Preliminary minimum detectable limit measurements in 208-L drums for selected actinide isotopes in mock-waste matrices

Preliminary minimum detectable levels (MDLS) of selected actinide isotopes have been determined in full-scale, 55-gallon drums filled with a range of mock-waste materials from combustibles (0.14 g/CM3) to sand (1.7 g/CM3). Measurements were recorded from 100 to 10,000 seconds with selected actinide sources located in these drums at an edge position, on the center axis of a drum and midway between these two positions. Measurements were also made with a 166Ho source to evaluate the attenuation of these mock-matrix materials as a function of energy. By knowing where the source activity is located within a drum, our preliminary results show that a simply collimated 90% HPGE detector can differentiate between TRU (>100 nCi/g) and LLW amounts of 239Pu in only 100s of measurement time and with sufficient accuracy in both low and medium density, low Z materials. Other actinides measured so far include 235U, 241Am, and 244Cm. These measurements begin to establish the probable MDLs achievable in the nondestructive assays of real waste drums when using active and passive CT. How future measurements may differ from these preliminary measurements is also discussed