Reactor Surface Contamination Stabilization

Category: Decontamination > Chemical Surface Cleaning > Chemical Foams or Gels
Reference # : OST/TMS No1839, DOE/EM-0428 Model No :

Production of polyurea formulations is done by various firms under license from Huntsman Chemical Corporation (Austin, Texas).The Master-Lee coating material is polyurea film, composed of a pre-polymerized resin and a “hardener” of diisocyanate that promotes the formation of InstaCote™ (Erie, Michigan). The polymer formulation is similar to polyurethane, but has added amino groups. The setting time to harden is 5 to 30 seconds. The coating will cure in 24 to 48 hours. The temperature of the area to be coated should be a minimum of 12.8°C (55°F). In order to ensure good adhesion without aggressive surface preparation, before spraying the polymer formulation a primercoat of a modified acrylic latex is applied with a hand-powered sprayer. (Master-Lee can apply InstaCote over a layer of foam, if desired.)The RedHawk film material is similar to that used by Master-Lee, except that the material is called PolyShield™, formulated by Specialty Products (Tacoma, Washington). The base layer of polyurethane is allowed to set for 5 minutes before the final layer is applied. The final layer, a polyurea film, is sprayed beyond the edges of the foam for direct adherence to the reactor face. The polyurea is based on amine-terminated polyester resins, amine chain extenders and diisocyanate. It has a service temperature of -51°C to 177°C (-60°F to 350°F) and is hydrophobic. A primer coat of a polyether glycol is required only where the film extends beyond the foam.

Benefits

The technology is suitable for DOE nuclear facilities or any other sites where radioactive or chemical contamination must be stabilized. The polyurea film alone is suitable where direct spraying on the surface to be stabilized is possible, such as flat surfaces or places with open access. For complex or congested equipment shapes, the use of a foam base layer should be considered. Where a non-toxic foam + film application is required, the Eurotech (La Jolla, California) coating system could be considered (but was not field-demonstrated).

Limitations

The maximum distance between the proportioner and the spray tip (maximum length of hose runs) is 91.5 m (300 ft). This is a design limitation based on the rating of the electrical transformer that energizes the hose heating system. Currently, there is no need to modify the two-layer innovative technology demonstrated at the Hanford Site C Reactor. Film-only systems would need multi-directional spray tips to cover the backside of complex shapes. Alternative methods of achieving coverage by one-layer systems might include attaching a mesh or screen or a rigid cover over the reactor face nozzle assemblies end caps. Then a film could be sprayed over the entire mesh or over the rigid cover.

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