Neutron Screening Measurements of 110 gallon drums at T Plant

Mozhayev, Andrey V. ; Hilliard, James R. ; Berg, Randal K.

Pacific Northwest National Laboratory (U.S.)

关键词: Neutron Measurements, Tru Waste, T-Plant, Configurable Neutron Slab System, Total Neutron Counting, Neutron Coincidence Counting, Wrap;   

RP-ID  :  PNNL-20119
RP-ID  :  AC05-76RL01830
RP-ID  :  1008244

美国|英语

来源: UNT Digital Library

【 摘 要 】

The Pacific Northwest National Laboratory (PNNL) Nondestructive Assay (NDA) Service Center was contracted to develop and demonstrate a simple and inexpensive method of assaying 110 gallon drums at the Hanford Site’s T-Plant. The drums contained pucks of crushed old drums used for storage of transuranic (TRU) waste. The drums were to be assayed to determine if they meet the criteria for TRU or Low Level Waste (LLW). Because of the dense matrix (crushed steel drums) gamma measurement techniques were excluded and a mobile, configurable neutron system, consisting of four sequentially connected slab detectors was chosen to be used for this application. An optimum measurement configuration was determined through multiple test measurements with californium source. Based on these measurements the initial calibration of the system was performed applying the isotopic composition for aged weapon-grade plutonium. A series of background and blank puck drum measurements allowed estimating detection limits for both total (singles) and coincidence (doubles) counting techniques. It was found that even conservative estimates for minimum detection concentration using singles count rate were lower than the essential threshold of 100 nCi/g. Whereas the detection limit of coincidence counting appeared to be about as twice as high of the threshold. A series of measurements intended to verify the technique and revise the initial calibration obtained were performed at the Waste Receiving and Processing (WRAP) facility with plutonium standards. Standards with a total mass of 0.3 g of plutonium (which is estimated to be equivalent of 100 nCi/g for net waste weight of 300 kg) loaded in the test puck drum were clearly detected. The following measurements of higher plutonium loadings verified the calibration factors obtained in the initial exercise. The revised and established calibration factors were also confirmed within established uncertainties by additional measurements of plutonium standards in various locations in the test drum. Due to necessity to dispense the blank test drum an alternative method of baseline determination was established during field measurements. Count rates of ambient background were corrected by the differences between observed background and blank test drum count rates which were previously determined over a series of measurements. Only 31 drums out of 352 counted during the intensive measurement campaign at T-Plant were determined to be Suspect TRU. 25 of these drums were re-measured at the WRAP facility using the SuperHENC. Of the 25 drums measured, 21 were confirmed to be TRU and the remaining four LLW.