DEFENSE NUCLEAR FACILITIES SAFETY BOARD

March 25, 1994

MEMORANDUM FOR:G. W. Cunningham, Technical  Director

COPIES:        Board Members

FROM:          Steven Stokes

SUBJECT:       Storage of Spent Ion Exchange Columns from the Hanford Site K-
               East and K-West Basins

1. Purpose:  This memorandum describes concerns with potential hydrogen
   accumulation resulting from the storage of spent ion exchange columns
   generated at the Hanford SiteK-East and K-West Basins.

2. Summary:  The current storage configuration of spent ion exchange resin
   columns from the K-Basins recirculation system has not been adequately
   assessed to determine if the build-up of explosive mixtures of hydrogen gas
   is possible.  An unreviewed safety question determination was performed to
   assess the storage of these columns in a chlorine vault in the K-West area
   but it failed to address the potential for buildup of hydrogen within this
   structure.

3. Background:  The K-basins water recirculation systems utilize replaceable
   filtration and ion exchange columns to remove particulate matter to 5 æm and
   soluble radioactive species, i.e.,  Cs-137 and Sr-90.  The lack of an
   approved disposal container has resulted in the interim storage of 39 spent
   ion exchange columns in a chlorine vault in the K-West area.  This interim
   storage configuration was initiated 3 years ago with the storage of 27 spent
   ion exchange columns.  Periodically, additional spent columns have been
   generated raising the total to the current level of 39.  Spent ion exchange
   resins generate hydrogen gas as a result of radiolytic decomposition of
   water and spent resin.  The long-term storage of these resins in the
   chlorine vault was questioned to ascertain if the appropriate safety
   considerations, i.e., the potential build-up of hydrogen gas, had been
   considered. 

4. Discussion/Observations:  The need for interim storage of spent ion exchange
   columns is a direct result of the failure to develop a waste management
   strategy for this waste stream.  About three years ago, the method used for
   determining if spent ion exchange columns were transuranic (TRU) waste was
   found to be incorrect. The TRU waste determination had been based on the
   activity of TRU radionuclides per total weight of the waste package rather
   than just the activity of TRU radionuclides per weight of waste matrix.  
   This necessitated an interim storage requirement until an adequate waste
   package could be developed and approved.   

   The current storage configuration includes placement of the spent columns
   in a burial box; these columns are vented via an activated carbon filter. 
   The burial box is then placed inside the chlorine vault.  The chlorine vault
   is a cement structure, which had been used to store a chlorine filled rail
   car (the chlorine was used for disinfection of potable water used in the K-
   West area).  

   The generation of hydrogen gas from spent ion exchange resins is a fairly
   well understood phenomenon and is based upon the radiolytic decomposition
   of water and ion exchange resin by alpha, beta, and gamma radiation.  This
   decomposition results in the formation of hydrogen gas, hydrogen peroxide, 
   and other decomposition products.

   The potential, therefore, exists for the buildup of hydrogen gas to
   explosive levels within the chlorine vault if the facility is not properly
   ventilated.  Based on interviews with Westinghouse Hanford Company (WHC)
   representatives of the K-Basin Waste Management Group and the review of the
   unreviewed safety question determination, the staff  determined  that no
   assessment has been done of  the potential for hydrogen buildup within the
   chlorine vault.  The staff believes that this is a significant safety issue
   that should have been addressed given the prolonged storage period in the
   chlorine vault.

   Other issues that result from decomposition of the ion exchange resin
   include:

          release of bound water, radionuclides, and chemically active
           soluble decomposition products due to excessive lifetime radiation
           doses to the resin (the Nuclear Regulatory Commission has
           established a 108 rad lifetime dose limit to reduce the impact of
           radiolytic decomposition of the resin); and

          a reduction in pH within the resin bed, which can increase
           corrosion concerns.

   These issues are not as immediate as the generation of hydrogen, but are
   important considerations for the disposal of these wastes.

5. Future Staff Actions.  The assessment of the safe-storage of the ion
   exchange columns in the chlorine vault will be followed closely. 
   Additionally, the disposition of these wastes will be monitored to ascertain
   if adequate precautions are taken to minimize potential impacts to public
   health and safety.