SENT TO M. WHITAKER 06/04/96

DEFENSE NUCLEAR FACILITIES SAFETY BOARD                          

                                               January 29, 1996

MEMORANDUM FOR:    G. W. Cunningham, Technical Director

COPIES:            Board Members

FROM:              C. H. Keilers, Jr.

SUBJECT:           Pantex - Review of Unreviewed Safety Question to
                   Increase Nuclear Weapon Staging in Zone 12 (PX-USQD-95-39-A)

1. Purpose:  This report documents a review by the Defense Nuclear Facilities
   Safety Board's (Board) staff of modifications to permit increased staging of
   nuclear weapons in Pantex Building 12-64.  The review focused on worker
   safety and propagation concerns and was performed by staff members F.
   Bamdad, C. Keilers,  J. McConnell (site representative), C. Miller, M.
   Moury, J. Preston, and H. Waugh (site representative).
  
2. Summary:  This unreviewed safety question addressed modifications to two
   bays in Pantex Building 12-64.  These modifications permit increased nuclear
   weapon staging by dividing each bay into five compartments separated by
   sandbag barriers.  In effect, each bay's inventory of high explosive and
   plutonium could increase by factors of up to two and five, respectively,
   compared to previous limits.

   The Department of Energy (DOE) considers the proposed staging activity to be
   lower risk than the disassembly operations currently permitted in these
   bays.  The proposed sandbag configuration is currently used in Department of
   Defense (DOD) and Pantex Zone 4 magazines and has been demonstrated to
   effectively avoid propagation across sandbag compartments in DOD tests.  The
   staff agrees that these tests demonstrated the effectiveness of the sandbag
   barriers, within the bounds of what was tested.  However, the protection
   provided by the weapon shipping containers may be more significant than
   commonly realized.  Also, it is not clear how effective the barriers would
   be if larger quantities of high explosive were detonated than those tested. 
   The high explosive limit may need to be reevaluated if other weapon systems
   are considered. 

3.   Background:  In October 1995, Mason and Hanger Silas-Mason (M&H) proposed
     modifications to increase weapon staging in two bays of Building 12-64.  M&H
     considers this would increase efficiency in weapon disassembly and reduce
     cross-site transportation and handling risks. (SEE FOOTNOTE 1).  However,
     the proposed activity also exceeded the amount of high explosive (HE) and
     plutonium (Pu) allowed in each bay.  In November 1995, DOE approved the
     change for W48 weapon systems only.  (SEE FOOTNOTE 2).

4.   Discussion:  

     Because of the potential consequences of releasing up to five times more Pu
     than previously evaluated, the Board staff has been closely monitoring
     progress on the M&H recommendation.  Following DOE approval, the Board staff
     still had unanswered relevant questions.  Therefore, the staff met and
     discussed these questions with DOE and M&H in Washington, D.C. on December
     12, 1995 and performed an on-site review on December 19, 1995.  This
     memorandum summarizes the basis for the M&H recommendation and DOE action,
     as documented in the references and discussed during the above meetings. 
     Major staff concerns are also identified, together with their resolution.

     Description of the Modifications:  The modifications consist of installing
     sandbag barriers that divide each bay into five compartments and of
     deactivating radiological detection systems that M&H considers are no longer
     needed because of reduced personnel access.  In effect, these modifications
     permit increasing the allowable HE/Pu inventory above that previously
     allowed in the Authorization Basis.

     High Explosive (lbs) old bay limit-230; new sandbag compartment limit-105; 
     new bay max. Allowable inventory-525; Plutonium (kg) old bay limit-25; new
     sandbag compartment limit-25; new bay max. Allowable inventory-125.

     Justification: DOE and M&H consider increased staging acceptable for the
     following reasons:

     a.   Reduced accident risk:  The proposed staging activity is considered
          lower risk than the disassembly operations currently permitted in these
          bays.  Staging accidents, particularly for weapons in shipping
          containers, have a low probability that is difficult to quantify because
          few accidents have occurred (i.e., insufficient data).  Operational
          restrictions, such as keeping forklifts out of these bays, will further
          reduce the probability and consequence of an accident.

     b.   Avoiding accidental propagation:  The proposed sandbag configuration is
          currently used in Department of Defense (DOD) and Pantex Zone 4
          magazines and has been demonstrated to be effective in avoiding weapon-to-weapon propagation across sandbag compartments in a series of DOD
          magazine tests (SEE FOOTNOTE 1).  

          During these tests, weapon systems without Special Nuclear Material
          (SNM) were detonated in magazines.  In general, the magazines were
          completely destroyed, but the detonation did not propagate to weapons in
          shipping containers in other sandbag compartments - proving the sandbag
          barrier concept.  In all cases, the magazine ceiling collapsed or was
          thrown.  Some "acceptor" weapons were translated in their shipping
          containers and effectively slammed against the wall. Pictures indicate
          that the shipping containers took considerable punishment but remained
          relatively intact.  The acceptor weapons within shipping containers
          appear unaffected. 

          Earlier in their test program, DOD also tested sandbag configurations
          using HE hemispherical charges in thin-wall containers.  During three of
          four tests (each with a different configuration), propagation did occur
          to one or more acceptor charges in other sandbag compartments, for
          undetermined reasons.  Resulting damage indicates that the acceptor
          charges did not translate before detonating.  Even though these charges
          were less robust than an actual weapon system, M&H interprets these test
          results to indicate that quasistatic overpressure could be a leading
          cause of propagation for the sandbag configuration.

          Staff Observations:  

          1.   The staff agrees that the DOD magazine test demonstrates the
               effectiveness of the sandbag barriers for avoiding weapon-to-weapon
               propagation, within the bounds of what was tested.  However, the
               plastic deformation and crush of the shipping containers may be more
               significant in avoiding propagation than commonly realized.  Also,
               it is not clear how effective the barriers would be if larger
               quantities of HE were detonated than those tested.  Charge weight
               limitations may need to be reexamined if and when other weapon
               systems besides W-48 are considered.

          2.   There appear to be no quantitative criteria for what blast-related
               environmental conditions are necessary to cause a weapon-to-weapon
               propagation across sandbag compartments.  Pressures were measured
               during the DOD tests, but measurements at the acceptor locations
               were considered inconsistent and hard to interpret.  Since no
               criteria exist, M&H addressed several propagation mechanisms by
               comparing the post-detonation environment expected for the bay to
               that calculated for the magazine tests, as discussed below.
     
     c.   Bay-to-magazine comparison: Following a postulated detonation of all the
          weapons in one compartment, the environmental conditions that might
          cause propagation to another compartment are either comparable or less
          severe for the bay than for the magazine tests.  Specifically, M&H
          considered quasistatic overpressure, shock, fragments, translation, and
          thermal effects as potential initiators for propagation.  Each is
          summarized below:

          -    Primary fragments: The DOD magazine tests showed the effectiveness
               of the sandbags at stopping primary fragments that could cause
               propagation.

          -    Secondary fragments: Robust weapon shipping containers appeared to
               be key to preventing propagation from collapsing structure during
               the DOD test.  Also, although the bay roof is heavier than the
               magazine roof, the bay roof is designed to open up and vent outward
               if a detonation occurs.  The bay roof should not collapse inward on
               the shipping containers.

          -    Shock:  The DOD tests demonstrated that direct shock waves should be
               adequately dissipated by the sandbags.  Also, the bays are
               physically larger than the magazines, so reflected shock waves in
               the bays should be lower than those in the DOD magazine tests.

          -    Quasistatic Overpressure: The bays have a larger volume than the DOD
               magazines tested and should have a lower peak quasistatic
               overpressure for the same charge weight.  M&H performed comparative
               analyses to determine the venting and pressure histories in the bays
               and the DOD magazines.  These analyses neglected the sandbags, which
               should be conservative since the sandbags displace a larger volume
               fraction in the magazines than in the bays.

          -    Thermal effects:  Since the bays are larger than the DOD test
               magazines, heat loss is expected to be more rapid and temperatures
               lower in a bay than a magazine.

          -    Translation:  Since the predicted blast impulses on the bay and
               magazine walls are comparable, the impulses on shipping containers
               and the resulting translation in a bay should be similar to those
               experienced during the DOD tests.

          Staff Observations:  

          1.   The staff has been concerned that the bays were not designed to
               protect internal equipment, such as weapons in shipping containers,
               from an internal blast.  They were designed to protect people within
               each bay from an external blast.  In fact, during the full-scale bay
               test, the wall nearest the charge collapsed into the donor bay,
               which would have damaged internal equipment (SEE FOOTNOTE 2).  A
               similar wall survived a subsequent half-scale test.

               This concern has been resolved.  First, the DOD tests indicate
               propagation will not occur and that the shipping containers can
               absorb considerable punishment without a weapon detonating, even if
               the surrounding structure is destroyed.  Second, the compartment HE
               limit is less than that tested during the bay full scale test (105
               and 300 lbs, respectively), and the weapons will be staged further
               from exposed walls than the charge location for the full scale test
               (about 11 feet vice 3 feet, respectively).  These combined effects
               would reduce the blast load on the nearest exposed wall and reduce
               the extent of structural damage, compared to the full scale bay
               test.

          2.   The staff has also been concerned that a small detonation may not
               fully open the roof and may then allow roof debris to fall back into
               a bay.  In particular, the full scale bay test indicates that most
               of the venting could occur through the doors before the roof
               sections fully rotate.4  Therefore, the M&H projection that a small
               charge weight (5 lbs) would rotate the roof sections may be
               unrealistically low. However, the staff does agree that a realistic
               charge weight from a weapon system(s) should provide sufficient
               energy to rotate the roof sections and that the roof should remain
               relatively intact, based on photographs from the bay half-scale
               test.  Therefore, this is no longer a concern.

          3.   Even though the 12-64 bays will be normally unoccupied and will be
               entered using the same precautions as Zone 4 magazines, the staff
               believes that the radiological monitoring and alarm systems should
               not be deactivated.  Unlike the Zone 4 magazines, these bays do have
               personnel in the vicinity nearly all the time (e.g., going to and
               from adjacent bays and buildings).  The bay radiation monitoring and
               alarm systems serve an important function in protecting these
               personnel.

5.   Future Staff Action: The staff will follow any efforts to extend weapon
staging in Building 12-64 to other weapon systems types.

Footnote 1: Picatinny Arsenal, "Establishment of Safety Design Criteria for Use
in Engineering of Explosives Facilities and Opertions."  Tech Report 3256, Report
4, Subdivided Igloo Weapon-to-Weapon Test, Hastings, Nebraska, Jan 16, 1964 to
Feb 14, 1965.

Footnote 2: US Army Engineer Waterways Experiment Station, "An Evaluation of the
Separated Bay Concept for a Munition Assembly Complex: An Experimental
Investigation of the Department of Energy Building 12-64 Complex," Tech Report
SL-83-6, September 1983.