United States Nuclear Regulatory Commission - Protecting People and the Environment

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