United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 96-13: Potential Containment Leak Paths Through Hydrogen Analyzers

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF NUCLEAR REACTOR REGULATION
                          WASHINGTON, DC  20555-0001

                               February 26, 1996


NRC INFORMATION NOTICE 96-13:  POTENTIAL CONTAINMENT LEAK PATHS THROUGH
                               HYDROGEN ANALYZERS


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 potential containment leak paths through
hydrogen analyzers. 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.

Description of Circumstances

On September 13, 1995, the licensee for Catawba Nuclear Station determined
that leakage from an internal component in a Unit 1 hydrogen analyzer panel
exceeded the containment bypass leakage limits specified in the technical
specifications (TS).  Testing, performed in response to several other
containment integrity concerns with the hydrogen analyzer systems, showed that
the source of the bypass leakage was a defective pump shaft seal on a sample
pump located inside the hydrogen analyzer cabinet in the auxiliary building.  

Two redundant hydrogen analyzer systems are installed at each unit at Catawba
to provide continuous indication of hydrogen concentration inside the
containment after a design-basis accident.  The analyzer panels are Teledyne
Analytical Instruments and are located in the auxiliary building adjacent to
the containment.  Each hydrogen analyzer system is connected to the
containment atmosphere with inlet instrument tubing that draws the sample
stream to the analyzer panel and with outlet tubing through which the sample
stream is returned to the containment atmosphere.  The inlet and outlet tubing
is isolated at the containment boundary by two containment isolation valves in
series on each line that do not receive an automatic containment isolation
signal.  The internal components of the analyzer panel also consist of
isolation valves, a small positive displacement pump, and an analysis volume. 
In standby conditions, containment isolation valves located on the inlet and
outlet lines are normally closed and the hydrogen analyzer is deenergized with
the internal isolation valves closed and the sample pump off.  After an
accident, emergency procedures direct the inlet and outlet isolation valves to
be opened and the hydrogen analyzer panel to be energized to begin sampling 


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                                                            February 26, 1996
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the containment atmosphere.  When the hydrogen analyzer panel is energized,
the internal isolation valves open and the sample pump starts. 

The licensee did not recognize during the development of the local leak rate
test and post-maintenance test procedures for the hydrogen analyzer
penetrations that the hydrogen analyzer panel was required to be energized and
its sample pump disabled to fully test the system as a containment boundary. 
Failure to energize the panel during leak rate testing results in an
incomplete containment boundary configuration and can allow an undetected
potential containment bypass path to exist.  The licensee analysis of the
potential dose consequences of the hydrogen analyzer containment bypass as-
found leakage showed that the calculated control room operator exposure from a
design basis accident would not exceed the criteria of General Design
Criterion 19 of Appendix A to Part 50 of Title 10 of the Code of Federal
Regulations (10 CFR) and calculated offsite exposures from a design basis
accident would not exceed the exposure guidelines of 10 CFR Part 100.

The licensee also identified a containment integrity concern associated with
the periodic calibration testing of the hydrogen analyzers.  The licensee
recognized that calibration testing allows a vent path from the containment
into the analyzer that was not Type C tested and would not automatically
isolate during a design-basis accident.

On November 9, 1994, the licensee for Braidwood Station, Unit 2, completed a
containment integrated leak rate test.  For this test, the 1/4-inch nominal
containment penetration hydrogen sensing lines for both trains were
disconnected outboard of the closed containment isolation valves, and a
balloon was placed on the end of each line to identify any leakage.  The
procedure did not specify whether to disconnect the sensing line inside the
hydrogen monitor cabinet or outside.  The operators who lined up the test
disconnected the lines inside the cabinet.  The licensee's investigation
concluded that when other operators restored the system after the test, they
observed the exterior sensing lines and assumed that the lines had been
reconnected.  Therefore, the sensing lines remained disconnected inside the
cabinet.  On January 31, 1995, the operations department wrote a problem
identification report to identify a growing difference in the hydrogen
readings on the A and B trains that are taken every shift.  On February 15,
1995, during troubleshooting, the A train lines were found to be disconnected,
approximately 3 months after they were disconnected.  

The hydrogen monitors at Braidwood are normally isolated.  However, during a
loss-of-coolant accident, the emergency operating procedures direct the
operators to put them in service to monitor containment hydrogen
concentration.  This would create an unfiltered release path from the
containment to the auxiliary building.  The licensee calculated that
regulatory limits would be exceeded within 3 hours if both monitors were
disconnected and within 5 hours if only one monitor were disconnected.  Area
radiation monitors near the hydrogen monitors and radiation monitors in the
auxiliary building exhaust would assist the operators in identifying the leak. 



                                                            IN 96-13
                                                            February 26, 1996
                                                            Page 3 of 3


Discussion

Because containment penetrations, systems, and equipment that will be exposed
to the containment atmosphere must be leak rate tested to ensure that
containment integrity is maintained after a design-basis accident, the 
procedures for these tests must adequately consider the penetration
configuration.  Additionally, because hydrogen monitor containment isolation
valves are normally procedurally opened after a design-basis accident, any
leakage in the hydrogen monitor system may bypass the containment and can
challenge regulatory radiological exposure guidelines.

This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation project manager. 


                                          signed by

                                    Dennis M. Crutchfield, Director
                                    Division of Reactor Program Management
                                    Office of Nuclear Reactor Regulation

Technical Contacts:  Peter Balmain, Region II
                     (803) 831-2963
                     Internet: pab1@nrc.gov
      
                     James Pulsipher, NRR
                     (301) 415-2811
                     Internet: jcp2@nrc.gov

                     John R. Tappert, NRR
                     (301) 415-1167
                     Internet: jrt@nrc.gov
Page Last Reviewed/Updated Thursday, November 21, 2013