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FNS Clean Experiment on Vanadium Cube

 1. Name of Experiment:
    FNS/JAERI Clean Benchmark Experiment on Vanadium Cube Assembly (1996)

 2. Purpose and Phenomena Tested:
    A 25.4 cm x 25.4 cm x 25.4 cm cube vanadium assembly was irradiated in the
    D-T neutron source of Fusion Neutronic Source (FNS) facility at JAERI. Neutron
    spectra down to 1 eV, dosimetry reaction rates, gamma-ray spectra and gamma-
    ray heating rates were measured at 3 positions up to 17.78 cm inside the
    vanadium assembly.

 3. Description of Source and Experimental Configuration:
    The experimental configuration was basically the same as those used for some
    previous clean benchmark experiments like the Lithium-Oxide, Graphite, Copper,
    Beryllium, Tungsten assemblies.
    The vanadium assembly was a cube with a side of 254 mm. Four side surfaces and
    a rear surface of the vanadium assembly was covered with a graphite reflector
    with the thickness of 50.8 mm, as shown in Fig. 1, to reduce leakage neutrons
    from the rather small assembly and incoming background neutrons from the outside.
    Purity of vanadium was higher than 99.7 %. The material compositions of the
    vanadium assembly and the surrounding graphite reflector are given in Table 1.

    The experimental assembly was located in front of the neutron source at a
    distance of 200 mm from the target. The tritium-titanium target of ~3.7E11 Bq
    was bombarded by a deuteron beam of 350 keV energy to produce D-T neutrons.
    The number of source D-T neutrons generated during each measurement was
    determined by the alpha-particle detector with an accuracy of 2~3 %. 

    The D-T neutron source can be roughly described as an isotropic point 14-MeV
    neutron source.  The source neutron spectrum and intensity, however, depend
    slightly on the emission angle. The angle-dependent source characteristics
    were investigated experimentally and theoretically in detail, and a source
    subroutine for the Monte Carlo transport code MCNP-4 has been prepared to
    simulate the source condition precisely. This routine is listed in [3]. A
    comparison between the measured and calculated angular distribution is given
    in Fig. 3.2.7. in [4]. As an adequate alternative to the use of the MCNP
    routine it is suggested in [1] that the source spectrum of neutrons emitted
    toward the 0 degree direction with respect to the deuteron beam direction can
    be used for the incident neutron spectrum on the whole front surface of the
    assembly. No quantitative estimation of difference between both sources could
    be though found in the available literature. The 0 degree source neutron
    spectrum is shown in Fig. 2, and input cards of MCNP for description of the
    source spectrum are shown in the MCNP sample input file. The si1 and sp1 cards
    indicate upper neutron energies of the energy bins in MeV and probabilities
    in the bins, respectively. The dir and vec parameters with the sb2 card are
    used for variance reduction with the source biasing method. The weight of a
    source neutron specified by the wgt parameter, 1.1261, is larger than 1.0
    because more D-T neutrons are emitted to the forward direction than in the
    backward direction with respect to the deuteron beam direction.  

    The tritium target region is also a source of gamma-rays, namely, target gamma-
    rays, created by interaction of the source neutrons with structural materials
    of the target. Consideration of the target gamma-rays, however, is not needed
    in calculations of gamma-ray heating rates because contribution of the target
    gamma-ray to the measured heating rates has been already subtracted in the
    experimental data.  On the other hand, the target gamma-ray contribution is
    involved in the measured gamma-ray spectra. The contribution at the detector
    positions deep inside the experimental assemblies is negligible, representing
    at most few percents, because the experimental assembly largely attenuates the
    target gamma-rays. Accordingly, it is not necessary to consider the target
    gamma-rays in transport calculations for the clean benchmark experiments.

    Since the V assemblies were located at least 4 m from the experimental room
    walls and floor, the contribution of the background neutrons and gamma-rays
    coming from the room walls and floor on the measured quantities was negligibly

 4. Measurement System:
    Two experimental channels for insertion of detectors were set on the lateral
    surface of the assembly, and detectors were placed on the central axis of the
    assembly at three positions: one on the front surface and other two inside
    the assembly at the depths of 76.2 and 177.8 mm. The report [1] states that
    the spectra measurements were performed one by one, we conclude therefore
    that the other experimental channels were closed (plugged with vanadium). 
    The dosimetric foils were irradiated together and simultaneously in plural
    detector channels.

    No information on the background correction was found in the literature.

    Six techniques were employed to measure neutrons and gamma-rays. The detailed
    description of the experimental techniques is given in [1] (pages 5-20):

    (1) 14 mm-diameter spherical NE213 liquid organic scintillator was used as
        the fast (above 2 MeV) neutron spectrometer. It was inserted into the
        experimental channel hole of 22 mm diameter. 
        Various sources of the NE213 measurement uncertainties are discussed in
        [1] (page 5) and the systematic errors are summarized in Table 2.

    (2) A pair of proton recoil gas proportional counters (PRC) was used to
        measure neutron spectrum in the 20 keV to 1 MeV energy range. The counter
        has a cylindrical shape with the outer diameter of 19 mm and the effective
        length of 127 mm. The counter is inserted into an experimental hole of
        21 mm in diameter with its pre-amplifier. PRC is made of type 304 stainless
        steel of a thickness of 0.41 mm.

        Two types of counters were used to measure neutron spectrum in a wide
        energy range. Hydrogen gas at 0.5677 MPa (5.789 kgf/cm2) with 1 percent
        of CH4 filled counter was used for low-energy neutrons from 3 keV to 150
        keV while for the high-energy neutrons from 150 keV to 1 MeV the counter
        was filled with 50-50 mixture of hydrogen and argon gases with 1.8 percent
        of nitrogen at 0.6102 MPa (6.222 kgf/cm2).

        Error Assessment: Possible error sources are gas pressure (number of
        hydrogen atom), n-p scattering cross section, fitting error for
        differentiation of recoil proton spectrum due to count statistics and
        calibration of recoil proton energy. The fitting error is the largest,
        ~ 3-10 % above 10 keV, while the other errors are expected to be less
        than 1%. Neutron spectra below 10 keV tend to become smaller due to the
        uncertainty of the W-value, which is the average energy loss per ion pair.
        The error due to W-value is not included in the experimental errors.

    (3) Slowing down time (SDT) method for the neutron spectrum from 1 eV to 300 eV.
        A BF3 gas proportional counter with an outer diameter of 14 mm and an 
        effective length of 99 mm, containing 96 % boron-10 (B-10) enriched BF3
        gas at the pressure of 71.5 kPa, was used for neutron detection. Using the
        standard thermal neutron field the effective number of B-10 atoms in the
        counter was determined to be 2.18E20 +- 3 %. The counter was inserted into
        one of the experimental holes of the experimental assembly.
        Experimental uncertainties associated with the measured spectra are
        summarized in Table 3. The overall experimental uncertainties are dominated
        mostly by the uncertainties of the energy calibration curves. The lowest
        and highest energies calibrated are 1.4 eV and 579 eV. In the energy ranges
        outside the calibration energies, roughly below 1 eV and above 1 keV, the
        adjusted calibration curves are used.

    (4) Dosimetry reaction rate of the Al-27(n,alpha)Na-24, Nb-93(n,2n)Nb-92m,
        In-115(n,n’)In-115m and Au-197(n,gamma)Au-198 reactions were measured by
        the foil activation method. Table 4 provides the characteristics for the
        reactions used.
        Typical Al and Nb sample size was 10 mm in diameter and 1 mm in thickness.
        Indium foils had dimensions of 10 x 10 x 1 mm3. In order to minimize the
        self-shielding effect for the Au-197(n,gamma) reaction, gold foils with a
        size of 10 x 10 x 0.001 mm3 were adopted.

        Experimental Error and Uncertainty: Major sources of the error for the
        reaction rate were the gamma-ray counting statistics (0.1 ~ several %)
        and the detector efficiency (2 ~ 3 %). The error for sum-peak correction
        was estimated less than 2 % depending on the decay mode and fraction of
        multiple gamma-ray cascade. The error for the decay correction was
        reflected from the error of half-life of the activity. If the half-life
        was accurate, the error for the saturation factor should be less than
        1 % even for the short half-life activities.
        The other errors associated with foil weight, gamma-ray self-absorption,
        irradiation time, cooling time and counting time were negligibly small.
        The error for neutron yield was estimated to be 2 %.  The overall error
        for the major part of reaction rate ranged between 3 ~ 6 %.  Some data
        for high threshold reaction in the deep positions suffered from poor
        counting statistics due to low activation rate.

    (5) Prompt gamma-ray spectrum were measured by a 40 mm diameter spherical
        BC537 liquid organic scintillation counter. Outer diameter of the detector
        is 48 mm and length including a photomultiplier assembly is 262 mm.
        Experimental uncertainty: As explained in (6) below, typical experimental
        uncertainties of the gamma-ray heating rate measured by TLDs range
        between 7 ~ 15 %. The gamma-ray spectra are normalized to the gamma-ray
        heating rates. Uncertainties of about 10 % is introduced by the
        normalization procedure. All of the rest of experimental uncertainties,
        such as statistical errors, uncertainties of the response functions,
        determination of source D-T neutrons and subtraction of decay gamma-rays,
        are less than 5 %.  Therefore, total experimental uncertainties are
        approximately 15 ~ 20 %. Note that only the statistical erorrs are
        included in the Table 10.

    (6) Gamma-ray heating rate were measured by thermoluminescent dosimeters
        (TLDs) in combination with the atomic number interpolation method.
        Gamma-ray heating rates of vanadium were deduced by interpolating the
        gamma-ray heating rates measured by three types of TLDs, Mg2SiO4 (MSO,
        effective atomic number Zeff = 11.1), Sr2SiO4 (SSO, Zeff = 32.5) and
        Ba2SiO4 (BSO, Zeff = 49.9).

        Sources of error in the measured gamma-ray heating rates are as follows:

        Statistical deviation of four TLDs      5 - 15 %
        Number of neutrons generated            2 - 3  %
        Calibration of the TLD reader             5    %

        Due to the subtraction of target gamma-rays and neutron response, the
        following uncertainties are to be added to the above errors according to
        the quadratic propagation of error.

        Response functions for neutrons    30 %
        Neutron energy spectra             10 %
        Target gamma-ray                   20 %

        Overall errors for the obtained gamma-ray heating rates of vanadium are
        ~ 10%, except at the positions in the front surface of the assemblies
        where they are 20 ~ 25 %.

 5. Description of Results and Analysis:
    The measured neutron spectra by the three methods at the depths of 76 mm and
    178 mm are shown in Figs. 3 and 4, respectively. The numerical data of the
    spectra measured by the NE213, PRC and SDT methods are given in Tables 5 - 7,
    respectively. Table 8 summarises integral neutron fluxes derived from the
    measured neutron spectra.
    The measured dosimetry reaction rates are shown in Table 9.
    The measured gamma-ray spectra at the positions of 76 mm and 178 mm are shown
    in Figs. 5 and 6, and the numerical data of the spectra are shown in Table 10.
    Table 11 summarises the measured gamma-ray heating rates in vanadium.

    Example of Experiment Analysis:
    Transport calculations with the MCNP-4A code are presented in [2]. The
    calculations were performed using the JENDL-FF, JENDL-3.2, ENDF/B-VI and
    EFF-3 nuclear data libraries.
    The sample input for the MCNP-4A code is given in file mcnp-v.inp. The
    input was taken from [1], except that the 0 degree source was used instead
    of the source subroutine (not provided in the document [1]).

 6. Special Features:

 7. Author/Organizer:
    Experiment and analysis:
    F. Maekawa, C. Konno, Y. Kasugai, Y. Oyama, Y. Ikeda
    Japan Atomic Energy Research Institute
    Tokai-mura, Naka-gun, Ibaraki-ken, 319-1195 Japan
    Phone: 81-292-82-6809 (for Y.O.) or -6015 (for H.M.)
    Fax: 81-292-82-5996 (for Y.O.) or -6365 (for H.M.)
    e-mail: oyama@cens.tokai.jaeri.go.jp
    or      fujio@cens.tokai.jaeri.go.jp

    Compiler of data for Sinbad:
    I. Kodeli
    OECD/NEA, 12 bd des Iles, 92130 Issy les Moulineaux, France
    e-mail: ivo.kodeli@oecd.org

    Reviewer of compiled data:
    Sea Shielding Engineering And Analysis (SEA)
    Avda. Atenas 75 Local 9
    Las Rozas 28230 MADRID

 8. Availability:

 9. References:

    [1] F. Maekawa, C. Konno, Y. Kasugai, Y. Oyama, Y. Ikeda: 
        “Data Collection of Fusion Neutronics Benchmark Experiment Conducted at
        FNS/JAERI”, JAERI-Data/Code 98-021 (1998).
    [2] F. Maekawa, Y. Kasugai, C. Konno, I. Murata, Kokooo, M. Wada, Y. Oyama, Y. Ikeda
        and A. Takahashi: “Benchmark Experiment on Vanadium with D-T Neutrons and
        Validation of Evaluated Nuclear Data Libraries by Analysis of the Experiment“,
        J. Nucl. Sci. Technol., Vol. 36, No. 3, p. 242-249 (March 1999)
    [3] F. Maekawa, C. Konno, K. Kosako, Y. Oyama, Y. Ikeda and H. Maekawa: 
        “Bulk Shielding Experiments on Large SS316 Assemblies Bombarded by D-T Neutrons,
        Volume II: Analysis“, JAERI-Research 94-044 (1994).
    [4] Y. Oyama: “Experimental Study of Angular Neutron Flux Spectra on a Slab Surface
        to Assess Nuclear Data and Calculational Methods for a Fusion Reactor Design“,
        JAERI-M 88-101 (1988).

    References to other useful documents can be found in the above reports.

10. Data and Format:

        Filename     Size[bytes]   Content
    ---------------- ----------- -------------
  1 fnsv-abs.htm       19,225  This information file
  2 fnsv-exp.htm       26,157  Description of experiment
  3 mcnp-v.inp         13,054  Input data for MCNP-4A calculations
  4 fnsv-1.gif         25,282  Figure  1: Sectional view of the vanadium assembly
  5 fnsv-2.gif         10,849  Figure  2: Source neutron spectrum emitted towards the
                                          0 degree from the target.
  6 fnsv-3.gif         20,330  Figure  3: Neutron spectra at z=7.6 cm in vanadium
  7 fnsv-4.gif         20,231  Figure  4: Neutron spectra at z=17.8 cm in vanadium
  8 fnsv-5.gif         17,683  Figure  5: Gamma-ray spectra at z=7.6 cm in vanadium
  9 fnsv-6.gif         16,920  Figure  6: Gamma-ray spectra at z=17.8 cm in vanadium
 10 j98-021.pdf    12,359,881  Reference JAERI-Data/Code 98-021
 11 fns-v.pdf         893,812  Reference J. Nucl. Sci. Technol., Vol. 36, No. 3

    File >fnsv-exp.htm contains the following tables:

      Table 1:      Material specification
      Table 2:      Systematic errors for neutron spectra measurements by NE213
      Table 3:      Uncertainties in measured neutron spectra by the SDT method
      Table 4:      Dosimetry Reactions used in the foil activation method
      Tables 5-7:   Measured neutron spectra
      Table 8:      Integral neutron fluxes
      Table 9:      Measured dosimetry reaction rates
      Table 10:     Gamma-ray spectra 
      Table 11:     TLD Measurements

   Figures are included in GIF format.

SINBAD Benchmark Generation Date: 09/2002
SINBAD Benchmark Last Update: 09/2002