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Open Access Publications from the University of California


Welcome to the McClellan Nuclear Radiation Center (MNRC). At the heart of the MNRC is the newest research reactor in the United States. The nuclear reactor at the MNRC attained first operation in 1990, and has over 30 years of productive service remaining.

The custom designed TRIGA (Training, Research, and Isotope Production General Atomics) reactor can operate at a steady state power of up to 2 MW or pulse to approximately 1000 MW for 20 milliseconds. Our staff of 20 reactor operators, health physics technicians, scientists and engineers has over 100 years of experience with the MNRC. Normal operations are 16 hours per day, five days a week, with two shifts. We have the flexibility to change operating schedules to meet customer requirements.

The MNRC was originally developed by the USAF to detect low-level corrosion and hidden defects in aircraft structures using neutron radiography. Since then, MNRC service has expanded to include computer tomography (three-dimensional neutron radiography), silicon doping, isotope production, neutron activation analysis, and radiation effects testing. We have the capability of moving materials and parts into the central core facility and locations adjacent to the core while the reactor is operating.

UCD McClellan Nuclear Radiation Center

There are 27 publications in this collection, published between 1997 and 2011.
Recent Work (27)

High temperature elemental losses and mineralogical

The elemental losses from ashes of common biomass fuels (rice straw, wheat straw, and wood) were determined as a function of temperature from 525 8C to below 1525 8C, within the respective melting intervals. The experimental procedure was chosen to approach equilibrium conditions in an oxidizing atmosphere for the specific ash and temperature conditions. All experiments were conducted in air and used the ashes produced initially at temperatures of 525 8C as reactants. Losses during the initial ashing at 525 8C were negligible, except for a K2O loss of 26% for wood and a Cl loss of 20% for wheat straw. Potassium losses are positively correlated with temperature for all fuel ashes. The K2O loss for wood ash commences at 900–1000 8C. Carbonate is detected in the wood ashes to about 700–800 8C and thus cannot explain the retention of K2O in the ashes to 1000 8C. Other crystalline phases detected in the wood ashes (pericline and larnite) contain little or no potassium. Petrographic examinations of high temperature, wood ash products have failed to reveal potassium bearing carbonates, sulfates, or silicates. The release of potassium, thus, appears to be unrelated to the breakdown of potassium-bearing crystalline phases. The straw ashes show restricted potassium loss compared to wood ash. The potassium content declines for both straw ashes from about 750 8C. Cristobalite appears in the straw ashes at about 700–750 8C and is replaced by tridymite in the rice straw ash from about 1100 8C. Sylvite (KCl) disappears completely above 1000 8C. The Cl content starts to decline at about 700 8C, approximately at the same temperature as potassium, suggesting that the breakdown of sylvite is responsible for the losses. The K–Cl relations demonstrate that about 50% of K (atomic basis) released from breakdown of sylvite is retained in the ash. The presence of chlorine in the ash is, therefore, best attributed to the presence of sylvite. Potassium is easily accommodated in the silicate melt formed at temperatures perhaps as low as 700–800 8C from dehydration, recrystallization, and partial melting of amorphous components. Loss of potassium persists for ashes without remaining sylvite and points to the importance of release of potassium from partial melt at temperatures within the melting interval for the fuel ashes.

Analytical Controlled Losses of Potassium from Straw

Accurate knowledge of the concentrations of potassium and other elements is critical for evaluating the effects of straw and other high-fouling biomass fuels in combustion boilers and other thermal systems. Development of accurate and precise analytical procedures is therefore essential for utilization of biomass fuels in energy production and high-temperature applications. By comparing the results of X-ray fluorescence (XRF) analyses with similar analyses done using instrumental neutron activation (INA), it is observed that 20-25% of the original K2O content of straw ashes and slag can be lost during sample preparation for analyses. The loss occurs during heating of the ashes to determine loss on ignition probably as a result of the breakdown of sylvite (KCl). This loss can be significantly reduced, but not completely eliminated, if the analyses are performed on ashes that have not previously been heat-treated. The study poses the cautionary note that similar losses may occur during XRF analyses of other agricultural and soil samples containing high amounts of alkali halogens.

Graphical user interfaces for the McCellan Nuclear Radiation Center (MNRC)

The McClellan’s Nuclear Radiation Center's control console is in the process of being replaced due to spurious scrams, outdated software, and obsolete parts; The intent of the new control is to eliminate the existing problems by installing a UNIX-based computer system with industry-standard interface software and incorporating human factors during all stages of the Graphical User Interface (GUI) development and control console design.

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