BENCHMARKING ORTEC ISOTOPIC MEASUREMENTS AND CALCULATIONS

Dewberry, R ; Raymond Sigg, R ; Vito Casella, V ; Nitin Bhatt, N

Savannah River Site (S.C.)

关键词: Criticality;    Solid Wastes;    Dimensions;    Photons;    Shape;   

DOI  :  10.2172/939425
RP-ID  :  SRNS-STI-2008-00053
RP-ID  :  DE-AC09-08SR22470
RP-ID  :  939425

美国|英语

来源: UNT Digital Library

【 摘 要 】

This report represents a description of compiled benchmark tests conducted to probe and to demonstrate the extensive utility of the Ortec ISOTOPIC {gamma}-ray analysis computer program. The ISOTOPIC program performs analyses of {gamma}-ray spectra applied to specific acquisition configurations in order to apply finite-geometry correction factors and sample-matrix-container photon absorption correction factors. The analysis program provides an extensive set of preset acquisition configurations to which the user can add relevant parameters in order to build the geometry and absorption correction factors that the program determines from calculus and from nuclear g-ray absorption and scatter data. The Analytical Development Section field nuclear measurement group of the Savannah River National Laboratory uses the Ortec ISOTOPIC analysis program extensively for analyses of solid waste and process holdup applied to passive {gamma}-ray acquisitions. Frequently the results of these {gamma}-ray acquisitions and analyses are to determine compliance with facility criticality safety guidelines. Another use of results is to designate 55-gallon drum solid waste as qualified TRU waste3 or as low-level waste. Other examples of the application of the ISOTOPIC analysis technique to passive {gamma}-ray acquisitions include analyses of standard waste box items and unique solid waste configurations. In many passive {gamma}-ray acquisition circumstances the container and sample have sufficient density that the calculated energy-dependent transmission correction factors have intrinsic uncertainties in the range 15%-100%. This is frequently the case when assaying 55-gallon drums of solid waste with masses of up to 400 kg and when assaying solid waste in extensive unique containers. Often an accurate assay of the transuranic content of these containers is not required, but rather a good defensible designation as >100 nCi/g (TRU waste) or <100 nCi/g (low level solid waste) is required. In these cases the ISOTOPIC analysis program is especially valuable because it allows a rapid, defensible, reproducible analysis of radioactive content without tedious and repetitive experimental measurement of {gamma}-ray transmission through the sample and container at multiple photon energies. The ISOTOPIC analysis technique is also especially valuable in facility holdup measurements where the acquisition configuration does not fit the accepted generalized geometries where detector efficiencies have been solved exactly with good calculus. Generally in facility passive {gamma}-ray holdup measurements the acquisition geometry is only approximately reproducible, and the sample (object) is an extensive glovebox or HEPA filter component. In these cases accuracy of analyses is rarely possible, however demonstrating fissile Pu and U content within criticality safety guidelines yields valuable operating information. Demonstrating such content can be performed with broad assumptions and within broad factors (e.g. 2-8) of conservatism. The ISOTOPIC analysis program yields rapid defensible analyses of content within acceptable uncertainty and within acceptable conservatism without extensive repetitive experimental measurements. In addition to transmission correction determinations based on the mass and composition of objects, the ISOTOPIC program performs finite geometry corrections based on object shape and dimensions. These geometry corrections are based upon finite element summation to approximate exact closed form calculus. In this report we provide several benchmark comparisons to the same technique provided by the Canberra In Situ Object Counting System (ISOCS) and to the finite thickness calculations described by Russo in reference 10. This report describes the benchmark comparisons we have performed to demonstrate and to document that the ISOTOPIC analysis program yields the results we claim to our customers.