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SBE 1.002

1. Name of Experiment:

Measurements for the JASPER Program Axial Shield Experiment (1990-91)

2. Purpose and Phenomena Tested:

This experiment was designed to extend the studies of the effectiveness of different
axial shield designs beyond the fission gas plenum and at the same time provide a
comparison of the neutron attenuation characteristic of stainless steel and boron
carbide as they are integrated into the designs.

3. Description of the Source and Experimental Configuration:

The neutron source was the Tower Shielding Reactor II (TSR-II) located at the Tower
Shielding Facility at Oak Ridge National Laboratory. The emergent source spectrum
was modified to be similar to that predicted for the LMR (liquid metal reactor) 
design. The spectrum modifier was composed of iron, aluminum, boral, followed by a 
radial blanket comprised of natural uranium, aluminum, and sodium.

The configurations to be studied included seven hexagons containing three different
internal geometrical designs. The designs consisted of: (1) a central blockage type
in which the coolant flowed around a central shield plug; (2) a rod bundle type in
which the shield material was in the form of small rods spaced for coolant flow; and
(3) an annular type in which the coolant flowed centrally through the fuel assembly.
These designs were used for two different shield materials, boron carbide and 
stainless steel. The configurations were positioned in the horizontal beam emerging
from the reactor shield, preceded by the spectrum modifier. The seven assemblies 
were contained in an aluminum honeycomb surrounded by boron carbide and contained in
a concrete slab. Changes were made by the removal and insertion of various hexagon 
assemblies into the aluminum honeycomb.

4. Measurement System and Uncertainties:

Four different types of detection systems were used in this experiment. A set of 
Bonner balls (3-, 4-, 5-, 8-, 10-, and 12-inches diameter) filled with BF3 gas was 
used to measure the neutron flux. In order to cover a range of neutron energies, the
counter was used bare, covered with cadmium, or enclosed in various thicknesses of 
polyethylene shells surrounded by cadmium. A NE-213 liquid scintillator measured the 
neutron spectrum from about 800 keV to 15 MeV. Spherical proton-recoil counters, 
filled with hydrogen to pressures of 1, 3, and 10 atmospheres, covered the neutron 
energy range from about 50 keV to 1 MeV. The Hornyak button detector consisted of a
lucite button interspersed with zinc sulfide mounted on a photomultiplier tube. It 
was used to measure the absorbed energy per gram and to define the neutron streaming
effect where small gaps existed in the mockup structure.

The uncertainty in the reactor power determination was assumed to be +/- 5%. The 
NE-213 and hydrogen counter measurements were expressed in terms of lower and upper
limits that represented a 68% confidence interval. Both of the spectra for these 
counters has an error of about +/- 5%. The error in the Hornyak button measurements
depends largely on the ability to maintain a constant temperature. The errors
assigned to both the Bonner ball and Hornyak button detector measurements should lie
within about +/- 10%.

5. Description of Results and Analysis:

Twelve different measurements of the neutron spectra were taken: (1) spectrum 
modifier, (2) B4C homogeneous hexagon, (3) SS homogeneous hexagon, (4) B4C central 
blockage + B4C homogeneous assemblies, (5) B4C central-blockage type assemblies,
(6) SS central blockage assembly + 6 SS homogeneous-type assemblies, (7) SS central-
blockage-type assemblies, (8) fission gas plenum + the 7 B4C central-blockage-type
assemblies, (9) B4C rod bundle + B4C homogeneous-type assemblies, (10) SS rod bundle
+ SS homogeneous-type assemblies, (11) B4C central Na channel assembly + B4C 
homogeneous-type assemblies, and (12) SS central Na channel assembly + SS 
homogeneous-type assemblies.

Data from the Bonner ball measuremens was predicted analytically by folding a 
calculated neutron spectrum with Bonner ball response functions. The NE-213 
spectrometer pulse-height data was unfolded with the FERD code to yield absolute 
neutron energy spectra. Pulse-height data from the proton-recoil counters was
unfolded with the SPEC-4 code. 

The measurements for each detector were referenced to the reactor power (watts) 
using the data from two fission chambers positioned along the reactor centerline as
a basis.

6. Special Features:

This report has recently been released by the U.S. Department of Energy.

7. Author/Organizer:

Experiment and Analysis:
    F.J. Muckenthaler*, R.R. Spencer*, H.T. Hunter*, A. Shono**, K. Chatani**
    * Oak Ridge National Laboratory
    ** Japan Power Reactor and Nuclear Fuel Development Corporation

Compiler of data for SINBAD:
    Jennifer Parsons, RSICC, Oak Ridge National Laboratory, P.O. Box 2008, Oak 
    Ridge, TN 37831-6362

Reviewer of compiled data:
    Hamilton Hunter, RSICC, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge,
    TN 37831-6362, fax 423-574-6182, e-mail h3o@ornl.gov

8. Availability:


9. References:

[1] F.J. Muckenthaler, R.R. Spencer, H.T. Hunter, A. Shono, and K. Chatani, 
    "Measurements for the JASPER Program Axial Shield Experiment," Oak Ridge 
    National Laboratory, ORNL/TM-11839 (August 1991).
[2] R.E. Maerker et al., "Calibration of the Bonner Ball Neutron Detectors Used at
    the Tower Shielding Facility," ORNL/TM-3465 (June 1971).
[3] C.E. Burgart and M.B. Emmett, "Monte Carlo Calculations of the Response 
    Functions of Bonner Ball Neutron Detectors," ORNL/TM-3739 (April 1972).
[4] B.W. Rust, D.T. Ingersoll, and W.R. Burrus, "A User's Manual for the FERDO and
    FERD Unfolding Codes," ORNL/TM-8720 (September 1983).
[5] J.O. Johnson and D.T. Ingersoll, "User's Guide for the Revised SPEC-4 Neutron
    Spectrum Unfolding Code," ORNL/TM-7384 (August 1980).
[6] F.J. Muckenthaler et al., "Measurements for the JASPER Program Fission Gas 
    Plenum Experiment," ORNL/TM-10422 (June 1987).

10. Data and Format:

    (1)-(14) Composition and analysis tables of different set-ups
    (15)-(16) Neutron fluxes on centerline at 179.1 cm behind the radial blanket
    (17)-(22) Bonner ball measurements
    (23)-(24) Neutron fluxes on centerline at 32.6 cm behind axial shield
    (25) Hornyak button measurements
    (26)-(27) Neutron fluxes on centerline at 98.3 cm behind axial shield
    (28)-(29) Neutron fluxes on centerline at 36.2 cm behind axial shield

    (1) Schematic of spectrum modifier-1
    (2) Schematic of radial blanket slab
    (3)-(10) SS and B4C hexagon assembly configurations
    (11) Schematic of heterogeneous fission gas plenum
    (12) Schematic of aluminum mesh
    (13) Lithiated paraffin background shield
    (14)-(15) Schematic of axial shield configurations
    (16)-(21) B4C and SS radial traverses using the Hornyak button
    (22) Schematic of fission gas plenum and seven B4C central leakage type mockups
    (23)-(27) B4C and SS radial traverses using the Hornyak button

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SINBAD Abstract Generation Date: 08/98
SINBAD Abstract Last Update: 08/98