NON-DESTRUCTIVE ASSAY OF TRANSURANIC (TRU) RAD-WASTE SLUDGES USING THE IMAGING PASSIVE ACTIVE NEUTRON (IPAN) TECHNIQUE

A new technique has been developed for assay of transuranic radioactive sludge waste in 208 liter drums. The method uses the high sensitivity of the Imaging Passive Active Neutron (IPAN) system to provide regulatory acceptable measurements on sludges. The technique has been field tested on IPAN drum counters at Rocky Flats and Hanford. In one application, assays are performed on Transuranic (TRU) and Low Level Waste (LLW) sludge waste that originated from an aqueous precipitation process. In a second application, the waste came from spent nuclear fuel (SNF) storage and will therefore be contaminated with fuel corrosion by-products including TRU isotopes and fission/activation products. Prior to assay, the SNF sludge is grouted with a cement mixture. A new calibration technique was developed specifically for these two challenging waste streams that uses a radial weighted average method to define the imaging response matrix. This method provides the required sensitivity to the height distribution of special nuclear material within the 208 liter drum, and makes use of the uniform radial distribution that will occur for a distribution of a large population of small particles in a homogeneous matrix. The active and passive modes of the IPAN provides a wide dynamic range of assay: from below the TRU/LLW sorting threshold of 100 nCi/g (3700 Bq/g) up to several hundred grams of Weapons Grade Pu Equivalent. For mixtures of uranium and plutonium, isotopic categorization can be performed by analysis of the ratio of the active and passive effective masses. Extensive validation and testing with specially designed surrogate sludge drums and radioactive standards have resulted in regulatory acceptance of this technique, permitting ultimate disposal of the sludge drums at the Waste Isolation Pilot Plant.