Mixed Nuclide Classification
See the letter from P.H. Lohaus to S. Arnold (Westinghouse Hanford Co.) dated January 4, 1993.
A request was made for NRC interpretation of the regulatory requirements in 10 CFR Part 61 paragraph 61.55 (a) (5) regarding the classification of wastes containing mixtures of long- and short-lived radionuclides. The question specifically requested clarification on whether radionuclides from both tables of 10 CFR 61.55 should be considered independently. Table 1 of 10 CFR 61.55 contains limits for long-lived radionuclides and Table 2 contains limits for short-lived radionuclides.
The staff position was that the waste generator should calculate the classification of the waste using the sum-of-the-fractions rule separately for the Table 1 isotopes. The following is an acceptable approach to classification of wastes containing both long- and short-lived radionuclides. First, the sum-of-the-fractions for the Table 1 isotopes should be calculated, and then, the sum-of-the-fractions for the Table 2 isotopes should be calculated. If the Table 1 sum does not exceed 0.1, the classification is determined by using Table 2 only. If the Table 1 sum is between 0.1 and 1, and the Table 2 sum is less than 1 for the Column 3 limits, the waste is Class C. In both cases the sums-of-the-fractions are calculated separately for the Table 1 isotopes and the Table 2 isotopes.
Regulatory references: 10 CFR 61.55
Subject codes: 9.0, 9.4