FY2010 - Oak Ridge National Laboratory

Seed Money Fund—
Reactor and Nuclear Systems Division
distribution and rate in the nuclear material. This then becomes the source in a second step—the transport
of fission particles to the detector. More complex problems, where interrogating particles also cause
reactions in structural materials, can be treated as well.
Three examples of scanning system problems were constructed that each contained a significant quantity
of highly enriched uranium embedded in normal materials: (1) a neutron source and a neutron detector for
water-filled 55 gal barrels, (2) a neutron source and both neutron and gamma detectors for a 40 ft
shipping container, and (3) a bremsstrahlung photon source and two neutron detectors for a steel-hulled
fishing trawler containing fish and ice in the main hold. New coding was added to the SCALE package to
convert the reaction rates in one step into a source term for the next step.
The multistep approach worked well for each example problem, and significant speed-ups (compared to
standard, analog calculations) were obtained. For the barrel scanning example, using the multistep hybrid
variance reduction was 200 times faster than analog. For the 40 ft shipping container, speed-ups ranged
from 5 to 100, depending on the materials inside the container (more attenuating materials gained more
from the variance reduction). For the fishing trawler problem, the analog method was not attempted due
to the difficulty of the problem. The multistep method computed the change in the detector responses due
to the nuclear material within a single day on one central processing unit.
Information Shared
Peplow, D. E., T. M. Miller, and B.W. Patton. 2010. “Hybrid Monte Carlo/Deterministic Methods for
Active Interrogation Modeling.” Proceedings of the American Nuclear Society Joint Topical Meeting
of the Radiation Protection and Shielding Division, Isotopes and Radiation Division, Biology and
Medicine Division, Las Vegas, Apr. 19–23.
00521
Development of a Machinable SiC-BN Ceramic Composite Compatible
with High-Temperature Molten Fluoride Salts
David E. Holcomb, Steve Nunn, Dane Wilson, and David L. West
Project Description
The overall project task is to evaluate the mechanical and fluoride salt corrosion properties of a recently
developed silicon carbide–boron nitride (SiC-BN) composite material. Key to the new composite material
being useful for engineering applications is combining the high hardness and mechanical strength of
silicon carbide with the ease of machinability of boron nitride while preserving their chemical inertness. If
the new material performs as anticipated, this work will serve as leverage for ORNL to create a larger
program focused on developing SiC-BN to the point where it can be used in engineered systems in
support of high-temperature energy transfer processes.
The project methodology is to fabricate a set of SiC-BN composite samples and experimentally measure
their molten fluoride salt corrosion performance. As a new composite material, the fabrication
methodology for producing SiC-BN has several variants with unresolved performance differences—
notably including corrosion properties. Two fabrication routes are being explored to create suitable
material test coupons. The first fabrication method employs reaction synthesis followed by hot pressing.
The second fabrication technique utilizes pressureless sintering instead of hot pressing, with the final
porosity being removed from the material by impregnating with a carbon bearing liquid.
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