ACRRF High-Bay Dose Calculations using MCNP (Part A)

Dodson, Zackary Glen [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)] (ORCID:0000000271704465); Cardoni, Jeffrey N. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)] (ORCID:0009000466954496)

doi:10.2172/3257082

DOE OSTI · 3257082

ACRRF High-Bay Dose Calculations using MCNP (Part A)

Dodson, Zackary Glen [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)] (ORCID:0000000271704465)·Cardoni, Jeffrey N. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)] (ORCID:0009000466954496)

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Abstract

Analytical tools and models have been developed as a starting point for directly assessing dose in the Annular Core Research Reactor Facility (ACRRF) due to reactor operation. Key results include peak dose along the Central Cavity (CC) centerline (beamline) at the cavity level, dose throughout the High-Bay (HB), and dose on the facility roof for partially-shielded reactor operation where the 4” insert is removed from the CC Shield Plug (SP). Model results in the beamline are benchmarked against measured doses from passive dosimetry evaluations. Personnel total (neutron and gamma) dose in the ACRRF HB is calculated using Monte Carlo N-Particle (MCNP). Various CC and SP configurations are analyzed, including unshielded (no SP) and partially shielded (SP installed but 4” insert removed). Novel application of Variance Reduction (VR) techniques, namely the Surface Source Write (SSW) and Surface Source Read (SSR) capabilities in MCNP, enable impressive resolution (in a Monte Carlo modeling sense) of dose throughout much the facility. The VR techniques reduce stochastic error for challenging tallies, with more advanced techniques explored in the companion to this report (Part B) [1]. Supplementary studies (including a verification analysis) and pedagogic evaluations in Part B involve neutron spectra, angular distributions, and the dose impact of facility characteristics. With the SP 4” insert removed and the Lead-Boron (44”) Bucket (LB–44) in the reactor cavity, Total Effective Dose (TED) within the CC beamline is ≈140 rem per 300 MJ of reactor yield (or 3900 rem per hour at 100% Steady-State (SS) power). With no SP (unshielded) and a Free-Field (FF) cavity, TED within the beamline is ≈610 rem per 300 MJ (or 17000 rem per hour at 100% SS power). Due to the predicted collimation of radiation by the reactor pool (and partial SP, if present), beamline dose is much greater than the scattered radiation field surrounding the cavity and reactor tank. Comparisons are made to beamline dosimetry measurements to validate the model. Model predictions agree reasonably well (⪅10%) with measured quantities of neutron fluence, gamma fluence, and spectral metrics. Away from the beamline, comparisons made to previous dose measurements in the HB agreement within an order of magnitude.

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Dodson, Zackary Glen [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)] (ORCID:0000000271704465), Cardoni, Jeffrey N. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)] (ORCID:0009000466954496). 2026-04-01. ACRRF High-Bay Dose Calculations using MCNP (Part A). https://doi.org/10.2172/3257082

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