====== Water Shield Design Issues ======

  * {{:engineering:prelim_water_shield_12-22-09.pdf|Sketches and Calcs, referred to below}}
  * Stick-Built Construction vs. Modular Construction
    - Stick-Built construction -- The water shield would be constructed in place in the FAARM space, from components transported underground.
      - Advantages:
        - Larger volumes
      - Disadvantages:
        - Larger underground workforce
        - More construction dirt and debris
    - Modular Construction -- The water shield would be constructed from modules constructed on the surface and transported underground for assembly into the full shield.
      - Advantages:
        - Better construction conditions and quality control
      - Disadvantages:
        - Smaller modules
        - More cage trips
    - One initial water shield design featured modular construction, with individual modules of 3m x 1.5m x 1.5m.  These dimensions are approximately the maximum size of the cage.  The modules are assumed to be comprised of structural steel and an exterior corrugated membrane.  The corrugated membranes were intended to prevent buckling (with thinner and lighter material), as well as interlock the modules to prevent an unobstructed path for particles. (pdf page 1)
    - The concept of compartmentalization of the water in individual modules is important in the structural analysis of the walls.  This is to limit the head in each module to 3m in the 8m high wall.  Then, as done for the roof beam, the stress in the membrane was calculated. (pdf page 3)
  * Structural Design
    - The structural design of the water shield began by considering a 1.5m thick slice of the 9m roof span.  There was assumed to be no live load; and a 3 m water dead load acting over the entire roof.  The maximum moment was then found to calculate the maximum tensile stress in this roof beam.  This tensile stress was used to find the stress in the membrane material. (pdf page 2)
    - Due to possible construction difficulties of the corrugated modules, a modified non-corrugated design was considered (pdf page 4).  This design called for two layers of modules with offset joints.  This design introduced some particle trajectories with only 1.5m of water, and some with 0m (as shown on page 4).  This was also an issue with the existing hot cells (pdf page 5).
    - For structural integrity, modules would need to be filled or emptied simultaneously with its neighbors.  Other issues are earthquake and sloshing loads, and the prevention of leaks.  Thermal effects on the modules could cause gap openings for particles.  Each module should have a high and low point for emptying, and for gasses.