Publications

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In real-world object identification systems, the operational mission may change from day to day. For example, a target recognition system may be searching for heavy armor one day, and surface-to-air assets the next, or a radiation detection system may be interested in detecting medical isotopes in one instance, and special nuclear material in another. To accommodate this 'mission of the day' type scenario, the underlying object database must be flexible and able to adjust to changing target sets. Traditional dimensionality reduction algorithms rely on a single basis set that is derived from the complete set of objects of interest, making missionspecific adjustment a significant task. In this work, we describe a method that uses many limited-size individual basis sets to represent objects of interest instead of a single unifying basis set. Thus, only the objects of interest for the mission at hand are used at any given time, and additional objects can be added to the system simply by training a basis for the new object. We demonstrate the modular identification system on the problem of identifying radioisotopes from their gamma ray spectra using nonnegative matrix factorization.

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Muons are subatomic particles capable of penetrating the earth's crust several kilometers. Muons have been used to image the Pyramid of Khafre of Giza, various volcanoes, and smaller targets like cargo. For objects like a volcano, the detector is placed at the volcano's base and muon fluxes for paths through the volcano are recorded for many days to weeks.

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Sandia National Laboratories (SNL) has limited inventories of, and activities with, fissile-material. Personnel who perform nuclear criticality safety (NCS) assignments do so on a part-time basis. Sandia's "tailored approach" to training and qualification of these personnel can serve as a model for others with "small" NCS programs. SNL uses a single set of qualification cards for qualifying nuclear criticality safety engineers (NCSE). Provision is made for: (1) training and mentoring of new NCSE with testing or other verification of their skills and knowledge and (2) "qualification by documentation" for staff who historically have been performing NCSE-like duties. Key areas for evaluation include previous formal education and training; demonstrated success in writing Criticality Safety Assessments (CSA) and related documents; interaction with the SNL criticality safety committees; and overall knowledge (e.g., as judged against the objectives in DOE-STD-1135). Gaps of knowledge are filled through self-study, training, or mentoring. Candidate mastery of topics is confirmed primarily by evaluation of work products and interviews. Completion is approved by the Criticality Safety Officer (CSO) - the closest SNL comes to having an NCS manager - and then management. In applying the tailored approach, NCSE candidates are not required to be subject-matter experts for all NCS-related facilities and activities at SNL at the time of qualification. Familiarity with each of the facilities and activities is expected, along with the ability to "self-train" when needed (e.g., analogous just-in-time [JIT] procurement). The latter is supported by identification of applicable SNL-wide fissile-material facilities and activities along with resource organizations and personnel in NCS, safety analysis, accountability, etc. The capstone is a discussion with the CSO, or other experienced NCSE, demonstrating the ability to explain in some detail how a specific NCS assignment would be tackled (e.g., options for gaining facility/activity knowledge, performing analyses, using resource personnel, and traversing the required peer- and committee-review processes).

A gas-cooled reactor may be coupled directly to turbomachinery to form a closed-Brayton-cycle (CBC) system in which the CBC working fluid serves as the reactor coolant. Such a system has the potential to be a very simple and robust space-reactor power system. Gas-cooled reactors have been built and operated in the past, but very few have been coupled directly to the turbomachinery in this fashion. In this paper we describe the option for testing such a system with a small reactor and turbomachinery at Sandia National Laboratories. Sandia currently operates the Annular Core Research Reactor (ACRR) at steady-state powers up to 4 MW and has an adjacent facility with heavy shielding in which another reactor recently operated. Sandia also has a closed-Brayton-Cycle test bed with a converted commercial turbomachinery unit that is rated for up to 30 kWe of power. It is proposed to construct a small experimental gas-cooled reactor core and attach this via ducting to the CBC turbomachinery for cooling and electricity production. Calculations suggest that such a unit could produce about 20 kWe, which would be a good power level for initial surface power units on the Moon or Mars. The intent of this experiment is to demonstrate the stable start-up and operation of such a system. Of particular interest is the effect of a negative temperature power coefficient as the initially cold Brayton gas passes through the core during startup or power changes. Sandia's dynamic model for such a system would be compared with the performance data. This paper describes the neutronics, heat transfer, and cycle dynamics of this proposed system. Safety and radiation issues are presented. The views expressed in this document are those of the author and do not necessarily reflect agreement by the government. © 2005 American Institute of Physics.