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SBE 15.001

US NRC Benchmark

1. Name of Experiment:

Pool Critical Assembly-Pressure Vessel Facility Benchmark (1980)

2. Purpose and Phenomena Tested:

The PCA Benchmark purpose was to validate the capabilities of the calculational 
methodology to predict the reaction rates in the region outside a reactor core 
when the neutron source, material compositions, and geometry are well defined.  
The PCA facility mocked-up the core-to-cavity region in an LWR.

3. Description of the Source and Experimental Configurations:

The PCA Source was composed of 25 material test reactor (MTR) new fuel elements, 
with a 93% U235 enrichment.  The light-water moderated reactor core contained 
fuel plates of 62.548-cm-length and arranged in approximately 40-cm-square.  
The core contained 4 control assemblies for reactivity control.  

The power distribution of the fuel elements were obtained from fission chamber
measurements and calculations.  The core power is symmetric, therefore only 1/2 the 
core needs to be specified. Individual fuel element powers are provided by a two-
dimensional distribution function.

The PCA mockup consists of stacked slabs of the following: 1)aluminum window 
simulator 2)Thermal Shield 3)Pressure Vessel Simulator 4)Pressure Vessel Cavity
Simulator (Void).  Water filled the gaps between the slabs of materials. 

4. Measurement Systems and Uncertainties:

The measurements were made with Np237 and U238 fission chambers and Rh103, In115, 
Ni58, and Al27 activation dosimeters at the core midplane.  The positions included 
key reactor capsule locations of 1/4 T, 1/2T, and 3/4T of the RPV.  The experimental
access tubes allowed centralized placement of dosimeters and were filled with a 
similar material that surrounded each tube to minimize flux perturbations.  

All fuel element specifications are within +/- 0.1 cm (2 sigma), and the 
experimental configuration is within +/-0.2 cm (2 sigma) of the specified 
dimensions.  The as-built and plan design specifications for the 12/13 experiment 
show differences of up to 0.4 cm for material placement.

The uncertainties for the measured equivalent fission fluxes are between 6 and 10%.

5. Description of Results and Analysis:

The measurements are reported at distances from the aluminum window simulator 
of 12, 23.8, 29.7, 39.5, 44.7, 50.1, and 59.1 cm.  All reaction rate measurements
are converted to Equivalent Fission Fluxes and normalized to the core neutron source
strength of 1 n/s.  The reaction cross sections, averaged over U235 fission spectrum
are provided.  Only the 12/13 results are provided here (12 cm water between 
aluminum window and thermal shield, 13 cm water between thermal shield and pressure 

6. Special Features:


7. Author/Organizer:

  Experiment and analysis:

W. N. McElroy, et al.
  Compiler of data for SINBAD:

Hamilton Hunter, Radiation Shielding Information Center, Oak Ridge National 
Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6362, fax 423-574-6182, e-mail 

  Reviewer of compiled data:

I. Remec, Nuclear Analysis and Shielding Section, Oak Ridge National Laboratory,
P.O. Box 2008, Oak Ridge, TN 37831-6363.

8. Availability:


9. References:

[1]     I. Remec and F. B. K. Kam "Pool Critical Assembly Pressure Vessel Facility
        Benchmark," NUREG/CR-6454 ORNL/TM-13205 1997.

[2]     W. N. McELroy, ed., "LWR Pressure Vessel Surveillance Dosimetry Improvement
        Program:PCA Experiments and Blind Test,"  NUREG/CR-1861
        (HEDL-TME 80-87 R5), July 1981. 

[3]     Personal Communication with I. Remec, June, 1998.

10. Data and Format:

    (1) PCA Fuel Element Position,
    (2) PCA Core Dimensions,
    (3) Dimensions of PCA ex-core components, 
    (4) Material compositions for PCA ex-core components

    Fig. 1 PCA Facility,
    Fig. 2 PCA plan view,
    Fig. 3 PCA elevation,
    Fig. 4 Fuel element position,
    Fig. 5 Fuel cell boundary/aluminum window
    Fig. 6 Fuel element
    Fig. 7 Fuel side plates
    Fig. 8 Fuel plates
    Fig. 9 Control rod
    Fig.10 PCA measurement coordinate system
    Fig.11 1/2 core integral power density
    Fig.12 1/4 core normalized measured power densities
    Fig.13 PCA Detector results

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Abstract Generation Date: 06/98

Abstract Last Update: 08/98