Coupling of MASH-MORSE Adjoint Leakages with Space- and Time-Dependent Plume Radiation Sources

Technical Report · Fri Apr 20 00:00:00 EDT 2001

DOI:https://doi.org/10.2172/786752· OSTI ID:786752

Slater, C O

In the past, forward-adjoint coupling procedures in air-over-ground geometry have typically involved forward fluences arising from a point source a great distance from a target or vehicle system. Various processing codes were used to create localized forward fluence files that could be used to couple with the MASH-MORSE adjoint leakages. In recent years, radiation plumes that result from reactor accidents or similar incidents have been modeled by others, and the source space and energy distributions as a function of time have been calculated. Additionally, with the point kernel method, they were able to calculate in relatively quick fashion free-field radiation doses for targets moving within the fluence field or for stationary targets within the field, the time dependence for the latter case coming from the changes in position, shape, source strength, and spectra of the plume with time. The work described herein applies the plume source to the MASH-MORSE coupling procedure. The plume source replaces the point source for generating the forward fluences that are folded with MASH-MORSE adjoint leakages. Two types of source calculations are described. The first is a ''rigorous'' calculation using the TORT code and a spatially large air-over-ground geometry. For each time step desired, directional fluences are calculated and are saved over a predetermined region that encompasses a structure within which it is desired to calculate dose rates. Processing codes then create the surface fluences (which may include contributions from radiation sources that deposit on the roof or plateout) that will be coupled with the MASH-MORSE adjoint leakages. Unlike the point kernel calculations of the free-field dose rates, the TORT calculations in practice include the effects of ground scatter on dose rates and directional fluences, although the effects may be underestimated or overestimated because of the use of necessarily coarse mesh and quadrature in order to reduce computational times. The second source calculation uses a point kernel like method to calculate directional fluences at points surrounding user-specified detector and structure locations and folds those fluences with MASH-MORSE adjoint leakages to calculate free-field and shielded fluences and dose rates and the indicated protection factors. Both source calculation methods were tested for determining dose rates at specified locations within a two-story concrete building. For two early time steps, results from the second method are 50 to 60% higher than those from the first method, but the protection factors differ by only a few percent. This indicates that the free-field and shielded fluence spectra are similar and differ mainly in magnitude. Other comparisons were made, and from the comparisons there was a perceived underprediction by TORT. That underprediction can be attributed to the coarse mesh and quadrature used in the calculations. The second method, while not rigorously correct, requires much less computer time for a reasonably good estimate of the shielded dose rates within a structure.

• Research Organization: Oak Ridge National Laboratory (US)
• Sponsoring Organization: US Department of Energy (US)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 786752
• Report Number(s): ORNL/TM-2000/335; TRN: US0109140
• Resource Relation: Other Information: PBD: 20 Apr 2001
• Country of Publication: United States
• Language: English

Related Subjects

22 GENERAL STUDIES OF NUCLEAR REACTORS
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
54 ENVIRONMENTAL SCIENCES
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
CALCULATION METHODS
DOSE RATES
ENERGY SPECTRA
PLUMES
POINT KERNELS
POINT SOURCES
RADIATION DOSES
RADIATION SOURCES
RADIATION ACCIDENTS
TIME DEPENDENCE
SPACE DEPENDENCE
M CODES
T CODES
COMPUTERIZED SIMULATION