Daniel F Hollenbach

Monte Carlo Criticality Methods and Analysis Capabilities in SCALE

Abstract This paper describes the Monte Carlo codes KENO V.a and KENO-VI in SCALE that are primarily used to calculate multiplication factors and flux distributions of fissile systems. Both codes allow explicit geometric representation of the target systems and are used internationally for safety analyses involving fissile materials. KENO V.a has limiting geometric rules such as no intersections and no rotations. These limitations make KENO V.a execute very efficiently and run very fast. On the other hand, KENO-VI allows very complex geometric modeling. Both KENO codes can utilize either continuous-energy or multigroup cross-section data and have been thoroughly verified and validated with ENDF libraries through ENDF/B-VII.0, which has been first distributed with SCALE 6. Development of the Monte Carlo solution technique and solution methodology as applied in both KENO codes is explained in this paper. Available options and proper application of the options and techniques are also discussed. Finally, performance of the codes is demonstrated using published benchmark problems.

Investigation of Backscatter X-Ray Imaging Techniques for Uranium Dioxide Fuel Rods

Radiography by selective detection (RSD), was investigated for its ability to determine the presence and types of defects in a UO2 fuel rod surrounded by zirconium cladding. Images created using a Monte Carlo model compared favorably with actual X-ray backscatter images from mock fuel rods. A fuel rod was modeled as a rectangular parallelepiped with zirconium cladding, and pencil beam X-ray sources of 160 kVp (79 keV avg) and 480 kVp (218 keV avg) were generated using the Monte Carlo N-Particle Transport Code (MCNP) to attempt to image void and palladium (Pd) defects in the interior and on the surface of the fuel pellet. It was found that the 160 kVp spectrum was unable to detect the presence of interior defects, whereas the 480 kVp spectrum detected them with both the standard and the RSD backscatter methods, though the RSD method was very inefficient. It was also found that both energy spectra were able to detect void and Pd defects on the surface using both imaging methods. Additionally, two mock fuel rods were imaged using a backscatter X-ray imaging system, one consisting of hafnium pellets in a Zircaloy-4 cladding and the other consisting of steel pellets in a Zircalloy-4 cladding which was then encased in a steel cladding (a double encapsulation configuration employed in irradiation and experiments). It was found that the system was capable of detecting individual HfO2 pellets in a Zircaloy-4 cladding and may be capable of detecting individual steel pellets in the double-encapsulated sample. It is expected that the system would also be capable of detecting individual UO2 pellets in a Zircaloy-4 cladding, though no UO2 fuel rod was available for imaging.

Current Status of the Oak Ridge Monte Carlo Codes: MORSE/SAS4 and KENO

Over the years, the Oak Ridge National Laboratory staff have developed a number of Monte Carlo codes. KENO V.a and KENO-VI are criticality safety codes that can be run stand-alone or by using the criticality safety analysis sequences CSAS and CSAS6. MORSE is a shielding analysis code that can be run stand-alone or through use of the shielding analysis sequences SAS3 and SAS4. All of these codes are part of the SCALE code system, which is widely distributed and used all over the world. As with any major computer code system, changes and improvements are inevitable. These changes occur for multiple reasons, including release of new compilers, faster and improved computers, and changing customer requirements. This paper provides a current overview of these Monte Carlo codes and a look at possible future enhancements.