Significance and Use
SNM monitors are an effective and unobtrusive means to search pedestrians for concealed SNM. Nuclear facility security plans often include SNM monitors as one means to help prevent theft or unauthorized removal of designated quantities of SNM from access areas. This guide describes a way to evaluate and categorize the relative performance of available SNM monitors that might be considered for use in a security plan.
The significance of the evaluation for monitor users is that evaluated monitoring equipment has a verified capability. Unexpected deficiencies such as low sensitivity for highly self-absorbing forms of SNM, lower than expected sensitivity in areas having high natural background intensity, or a high nuisance-alarm probability from electronic noise or faulty alarm logic often can be detected during evaluation and corrected before a monitor is placed in operation or further marketed.
The significance of the evaluation for monitor manufacturers is that it may disclose deficiencies in design or construction that, when corrected, will improve the product. A monitor verified to be in a particular sensitivity category will be a product that customers who need that level of performance can purchase in good faith.
The established sensitivity categories for evaluated monitors will provide information to regulatory agencies on the performance range of monitoring equipment for detecting small quantities of SNM.
Independent monitor evaluation will encourage monitor manufacturers to provide appropriate documentation for calibrating and operating their monitors to obtain the best possible performance for detecting SNM.
The underlying assumptions in this guide are that SNM monitors are applied in a wide range of background environments at facilities that process a variety of chemical and physical forms of SNM. The operational experience with a monitor at one facility provides little comparative information for a user of SNM monitors at another facility where the environment and materials are different. A laboratory evaluation in a characterized environment using characterized test sources and providing information on both SNM detection probability and nuisance alarm probability does provide useful comparative information on different monitors.
The user of evaluation results is warned that the results are comparative ones for selection of monitoring equipment used to detect small quantities of SNM. Obtaining equivalent or better results for monitoring small quantities of SNM at any facility rests on properly installing the monitor at an appropriate location, maintaining monitor calibration, keeping the monitor in good repair with a testing and maintenance program, and providing proper training for operating personnel.
The evaluation uses essentially unshielded test sources; hence, results are based on detecting the entire gamma-ray or neutron spectrum of the sources. The effect of deliberate use of shielding materials on the performance of SNM monitors is beyond the scope of this guide.
Scope
1.1 The requirement to search pedestrians for special nuclear material (SNM) to prevent its theft has long been a part of both United States Department of Energy and United States Nuclear Regulatory Commission rules for the physical protection of SNM. Information on the application of SNM monitors to perform such searches is provided in Guide C1112. This guide establishes a means to compare the performance of different SNM pedestrian monitors operating in a specific laboratory environment. The goal is to provide relative information on the capability of monitors to search pedestrians for small quantities of concealed SNM under characterized conditions. The outcome of testing assigns a sensitivity category to a monitor related to its SNM mass-detection probability; the monitor’s corresponding nuisance-alarm probability for that sensitivity category is also determined and reported.
1.2 The evaluation uses a practical set of worst-case environmental, radiation emission, and radiation response factors so that a monitor’s lowest level of performance in a practical operating environment for detecting small quantities of SNM is evaluated. As a result, when that monitor is moved from laboratory to routine operation, its performance will likely improve. This worst-case procedure leads to unclassified evaluation results that understate rather than overstate the performance of a properly used SNM monitor in operational use.
1.3 The evaluation applies to two types of SNM monitors that are used to detect small quantities of SNM. Both are automatic monitors; one monitors pedestrians as they walk through a portal formed by the monitor’s radiation detectors (walkthrough or portal monitor), and the other monitors pedestrians who are stationary for a short period of time while they are monitored (wait-in monitor). The latter can be a portal monitor with a delay mechanism to halt a pedestrian for a few seconds or it can be an access-control booth or room that contains radiation detectors to monitor a pedestrian waiting for clearance to pass.
1.4 The values stated in SI units are to be regarded as standard.
1.5 This standard does not purport to address the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
