Non-destructive technique to verify clearance of pipes

Abstract

A semi-empirical, non-destructive technique to evaluate the activity of gamma ray emitters in contaminated pipes is discussed. The technique is based on in-situ measurements by a portable NaI gamma ray spectrometer. The efficiency of the detector for the pipe and detector configuration was evaluated by Monte Carlo calculations performed using the MCNP code. Gamma ray detector full-energy peak efficiency was predicted assuming a homogeneous activity distribution over the internal surface of the pipe for 344 keV, 614 keV, 662 keV, and 1332 keV photons, representing Eu-152, Ag-118m, Cs-137, and Co-60 contamination, respectively. The effect of inhomogeneity on the accuracy of the technique was also examined. The model was validated against experimental measurements performed using a Cs-137 volume calibration source representing a contaminated pipe and good agreement was found between the calculated and experimental results. The technique represents a sensitive and cost-effective technology for calibrating portable gamma ray spectrometry systems and can be applied in a range of radiation protection and waste management applications

Radiological Characterization of Contaminated Pipes of Different Dimensions and Densities

“…).The nonhomogeneous activity distributions represent the worst envisaged cases of inhomogeneity. The models were validated against experimental measurements [3].The measurements bias due to possible inhomogeneity in the distribution of the activity was examined for cylindrical pipes of different density and dimensions. Although in a first approximation the selected four cylindrical pipes have different dimensions, the ratio length/diameter/thickness remains the same in all cases (Table 1).…”

Measurement of low-activity uranium contamination by gamma-ray spectrometry for nuclear decommissioning

“…For in-situ measurements, both scintillators and semi-conductors are used, predominantly NaI scintillators and HPGe detectors, while for laboratory measurements on samples, highresolution detectors such as HPGe are preferred [8]. Depending on the expected activity, a calculation of the minimal detectable activity (MDA) must be made prior of the in-situ measurements for either NaI or HPGe, either experimentally or using Monte Carlo simulations [9]. Dedicated software have been developed to help the characterization of complex geometries, for example, the In-Situ Object Counting System software [10].…”

Techniques Used for Clearance of Radioactive Waste

“…Furthermore, two activity distributions were modelled; representing the worst envisaged cases of activity distributions in order to examine the effect of activity inhomogeneity on the accuracy of the technique. The detector efficiencies for 614 keV photons (Ag108m) as a function of the detector-pipe distance were predicted by the use of the MCNP code [5]. The results of inhomogeneous activity distribution were compared to the results obtained from the homogeneous distribution case (see figure 1).…”