TRANSMITTED TO DOE/M. WHITAKER 7/5/95

DEFENSE NUCLEAR FACILITIES SAFETY BOARD

April 26, 1995

MEMORANDUM FOR:     G. W. Cunningham, Technical Director

COPIES:        Board Members

FROM:               Richard E. Tontodonato, Technical Staff

SUBJECT:       Trip Report - Review of Hanford Site High-Level Waste Tank Safety and
               Characterization, March 14-16, 1995

1.     Purpose:  This trip report documents a visit by Board staff members (David Lowe, Randall
       Robinson, and Richard Tontodonato) to the Hanford Site on March 14-16, 1995, to review
       Westinghouse Hanford Company (WHC) efforts to develop a new approach for
safety-related characterization of Hanford's high-level waste tanks.

2.     Summary:  WHC is continuing to develop a new approach for safety-related characterization
of  Hanford's high-level waste tanks that would significantly reduce sampling requirements.  The
       new strategy would declare a tank safe, based on the characteristics of the waste surface and
       the absence of flammable or toxic vapors in the tank dome space.  The principal difficulty
       with this approach is that it requires deducing and analyzing all possible hazardous
       conditions in tanks which have not been characterized.  Significant portions of the new
       strategy are based on simplified models and simulants that may not adequately represent tank
       wastes, and WHC has not determined how or when postulated waste properties will be verified  with actual tank
waste samples.

3.     Background:  Characterizing the tank wastes is key to resolving high-level waste tank safety
       issues at the Hanford Site.  On July 19, 1993, the Board issued Recommendation 93-5, which
       addresses the need for the Department of Energy (DOE) to undertake a comprehensive
       reexamination and restructuring of the characterization effort.  The recommendation sets
       goals of two years for completing safety-related sampling and analysis for watch list tanks
       and three years for other tanks.  The Board accepted DOE's Implementation Plan on March 25,
       1994, and members of the Board staff have visited the Hanford Site seven times since November
       1993 to review implementation of Recommendation 93-5.  This review was conducted as a follow-
       up to the previous reviews and in preparation for a public hearing held in Richland,
       Washington, on March 29, 1995.

4.     Discussion:

  a.   High-level waste tank safety strategy:  In the original Data Quality Objectives (DQO)
       documents prepared in accordance with the DOE Recommendation 93-5 Implementation Plan,
       WHC proposed to determine whether the high-level waste tanks were safe by sampling and
       analyzing full-depth core samples from each tank.  Based on difficulties subsequently
       encountered in obtaining core samples and on a desire to minimize tank sampling, WHC is
       now developing a justification for only obtaining surface and vapor samples from most
       tanks.

       This approach requires that WHC deduce all possible hazardous conditions which could have
       developed in the tanks over the past fifty years and assess whether or not vapor and
       surface sampling can adequately detect them.  This difficult task is further complicated
       by the limited information available regarding the exact nature of the tank wastes. 
       Sampling to date has been limited, and historical records are typically not complete,
       reliable, or necessarily representative due to inadequate operational controls in the
       past as well as chemical and radiolytic processes occurring in the tanks.  Because of
       these problems, WHC has relied extensively on simplified models and simulants to develop
       the new strategy.  Key elements of the strategy and their shortcomings are summarized
       below:

       1. Accident initiators:  WHC's surface sampling strategy assumes that accidents can
          only be initiated by events in the tank dome space or on the waste surface.  This
          requires defining the depth beneath the surface which can be affected by a surface
          initiator as well as analyzing the potential for subsurface initiators.

          A consultant to WHC presented a simplistic analysis of how a surface event (e.g.,
          a hot object falling onto the waste) can affect material below the waste surface. 
          The event was modelled as purely conductive heat transfer between two infinite
          planes at different temperatures.  The analysis concluded that only the top four
          inches of waste are likely to be affected by surface events.  Although WHC agreed
          with this conclusion, this analysis is flawed.  A review by the Board staff found
          that the consultant did not analyze the chosen model correctly, underestimating the
          affected depth by more than a factor of two.  Further, the model assumes the waste
          surface is a uniform, impenetrable solid.  Convective heat transfer is neglected,
          as are cracks and holes in the surface and the likelihood that an impacting object
          will penetrate some depth into the waste.

          If the waste below the surface is dry and reactive, a subsurface initiator such as
          a local hot spot, criticality excursion, electrical short, or lightning strike on
          an instrument tree or other equipment in the waste could set off a runaway chemical
          reaction.  WHC has analyzed the potential for hot spot formation in ferrocyanide
          sludges and concluded it is unlikely, but the likelihood of forming hot spots in
          other waste types has not been assessed.  WHC has also evaluated the initiation
          potential for equipment in the tanks, criticality, and lightning, and concluded that
          lightning was the only credible subsurface initiator that was not already mitigated. 
          WHC as not yet decided what must be done to ensure lightning will not cause tank
          accidents, and it is not clear when a course of action will be defined.  As stated
          in the report of the February 28 - March 2, 1995, staff review of tank farm
          electrical systems, this problem warrants prompt attention.

       2. Fuel-nitrate reactions:  The proposed strategy will not attempt to determine which
          tanks contain reactive mixtures of fuels and oxidizers, such as non-volatile organic
          materials and/or ferrocyanide compounds mixed with nitrates.  Instead, WHC intends
          to assess whether the waste surface is wet enough to preclude propagating exothermic
          reactions.  This approach requires understanding how water is distributed in the
          tanks and how much water is required to prevent reactions from propagating.

          WHC believes that saltcake wastes may become dry and plans to assess whether
          saltcakes contain enough fuel to present a  hazard.  However, WHC believes that
          sludges, with few exceptions, are uniformly wet and will remain wet for the
          foreseeable future.  These conclusions are based on studies of moisture retention
          in kaolin clay, limited work with ferrocyanide sludge simulants, the limited
          sampling results currently available, and modelling of evaporation processes in
          tanks.  WHC believes that most sludges contain small (micron range) particles,
          resulting in capillary forces that are strong enough to preclude global water loss
          and prevent dryout of locally heated regions.  However, WHC acknowledges that
          shallow tanks and tanks with higher decay heat loads may still become dry.  In fact,
          low moisture contents have been found in several sludge samples (1 to 17% in tank
          241-BX-101, 3 to 9% in tank 241-BX-108, as low as 13.5% in tank 241-C-103).  The
          staff believes that WHC's conclusion that sludges are uniformly wet needs to be
          verified by a core sampling program that explores the relevant variables (e.g.,
          sludge type, decay heat load, waste height, interim stabilization, etc.) in actual
          waste tanks.  WHC agrees that actual wastes need to be more thoroughly investigated,
          but has not yet decided how to do this.

          WHC is also testing waste simulants to define the energy content of ferrocyanide
          compounds and various organic constituents in wastes.  This testing defines the fuel
          concentration required to sustain a propagating exothermic reaction in dry materials
          and the amount of water needed to prevent such reactions.  A WHC consultant has
          developed a thermodynamic model showing that the energy content required to sustain
          a propagating reaction is directly proportional to the ignition temperature of the
          material.  Based on this model, WHC has concluded that wastes with an energy content
          below 290 calories per gram or containing greater than 20 weight percent moisture
          cannot sustain a propagating reaction.  Experimental results for several simulant
          materials support both criteria.

          However, testing with actual wastes has been limited to specimens too small for
          propagation tests, and it has not been proven that the simulants accurately
          represent the propagation behavior of real wastes.  Furthermore, the staff believes
          that WHC has not adequately shown that its propagation model will be conservative
          when applied to real wastes.  The principal staff concerns are summarized in the
          appendix to this report.

       3. Other organic reactions:  Organic liquids in the tanks have the potential to undergo
          pool fires or, if entrained in saltcake or sludge, wick-stabilized fires.  WHC
          believes liquid organics can be detected by vapor sampling.  While significant
          organic pools will likely emit detectable vapors, WHC has not defined the screening
          criteria for organic vapors.  Also, it has not been demonstrated that vapor sampling
          will reliably detect organic liquids entrained in sludge or saltcake.

       4. Flammable gases:  WHC plans to continue screening for flammable gases using vapor
          sampling at a single location in each tank.  This appears to be adequate for
          assessing the steady-state flammable gas concentration.  Continuous hydrogen
          monitoring instruments have been installed in all tanks suspected of undergoing
          periodic gas releases based on observed level fluctuations.

  b.   Tank characterization technical basis:  WHC stated that the DQO for safety-related tank
       waste characterization will be completed by April 1995, and the DQOs for waste retrieval
       and disposal will be completed by June 1995.  Overall integration of the sampling program
       is scheduled for August 1995.

  c.   Tank sampling status:  WHC is still far behind the sampling milestones DOE committed to
       in the Recommendation 93-5 Implementation Plan.  As of March 13, 1995, the following
       sampling has been accomplished:

              Rotary mode core sampling - 1 tank, variable recovery
              Push mode core sampling - 2 tanks good recovery, 2 tanks poor recovery
              Auger sampling - 10 tanks, variable recovery
              Liquid grab sampling - 21 tanks
              Vapor sampling - 26 tanks

       WHC personnel believe they now understand which types of waste are suitable for push mode
       sampling and expect to achieve more consistent results in future push mode attempts. 
       WHC has restricted the rotary mode sampler to push mode operations due to poor sample
       recovery in segments requiring rotary drilling.  WHC has consulted with the Army Corps
       of Engineers and also assembled a Tank Sampling Advisory Panel to provide recommendations
       on improving the existing core and auger samplers and developing new tools.  WHC is
       currently evaluating a list of 40 suggestions from these reviewers.  WHC has also
       assessed ways to improve the availability of the rotary mode system and is evaluating
       47 potential improvements.  By June 1995, WHC plans to field test improvements to the
       rotary mode system on an actual tank.

  d.   Laboratory issues:  Because of the slower than expected pace of tank sampling, WHC no
       longer plans to use the PNL 325 laboratory or the Idaho National Engineering Laboratory
       (INEL) for routine tank waste sample analyses.  WHC does not expect to use INEL in the
       future, and expects to use the PNL 325 laboratory for research and development work and
       for unique analyses not available at the WHC 222-S laboratory.  The associated reduction
       in the PNL 325 workforce, coupled with the difficulty of locating and hiring qualified
       radiochemists, could make it difficult for the analytical laboratories to keep up with
       sampling operations if WHC succeeds in significantly improving the sampling rate.

5.     Future Staff Actions:  The staff will continue to closely follow implementation of
       Recommendation 93-5.  The staff plans to conduct a video conference with WHC and DOE in late
       April or early May 1995 to further discuss proposed revisions to the characterization program
              strategy and efforts to improve sampling techniques.APPENDIX

                                        
           Staff Concerns with Proposed Westinghouse Hanford Company
                         Moisture and Energetics Limits
                                        
The new limits Westinghouse Hanford Company (WHC) has proposed to identify wastes which may
undergo runaway chemical reactions are based entirely on testing of simulant materials with much
simpler compositions than actual wastes.  Testing with actual wastes has been limited to specimens
too small for propagation tests, and it has not been proven that the simulants accurately
represent the propagation behavior of real wastes.  Furthermore, the Defense Nuclear Facilities
Safety Board (Board) staff believes that WHC has not adequately shown that its propagation model
will be conservative when applied to real wastes.  The principal Board staff concerns are
summarized below:

       The 290 calories per gram energetics criterion was obtained using data for sodium
       acetate, which has the highest ignition temperature of any simulant tested.  Using the
       ignition temperature for any of the other simulant materials (e.g., ferrocyanide or
       hydroxyethylethylenediaminetriacetate (HEDTA)) would result in a considerably lower
       safety limit.  WHC's consultant used the ignition temperature for sodium acetate because
       he believed it provided a "reasonable (not too conservative)" energy limit.  While this
       limit is conservative relative to the simulant test data, it has not been shown that it
       will be conservative relative to actual waste behavior.

       Propagation testing used nominally dry reagents, but the actual starting moisture content
       of organic simulants was not determined.  Water absorbed or adsorbed onto the starting
       materials will inhibit propagating reactions.  This will result in overestimating the
       energy needed to start a reaction in dry material and underestimating the amount of water
       needed to prevent a reaction.  (Moisture measurements for tank waste samples are done
       using thermogravimetric analysis, which will detect all absorbed water and some of the
       adsorbed water.)

       WHC has not estimated the significance of other errors built into the model.  The model
       assumes the starting temperature of the wastes is negligible (i.e., 0 C), whereas the
       actual wastes have temperatures up to 94 C (tank 241-SX-108).  The model also assumes
       that the heat capacities of the reactants and the combustion products are equal, and used
       average (not worst case) simulant heat capacities instead of actual waste properties. 
       Similarly, the magnitude and effect of errors in measuring ignition temperatures and
       other test parameters have not been considered.