Most of the radioactive work is done in hoods rather than dry boxes, although the latter are gaining favor. There are two ventilating sys- tems: (a) that for low activity hoods, in which possibly radioactive gases are blown up a stack local to the building. (b) That for reaction vessels (the "off-gas" system) in higher activity isotope preparation and research. This goes to a precipitron (Trion) and in turn to a stack. The gas from the surrounding hood is again blown to a stack.

liquid disposal Two drainage systems distinguish the strongly active and weakly active waste solutions. The former goes to the pile canal system, which uses sand filters in conjunction with evaporators. Back washing at periodic intervals cleanses the sand. Tank forms are used to store active con- centrate, with concrete tanks buried in restricted zones. The latter is fed in after the filtration. In some hoods, there are two levels of the floor, the "semi-hot," built up above the level of the "hot."

Shielding For low level hoods, only glass is used; for higher level, lead bricks are piled in front of the working equipment with corners knocked out to admit controls, auxiliary lines, etc.; for very high levels the lead (6") is permanent, with narrow vertical slots every so often, filled with bricks, but leaving access. Remote manipulators are not used extensively except in the packaging of isotopes, where mirrors and gear-control mechanisms operate behind a high, thick lead wall.

Construction The most effective hood is the all stainless-steel type made by Kewaunee (see , June 1950) in conjunction with ORNL tests. It has a 50-100 ft/sec face velocity, with openings near the front, blower in back at top.

After learning of our needs and budget, the ORNL people strongly recommended that we visit or have visit Nels Garden of the University of California Radiation laboratory. In his Health Chemical Laboratory, he makes use of simple improvised equipment, and adopts a philosophy of never letting radioactive material contaminate extraneous surfaces.

As examples of his techniques, the following were mentioned:

1. Wooden frames, plywood covered for dry boxes. Used instead of hoods. 2. Bulk filter material bought and installed locally. Blower fans simple type, need not be decontaminated 3. Tygon tubing, heat treated, accordian pleated for use as seal on remote manipulators. 4. Second-hand boiler for evaporation and concentration of active wastes. 5. Emergency holding tank with various outlets. (Has never been used in 2 yrs., which indicates the care used in handling material.)

1. Air Meza Corporation makes precipitators in sections; can buy one, two, or as many as needed. 2. Substitute for hard-to-get stainless steel Amerkote (vinyl resin) Headquarters in California. Parent Co. is American Concrete Pipe Co.; branch in Knoxville. 3. Closed vacuum system for draining solutions from one system to another. 4. ORNL looking into low carbon steel as a substitute for stainless. 5. Chemical Warfare Service gas filters are effective, may be readily obtained. Arthur D. Little filters remove 99+% particulate matter. 6. In design of hoods, space should be left for adding more filters as desired. 7. Dry boxes made by S. Blickman, Weehawken, N. J. are inexpensive. 8. Prints are available at ORNL Engineering Section on various equipment.