On-the-fly Doppler Broadening with Probability Table Interpolation for Unresolved Resonance Region in RMC
- Department of Engineering Physics, Tsinghua University, Beijing, 100084, CHINA (China)
- Department of Reactor Core Design, Shanghai Nuclear Engineering Research and Design Institute, Shanghai 200233, China (China)
With the rapid development of computational power and parallel algorithms, Monte Carlo method has been widely investigated and used in neutron transport simulations due to its advantages in geometry modelling and usage of continuous energy point-wise cross sections. Nowadays the road has been paved to couple Monte Carlo codes with thermal-hydraulics codes to make multi-physics calculations. One of the most important aspects of thermal-hydraulics feedback is the detailed temperature distribution, which demands temperature dependent cross sections in neutron transport simulations. The conventional pre-generated cross section libraries at each temperature point are no longer feasible for detailed temperature distributions because of tremendous memory footprint. Hence, different on-the-fly Doppler broadening methods have been proposed for resolved resonance energy region and thermal energy region, such as the interpolation, regress model fitting, multipole representation (MPR), target motion sampling (TMS) and different integration algorithms based on Doppler broadening equation. Compared to resolved resonance energy region and thermal energy region, the representation of cross sections in unresolved resonance region is slightly different. As a result of the limitation of experiment measurements, the overlapped resonances cannot be distinguished from each other and the statistic average resonance parameters are given in the evaluated nuclear data file. In early applications, infinite-dilute pointwise cross sections were obtained from average parameters and were directly used in neutron simulations. However, it was proven that these infinite-dilute pointwise cross sections cannot capture the energy self-shielding effect, thus leading to an overestimate of reaction rates and usually an underestimate of k{sub eff} owing to the increased absorption rates and increased scattering probability to energy below unresolved resonance region where the capture-to-fission ratio is typically higher. This phenomenon is of great importance especially for problems where there is a considerable flux in unresolved resonance region. Then the probability table method was put forward by Levitt to take energy self-shielding effect into account, which provides probability distribution function of cross sections in unresolved resonance region instead of specific cross section values. The probability distribution function is presented in the form of tables and the mean values are equal to the infinite dilution cross sections. To obtain the temperature dependent cross sections in unresolved energy region, there are two different methods. One is to calculate cross sections directly from average resonance parameters and their statistical distributions , which is effective and precise but time-consuming. The other is to interpolate between pre-generated probability table files, which is much more efficient. In this paper, on-the-fly Doppler broadening of cross sections in unresolved resonance regions based on probability tables interpolation was implemented in RMC codes as a supplement to on-the-fly Doppler broadening for resolved resonance energy region and thermal region, which is based on the integration of Doppler broadening equation. The results of criticality calculation and depletion calculation show that on-the-fly Doppler broadening for the whole energy region is accurate and efficient. (authors)
- OSTI ID:
- 23042832
- Journal Information:
- Transactions of the American Nuclear Society, Journal Name: Transactions of the American Nuclear Society Vol. 115; ISSN 0003-018X
- Country of Publication:
- United States
- Language:
- English
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On-the-fly Doppler broadening of unresolved resonance region cross sections
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Related Subjects
97 MATHEMATICS AND COMPUTING
ALGORITHMS
CAPTURE-TO-FISSION RATIO
COMPUTERIZED SIMULATION
CRITICALITY
CROSS SECTIONS
DISTRIBUTION FUNCTIONS
DOPPLER BROADENING
GEOMETRY
INTERPOLATION
MONTE CARLO METHOD
NEUTRON TRANSPORT
NEUTRONS
NUCLEAR DATA COLLECTIONS
REACTION KINETICS
SAMPLING
SCATTERING
SELF-SHIELDING
TEMPERATURE DEPENDENCE
TEMPERATURE DISTRIBUTION
THERMAL HYDRAULICS