Penetration of Tritium in Concrete
S. I. Baker
Decontamination and decommissioning of the Argonne National Laboratory Chicago Pile-5 (CP-5) Research Reactor has reached the stage at which the reactor and all its shielding and operating systems have been removed. Only the building and its infrastructure (i.e., heating, ventilation, sump pumps, fire protection, etc.) remain. Residual radioactivity except for tritium has been reduced to about 0.3 GBq. Since the reactor was heavy-water moderated and operated for almost 20 years at five megawatts, residual tritium (3H) remains in the concrete walls and floors of the building. Argonne staff has completed a characterization study to measure the concentrations of tritium in these building components. In the course of this study laboratory personnel collected over 100 core samples. Typical concentrations within the containment shell were approximately 10 Bq g-1. The uniformity of concentration is indicative of airborne tritiated water vapor. At most locations, coring only penetrated 10-15 cm below the surface. On the main floor, a few samples were taken at greater depths. Tritium concentrations were somewhat higher in the samples taken at greater depths than those taken at shallower depths in the same hole. Measurements taken on the service floor, near the pedestal that supported the reactor showed evidence of a tritiated water spill from the primary cooling system. Tritium concentrations exceeded 4,000 Bq g-1 in several concrete floor samples. If leached into water, the tritium concentration would greatly exceed the U.S. Department of Energy's Derived Concentration Guide of 74 Bq mL-1 for on-site discharge. Tritium was found throughout the 120-cm-thick concrete floor and in the soil beneath. The penetration profiles indicated slow movement of tritium with very low concentrations (maximum of 7 Bq g-1) in the soil, compared with the peak concentrations in the concrete.
This abstract was presented at the 35th Annual Midyear Meeting, "Decommissioning and Environmental Restoration", Decommissioning 3 Session, 2/17/2002 - 2/20/2002, held in Orlando, FL.