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Alternative Criticality Accident Detection System
Posted on May 4th, 2015

Approximately 60 criticality accidents have been recorded worldwide due to uncontrolled fission reactions involving uranium or plutonium. These accidents have resulted in injuries and fatalities from significant overexposures to gamma and neutron radiation. Detecting criticality events has typically involved the use of redundant detectors to measure prompt fission neutrons and prompt fission gammas that are emitted during the event. The challenge in detecting these events is principally associated with criticality events that occur as pulses in very short durations (microseconds to milliseconds). Some detection systems rely on concurrent alarms in multiple detectors in an area to identify (alarm) a criticality event. These systems are costly and can be vulnerable to false positive alarms due to subtle changes in background radiations.

An alternative criticality detection system was designed by Adam Kryskow and Eric Darois of RSCS. This system relies upon the emissions from short-lived activated materials from neutron interactions with the materials contained within a DRM-2NC Geiger-Mueller detector (manufactured by Mirion Technologies) and materials surrounding the detector. The anticipated induced short-lived activated radionuclides, their associated emitted radiations, and GM detector responses were modeled using monte-carlo methods as a function of decay time. These calculations were used to predict the unique detector response decay patterns for various types and intensities of criticality events. These calculations and predictions were used to develop the system’s algorithms that constantly monitor for the characteristic decay patterns, and if identified within statistical bounds, will actuate a criticality alarm. If an alarm is not activated, the system continues to measure gamma radiation as a “normal” area monitor with its associated alarm functions. Performance tests were performed at the White Sands criticality test facility and these results indicated that the alternative criticality detection system was capable of meeting all ANSI criticality accident criteria. This system was found to be sensitive to the minimum accident of concern and had an extremely low likelihood of false alarm.

The research and development of this alternative criticality detection system was led by Adam Kryskow in support of his Masters of Science thesis. Adam defended his thesis this spring and has met the requirements for a degree of Master of Science in Radiological Sciences and Protection from the Department of Physics and Applied Physics at the University of Massachusetts Lowell. RSCS congratulates Adam on the completion of this ground breaking research and on his recent academic accomplishment.

For more information on the criticality detection system, please contact us.

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