One of the longstanding obstacles to the use of the MCNP Monte Carlo code' for reactor physics calculations has been its requirement for nuclear data libraries at the temperature associated with the application of interest. Recently, however, an auxiliary code, named 'doppler,' has been developed that uses an existing nuclear data library as the basis for generating a new library at the desired temperature. doppler has simple input and is straightforward to use. Libraries generated with doppler and based on the existing ENDF66 library have been developed for three hot Kritz benchmark. Results obtained from MCNPS for those hot benchmarks and their cold (ie., room-temperature) counterparts are presented herein

MacFarlane, R. E. (Robert E.)

Mosteller, R. D. (Russell D.)

White, M. C. (Morgan C.)

UNT Digital Library

Approved for publlc release: dlstrlbution is unlimited. Title. Author(s). Submitted to. Analysis of Hot and Cold Kritz Benchmarks with MCNP5 and Temperature-Specific Nuclear Data Libraries Russell D. Mosteller Robert E. MacFarlane Morgan C. White Advances in Nuclear Fuel Management Ill Hiiton Head, SC October 5-8, 2003 N A T I O N A L  L A B O R A T O R Y  Los Alamos National Laboratory, an affirmative actionlequal opportunity employer, is operated by the University of California for the US. Department of Energy under contract W-7405-ENG-36. By acceptance of this article, the publisher recognizes that the US. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or to allow others to do so, for US. Government purposes. Los Alamos National Laboratory requests that the publisher identify this article as work performed underthe auspices of the US. Department of Energy. Los Alamos National Laboratory strongly supports academic freedom and a researcher's right to publish; as an institution, however, the Laboratory does not endorse the viewpoint of a publication or guarantee its technical correctness. Form 836 (8/00) Analysis of Hot and Cold Kritz Benchmarks with MCNPS TM and Temperature-Specific Nuclear Data Libraries Russell D. Mosteller Diagnostics Applications Group (X-5) Applied Theoretical and Computational Physics Division Los Alamos National Laboratory Robert E. MacFarlane Nuclear Physics Group (T- 16) Theoretical Division Los Alamos National Laboratory Morgan C. White Diagnostics Applications Group (X-5) Applied Theoretical and Computational Physics Division Los Alamos National Laboratory Submitted for Presentation at Advances in Nuclear Fuel Management I11 Hilton Head, SC October 5-8,2003 MCNP is a trademark of the Regents of the University of California, Los Alamos National Laboratory Analysis of Hot and Cold Kritz Benchmarks with MCNPSTM and Temperature-Specific Nuclear Data Libraries Russell D. Mosteller, Robert E. MacFarlane, and Morgan C. White Los Alamos National Laboratory One of the longstanding obstacles to the use of the MCNP Monte Carlo code' for reactor- physics calculations has been its requirement for nuclear data libraries at the temperature associated with the application of interest. Recently, however, an auxiliary code, named "doppler," has been developed that uses an existing nuclear data library as the basis for generating a new library at the desired temperature. doppler has simple input and is straightforward to use. Libraries generated with doppler and based on the existing ENDF66 libraj! have been developed for three hot Kritz  benchmark^.^,^ Results obtained from MCNPS for those hot benchmarks and their cold (Le., room-temperature) counterparts are presented herein. For continuous-energy cross sections, doppler starts with library data for a temperature below the desired temperature, and it broadens the resonance cross sections up to the desired temperature using a kernel broadening method identical to the one used in the NJOY' processing that created the original data library. For thermal S(a,p) tables, doppler works with two sets from the data library with temperatures that bracket the desired temperature, and it interpolates for the new cross sections and (E',p) emission events. If probability tables for the unresolved resonance range are present, doppler also interpolates for new probability tables at the desired temperature using library data for temperatures above and below the desired value. The new customized data sets are written in the user's working directory, and a modified xsdir file is also created there. The user then can specify new materials, old materials, or a combination of them to be used in subsequent MCNP calculations. Description of Benchmarks The benchmarks selected for this study are those from the Kritz-2 series that are documented in Ref, 3: Kritz-2: 1, Kritz-2: 13, and Kritz-2: 19. All three configurations consisted of rectangular lattices of fuel rods immersed in water inside a cylindrical pressure tank, and all three had both cold and hot cases. Kritz-2: 1 and Kritz-2: 13 employed low-enriched UO, fuel, while Kritz-2: 19 used mixed-oxide (MOX) fuel. Criticality was achieved by adjusting the height of the water. The temperatures of the hot cases ranged from 235.9 "C to 248.5 "C, and they were pressurized so that the water remained liquid. The lattices were not placed in the center of the pressure tank but instead were placed near its wall. Consequently, the moderator region between the edge of the lattice and the wall of the tank is considerably thinner on the south and west sides of the lattice than on the north and east sides. -- MCNP is a trademark of the Regents of the University of California, L O ~  Alamos National Laboratory Kritz-2: 1 contained a 44x44 array of fkel pins enriched to 1.86 wt.% and clad in Zircaloy-2. At room temperature, the radius of the fuel pellets was 0.529 cm, the outer radius of the cladding was 0.6 125 cm, and the lattice pitch was 1.485 cm. At cold conditions (1 9.7 "C), the water contained 217.9 ppm of boron, and the critical axial buckling was 1.475 x cm'2. At hot conditions (248.5 "C), the water contained 26.2 ppm of boron, and the critical axial buckling was 6.25 x ern-,. Kritz-2: 13 contained a 40x40 array of the same fuel pins as Kritz-2: 1. However, the lattice pitch (at room temperature) was increased to 1.635 cm. At cold conditions (22.1 "C), the water contained 45 1.9 ppm of boron, and the critical axial buckling was 8.01 x ern‘,. At hot conditions (243.0 "C), the water contained 280.1 ppm of boron, and the critical axial buckling was 5.98 x ern-,. Kritz-2:19 contained a 25x24 array of MOX fkel pins with 1.50 wt.% PuO,. The remainder of the fuel was depleted UO,, with 0.16 wt.% 235U. The fkel pins were clad in Zircaloy-2. At room temperature, the radius of the fbel pellets was 0.4725 cm, the outer radius of the cladding was 0.5395 cm, and the lattice pitch was 1.80 cm. At cold conditions (21.1 "C), the water contained 4.8 ppm of boron, and the critical axial buckling was 1.637 x loF3 ern-,. At hot conditions (235.9 "C), the water contained 5.2 ppm of boron, and the critical axial buckling was 7.15 x ern-,. Analvsis and Results Two sets of continuous-energy nuclear data libraries were generated using doppler. The libraries for the hot UO, cases were generated at 245 "C, while the libraries for the hot MOX case were generated at 235 "C. Both sets of libraries were generated using the existing ENDF66 libraries as a starting point. MCNP5 calculations were performed for the six benchmarks. ENDF66 libraries were used for the cold cases, and the temperature-specific libraries were used for hot cases. All cases were run with 250 generations of 5,000 neutron histories each. The first 50 generations were discarded from the statistics so that the results for each case are based on 1,000,000 active neutron histories. The models are essentially two-dimensional, because they are axially uniform with heights that correspond to the critical axial buckling. Results from the six calculations are presented in Table 1, along with the benchmark values and values obtained previously6 with the HELIOS collision-probability code.7 The HELIOS results are based on nuclear data from ENDF/B-VI release 3 (ENDF/B-VI.3), while the ENDF66 library is based on ENDFIB-VI.6. The changes made between the two releases should have little impact on the results for these benchmarks.' However, the resonance integral for 238U in the HELIOS library was reduced slightly from the ENDF/B-VI.3 value, and this reduction has been shown to increase reactivity by approximately 0.003 Ak for low-enriched uranium lattices at room temperature.' When allowance is inade for this difference, the MCNP5 results are in good agreement with the HELIOS results for all six benchmarks. Table 1. Comparison of Results for Kritz-2 Benchmarks. Core Kritz-2: 1 Kritz-2: 13 Kritz-2: 19 Temperature ORNL Helios LANL MCNP5 (“C) Benchmark (ENDF/B-VI. 3) (ENDF/B-VI.6) 19.7 I l , O O O O = t  0.0008 I 1.0000 I 0.9976 f 0.0007 248.5 I 1.0000~0.0008 I 0.9971 I 0.9913 fO.0007 22.1 1 .OOOO f 0.0008 1.0012 0.9982 f 0.0007 243 .O 1.0000 f 0.0008 0.9995 0.993 1 f 0.0007 21.1 I 1.0000~0.0008 I 1.0013 I 1.0016~0,0007 235.9 1.0000 k 0.0008 1.0003 1.0028 f 0.0007 Pinwise fission rates also have been computed and compared with measured results. The RMS difference between the calculated means and the corresponding measured values is 2% - 3%, which is comparable to the statistical uncertainty associated with the calculated values. Conclusions The doppler code has been developed to produce temperature-specific continuous-energy nuclear data libraries for MCNP. Its input structure is simple, and it is straightforward to use. In this study, it has been employed to generate temperature-specific libraries for hot UO, and MOX benchmarks. MCNP5 results using those libraries are in good agreement with results from the HELIOS code after allowance has been made for library differences. Acknowledgment This research was performed at Los Alamos National Laboratory under the auspices of contract W-7405-ENG-36 with the U. S. Department of Energy. References 1. X-5 Monte Carlo Team, “MCNP -- A General Monte Carlo N-Particle Transport Code, Version 5,” Los Alamos National Laboratory (to be issued). 2. Joann M. Campbell, Stephanie C. Frankle, and Robert C. Little, “ENDF66: A Continuous- Energy Neutron Data Library for MCNP4C,”Proc. 22*h Biennial TopZ. Mtg. Radiation Protection and Shielding Div., Santa Fe, New Mexico, April 2002, pp. 19-37, American Nuclear Society (2002). 3. Erik Johansson, “Data and Results for JSritz Experiments on Regular H,O/Fuel Pin Lattices at Temperatures up to 245 ‘C,” Studsvik/NS-90/133, ISBN 91-7010-143-4, Studsvik AB, Sweden (November 1990). 4. 1. Remec, J. C. Gehin, P. D’hondt, and E. Sartori, “OECDNEA Kritz-2 UO, and MOX Benchmarks,” Proc. Int. Con$ New Frontiers Nucl. Tech. : Reactor Physics, Safety, and Highperformance Computing (PHYSOR 2002), Seoul, Seoul, Korea, October 2002, American Nuclear Society (2002). 5 .  R.E.MacFarlane and D.W.Muir, The NJOY Nuclear Data Processing System, Version 91,” LA- 12740M, Los Alamos National Laboratory (October 1994). 6 ,  Private communication, J. C. Gehin, Oak Ridge National Laboratory (December 2002). 7. Eduardo Villarino, Rudi J. J. Stamm’ler, Aldo Ferri, and Juan J. Casal, “HELIOS: Angularly Dependent Collision Probabilities,” Nuc. Sei. Eng., 112, pp. 16-3 1 (September 1992). 8, Russell D. Mosteller, “Testing of the ENDF66 Nuclear Data Library with MCNPTM Criticality Validation Suite,” accepted for presentation at the 2003 Annual Meeting of the American Nuclear Society, San Diego, CA, June 1-5,2003. 9. Russell D. Mosteller, “HELIOS Calculations for UO, Lattice Benchmarks,” Proc. Int. Cor$ Physics Nucl. Sci. Tech. (PHYSOR 98), Hauppauge, New York, October 1998, pp. 1274- 1281, American Nuclear Society (1998). 

Analysis of hot and cold Kritz benchmark with MCNP5 and temperature-specific nuclear data libraries

https://digital.library.unt.edu/ark:/67531/metadc926928/m2/1/high_res_d/976570.pdf

Analysis of hot and cold Kritz benchmark with MCNP5 and temperature-specific nuclear data libraries

Abstract

Similar works

Full text

Available Versions

UNT Digital Library