ML20062B375

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Special Rept Iir 2-C90-0294:on 900914,RCS Leakage Resulted in Unit Cooldown to Cold Shutdown.Caused by Mfg Deficiency in Modified Blind Hubs.Unacceptable Hubs Identified & Replaced
ML20062B375
Person / Time
Site: Catawba Duke Energy icon.png
Issue date: 10/15/1990
From: Hampton J
DUKE POWER CO.
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
IIR-2-C90-0294, IIR-2-C90-294, NUDOCS 9010240310
Download: ML20062B375 (8)


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Subject:

- Catawba Nuclear Station Docket 50-414 1

Special Report

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.IIR C90-067-2; PIR'2-C90-0294 1

. Gentlemen:

Att' ached 5is.a report concerning' UNIT COOLDOWN TO.~ COLD-'
SHUTDOWNLDUE TO REACTOR COOLANT SYSTEM LEAKAGE.

This report isisubmitted as a "Special" Report to ensure!

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-industry awareness of this event.

The health and safety 4

of the.public were"not'affected-by this incident.

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,o Very truly yours, A

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1 iJ..Wi Hampton Station Manager I

6 ken: REPORT.SP

' Mr. : S. D. - Ebneter American Nuclear Insurers i

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Regional ~ Administrator, Region II c/o Dottie Sherman,--ANI' Library

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.U.,S. Nuclear Regulator Commission The Exchange,-Suite'245'

.101'Marietta Street, NW, Suite 2900 270 Farmington Avenue.

Atlanta,'GA 30323 Farmington, CT 06032 i

d M &.M Nuclear. Consultants Mr. K. Jabbour 1221 Avenues.of the Americas U. S. Nuclear Regulatory Commission-

New York','NY. 10020 office of Nuclear. Reactor Regulation-Washington, D.'C.

20555.

.INPO Records Center Suite 1500 Mr. W. T. Orders s1100 circle 75 Parkway NRC Resident Inspector Atlanta; GA 30339 Catawba Nuclear Station-10C109 9010240310 901015 ADOCK0500g4 g

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CATAWBA' NUCLEAR STATION-PROBLEM INVESTIGATION REPORT-NO. 2-C90-0294

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~ UNIT COOLDOWN TO COLD' SHUTDOWN DUE TO REACTOR COOLANT SYSTEM LEAKAGE ABSTRACT-I On September 14,,1990 at approximately 0200 hours0.00231 days <br />0.0556 hours <br />3.306878e-4 weeks <br />7.61e-5 months <br />, with Unit"2 in Mode 3, Hot

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Standby,. vendor personnel were'in the process of performing-a leak repair on a.

. Core Exit Thermocouple Nozzle Assembly (CETNA)-on-the Reactor Vessel head.

In Lorder'to perform the: leak repair,~it was necessary to drill through a modified

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'. blind hub'(part of the Grayloc flange t.c the CETNA) into the Reactor Coolant (NC) System pressure boundary.

.A sealantiinjection valve was installed during this process ~to provide isolation at the pressure boundary. After the final l drilling was completed, the sealant injection valve would not close. A second' valve was-threaded.into the back'of the first valve, but before it could be

-closed the entire assembly ejected from the' hole. A conservative decision was-made to consider the leakage'as NC system pressure boundary leakage'. ~ Unit 2 commenced cooldown.,to Mode 5, Cold Shutdown, and an-Unusual Event.was declared.

.An analysis will.be performed to determine the cause(s)fof this'failurei The original CETNA leaks are attributed to a: Manufacturing Deficiency in that'the modified blind hubs;did not taeet dimensional requirements during fabrication.

i The unacceptable; hubs were identified and replaced. This report is being submitted'as.a Special Report!

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BACKGROUND

' The Reactor Coolt.nt' [EIIS: AB] (NC) System is designed to transporb heat from the ;

Reactor to the-Steam Generators [EIIS:HX]'(S/Go), where heat is transferred to-

'the Feedwater.[EIIS:SJ)-(CF) System and Main Steam [EIIS:SD] (SM) System of the secondary. side. The/NC System-consists of four identical ~ heat transfer loops t

connected in parallel to the Reactor Vessel [EIIS:VSL].

The Incore Instrumentation [EIIS:IG] (ENA) System =provides'information on the

' neutron flux distribution and fuel assembly outletctemperatures at selected core locations. Chromel-alumel.thermocouples are threaded into guide tubes that penetrate the Reactor Vessel head through seal assemblies,4 and: terminate 1at.the-exit flow end of the fuel assemblies.

-Catawba Unit 2. utilizes a Core Exit Thermocouple Nozzle' Assembly (CETNA) to provide the.NC' System pressure boundary seal.where the: thermocouple 11eads

penetrate the Roactor Vessel head. There are five CETNAs on Unit 2 identified-as1 connections #74 through 78.

The CETNA, supplied by Combustion' Engineering, M

-Inc'. (CE),-consists of a nozzle assembly which is threaded and seal _ welded-to

.the Reactor vessel head-nozzle, a Grayloc clamp set,La modified blind hub to Lform tho'second halffor the flange and house Grafo11 packing. rings; drive sleeve and nut;' thrust bearing and washers, and'a hinged split collar to retain the assembly. Gray Tool Company manufactured the original Grayloc clamp sets,.

including tho modified blind hubs. Gray Tool later.gave up their N-stamp.and turned over the manufacturing responsibility for these parts to CE.

During the.

Catawba Unit 2'End-of-Cycle 2 (2EOC2) refueling outage; discoloration was found on three of1 he original modified blind-hubs (manufactured by Gray Tool); As'a t

conservative measure, these hubs were replaced with spare hubs manufactured by' CE.

Leakage inspections were conducted:during'startup, and no leakage was noted.

Technical Specification (T/S) 3.4.6.2 requires NC system leakage to be limited to no pressure boundary leakage during Mode 1, Power operation, Mode 2, Startup,.

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- Mode 13, Hot' Standby, and Mode 4, Hot Shutdown. " Pressure boundary leakage is i

defined:as-leakage.(other than S/G tube leakage)'through.a non-isolable fault in a NC system component body, pipo (EIIS: PSP]. wall, or vessel wall. With any~

ptessure boundary. leakage present, the required action 1s to be11n at least Hot 1

Standby within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Mode 5, Cold Shutdown, within the following 30

' hours. The T/S Bases states that pressure boundary leakage'of any magnitude;isi

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unacceptable since it may be-indicative of an impending gross failure of the, 1

pressure boundary.-

g EVENT-DESCRIPTION i

-On1 June 10, 1990, Unit 2 was shutdown for the End-of-Cycle 3-(2EOC3) refueling

outage.- Following cooldown, it was noted that Core Exit Thermocouple Nozzle j

. Assemblies.(CETNAs) had been leaking at the Grayloc flange connection.

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g f-Maintenance Engineering Services (MES) contacted Design Engineering.and the CETNA supplier,4 Combustion Engineering (CE), to evaluate the reason.for the-

' leaks so that corrective-action could be taken prior to restart. During disassembly _of the CETNAs,.a breakaway torque. check was performed on the Grayloc clamp nuts. The' breakaway torque results indicated that the bolting material' 4

.had relaxed during plant operation, therefore, CE recommended a new torque procedure for the Grayloc flange connection, which Design approved for use at Catawba.-

On Augus.t. 19, 1990 the CETNAs were reassembled using the new torque procedure j

per Work Request'(W/R) 5312 SWR.

'A "On September 4', '1990 with Unit 2' in Mode 4, Maintenance inspected the Reactor q

Vessel-head and CETNAs for leakage. CETNA #74 had boron residue present, i

' indicating leakage had occurred, but did not appear to be leaking at this time, j

CE was contacted and recommended that the CETNAs be rechecked in. Mode 3, due to i

a' design feature that provides better seating nt higher pressures, j

On September 5 at 2355 hours0.0273 days <br />0.654 hours <br />0.00389 weeks <br />8.960775e-4 months <br />, Unit 2 entered Mode 3.

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LOn-September 6,-the CETNAs were reinspected and no-leakage was identified.

On-September'8, another inspection was performed and boron residue was found on CETNAs #74'and N76 in the area of'the lower Grayloc clamp seal. On September 9,

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Maintenance cleaned the boron residue.from both leaking CETNAs and observed a-g small steam leak'at #76 (#74 did not appear to be_ leaking at this time)..CE was contacted and recommended that'a torque check pass be performed on'the Grayloc flanges.. Maintenance performed the_ torque check on #76 and did not note any nut

' movement, Indicating the proper torque existed. On September 10, the CETNAs were inspected several times, andiboth #h and #76 were leaking _a small amount--

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of steam. -At the time,. leak' repair by injection of a sealant atsthe Grayloc-

, ' connection was considered. This process is regularly used throughout the j

i industry for repair of leaks under pressure.

MES,' Design, and-CE conducted I

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' extensive evaluations to establish a sealant injection leak repair procedure for l

the CETNAs.- During this evaluation process on September 12 at 0500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br />, Unit y

2. entered Mode 2 for completion of Zero Power physics Testing (ZPPT).

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'On September 13, Catawba Nuclear Station. Modification (NSM) CN-20626 and:the' I

required 10CFR50.59 evaluation were approved to allow injection af_a sealant into the.CETNA seal ring areasz on,#74 and #76. The process consisted of' e

? partially drilling into the~ modified blind hub at the Grayloc, flange, tapping:

l thel hole,. inserting a threaded sealant' injection valve-[EIIS
V), and drilling i

F through the remaining hub thickness to the NC system pressure boundary.

The

-sealant' injection valve would then be: closed to isolate the pressure boundary, and reopened when;the sealing process wasto begin. Mock-up training sessions were. conducted to familiarize workers with the repair procedure and the Jconfiguration of the. involved components. W/R 3109 MES was originated to

. implement this modification.

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  • 10n, September-13 at:1200 hours, Unit 2 entered Mode 3 to. allow c: ETNA repair work

'to begin. At'approximately 2130 hours0.0247 days <br />0.592 hours <br />0.00352 weeks <br />8.10465e-4 months <br />, a pre-job meeting was held between-(Radiation protection (Rp), MES, Maintenance,'and Utilities Support Specialist,

.Inc)--(USSI)/ who had been contracted by Duke power to perform the repair work.

,,p i:Rp requested that the area be cleaned prior to work beginning so that the Dinit'ial part of the job'could be performed without respirators and additional-protective wear. The cleaning'was completed at approximately 2300 hours0.0266 days <br />0.639 hours <br />0.0038 weeks <br />8.7515e-4 months <br />. 'Also q

-during~ pre-job; preparations, each sealant injection ~ valve was cycled several' times to' ensure proper; operation.

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on September,.14 at;approximately 0020 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />, USSI personnel entered the area to

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begin: work on CETNA #76.. 'The initial-drilling was performed, the hole was'

. tapped, and'the sealant injection valve was: inserted. At approximately 0200 V,

hours the final' drilling into the NC system pressure boundary was completed.

As.

'theLdrill bit wastretracted from the hole, USSI personnel attempted to close the

.-sealant injection valve, but th'e valve would not close. They then screwed a isecond sealant injection valve into the back of the-first valve, while holding

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-the: first ; valve in place. -When the first valve was released 1n order to close the1second: valve, the entire essembly ejected from the hole. =Within minutes, a

~ conter punch was ' tapped einto t he hole to attempt to plug the opening. -Leakage was reduced but-did not stop :ompletely. USSI personnel left the area at this

~ time to locate another size r. enter punch to better plug the hole. At j

L approximately 0305Jhours, UFSI attempted to' insert a center punch with a.187 inch diameter, but-was 'unst.ccessful. The original center punch was reinserted, again reducing the leak'bst not completely stopping it.

4-Soon after the problem (occurred, the Shift Manager, Shift Supervisor,'MES,-and Maintenance met to evaluate the NC system leakage. A conservLtive decision was reached to considerLthe loakage as NC system pressure boundart 1sakage. The T/S 3.4.6.2 action statement was entered and preparations began far cooldown to Mode

' 5.

m On September.14 at 0710 hours0.00822 days <br />0.197 hours <br />0.00117 weeks <br />2.70155e-4 months <br />, operations commenced cooldown to Mode 5.

Also at this-time,:an Unusual: Event was declared and proper notifications were made per

= Catawba Emergency Response procedures. Even though leakage had been reduced by W

' installation of the center punch, efforts continued to minimize the leakage'to prevent contamination of.other components in the area.

O On September 14 at 1428 hours0.0165 days <br />0.397 hours <br />0.00236 weeks <br />5.43354e-4 months <br />, Unit 2 entered Mode 4.

on September 14 at approximately 1530 hours0.0177 days <br />0.425 hours <br />0.00253 weeks <br />5.82165e-4 months <br />, USSI personnel installed a modified-m#D C-clamp in place of the center punch at CETNA #76 in order to minimize leakage.

This reduced leakage even:further, but not completely.

'On September 14 at 2338 hours0.0271 days <br />0.649 hours <br />0.00387 weeks <br />8.89609e-4 months <br />, Unit 2 entered Mode 5 and the Unusual Event was terminated.

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Following-Unit.2:cooldown to Mode 5, CE;and Gray Tool' representatives were..

onsite to assist"in'the final CETNA repair work. 'While inspecting the spare 3

modified blind hubs manufactured by CE, it was determined that the hubs,did not' meet tholdimensiona11 tolerances required for these' parts. 'After evaluation,>1t was also determinedithat -the: dimensional error would-have prevented. proper seal seating-contact:when installed. The original' hubs manufactured by Gray Tool' twere checked'and no dimensional problems were.found. -All.five CETNAs were subsequently checked to verify which hub (CE or Gray Tool) was currently.

installed.: CETNAs 874, 76, and 78 had hubs manufactured by C", and #75~and 77' had'the' original hubs manufactured by' Gray Tool. The original Gray 20n1 hubs for; connectors #74,c76,.and 78 were located,-cleaned, and inspected. No dimensional problems. wore found, and the hubs were approved for rouse.

Onl September '21,! the original modified blind hubs manufactured by Gray Tool were-

~ installed at.CETHAs.N74,176, and 78. -After this replacement was complete, all five. Unit 2 CETNAs-had-dimensionally acceptable hubs in place.

On September 25 at 2318 hours0.0268 days <br />0.644 hours <br />0.00383 weeks <br />8.81999e-4 months <br />, Unit 2 entered Mode 4.

On September 26 at approximately 1530 hours0.0177 days <br />0.425 hours <br />0.00253 weeks <br />5.82165e-4 months <br />, Maintenance inspected all five

CETMAs:for leakage. No leakage was noted.

On September-27 ats0449 hours0.0052 days <br />0.125 hours <br />7.423942e-4 weeks <br />1.708445e-4 months <br />, Unit 2-entered Mode 3.

At approximately 2130 hours0.0247 days <br />0.592 hours <br />0.00352 weeks <br />8.10465e-4 months <br />, Maintenance again inspected all five CETNAs..No leakage was noted.

CONCLUSION LWhile attempting to repair the leaking CETNAs, the sealant-injection valve installed at the tK: system pressure boundary would not close. A second valve

-was-threaded <into the back<of-the. original.valvo, but before the second valve could be' closed the' entire assembly ejected from the hole. MES will perform a root' cause analysis to deterndne the cause(s) of' the failures associated with the sealant injection valve. This report will'be revised upon~ completion of this analysis'.

The: original;CETNA' leaks are attributed to a Manufacturing Deficiency in that the modified blind; hubs manufactured by CE did not meet required dimensional tolerances. The' original hubs manufactured by Gray Tool were-checked-and met' the dimensional requirements. Inspection of all five CETNAs revealed that #74, 76, and 78'had-hubs supplied by CE.

These CETNAs'were' identified as the ones that had' experienced leakage..The original hubs manufactured by Gray Tool were located,1 cleaned,;and; inspected. ;No,dimoncional problems were noted and they H'

were installed'on! Unit 2.

All:five Unit 2 CETNAs'now have dimensionally acceptable modified blind hubs installed. During subsequent startup preparations, Maintenance inspected all five CETNAs in Mode 4, and again in Mode 3, for. leakage. No leakage was noted.

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E After investigations concerning the improperly manufactured hubs, CE feels that the improper hubs are isolated to Catawba-2, Millstone-3, and CE-Stock. All Limproper hubs,at Catawba have been located.

In addition, CE contacted Millstone-3lto advise them of the, improper hubs. The Duke Power Quality

' Assurance Vendor Division has been contacted and advised of this problem.

.Thtl decision to consider the leakage as Reactor Coolant System pressure boundary.

leakage, and the resultant Unit cooldown 'and declaration of an Unusual' Event,

  • ,'3 was a conservative action not' strictly required by' Catawba Technical-j,; (,

' Specifications. Pressure-boundary leakage limits are established to preclude growth of defects to the point where coplant leak rates. pose a threat to nuclear-safety. Unit shutdown ~is required before crack propagation recults in'.

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-potentially limiting leak rates'.

The drilling of a 3/16 inch diameter hole 1s l

_'not-considered.to have posed a demonstrable potential for propagation., Leakage through the drilled hole was well-within the capability of the normal charging

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_ system _and posed no danger to unit safety. This event was conservatiYely-

. reported to the NRC under'the provisions of 10CFR50.72. This' report is l' "

_ sub:nitted as a Special Report and is not required under 10CFR50.73.

This oventLwas cons'idered for reportability under the requirements of 10CFR Part

-211with the conclusion that cxistence of a substantial: safety hazard was not demonstrated. Leakage through the CETNA was of a magnitude that'would have

remained.well within the capability of.the normal charging system. The

_ potential for a' catastrophic failure of the CETNA,J1eading to a loss of coolant accident and. safety system challenge, was not created as a result of the

.out-of-tolerance fittings Further,-the vendor concluded that only two plants,_

,-Catawba Unit 2-and Millstone Unit 3, could potentially have the out-of-tolerance parts. - Thus, it was concluded that a Part 21' report was not required. This report is submitted as a Special Report to ensure industry awareness of this

= event.

A' review of the OEP database for the past 24 months revealed one event.in which' an operating. Unit was shutdown due.to a Manufacturing Deficiency (LER 413/90-24). This ' incident involved a Nuclear Service Water [EIIS:BI] (RN)

System purp [EIIS:P) motor,[EIIS:MO] for which a stator had been manufactured

'approximately.0.1 inches shorter than required. Two other events in this time period were_ attributed'to Manufacturing Deficiencies. LER 414/89-01 involved a

. Reactor Trip due to a fuse that failed on a feedwater control valve. LER 413/89-26 documented an unexpected Hydrogen Skinner Fan [EIIS:BLO] breaker

[EIIS:BRK] trip due to a defective Westinghouse breaker. These two incidents are different-from.the incident in this= report in that they were not attributable to dimensional requirement inaccuracies. Per Nuclear Safety

? Assurance-guidelines, this11s not a recurring problem.

, CORRECTIVE ACTION-SUBSEQUENT 1)'After the sealant injection valve assembly ejected from the NC system pressure boundary, Unit 2 commenced cooldown to Mode 5 and an Unusual Event was declared.

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2) During: subsequent investigations, the spare modifiSd blind hubs

. q) manufactured by CE'were inspected'and'it was determined that they did notf meetthedimensionalreq0irementsforthesepqrts, f

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3) The original ~ hubs manufactured,hv Gray *.,ol'were inspected. I No dime'nsional' problems were noted, e

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-4) All five, Unit.2 CETNAs wore inspected to determine whether CE or Gray Tool $

hubs were installed. -CETNAs #74, 76, and 78 were identified as having CE:

hubs installed.

'5) The original Gray Tool hubs for CETNAs'#74, 76, and 78 were lo'cated,-

_ cleaned, and_ inspected. All were acceptable for installe.cion on_ Unit 2, 4?:'

and-were installed per W/R 5312 SWR.

6) Maintet.snce inspected all five CETNAs for leakage during Mode 4,'and againt in Mode 3.

Noileakage was noted.

~7)-The~Duk'e PewerLQuality Assurance Vendor Division was. contacted and-advised

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-of the prob.' ems concerning the hubs manufactured by CE.

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-PLANNED

'1) An analysis will be performed'to dotermine the cause(s) of-the failures

' associated with the sealant injection valvo.

2) This report will be revised upon completion of the sealant injection-valve canalysis.

1 SAFETY ANALYSIS 4

1 1 Following;this. incident, Performance conducted a; review of Operator hid Computer

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.'(OAC)= data to establish the leakage' rate at.the~ repair location. An initial

_jW reviewfindicated that NC system leakage at the.CETNA was'6'to 9 gpm. After a detailed _ review lof plant evolutions in progress during the incident,' the' actual 3-

. leakage rate was determined toibe les3 than 5.gpm.

A leak of this magnitude is well within normal' charging pump cap.bility-(approximately 150 gpm)-and falls.

'welltbelow the limits of a smell'h nak Loss of Coolant Accident'(LOCA)~. The; actualthole. diameter (.1875 inches) was less than the hole size of.375 inches

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_ considered in Section 15.6.5-of the Catawba Final Safety Analysis Report (FSAR);

for'which NC system inventory-can-be maintained by one-charging pump.

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LThe_ health and safety of tho'public were not affected by this incident.

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