ML20040C524
| ML20040C524 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 09/25/1981 |
| From: | Masnik M Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19248B746 | List: |
| References | |
| FOIA-81-362 NUDOCS 8201280094 | |
| Download: ML20040C524 (4) | |
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ASIATIC CLAMS CAUSE SHUTDOWN OF ARKANSAS NUCLEAR ONE-UNIT 2 Division of Engineering Technical
Contact:
Michael T. Masnik.
Environmental Engineering Branch On September 3,1980, Arkansas Nuclear One-Unit 2 (ANO-2) was shut down because attainable service water flow to the containment cooling units (CCU) was less than the license requirement. The licensee detenn~aed that the cause of the inadequate flow was due to " intrusion of Asiatic Clams (Corbicula sp.) into the CCOs". Subsequent flow testing and inspection of the balance of the Unit 2 service water system and the Unit 1 (not operating due to steam generator tube leak) service water system indicated fouling by Corbicula sp. with reduction in attainable flow in the containment spray pump and low pressure in,}ection pump seal coolers located in the Unit 2 auxiliary building and in two of the four Unit 1 CCUs.
It was reported that while many live clams were found in the Unit 2 CCU system, only a few live clams were found in the fouled Unit 1 CCus and that only shells and shell fragments were found in the Unit 2 seal coolers. The licensee partially cleaned the systems in both units using backflushing, high flow rate flushing, and mechanical operations where access permitted. Although no precise quantitative measurements of the amount of live specimens and shell and shell fragments removed from the CCUs was made, it was reported that approximately a 55-gallon drum full of material was removed from each of the two units (ANO-1 andANO-2). The majority of the material removed was from inside the CCUs ahead of the condenser tubes which are 16 mm in diameter.
Shells reportedly ranged in size from 20-25 mm in Unit 1 and Unit 2 CCUs.
Shells removed from the seal i
cooling units were smaller (% 18 mm).
Chlorine was introduced by the licensee I Q 94 810925 F
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. 1 in an effort to kill remaining clams that were in the CCus and piping to prevent further deterioration of flow rates.
Cleaning efforts were only partially effective
_ in restoring flow. The 1_icensee subsequently applied _ for a license amendment to permit restart of ANO-2 with a loWar flow attainable in the CCUs. The Environmental Engineering Branch (EEB) was asked to review the licensee's proposed eradication and control program.
Based on a review of.available literature and discussions with experts at ORNL and TVA, it was concluded that shock chlorination is not an effective method of eliminating Corbicula sp.
The organism's response to free available chlorine is to clam up and wait until chlorination ceases.
Concentrations as high as 40 ppm for 54 hours6.25e-4 days <br />0.015 hours <br />8.928571e-5 weeks <br />2.0547e-5 months <br /> have been unsuccessful in achieving 100% mortality.
Corbicula sp. however do succumb quickly when heat shocked. A 100% mortality has'been demon'strated when shocked with water at a temperature of 120'F after a few minutes.
Thus, the licensee was advised that the most effective way to achieve 100% mortaldy In'~ inaccessible pipe runs and CCU condenser tubes and thereby arrest further growth, is by heat treating the system.
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Neither heat treatment nor shock chlorination will prevent reintroduction of Corbicula sp. during future surveillance tests.
Clams may be introduced into the system eith'er in a non-valved or valved stage of development. Non-valved larvae would be easily killed. during surveillance testing by continuous chlorination. Valved larvae are not susceptt51e to chlorine. TVA has reportedly e
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developed a screening technique that removes valved larvae from the inflow using a.8 nm mesh screen.
The combination of continuous chlorination during periods of peak' larval density and screening of all critical service water on a year around basis-appears to be an effective control technique.
Yearly heat treatment during refueling outages may also provide additional protection against reestablishment.
The licensee, acting on the EEB information, heat treated the CCUs and associated piping in both units with water at a temperature of 170 F for 30 minutes.
The surface temperature of attendant piping was measured at 152*F.
Dr. Michael Masnik of the Aquatic Resources Section visited the site subsequent to the heat treating operation and collected specimens, examined piping runs and the CCUs, and discussed future control measures with station personnel.
The licensee was cautioned that the clams, which do not attach to the substrate in the adult life stage,.may cause a more serious fouling problem after death than when alive. _Shell_ gapping, which usually occurs when clams _ die _,_ chang.es the hydrodynamic profile of the organism, making it more susceptible to. movement within the system.
Decomposition of the soft tissues results in intially reducing the specific gravity of the organism to the point where it is often lighter than water, again increasing its potential for movement.
If a signifi-cant number of Corbicula sp. still remain in the system and the system remains untested until the next scheduled surveillance test (every 14 days) there is the possibility that the increase in mobility could result in significant fouling and resultant flow reduction.
Should an emergency arise requiring j
the use of the CCU's, flows through the CCUs may not be attainable. The licensee has subsequently agreed to perform the surveillance testing of the
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CCUs on an every other day schedule for the first two weeks.
Fouling of CCUs because of increased shell mobility is expected to occur ov r a number of days, therefore any reduction in flow would be detected by the increased surveillance The applicant intends to thoroughly clean the system and to incorporate control procedures and equipment during the spri.79 refueling outage.
It is the staff's opinion that heat treating should prevent further growth of clams currently in the system and that larvae entering the system will not grow to an' extent which would result in deterioration of flow rates prior to the spring cleaning. The potential flow reduction due to increased shell mobility and the effectiveness of the heat treating operation in n;aintaining stable flow coriditions during the interim period will be verified by surveillance testing.
There are indi, cations that the geographic range of Corbicula sp. is still expanding in the United States-Approximately 30 operating units are 1ocated
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on water body types that provide suitable habitat and are within the range, f this species.
In view of the organism's demonstrated potential for creating l
safety _related ' problems in"reactdf facilities, a bulletin is being~ drafted
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l which will alert the industry to the potential problem and means of controlling l
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