Environmental effects from operation of the waste calcination facilities.

Abstract

Operation of the Waste Calcining Facility (WCF) at the National Reactor Testing Station in Idaho was initiated on 8 December 1963. As a result of 311 days of continuous operation, about 305 c of 106Ru and trace amounts of 90Sr, 137Cs and 144Ce were released from a 73-m stack. In the calcining process, liquid radioactive wastes and an acid solution of aluminum nitrate are converted to solids. Most of the radioactive fission product oxides formed are solids at all operating temperatures. These are removed by various clean-up stages. The predominant form of ruthenium, RuO4, however, is liquid or gaseous at these temperatures. Although absorbers removed 99.9 per cent of the ofF gas ruthenium, significant amounts were found in the WCF ofF gas. The variation of release rates observed at the stack (a maximum of 5.5 × 10−4 μc/cm3 and an average of 1.9 × 10−7 μc/cm3), with the exception of certain abnormal events occurring during and immediately following the calcining operation, Here proportional to the levels of ruthenium in the liquid wastes being processed. Monitoring was conducted during and after operation of the WCF. This involved high-volume air samples, fallout plates, and vegetation and soil samples. Significant amounts of 106Ru on vegetation were found as far as 16,000 m from the stack, with a maximum of 2.2 × 10−3 μc/g at 1600 m. Comparison of these activities with concentrations of 106Ru in air indicates the deposition velocity was about 0.5 cm/sec. In order to more fully evaluate the impact of a calcining operation on the environment, a diffusion model has been formulated to predict integrated concentrations of radioactive materials resulting from the long term release from a single stack. The model presented utilizes daily source terms of 106Ru and hourly meteorological data. Comparison of model predictions with air sampling data and deposition data showed close correspondence. The results of these studies lead to the following conclusions. (1) Only the oxides with a very low boiling point were released in significant amounts. These release ratios were also quite low (an average reduction factor greater than 103). (2) From the limited verification data available, the dispersion model presented seems to be a reasonable approach and is useful for considering the long-term impact of continuous releases from an operating facility. (3) Native vegetation is adequate for monitoring purposes and provides an inexpensive and continuous record of the impact of radioactive releases on the environs. (4) There was no significant hazard from operation of the WCF. Calculations indicate that the total dose at the point of maximum integrated concentration was about 0.1 rad to the lung.