supply and return side of the coolers. On the inlet side, clans were found in the three-inch service water headers that supply the coolers as well as in the cooler inlet water boxes.
The piping on the return side was found clean, and no clams were found in the outlet of the coolers.
Cl ams were removed from the "A," "C,"
and "D" containment coolers. The "B" containment cooler had been removed from service on March 17, 1980, and has been blank flanged. The clams found in the containment coolers were comprised of some live clams but most of the debris was shells. The average size of the clams was about 15 to 16 mm (approximately 5/8 inch). The service water, which is taker from the Dardanelle Reservoir, is filtered before it is pumped through
. the system.
The strainers on the service water pump discharges were examined and found to be intact.
Since these strainers have a 3/16-inch mesh, much smaller than some of the shells found, it indicates that clams had been growing in the system.
The ANO-2 technical specifications require that the flow rate of the service water through the containment air coolers be verified monthly. Apparently, during previous surveillance tests of the containment cooling units at the ANO-2 facility, Asiatic clam larvae were present in the service water and were pumped with the water into the containment coolers. On completion of the surveillance test, the service water was left stagnant in the coolers. The larvae present grew rapidly which resulted in the flow blockage evidenced by the data obtained from the August 20, 1980 surveillance test.
Following the discovery of Asiatic clams in the containment coolers of Unit 2, the licensee examined other equipment cooled by service water in both Units 1 and 2.
Inspection of other heat exchangers in the Unit 2 service water system revealed some fouling or plugging of additional coolers (seal water coolers for both redundant containment spray pumps and one low pressure safety injection pump) due to a buildup of silt, corrosion products, ano debris (mostly clam shell pieces).
The high pressure safety injection (HPSI) pump bearing and seal coolers were found to have substantial plugging in the 1/2-inch service water supply lines. The plugging resulted from an accumulation of silt and corrosion products.
The high pressure injection pumps are horizontal pumps with the impeller between the shaf t bearings. These pumps have four coolers, piped in parallel, that are supplied by service water, two bearing oil coolers and two seal water coolers.
Each high pressure injection pump is provided with instru-mentation to neasure differential pressure across the four coolers.
- However,
. the pressure taps are located such that the indicated pressure drop is that across the four coolers in parallel rather than each individual cooler.
Being vertical pumps, the low pressure injection pumps and the containment spray pumps each have only a single seal cooler.
These seal coolers are also provided with instrumentation to measure differential pres:ure.
It was stated by the licensee that the differential pressure across the seal and bearing coolers on these pumps was not recorded as part of the monthly surveil-lance program.
Clam shells were found in some auxiliary building room coolers and in the auxiliary cooling water system ( ACWS) which serves non-safety-related equipment in the turbine building. Tne ACWS is a continuously running system as contrasted to the service water system in which most components are isolated during normal power operation.
The examination of the Unit 1 service water system revealed that the "C" and "D" containment coolers were c3 ogged by clams. Clams were found in the three-inch inlet headers and in the inlet water boxes.
However, no clams were found in the "A" and "B" coolers. This fouling was not discovered during surveillance testing because there was no flow instrunentation on these coolers. Further investigation revealed that the service water strainer serving the "A"
and "B" coolers was intact while the one serving the "C"
and "D" coolers was broken.
The licensee reasoned that the clans found in the "C"
and "D" coolers did not grow in the system but were swept in through the broken strainer.
The service water system in Unit I was not fouled other than stated above, and the licensee attributed this to the f act that the service water pump suctions are located behind the main condenser circulating pumps in the intake structure.
It was thought that silt and clams entering the intake bays would be swept through the condenser by the main circulating pumps and would not
. accumulate in the back of the intake bays.
In contrast, Jnit 2 has no main circulating pumps in its intake structure because condenser heat is rejected through a cooling tower via a closed cooling system.
As a result of lower flow rates of water through the Unit 2 intake structure, silt and clams could have a tendency to accumulate more rapidly in Unit 2 than in Unit 1.
The intake bays of Unit 1 and Unit 2 are normally scheduled to be cleaned each refueling outage, however, ANO-2 was in their first fuel cycle.
During the September outage, the Unit 2 intake bays were cleaned and an estimated 150 to 500 cubic feet of clams and silt were removed. Clans have also been found in the emergency cooling pond at ANO.
As a first step in correcting the fouling problem, AP&L manually cleaned out the shells and debris from the service water headers.
They then flushed and back flushed the service water system.
This included a one-half hour flush with 77 C (170 F) water obtained from the auxiliary boiler.
Exposure to water at this high temperature will result in 100 percent mortality for any clams that were still in the system.
In addition, at Unit 2, the licensee has begun to monitor the flow through the containment coolers on a biweekly basis any time the plant is in operation.
The data will be trended to ensure any flow degradation is detected.
Service water flow through the HPSI pump seal and bearing coolers is being checked quarterly. During Unit 2's 1981 spring refueling outage, provisions for flow rate measurements were added to a nunber of conponents cooled by service water.
Also, mucn of the small carbon steel, service water supply, and return piping was replaced with 316 L stainless steel piping.
The 1/2 and 3/4-inch iines were replaced with one-inch lines.
The service water pump bays and pump discharge strainers were cleaned and additional components were inspected and flow tested.
. f During Unit l's January 1981 refueling outage the licensee added flow orifices and indicators to the service water supply headers for the containment coolers.
The technical specifications were also changed to require biweekly measurements of service water flow rate through these coolers.
Isolation valves were added to the service water supply lines for a number of components in order to facilitate the installation of flow rate measuring devices at a later date. The service water pump bays and pump discharge strainers were cleaned and additional components were inspected.
The service water chlorination schedule at both plants has been changed to coincide with the performance of surveillance tests. This will ensure that normally isolated components are laid-up with chlorinated water.
In addition, the fire protection system for both units is being flushed periodically even though no fouling has been observed in the system.
AP&L is continuing their review of this matter and they are developing a long-term plan for improving the service water system.
In the interim the licensee
' eels that these measures, the periodic cleaning of the service water intake bays and pump discharge strainers, the chlorination of the service water and tne flow rate reasurenents, will prevent significant fouling of components cooled by service water from occurring or going undetected.
1.2 Brunswick Brunswick 1, wnich was shut dowr, or, April 17, 1981 to begin a scheduled naintenance ;utage, experienced a total ' ass of residual neat removal (RHR) swability an April 25 when the baffle plate which divides the water box of RHR heat exchanger (HX) 1A failed allowing service water to bypass the HX tubes. RHRHX 13 was out of service for maintenance at the time as a result of a prior commit ent (icA-2 80-20) by the licensee, Carolina
\\
. Power and Light Company (CP&L).
The damage was caused by excessive differential
~oressure across the baf fle plate, when a second RHR ser rice water pump was startet due to the aegradation of cooling capability observed by the operators.
The degradation of cooling capability stemmed from the buildup of shells and shell fragments from marine organisms which blocked the HX tubes.
During the time that b f t. trains of RHR were out of service an alternate cooling flow path was first established using the spent fuel pool HXs, the cendensate storage tank, ard tne core spray system to provide makeup to the reactor vessel.
Later, a flow path was established using the main condenter as a heat sink.
In this mtee of cooling, the main steamlines were fle'ded ai I
and the i,ater level in the condenser was raised above the tubes. Reactor water was then circulated through the condenser using the turbine bypass v al ves. Before im tiating this mode of cooling, however, the main steamline pipe hangers-.had to ce oinned so that the weight of water in the flooded-lines wouTd nrt cause excessive deflecticn of the piping.
In order to return to a normal cooling flow path as expeditiously as possible, temporary repairs were performed.
These consisted of cleaning the shells from the 1A RHRHX, j u<ing the baf fle plate back into position and welding stif fening ribs to the baf fle plate for supacr t.
As a result of the orobiuns found on the Unit 1 RHRHXS a special inspection
.vas cerformed ca the Unit 2 RHRHXs. An ultrasonic examination of RHRHX 2A indicated that the baf fic plate was not displaced.
Flow tests, however, indicated
- s higher than norma d i f f e rent ? >', pressure (DD) at design flow.
Similar examinations of RHRHX ZB indicated that the baffle plate was displaced.
Both HXs were declared inoperable and Unit 2 was shutdown using RHRHX 2A at reduced
. capacity due to the flow blockage.
After Unit 2 was in cold shutdown the main condenser was used as the heat sink, as was done on Unit 1.
This allowed both RHRHXs to be taken out of service so that they could be simultaneously repaired.
The RHRHXs at Brunswick are vertical "U" tube HXs and are arranged such that the wat,r box is below the copper nickel (Cu Ni) tubesheet. The water box of the HX is carbon steel explosively clad with Cu Ni and has a 70-30 Cu Ni ( ASME SB-402, Alloy 715) baffle plate that separates the inlet and outlet service water flow. The one-inch thick ba,ffle plate, fabricated from Cu Ni, is welded on top to the tubesheet and on the sides to the water box.
The botton of the baffle plate extends approximately 3/8 inch into a machined groove in the water box cover which, along with the baffle plate to tubesheet weld, provides lateral stiffness. The baf fle plate is 54-1/2 inches wide and 44-3/4 inches high and can generate significant horizontal and bending forces even at relatively low DPs due to its large surface area.
It was stated by the licensee that ASME Code allowable stress would be reached in the baf fle plate at a DP of 10.4 ps4 The licensee, however, was of the opinion that the deflections were caused by DPs between 50 and 100 psi since they had experienced DPs of 30 psi with no apparent damage to the baffle plate.
The inspection of the RHRHXs revealed the following:
Unit 1 RHRHX 1A The baffle plate was displaced nine inches.
Unit 1 RHRHX 1B The baffle plate was displaced nine inches and the
, r portion of the side welds pulled loose.
The sidewelds within eight to t.
nches of the tubesheet remained intact.
. Unit 2 RHRHX 2A The baf fle plate was intact. A layer of shells and shell fragments approximately 1/4 to 1/2 inch in depth was found on the inlet side of the water box cover.
When held up against the tubesheet by the flow, these shells provided some flow blockage to approximately 60% of the tubes.
Unit 2 RHRHX 2B The baf fle plate was displaced approximately three inches at the bottom center. The deflection started three inches from one side of the water box and extended to nine inches from the opposite side. The side welds were intact and a layer of shells and shell fragments from two to five inches deep was found on the inlet side of the water bon cover.
Approximately 50% of the tubes had some shell blockage.
Further examination of the service water,ystem revealed that the 30-inch concrete lined nuclear and conventional service water headers were completely covered; principally, with marine organisms that are enclosed in a calcareous shell or test.
Species present included the American oyster, Blue mussel, barnacles, and serpulids (tubeworms). The most frequently encountered non-calcareous organisms were hydrozoans and polycheate worms. The most common species encountered was the American oyster.
These organisms formed a layer approximately one-inch thick on tne bottom of the pipe tapering off to 1/2 inch on the '.op.
As was expected, more organisms were found in the larger diameter pipes, where flow rates are lower (about 3.36 fps in the 30-inch header with one service water pump running) than in the smaller diameter pipes with higher flow rates.
Settlement of marine larvae is dependent
. on flow velocity and larvae have difficulty attaching if the flow velocity is above four fps.
It was also noted that tFe 3ccumulation of organisms decreased proportionately with the distance from the intake structure.
This may be due to the existence of an unfavorable temperature gradient or a depletion of the food supply.
Pipes which are normally isolated were, for the most part, found to be clean.
Isolated portions of the system including the RHRHXs are generally laid-up with well water.
Detailed information on the location and extent of marine growth is sFown in Figure 1.
Live organisms were not found in the RHRHX3, only shells and shell fragments that had been apparently swept into the water box during the operation of the RHR system.
The reason for this is the RHRHXs are generally laid-up with well water. Also, the Cu Ni water box surfaces are toxic to marine organisms.
The Cu Ni prevents attachment and growth of marine organisms during system operation. Although it was indicated that in some cases 50 to 60% of the RHRHX tubes had some flow blockage, the actual amount of debris removed from the tubes amounted to approximately one cup per HX as compared to the several gallons of shells found in some of the inlet water boxes.
The shells are preferentially swept into the RHRHXS since they are at a low elevation (ten foot) in the reactor building and form a trap in the service water system.
The service water is supplied to the RHRHXs from the 50-foot elevation where the RHR service water pumps are located.
After leaving the PHRHX, the service water piping returns to the 50-foot elevation before exiting to the circulating water discharge canal.
Shell growth was not detected in the four diesel generator heat exchangers or in the core spray pump room cooler; however, approximately one handful of shell fragments was found in each of these heat exchangers.
a Since the amount of loose shells and shell fragments found in the heat exchangers was relatively small compared to the amount of oyster grcwth in the service water headers, it is thought that, statistically, son mall percentage n+
the organisms, principally young oysters (oysters can live as long as 40 years) died in the system. As their shells detached, they were swent, by the flow in tra piping into the heat exchangers where they gradually accumulated.
Due to the turbulence in the inlet water box the shell debris was held suspended in the flow and could not settlu on the water box cover. The shells and shell fragments impinged and were held against the tubesheet, blocking the tubes, by the differential pressure between the inlet and outlet water box.
As the number of blocked tubes increased, the differential pressure became greater until ultimately, thc baffle plate became displaced.
Some shells were found in the turbine building closed cooling water (TBCCW) system heat exchangers. The TBCCV and the reactor building closed cooling water (RBCCW) are not safety-related systems.
Both the RBCCW heat exchangers, the TBCCW heat exchangers can be taken out of service for extended periods, inspected, and cleaned as needed.
It was stated by the licensee that during the initial startup of Brunswick, shells and shell fragments were found in the service water and circulating water systems.
At that time, there were no provisions for chlorinating.
A study was begun which concluded that chlorination would provide an effective means of contrciling marine growth in the plant. A chlorination program was begun il the spring / summer of 1975, prior to commercial operation of 1/
Unit 2,~
which called for continuous chlorination of the service water except during times when the screen wash pumps were operating, and chlorination of the circulating water for two hours a day.
This amounted to 1/ Unit 2 began conmercial operation on November 3,1975 and Unit 1 on Marcn 18, 1977.
< adding 300 pounds of chlorine a day for each service water pump that was operating, yielding a free residual chlorine concentration of about 1 ppm at the RHR heat exchangers and an undetectable concentration at the plant discharge cue to the dilution with the circulating water from the main condensers.
(Figures 2 and 3 show the chlorination system.) As can be seen from Table 1, the chlorination was stopped during the spring / summer 1980 outage. This was done primarily to protect employees from being overcome by r.hlorine while working near the intake or on the associated piping.
During the 1980 summer outage, a fine mesh screen (1 mm) was temporarily added to one bay of the circulating water intake on a trial basis in an attempt to reduce fish entrainment.
In going from the 3/8-inch mesh to the one millimeter mesh, continuous screen washing was required.
Screen wash water was taken from the service water intake bay.
Chlorination was reinitiated ir November 1980, after overcoming a series of mechanical and electrical problems. Due to the proximity of the chlorination piping and the screen wash pump suction in the intake bay highly chlorinated water was taken up by the screen wash system. This resulted in a high fish kill.
To eliminate this problem a dike was installed, in April 1981, in the 1-A service water bay between the service water pumps and the ch7orination piping (see Figure 3).
Chlorination was reinitiated on May 10, 1981.
By this time the chlorination had been stopped for approximately 14 months. This corresponds with the size of the oyster shells that were found.
The largest oysters were approximately 1 to 1-1/2 inches in total length, or about one year old.
As a first step in cleaning out the piping, the licensee flushed the Unit 2 nuclear service water header for 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> with heavily chlorinated water prior to cleaning. The Unit 2 conventional neader was chlorinated for 190 nours and then flushed for 250 hours0.00289 days <br />0.0694 hours <br />4.133598e-4 weeks <br />9.5125e-5 months <br /> using the RBCCW HX water boxes as a collection
, point for shells. Figure 4 shows the chlorination and flush paths for the conventional and nuclear service water headers.
Since shells were still found after 260 hours0.00301 days <br />0.0722 hours <br />4.298942e-4 weeks <br />9.893e-5 months <br />, the licensee cont'uded that cleaning the system by flushing was inef fective and resorted to mechanical cleaning.
Workers entered the Unit 2 nuclear header in the service water building and mechanically scraped the pipe walls. As previously mentioned, a one-inch layer of shells was found at the bottom of the pipe.
This tapered off to one-hal f inch of shells at the top.
The header was then backflushed and the shells were washed out onto the service water building floor. The conventional header and the smaller pipes were Hydrolazed (a process utilizing water sprayed radially through a nozzle at 8,000 to 10,000 psi).
Figures 1, 5, 6, and Table
- give more details as to where and what types of shells were found and how each section of pipe was cleaned.
Following the cleaning operations, the buckled RHR heat exchanger baf fle plates were replaced and the heat exchangers were returned to their original design snecifications (see Figure 7).
Due to the Cu Ni used in these components, neither the welds nor the baffle plates themselves are as strong as in other GE plants utilizing similar HXS with carbon steel baffles and water boxes.
Figure 3 illustrates the deformation found in the heat exchangers, and Table 3 summarizes the work which has been performed.
In addition, a monitoring program has been initiated at Brunswick (see Table 4).
The RHR heat exchangers will be tested monthly, at which time the flow rate and DP across the heat exchangers will be neasured.
The licensee stated that a sharp rise in DP would be expected as shells accumulate in the heat exchanger.
a
- The RBCCW and TBCCW heat exchangers will continue to be periodically inspected.
The service water headers will also be inspected on an annual basis.
CP&L has made a commitment to modify the screen wash system by 1983.
Fine mesh screens (1 mm) will be permanently installed in the circulating water bays and unchlorinated water will be used for the screen wash. The service water system will retain the 3/8 inch mesh screens. All of these screens are Cu Ni.
The licensee feels that these measures will prevent any significant fouling of the service water system.
2.
BIOLOGICAL CHARACTERISTICS OF SOME FOULING ORGANISMS 2.1 Asiatic Clame, Corbicula Species (so.)
The Asiatic clam was first found in the United States in 1938 in the Columbia River near Knappton, Washington.
Since that time, they have spread rapidly across the country and are now reported in at least 33 states. The species of Asiatic clam introduced into this country is typically found in freshwater, but there are several other species found in Asia that prefer brackish water.
There is presently some disagreement among experts as to which species is present in the United States. The possibility also exists that what is typically called the Asiatic clan in this country may represent several species.
. 'ae freshwater clams, such as have been found at ANO and other power plants, are monoecious, i.e., a single organism possesses both sexes and can reproduce by itsel f.
Thr adult clam reportedly releases planktonic larvae ranging in size from 200 to 240 microns.
In a relatively short time, the larvae cease to drift in the water and settle on a substrate (river bed, pipe, etc.).
They begin to attach themselves to the substrate by means of a single secreted byssus, or threadlike holdfast.
This byssus generally dissolves by the time the clams reach a size of 6 mm, correspcnding to an age of about six months.
After the byssus dissolves they are thought to be otherwise unattached and free to be swept along in the flow of water. There seems to be some controversy ov*r this point, however, since mature clams have been reported " attached" to the upper inside surface of horizontal pipes even after the pipes were drained. A possible explanation for the observation is that these clams have been encrusted in place by corrosion products.
Normally, if the substrate is muddy or silty, the clams will reside in the top two to three inches.
Although the Asiatic clams have limited mobility by means of a " foot" which they extend, they generally reside in stagnant areas of piping or areas of low velocity where they tend to settle out of the flow.
Corbicula sp. reach sexual maturity within the first year. The peak spawning season occurs when the water temperature is between 62 F and 75 F, typically in May and September at ANO. One aault clam can release many thousands of larvae in one season at a rate of 300 to 400 per day during the peak.
Corbicula sp. generally have a life expectancy of two to four years, can grow up to 60 nm in length, and have proven to be very hardy.
. Studies performed on these clams have shown them to be resistant to chlorination. The results of a series of tests performed at the Savannah River Facility showed that mature Corbicula sp. had as much as a 10% survival rate aft.r being exposed to high concentrations of free residual rhlorine (10 to 40 ppm) for up to 54 hours6.25e-4 days <br />0.015 hours <br />8.928571e-5 weeks <br />2.0547e-5 months <br />. When the clams were allowed to remain buried in a couple inches of mud, their survival rates were as high as 65%.
In studies 2/
on shelled larvae'~ approximately 200 microns in size, TVA reported preliminary results which indicated that a total chlorine residual of 0.30 to 0.40 ppm for 96 to 108 hours0.00125 days <br />0.03 hours <br />1.785714e-4 weeks <br />4.1094e-5 months <br /> would be required to achieve 100% control of the Asiatic clan larvae.
Intermittent chlorination appears to be inef fectual since the organisms can close their valves (shells) becoming anaerobic till the chlorination Ceases.
Nuclear power plants generally chlorinate intermittently according to a predetermined schedule (e.g., Monday, Wednesday, and Friday for 15 minutes).
Sodium hypochlorite, typically used for chlorination, is injected at the intake structure until the total free chlorine concentration has reached its allowable limit (usually 1 ppm) at the systen discharge.
In view of the information above, it appears that the chlorination procedures presently followed by nuclear power plants are ineffective in controlling Asiatic clams.
Corbicula sp. has also shown an amazing ability to survive even when removed from the water.
Average +imes to death, when left in the air, have been reported for an environment with low relative humidity as 6.7 days at 30 C (86 F) and 13.9 days at 20 C (68 F).
For a high relative hundity environment, times to death of 8.3 days at 30 C and 26.8 days at 20 C have been reported.
2/
There are conflicting reports as to whether Corbicula sp. intermittently release unshelled larvae or only shelled larvae.
Inis may have an effect on the larvae's tolerance to chlorine.
. On the other hand, Corbicula sp. has shown a much greater sensitivity to heat.
Tests performed by TVA resulted in 100% mortality of clam larvae, very young clams, and 2 mm clams when they were exposed to 47 C (117 F) water for two minutes. Mature clams, up to 14 mm, were also tested and all died at 47 C following a two-minute exposure. A stctistical analysis of the two-minute exposure test data revealed that a temperature of 49 C (120 F) was necessary to reach the 99% confidence level of mortality for clams of the size tested.
It snould be noted that Asiatic clams may cause a more serious fouling problem after death then wten alive.
Shell gapping, which usually occurs when clams die, changes the hydrodynamic profile of the organism, making it more susceptible to being swept along by the flow within the system.
Decomposition of the soft tissue results in the production of gases that can initially reduce the specific gravity of the organism to the point where it is often lighter than water, again increasing its potential for movenent.
In addition, within a couple of weeks after death, the two shells of the clam will separate thus increasing the potential for flow blockage.
2.2 Blue Mussels, Mytilus Edulis The blue mussel is a saltwater organism.
Like the Asiatic clan, it is monoecious. The adult mussel releases planktonic larvae that briefly settle on seaweed away from the adult mussel beds when they 2 e cetween 250 and 350 microns.
Following this primary settlement, they pass through a migratory phase during which thev are transported by water currents. The young nussels may attach and detach more than once during tnis phase, thus ensuring a wiue di s pe rsal.
When they have grown to between 0.9 and 1.5 mm, they settle, often on established beds, and begin to permanently attach themselves.
At
. first, the young mussels attach themselves with their extendable " foot."
Pdthin minutes, they begin to form a series of byssus threads, secreted by the foot. The thread is protein that is tanned by the formation of hydroxyl linkages between the long protein molecules.
The result is a smooth, tough, elastic thread. When the mussels are young, several threads can be formed in an hour; later in life the threads are formed only slightly faster than they are worn away.
Since the mussels continue to form byssus threads throughout their life, they have the ability to reattach if they become dislodged.
The blue mussel reaches sexual maturity in about two years, or when they attain a size of approximately 50 mm.
Their peak spawning season is in the late spring and early summer. One adult mussel will release thousands of larvae per year.
The life expectancy of the blue mussel is very temperature dependent.
It can vary from as little as four to five years in a warm environment to as much as 24 years in a cool environment.
They can grow to 30 mm in length during the first year and reach a size of 76 mm in five to s0ven years.
Mussel fouling reportedly can be controlled by a combination of chlorination and water speed.
It seems that continuous chlorinaticn at residual levels of 0.5 ppm and water speeds of more than 1.5 m/sec is effective in their cont rol.
Chlorine reduces the mussel's " foot" movement discouraging the settlement and initial attachment of young mussels. High water flow rates produce the same effect. Chlorine weakens the byssus threads of established mussels by producing incompletely linked protein molecules in the threads.
It also slows the rate of thread formation.
In addition, the presence of chlorine reduces the growth rate of the mussels. Intermittent chlorination seems to have no significant ef fect since the mussels can rapidly form new byssus threads when the chlorination is stopped.
. Studies performed by the Southern California Edison Company have sacwn heat to be an ef fective means of control for mussels.
One-hundred percent mortality was achieved when blue mussels were exposed to 97 F (36 C) water for 3.6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />,101'F (38.3 C) water for i.2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, or 105 F (40.6 C) water for 0.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
Like the Asiatic clam, mussels may also pose a problem even af ter they are dead.
They become detached within three to five days after their death and are then free to be picked up by the current. Also, since they tend to grow in clumps, sudden high flow rates can cause a large group to be broken off without warning and thus cause flow blockages.
2.3 American Oysters, Crassor'-aa Virginica The American oyster is found in a saltwater environment. Unlike the clans and mussels, the oysters are dioecious; i.e., they br<e separate sexes.
The adult oysters release either eggs or sperm into the water, depending on *,neir sex, and it is there that the fertilization takes place. Within three days the larvae, which are about 315 microns, begin to settle.
The young oyster permanently cements itself into place by secreting a substance which hardens, forming a very strong but brittle bond.
The American oyster reaches sexual maturity in about two years. Thei r reproductive cycle is temperature dependent and spawning is of ten triggered by a sharp rise in tenperature. The peak usually occurs in late spring and summer.
An individual oyster may spawn several times over a four to six-week period and will releasr. thousands of eggs or sperm.
Dysters have been known to live as long as 40 years and reach sizes of 350 mm (14 inches). A young oyster will grow to about 10 mm in the first six weeks and to about 90 mm in two to four years.
. Studies conducted on oysters have shown tf ;t the larvae are more ;ensitive to chlorination than the adults.
The 46-hour median effective concentration (EC50) f chlorine for larvae is 0.005 ppm.
The 96-hour EC r late 50 juvenile oysters is 0.023 ppm. Pumping-3/
oy adult oysters is reduced at a chlorine level of 0.05 ppm and completely stopped at 1.00 ppm. The adult oyster's sensitivity to chlorine, however, is very temperature dependent.
The oyster's physiological state also affects its resistence to chlorine.
Just after spawning and during the summer, when they are subjected to elevated temperatures, they are most sensitive to chlorine.
Oysters seem to be less sensitive to heat than clams and mussels.
The critical thermal maximum temperature has been given as 48.5 C (120 F).
However, some decrease in pumping rate is observed above 32 C (90'F).
It has been found that oysters can be killed by 3 short expose; e to temperatures well below the thermal mortality point for the species if the transition is rapid and the temperature change is great.
Water speed can also play a part in oyster control. Tha larvae are unable to attach if the flow rate is greater than 4 ft/sec.
Unlike the clams and mussels, the oyster's lower shell will remain attached even after death, providing an ideal :ubstrate for subsequent larv31 settlement and tne growth of new organisms.
(This is true for barnacles and tubeworms as well. )
In a rapid flow, the oyster will lose its top shell a cou?le of weaks after death, iowever.
These shells are then free to be swept along by the current.
-3/ Pumping is the process by which oysters take in and internally circulate water in order to get food and oxygen. An average adult oyster pumps at a rate of 3.5 gph and can live for approximately a week without pumping in an anaerobic state.
. 3.
POTENTIAL EFFECTS OF FOULING BY A0 VATIC ORGANISMS ON THE OPERABILITY OF SYSTEMS AND COMPONENTS The principal concern stemming from the growth of fouling organisms in service water systems is the potential for co aon cause failure of redundant components due to flow blockage.
The events previously described, that occurred at the ANO and Brunswick stations, although not serious in actual consequence, clearly are precursors to a possible common cause failure.
The nature of bivalve fouling in piping systems is such that it may go unnoticed, or not severely degrade system performance, until the system is called upor, to function following an incident.
Some of the ways that this can be postulated to occur are described below.
a.
During normal operation particularly if an adequate control program is not being followed, fouling organisms can grow in large diameter piping l' the flow velocity is low.
A quantity of fouling organisms sufficient to cause severe flow blockages in safety-related coolers could accumulate in such piping without causing significant flow degradation. Therefore, situaUon such as this could go undetected for a long time since a 7
large accumulation of fouling organisms would be required before any noticeable flow degradation was observed. These fouling organisms may potentially be sicwly swept into components requiring cooling water causing tube plugging and degraded performe ;e.
If additional service water pumps are started following an incident, the tendency for live organisms, shell fragments and other debris to be swept down the piping into heat exchangers would increase due to the higher flow velocity.
. b.
Fouling organisms also thrive in stagnant runs of piping in operating systems or in piping systems which have been inactive for long periods of time.
Particularly during initial construction or extended maintenance outages, systems that would normally be operating may be laid-up for months or even years without the implementation of an adequate control program, allowing fouling organismc ample time to become established in systems that otherwise might be unaffected during operation. The concern here is that plants could begin operation without the opera, s being aware of the fouling that could exist.
An example of this, that did not go undetected by the licensee, is the recent occurrence at San Onofre Unit 1.
This plant had been shutdown for steam generator tube repairs for over one year.
During this time, the periodic flushing of the system with heated water (heat treatment) normally used by the licensee to control the growth of marine organisms, was curtailed.
Due to the lack of periodic heat treatment the licensee discovered, after observing a low saltwater coolant flow rate, that gooseneck barnacles were present on the component ~^91ing water heat exchanger discharge tubesheet and in the saltwater discharge piping.
The growth of the barnacles effectively reduced the flow area of the piping causing low flow and caused the malfunctioning of a butterfly val ve.
Fire protection systems using service we.-er are also a prime candidate for fouling by aquatic organisms since they inherently contain stagnant branch lines that are conducive to marine growth.
Branch lines in fire protection sprinkler sys+ ems can be as small as one-inch nominal
, pipe size, and sprinkler heads generally have orifices of one-half inch.
These would be suscept'oie to plugging.
In addition, live organisms or shell fragments would be swep: toward the open sprinkler head in the event of a fire.
c.
Seismically diked emergency ponds utilized by some power plants as the ultimate heat sink could also support the growth of Asiatic clams.
If make-up to the pond is from a waterbody 4n which the Asiatic clams are known to be present, then it is likely that clams will be found in the ultimate heat sink and possibly in the service water supply header leading to the plant from the ultimate heat sink.
Under design heat loads (e.g., post-LOCA) ultimate heat sink temperatures could reach 110 to 120 F during summer months. This is hot enough to cause a substantial mortality of the clam population. As discussed previously, dead clams may be more of a problem than live organisms, since they are more easily swept along by the flow. Therefore, following a LOCA that resulted in high pond temperatures, service water system performance could be gradually degraded if the dead clams are swept into the system.
Even if the temperature of the ultimate heat sink does not reach the point that causes clam mortality, clams residing in the service water supply header could still be swept along the piping if the flow velocity is sufficiently high.
Since the service water supply neaders can be quite long, even a moderately dense infestation may translate into a large volume of clams.
A small percentage of these, if swept along the piping, could overburden automatic backwash service water strainers.
. d.
Although all nuclear power plants are designed to withstand a seismic event, the vibratory motion induced by such an event may cause fouling organisms such as oysters, that attach themselves to piping walls by a strong but bri',tle bond, to be broken loose in sufficient quantities by the pipe flexure to cause flow blockage in cooling water systems.
L. ; similar manner, during a seismic event, piping severely encrusted with corrosion products may release a substantial amount of debris which can collect in equipment bearing or seal coolers blocking the cooling water flow.
In both cases,the buildup of fouling organisms or corrosion products may not noticeably degrade system performance during normcl operation; however, the performance of both redundant systems could be simultaneously degraded following a seismic event.
Since the reactor coolant system is seismically designed, a LOCA is not postulated to result from a seismic event. A degradation of the service water system, in this case, would not be an immediate safety concern but may lengthen the time required to go to cold shutdown as a result of the unavailability or diminished heat removal capacity of the shutdown cooling system.
e.
Seal coolers are generally provided on pumps that may be called upon to pump heated water from the containment sump following a LOCA; for example, high and low pressure injection pumps, containment spray pumps er residual heat removal pumps.
Surveillance testing of these pumps is, by necessity, performed witn water at ambient temperature.
This is not representative of the temperatures of water encountered during the post-LOCA recirculation mode of operation.
Therefore, 11 flow blockage existed in the pump seal coolers due to the growth of fouling organisms or a buildup of silt or corrosion products it could go unnoticed during pump surveillance testing unless flow measurements through the coolers were part of the test. There are two reasons for
- this:
(1) since the pumped fluid is at ambient temperature, seal cooling may not be necessary and no seal degradation would be observed even after hours of running without cooling water; and (2) generally, surveillance testing is of such a short duration that no noticeable seal degradation would occur even if cooling flow were necessary for sustained operation.
Since pumps required during the post-LOCA recirculation are generally located outside primary containment (in.the auxiliary building) degraded pump seals would result in the leakage of radioactively contaminated water outside containment.
Similarly, pumps provided with bearing lube oil coolers could be susceptible to flow blockages due to fouling organisms or the accumulation of corrosion products or silt deposits. Flow blockages in these coolers could also go unnoticed during surveillance testing unless the cooling water flow was monitored.
This could result in premature bearing failure when the pumps are needed to run for an extended period of time, e.g.,
following a LCCA.
4 ACTIONS TAKEN BY OTHER NRC 0FFICES 4.1 Office of Nuclear Reactor Regulation The Operating Reactor Assessment Branch (ORAB) is conducting a gene /ic study of service wat-
. en mal functions.
Oak Ridge National l aboratory (ORNL) is assisting in this study and will review all past ever;s in which the service water system was partially or completely lost.
E1phasis will be placed on those events which highlighted the potential f;r common cause failure of safety-related equipment; for example, the ANO and Brunswick
. events discussed in this report, the Calvert Cliffs event in which instrument air leaked into the service water system temporarily disabling both redundant trains, the leakage of fan coolers at Indian Point Unit 2, that led to flooding of the containment and reactor cavity pit, and the Rancho Seco event in which a buildup of corrosion products blocked the flow of service water to the high pressure injection pump lube oil coolers. Following an evaluation of such events, ORNL will provide ORAB with a description of the causes of each event and the actions which would have been required to prevent or detect the problem early on.
This task is scheduled for completion by October 1981.
ORAB will attempt to correlate specific plant design features, surveillance programs and preventive measures with the magnitude and types of service water problems reported in LERs and the responses to IE Bulletin 81-03 (see Section 4.2).
Based on the results of this study, ORAB will recommend corrective actions in order to improve the reliability of service water systems.
In addition to the service water study, ORAB is reviewing the design of baf fle plates in "U" tube heat exchangers similar to those used at Brunswick.
They will determine if a generic problem exists and if the design is appropriate for the given application. The Division of Engineering is assisting ORAB in this study.
. 4.2 Office of Inspection and Enforcement In April 1981, IE issued Bulletin 81-03, " Flow Blockage of Cooling Water to Safety System Components by Corbicula sp. ( Asiatic Clams) and Mytilus sp. (Mussels)."
It addressed the potential for flow blockage in service watar systems by Asiatic clams and mussels (see Section 5 for licensee responses).
In July 1981, IE Information Notice 31-21, " Potential Loss of Direct Access to Ultimate Heat Sink," was issued.
This notice described the loss of the normal decav heat renoval system 6t Brunswick.
It also emphasized the need for licensees to initiate appropriate actions, as described in IEB 8103, for any aquatic organisms that could cause fouling at their plant.
IE is ccnsidering the need to issue a supplement to IEB 81-03 to include other fouling organisms.
5.
RESPONSES TO IE BULLETIN 81-03 On April 10, 1981 th' Office of Inspection and Enforcement issued IE Bulletin 81-03, Flow Blockage of Cooling Water to Safety System Components by Corbicula sp. (Asiatic Clam) and Mytilus sp. (Mu s sel ). The Bulletin requested licensees to determine whether either species was present in the vicinity of their station and tne extent of any fouling these organisms may have caused in fire protection or safety-related systems.
The responses to this Bulletin have been received from all but a few of the operating plants.
The responses received represent 50 sites; of these, 18 sites reported positive findings.
Eleven sites have seen some evidence of Corbicula sp., and seven sites have seen evidence of Mytilus sp.
This has ranged from occasional findings of a few shell fragments in the main condenser to major infestations as described in Section 1 of this report.
An additional four sites have reported tnat, while Corbicula sp. were not
. yet present in the intake canal, they were present in either source or receiving waterbodies and infestations at the plant were likely in the future.
The Bulletin also askea licensees to describe their methods for preventing and detecting any future fouling at their plant. A combination of chlorination, heat treatment, flushing, backflushing and the installation of strainers were the preventive actions taken by most of the af fected plants. Many of them routinely inspect the intake canal, the pump discharge strainers and the main condenser, cleaning them out as needed.
Detection methods included surveillance programs comprised of visual inspections and measurements of flow, differential pressure, and temperature at various system locations.
These actions by the licersees can be expected to have varying degrees of effectiveness depending on the frequency with which they are performed and the severity of the infestation present at and around the plant.
IE Bulletin 81-03 addressed fouling by Asiatic clams and mussels only.
Therefore, most plants discussed only these two species in their responses.
Some plants, however, mentioned the presence of other fouling organisms such as other species of clams, freshwater sponges and oysters, barnacles, and tubeworms.
In addition, a number of plants reported fouling problems caused by mud and silt.
In some cases, they claimed this to be a bigger problem at the plant than bivalve fouling.
6.
FINDTNGS (a) Common cause service water system failures affecting redundant system; can result from system fouling and flow blockages caused by the preser ce of aquatic organisms, the accumulation of silt, or the buildup of corrosion products.
. (b) Periodic surveillance testing of components currently required by plant technical specifications may not uncover actual system flow blockages or the potential for flow blockages that can occur when the system is required to operate for extended periods of time following an incident.
(c) The presence of organisms that can cause fouling in service water systems can be ef fectively controlled, even when such organisms are plentiful in the source or receiving waterbodies, if the proper control strategies, consisting of surveillance, chlorination, heat treating and flushing are developed and implemented.
(d) During periodic equipment surveillance testing, flow through coolers, such as pump ;eal and bearing coolers or room coolers, is generally not required to be verified by the plant technical specifications.
(e) In view of the baffle plate failure in RHRHXs at Brunswick, periodic measurement of flow and differential pressure across multiple pass HXs may not be adequate to allow accurate determination of a heat exchangers operability.
(f) Without an effective control program, fouling organisms can flourish in large diameter service water headers that normally have low velocities.
A large accumulation of marine organisms in such piping can go unnoticed since it will not significantly degrade the system flow rates. Over a period of time, however, debris consisting of shells, shell fragments or live organisms may be swept, by the flow, into heat exchangers and equipment coolers causing flow blockages.
In some cases following an incident, higher flow rates due to the operation of additional service nater pumps may sweep debris more rapidly into the components being cooled.
. (g) During initial plant construction or extended maintenance outages service water systems or fire protection systems may be laid-up for long periods of time.
Programs to control fouling organisms may not be implemented during the initial construction. During extended maintenance outages, abatement programs normally implemented during operation may be suspended.
In either case, systems laid-up with service water are vulnerable to fouling by aquatic organisms. Also, system flow paths not normally prone to clogging due to high velocities during power operation are subject to fouling during extended periods of lay-up with service water.
7.
RECOMMENDATIONS (a) IE Bulletin (IEB) 81-03, confined specifically to flow blockages in cooling water systems caused by Asiatic clams or mu.csels, was issued April 10,1981.
Since that time, Brunswick has experienced flow blockages in their RHRHXs due to the accumulation of oysters in the service water piping, and San Onofre Unit i reported flow blockage of the saltwater cooling system due to gooseneck barnacles.
Therefore, it is recommended that a supplement be issued to IEB 81-03, broadening the scope of the Bulletin to address flow blockages of cooling water systems caused by any type of fouling organism as well as the accumulation of silt or corrosion products.
(b) The capability to measure cooling water flow should be provided for all safety-related equipment cooled by open cycle service water systems on operating plants, as well as plants under construction.
Pe rmanently mounted flow instrumentation may not be recessary. As a minimum, however, provisions should be available to allow the temporary installation of flow measuring instrumentation during surveillance testing.
. (c) In line with recommendation (b) above, plant technical specifications should be revised to call for pericdic measurement of cooling water flow to all safety-related equipment to verify that it is within accepteble limits.
(d) The measurement of flow and differential pressure on multiple pass heat exchanger; is not sufficient to guarantee the design performance of these heat exchancers if internal bypass leakage between passes exists.
This bypass leakage may be undetectable by flow and differential pressure measurements. A more reliable means of measuring heat exchangers performance is by periodically calculating the overall heat transfer coefficient of the heat exchanger and comparing it to the design valve specified by the manufacturer. Therefore, it is recommended that technical specifications provided for multiple pass heat exchangers require the periodic verification of the overall heat transfer coefficient.
(e) A review of the available biological data on Asiatic clams indicates that there are information gaps or conflicting observations.
Questions such as whether arl ult clams can attacn themselves to piping, and if so are there any outside stimuli that could cause them to detach enmass or atother one or more species of Asiatic clams exist in this country, should be answered in order that proper preventive action can be taken to safeguard against undetected clam infestations and potential mechanisms for common cause failure. The Office of Nuclear Reactor Regulation should consider initiating a research program to address the above concerns.
. (f) At sites where the potential exists for substantial fouling by bivalves or other organisms, plant technical specifications should require periodic inspections of service water systems, particularly large diameter headers that normally operate with low flow velocities.
Large accumulations of such organisms may otherwise go undetected, possibly resulting in flow blockages when the system is required to operate following an incident.
(g) It is recommended that, at sites where the potential for substantial fouling exists, control strategies be developed and implemented as appropriate during the initial construction and should not be curtailed during plant outages. This would help to prevent the establishment of organisms in plant systems, particularly those where growth of such organisms is not expected and, therefore, possibly could go undetected.
8.
CONCLUSIONS Accumulation of fouling organisms, silt or corrosion deposits each represent a potential mechanism for common cause flow blockage of the redundant trains in the service water system.
The principal concern is that, with each of these mechanisms, degradation of service water system performance generally occurs slowly and may go unnotic3d until systems required to function following an incident become inoperable due to a lack of cooling water. Therefore, at sites where potentially troublesome fouling organisms are found in the supply or receiving waterbody, open cycle service water systems should be required by technical specifications to be inspected periodically, particularly tne large diameter piping with normally low service water velocities, since these are conducive to the growth of fouling organisms.
In such piping, growth of organisms could be substantial before any flow blockage was noticed.
, Additionally, cooling water flow supplied to each safety-related equipment cooler, room cooler, or heat exchanger should be required by technical specifications to be periodically verified to assure that the equipment will perform satisfactorily.
Finally, if licensees are aware that potentially troublesome fouling organisms are present in the supply or receiving waterbody at particular sites, control strategies can be developed to prevent these organisms from accumulating to a large extent in plant piping. With the awareness of the potential for fouling and implementation of effective control and surveillance strategies, plants can be safety operated even at sites where fouling organisms such as Asiatic clams abound in the supply or receiving waterbodies.
s T'A 8 L E.l.
Chronolocy of Chlorinator Outace
-February 22, 1980 - Train *c shutdown due to mechanical and electrical problems.
-Marth 15,1980, to September 21, 1980 - Unit Nos.1 and 2 outages. ' ne: /-4.
J
-September 1980 - Restart of Chlorinator System failed cue to electrical problems with heaters and controis.
-October 1983 - Restect cf Chicrinator System revealed holes in the evaporators.
Evaporetors were replaced.
-October 31, 1980 - The Cplorinator System was run ?ce trree days.
The system was sh it down because of #ish kill.
-November,1980 - Attempts were made tc opcrate tne system ir T manner that would not kill fish.
-December 1980 - Contacts were made with involved groups to resolve the problem of chlorine in the screta wash.
-January 1981 - Trouble ticket suomitted to have. dam installec.
-March 1981 - A secord trouble ticket was submitted.
-April 1981 - The dem was installed in l A service water bay.
-May 1981 - Systra line up was cospletee.
Held up start uo ca: to oysters in heat exchangers.
-May 10,1951 - Res'.arted chlorinet-ion.
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'lhe following 13. a breakdown of the work perturn.ed on both Unit 1 a: c Unit 2 RHR heat exchangers:
2A R!!R Heat Exchancer Spring 1980
- Heat exchanger inspected and inlet and outlet elbows replaced (PM 79-232T).
Eaffle plate inspected and degradation noted.
a k0 13 May 81
- Heat exchanger drained.
3affle plate inspected with no signs of deformation.
Exchanger cleaned of shells and put back into service 14 May 81.
3 Jun 81
- High SP noted across baffle plate.
Exchanger cleaned of shells, no signs of deformation.
.Seturned to service 4 Jun 51.
2B RHR Heat Exchancer Spring 1980
- Heat exchanger inspected and a 9 inch deflection discovered in baffle plate. Vertical plate attachment welds cracked
% 33 inches. Eaffle plate and elbows replaced per PM 79-232s and returned to service.
6 May 81
- Exuianger drained and inspected.
A 3 inch deflecti:n of plate noted.
Fillet welds along side walls showed one 2 inch crack.
Saffle plate recoved and heat exchanger bolted up and put back into service on 9 May 81.
Unit used as flow path wi:hout plate with heavy chlorination of service water sys:er.
16 May 81
- Exchanger drained and lower thennel head cnce aga n removed so that baffle plate replacenent work cculd begin.
.ic rk completed on 24 May 81 and returned to service.
lA RHR Heat Exchanger 25 Apr 81
- Lack of heat transfer noted by Operations.
Heat exchanger drained to flow and charnel head removed. A 6 to 9 inch deflection noted and plate jacked into position wi:h porta-powers. 3 racing stays welded to back of plate for temporary support.
Heat exchanger head reinstalled and pu:
back into service 27 Apr Sl.
2 Jun 81
- Exchanger drained and Icwer channel head rer:ved.
Permano.:
repair replaced baf fle plate and inle and cutle: elbows per PM 79-231T. Work completed on 13 Jun 61.
Awai:ing reinstallation e inle: isolation valve (reneved for vessel hydro) before retur ning to service.
13 P.HR Heat Ex c ha nc e r 19 Apr 81
- Heat exchanger drained and 2nspe::ed. A deficcrice of ; to 9 inches noted on baffle pla::.
Pla:e replaced alen
.-ith inic:
and outlet elbows via FM 79-2310.
L'ork compel ec er 31 May 31 and returned.to service.
3 Jun 31
- Hich
^.P noted across baffle nlate.
Plans re :, ; r ;- :nd reneve channel head in crder to clean shc1;s - : c- : s :i v e c,.
scheduled for 18 June 51.
TSSLE 3
Heat Exchanger Monitorina Procram I.
Short Term RHR Heat Exchangers Divider plate AP monitoring Verification of design AP Trend analysis of AP Heat transfer evaluation Other Safety Related Heat Exchanaers Internal inspections II.
Long Term RHR Heat Exchanaers Periodic test for checking aP Other Safety Related Heat Exchangers Periodic tests requiring internal inspection R@lG k
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