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PrintHome > NRC Library > Document Collections > Generic Communications > Information Notices > 1993 > IN 93-63 Information Notice No. 93-63: Improper Use of Soluble Weld Purge Dam Material                                 UNITED STATES                         NUCLEAR REGULATORY COMMISSION                     OFFICE OF NUCLEAR REACTOR REGULATION                            WASHINGTON, D.C. 20555                                August 11, 1993NRC INFORMATION NOTICE 93-63: IMPROPER USE OF SOLUBLE WELD PURGE DAM MATERIALAddresseesAll holders of operating licenses or construction permits for nuclear powerreactors.PurposeThe U.S. Nuclear Regulatory Commission (NRC) is issuing this informationnotice to alert addressees to the potential consequences of improper use ofsoluble weld purge dam material inside piping to prevent water from reaching aweld location.  It is expected that recipients will review the information forapplicability to their facilities and consider actions, as appropriate, toavoid similar problems.  However, suggestions contained in this informationnotice are not NRC requirements; therefore, no specific action or writtenresponse is required.BackgroundOn February 21, 1985, the NRC staff issued Information Notice 85-13,"Consequences of Using Soluble Dams."  Before that, the NRC staff had issuedInformation Notice 81-07, "Potential Problem With Water-Soluble Purge DamMaterials Used During Inert Gas Welding," on March 16, 1981.  Theseinformation notices described problems with two types of soluble dam material. Description of CircumstancesOn May 1, 1993, personnel at the Edwin I. Hatch Nuclear Plant, Unit 1 wereincreasing reactor temperature and pressure at the end of a refueling outageto conduct a Class 1 system leakage test in accordance with Section XI of theAmerican Society of Mechanical Engineers Boiler and Pressure Vessel Code.  Allcontrol rods were fully inserted, reactor coolant temperature was about 63� C[145 �F], and reactor pressure was about 800 kilopascal (kPa) [115 pounds persquare inch absolute (psia)].  A low reactor water level full reactorprotection system actuation signal and a partial Group II isolation actuationoccurred unexpectedly because the "B" channel reactor water level instrumentswere indicating erroneously low reactor water levels.  The "A" channelinstruments and instruments supplied by other reference legs indicated"upscale" and high levels as expected since the reactor vessel had beenflooded for the leakage test.  The control room recorders for the "B" channelindications initially indicated "onscale" and decreasing.  9308030274.                                                            IN 93-63                                                            August 11, 1993                                                            Page 2 of 3After some time, the "B" channel reactor water level indications slowlyreturned to the "upscale" readings and the reactor protection signals werereset.  The heatup was stopped, the "B" channel reactor water levelinstrumentation was declared inoperable, and an investigation was conducted. Operators made several unsuccessful attempts to correct the problem.  Duringbackfilling of the "B" channel reference leg with a hydrostatic test pump,pressure increased to about 2500 kPa [365 psia] and then suddenly decreased tobelow 800 kPa [115 psia].  This decrease was attributed to the clearing ofsome type of blockage from the reference leg.  DiscussionThe investigation showed that the most likely cause of the blockage wassoluble weld purge dam material that had not been used properly during amodification of the piping associated with the "B" channel condensing chamber. The modification required cutting out and then rewelding sections of thereference-leg piping.  To complete this work, a temporary plug had beeninstalled in the associated reactor vessel penetration, but did not provide acompletely watertight seal.  To perform a dry weld on the reference leg, thesoluble weld purge dam material was used to plug the reference leg near theweld location.  The welders rolled the material into a plug several incheslong and forced it into the 2.5 centimeter [1-inch] diameter reference-legpiping.  The soluble weld purge dam material is Dissolvo WLD-35, but is frequentlycalled rice paper.  It is intended to contain or dam weld purge gas insidepiping at a weld location.  Once the weld is completed, the piping is filledwith water and the paper is supposed to dissolve completely.  Plant managersat Hatch consider the use of the material to absorb small quantities of wateran acceptable welding practice.  A licensee event review team concluded that the rice paper had not dissolvedcompletely because air was trapped on the downstream side of the roll, whichprevented the paper from becoming saturated.  Testing with models of similarpiping arrangements and material showed that significant periods of time couldelapse before the material dissolved completely.  Dissolution of the paper isdependent on sufficient exposure to water, and large accumulations of tightlypacked rice paper could prevent the paper from dissolving completely.  Testingsuggests that the length of a plug of the material should be limited to lessthan 2.5 centimeters [1 inch].  When contacted, the vendor for the materialconfirmed that the length of the material should not be more than one pipediameter to ensure that it dissolves completely.  The licensee initiated corrective actions, including requirements for post-maintenance functional testing to ensure that the material has dissolvedcompletely whenever it is used to plug piping.  Training will be conducted toprovide guidance on the appropriate quantity of material to use in suchapplications.  This issue is discussed in Licensee Event Report 50-321/93-006and in NRC Inspection Report 50-321,366/93-06. .                                                            IN 93-63                                                            August 11, 1993                                                            Page 3 of 3The event described above serves to highlight the potential consequences ofimproper use of soluble weld purge dam material.  Failure to provide adequateinstructions to workers and inadequate post-maintenance functional testing canresult in blockage of piping and inoperability of systems.  This information notice requires no specific action or written response.  Ifyou have any questions about the information in this notice, please contactthe technical contact listed below or the appropriate Office of NuclearReactor Regulation project manager.                              ORIGINAL SIGNED BY                              Brian K. Grimes, Director                              Division of Operating Reactor Support                              Office of Nuclear Reactor RegulationTechnical contact:  Len Wert, RII                    (912) 367-9881Attachment:  List of Recently Issued NRC Information Notices.Page Last Reviewed/Updated Tuesday, November 12, 2013Home- News   Releases
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