SINBAD ABSTRACT NEA-1517/70

Neutron Leakage from Water Spheres (NIST Experiment)

1. Name of Experiment: ------------------ Neutron Leakage from Water Spheres (NIST Experiment) (~1990) 2. Purpose and Phenomena Tested: ---------------------------- Fission reaction rates for four nuclides -^{235,238}U,^{237}NP, and^{239}Pu - were measured in the leakage spectrum outside spherical water moderators of various radii surrounding a^{252}Cf neutron source. 3. Description of the Source and Experimental Configuration: -------------------------------------------------------- The measurements were performed at the National Institute of Standards and Technology (NIST), Gaithersburg, Maryland, US. A thin-encapsulated^{252}Cf neutron source was suspended by a thin-walled stainless steel tube at the center of a spherical shell of stainless steel. A pair of double-fission chambers were positioned symmetrically on opposite sides of the container. Measurements were performed with the stainless steel tube and spherical container, either dry or filled with very pure water. Measurements were performed with and without cadmium covering the fission chambers. Three sets of measurements utilizing different sized containers were performed for foils of^{235,238}U,^{237}NP, and^{239}Pu. The stainless steel containers for the three sets of measurements had radii of 3.81, 5.08, and 6.35 cm (1.5, 2.0, and 2.5" radii), with corresponding average foil positions of 7.62, 7.62 and 9.525 cm. Therefore, for each foil location and foil type, four measurements were made: no water or cadmium (Bare), no water with cadmium (Cd), water and no cadmium (H_{2}O), and water with cadmium (H_{2}O + Cd). 4. Measurement System and Uncertainties: ------------------------------------ Each of the two fission chambers positioned on the opposite side of the sphere contains two detector surfaces, labeled TARGET B and TARGET T. The fission rates for four isotopes (^{235,238}U,^{237}NP, and^{239}Pu) were measured for both target positions. The respective T and B targets were always loaded with the fissionable deposit of the same nuclide. In the experiments the counts from the symmetric deposits are averaged to give a result which is less sensitive to the exact positioning of the source. The geometric average of the two rates has been found to be constant within +/- 0.5% (1 sigma) even in a very extreme case when the respective fission rates (per unit mass) from the two sides were as much as 15% discrepant. 5. Description of Results and Analysis: ----------------------------------- The quantity tabulated is: {[fissions /(fissionable nucleus x source neutron)] * 4*pi*r²}, which has the units of a nuclear cross section. Here r² is mean-squared-radial distance to the fissionable deposits from the source center. Monte-Carlo code MCNP, using ENDF/B-V and ENDF/B-VI cross sections has been used in refs. [2], [3] and [4]. The following MCNP input data obtained from [5] are included here: |=======================================================| | filename | experiment | sphere | calculations | | | modeled | radius | for fission in | |=======================================================| | nocdnoh2.i15 | bare | 1.5 | U5, U8, Pu9, Np7 | | 17f2u.i15 | water | 1.5 | U8, Np7 | | cdnoh2ou.i15 | cd | 1.5 | U5, U8, Pu9, Np7 | | cddxtu.i15 | cd+water | 1.5 | U5, U8, Pu9, Np7 | | 14f2dxtu.i15 | water | 1.5 | U5, Pu9 | |-------------------------------------------------------| | nocdnoh2.i2 | bare | 2.0 | U5, U8, Pu9, Np7 | | nbs3i17u.i2 | water | 2.0 | U8, Np7 | | cdnoh2ou.i2 | cd | 2.0 | U5, U8, Pu9, Np7 | | cdcov10u.i2 | cd+water | 2.0 | U5, U8, Pu9, Np7 | | nbs3i14u.i2 | water | 2.0 | U5, Pu9 | |-------------------------------------------------------| | nocdnoh2.i25 | bare | 2.5 | (not measured) | | h2nocdhi.i25 | water | 2.5 | U8, Np7 | | cdnoh2o.i25 | cd | 2.5 | (not measured) | | h2ocd.i25 | cd+water | 2.5 | U5, U8, Pu9, Np7 | | h2nocdlo.i25 | water | 2.5 | U5, Pu9 | |=======================================================| The experimental results from Table 3 are to be compared with results from tallies 2 and 12 from the MCNP runs. These MCNP results have to be multiplied by 4*pi*r**2, where for the 1.5 inch and 2.0 inch spheres the range for r is 7.606 - 7.634, whereas for the 2.5 inch spheres the range is 9.511 - 9.539. Therefore one should multiply the tally results by: 4 * pi * 7.62**2 for the 1.5 and 2.0 inch sphere experiments 4 * pi * 9.525**2 for the 2.5 inch sphere experiments These average r values correspond to the "average foil positions" as mentioned in section I ("Benchmark Specifications") of nist-exp.htm. 6. Special Features: ---------------- None 7. Author/Organizer ---------------- Experiment and analysis: D. M. Gilliam (*), J. F. Briesmeister (**) (*) NIST, Physics Laboratory, Ionizing Radiation Division Gaithersburg, MD 20899, US (**) LANL, Radiation Transport Group, Los Alamos, NM 87545, US jfb@lanl.gov Compiler of data for Sinbad: S. Kitsos OECD/NEA, 12 bd des Iles, 92130 Issy les Moulineaux, France Reviewer of compiled data: I. Kodeli Institute Jozef Stefan, Jamova 39, 1000 Ljubljana, Slovenia ivan.kodeli@ijs.si Acknowledgement: We thank dr. Steven C. van der Marck from NRG, NL, for his comments and suggestions. 8. Availability: ------------ Unrestricted 9. References: ---------- [1] D. M. Gilliam: Specification of the Neutron Leakage Benchmark, NIST, Private communication, 7.12.2000. [2] D. M. Gilliam and J. F. Briesmeister: Neutron Leakage Benchmarks for Water Moderators, ASTM-EURATOM Reactor Dosimetry Meeting, Vail, August 1993. [3] D. M. Gilliam and J. F. Briesmeister: Benchmark Measurements and Calculations of Neutron Leakage from Water Moderators, Proc. Intl. Topical Meeting on Advances in Mathematics, Computations, and Reactor Physics, April 28-May 2, 1991, Pittsburgh, PA, Vol. 2, pg 9.1 4-1 - 4-2. [4] S. C. Frankle and J. F. Briesmeister: Spectral Measurements in Critical Assemblies: MCNP Specifications and Calculated Results, LA-13675, December 1999, pages 37 ff concern the NIST experiment. [5] J. F. Briesmeister: MCNP Models and Input Files for the NIST 1.5in, 2.0in and 2.5in radius water sphere, LANL-X6, 11 December 2000, private communication. [6] J. A. Grundl, D. M. Gilliam , N. D. Dudey, and R. J. Popek: Measurement of Absolute Fission Rates, Nuclear Technology , Vol. 25, 1975, p 237. [7] J. A. Grundl and C. M. Eisenhauer: Proc. Conf. Nuclear Cross Sections and Technology, Washington, D. C., March 1975, NBS Special Publication 425, p 250. 10. Data and Format: --------------- Filename Size[bytes] Content ---------------- ----------- ------------- 1 nist-abs.htm 12.269 This information file 2 nist-exp.htm 27.177 Description of Experiment 3 14f2dxtu.i15 19.053 Input data for MCNP calculations (1.5in sphere) 4 17f2u.i15 10.936 Input data for MCNP calculations (1.5in sphere) 5 cddxtu.i15 15.482 Input data for MCNP calculations (1.5in sphere) 6 cdnoh2ou.i15 11.201 Input data for MCNP calculations (1.5in sphere) 7 nocdnoh2.i15 10.053 Input data for MCNP calculations (1.5in sphere) 8 cdcov10u.i2 14.990 Input data for MCNP calculations (2.0in sphere) 9 cdnoh2ou.i2 11.169 Input data for MCNP calculations (2.0in sphere) 10 nbs3i14u.i2 18.496 Input data for MCNP calculations (2.0in sphere) 11 nbs3i17u.i2 10.843 Input data for MCNP calculations (2.0in sphere) 12 nocdnoh2.i2 10.037 Input data for MCNP calculations (2.0in sphere) 13 cdnoh2o.i25 11.184 Input data for MCNP calculations (2.5in sphere) 14 h2nocdhi.i25 10.843 Input data for MCNP calculations (2.5in sphere) 15 h2nocdlo.i25 18.523 Input data for MCNP calculations (2.5in sphere) 16 h2ocd.i25 15.016 Input data for MCNP calculations (2.5in sphere) 17 nocdnoh2.i25 10.045 Input data for MCNP calculations (2.5in sphere) 18 nist-1.gif 17.913 Figure 1: Typical Experimental Arrangement 19 nist-2.gif 10.323 Figure 2: Neutron Source 20 nist-3.gif 12.108 Figure 3: Neutron Source Holder 21 nist-4a.gif 20.268 Figure 4a: Geometry of 1.5 inch radius water sphere 22 nist-4b.gif 20.343 Figure 4b: Geometry of 2.0 inch radius water sphere 23 nist-5.gif 9.149 Figure 5: Fission Chamber Stems 24 nist-6.gif 37.877 Figure 6: NBS Aluminum Fission Chamber Components 25 nist1.pdf 899.729 Reference 26 nist2.pdf 715.655 Reference 27 nist3.pdf 423.245 Reference 28 nist4.pdf 1.445.888 Reference TABLES 1. Composition of the Source, Source Holder, and Structures 2a. Dimensions and Materials of Fission Chambers 2b. Cd-covered Detectors 3. Results of Experiments 4. Experimental results for T and B positions (1.5 in water sphere) 5. Experimental results for T and B positions (2 in water sphere) SINBAD Benchmark Generation Date: 04/2001 SINBAD Benchmark Last Update: 02/2004