Publications

This document presents the facility - recommended characterization of the neutron, prompt gamma - ray, and delayed gamma - ray radiation fields in the Annular Core Research Reactor ( ACRR ) Fueled - Ring External Cavity II (FREC - II) for the free - field environment at the core centerline. The designation for this environment is ACRR - FRECII - FF - cl. The neutron, prompt gamma - ray, and delayed gamma - ray energy spectra, uncertainties, and covariance matrices are presented as well as radial and axial neutron and gamma - ray fluence profiles within the experiment area of the cavity. Recommended constants are given to facilitate the conversion of various dosimetry readings into radiation metrics desired by experimenters. Representative pulse operations are presented with conversion examples.

The Annular Core Research Reactor (ACRR) recently underwent a multi-department effort to characterize the neutron energy leakage spectra in the reactor High Bay for multiple shielding configurations. The ACRR Operations Department identified and obtained a Rotating Neutron Spectrometer (ROSPEC) from Los Alamos National Laboratories (LANL) for obtaining neutron energy spectra. Spectra were obtained in the following facility configurations; Fuel Ringed External Cavity, Version II (FREC-II) decoupled with the standard FREC shield plug installed with the following operational permutations: the 4-inch central cavity (CC) shield plug removed in both a free-field (FF) and 44(3y (Blead-boron (LB-44) bucket neutron modifier configuration, fully shielded CC plug FF condition, neutron radiography collimator aperture settings 250:1, 125:1, and 65:1, FREC-II coupled with both the lightweight (2T1) and standard shield plug configurations. The ROSPEC spectrum results were unfolded, evaluated and weighted using the International Commission on Radiation Protection (ICRP) 103 neutron radiation weighting factors to obtain a ratio amongst the different shielding configurations at the ACRR. Results of the collected spectra confirm that the predominant neutron energy range in the High Bay area is less than or equal to 250 keV.

This document presents the facility-recommended characterization of the neutron, prompt gamma-ray, and delayed gamma-ray radiation fields in the Annular Core Research Reactor (ACRR) for the cadmium-polyethylene (CdPoly) bucket in the central cavity on the 32-inch pedestal at the core centerline. The designation for this environment is ACRR-CdPoly-CC-32-cl. The neutron, prompt gamma-ray, and delayed gamma-ray energy spectra, uncertainties, and covariance matrices are presented as well as radial and axial neutron and gamma-ray fluence profiles within the experiment area of the bucket. Recommended constants are given to facilitate the conversion of various dosimetry readings into radiation metrics desired by experimenters. Representative pulse operations are presented with conversion examples. Acknowledgements The authors wish to thank the Annular Core Research Reactor staff and the Radiation Metrology Laboratory staff for their support of this work. Also thanks to Drew Tonigan for helping field the activation experiments in ACRR, David Samuel for helping to finalize the drawings and get the parts fabricated, and Elliot Pelfrey for preparing the active dosimetry plots.

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The Annular Core Research Reactor (ACRR) at Sandia National Laboratories (SNL) is an epithermal pool-type research reactor licensed up to a thermal power of 2.4 MW. The ACRR facility has a neutron radiography facility that is used for imaging a wide range of items including reactor fuel and neutron generators. The ACRR neutron radiography system has four apertures (65:1, 125:1, 250:1, and 500:1) available to experimenters. The neutron flux and spectrum as well as the gamma dose rate were characterized at the imaging plane for the ACRR's neutron radiography system for the 65:1, 125:1 and 250:1 apertures.

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