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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 - 235,238U, 237NP, and 239Pu - 
    were measured in the leakage spectrum outside spherical water moderators
    of various radii surrounding a 252Cf 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 252Cf 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 235,238U, 237NP, and 239Pu. 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 (H2O), and water with cadmium (H2O + 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 (235,238U, 237NP, and 239Pu) 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*rē},

    which has the units of a nuclear cross section. Here rē 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