Abstract
The Neutron Radiography Reactor at Idaho National Laboratory (INL) has two beamlines extending radially outward from the east and north faces of the reactor core. The control rod withdrawal procedure has recently been altered, potentially changing power distribution of the reactor and thus the properties of the neutron beams, calling for characterization of the neutron beams. The characterization of the East Radiography Station involved experiments used to measure the following characteristics: Neutron flux, neutron beam uniformity, cadmium ratio, image quality, and the neutron energy spectrum. The ERS is a Category-I neutron radiography facility signifying it has the highest possible rank a radiography station can achieve. The thermal equivalent neutron flux was measured using gold foil activation and determined to be 9.61 × 106 ± 2.47 × 105 n/cm2-s with a relatively uniform profile across the image plane. The cadmium ratio measurement was performed using bare and cadmium-covered gold foils and measured to be 2.05 ± 2.9%, indicating large epithermal and fast neutron content in the beam. The neutron energy spectrum was measured using foil activation coupled with unfolding algorithms provided by the software package Unfolding with MAXED and GRAVEL (UMG). The Monte-Carlo N-Particle (MCNP6) transport code was used to assist with the unfolding process. UMG, MCNP6, and measured foil activities were used to determine a neutron energy spectrum which was implemented into the MCNP6 model of the east neutron beam to contribute to future studies.
Highlights
The Neutron Radiography Reactor (NRAD) facility is a TRIGA-Mark II reactor that produces power up to 250 kWth
The number of radioactive nuclides produced is directly related to the activity of the foil after exposure in the neutron beam per Equation (1) [14], where A represents the activity of the foil after the exposure time texp, N is the number of atoms of the nuclide being irradiated (198Au atoms in the gold foil in this case), σ is the microscopic cross-section of the desired reaction, λ is the decay constant, φo is the neutron intensity incident on the foil and φ is the uncorrected average neutron flux measured from the foils
The image quality is an important metric to characterize for a neutron beam that is used for a neutron imaging facility
Summary
The Neutron Radiography Reactor (NRAD) facility is a TRIGA-Mark II reactor that produces power up to 250 kWth. The East Radiography Station (ERS) neutron beam extends 4.57 m through air and a helium filled aluminum tube starting at the outer east edge of the reactor core. The ERS has an elevator shaft, filled with argon gas, directly connected to the hot cells above which allows easy access to used fuel or other highly radioactive materials in the hot cell. Two complete neutron beam characterizations have been performed at NRAD in the past 30 years, once in 1992 [7] and again in 2013 [8]. Additional fuel elements were added to the NRAD reactor core in 2013, after which the ERS neutron beam was characterized to understand the impact of the new fuel on the beam performance [9]. Each characterization was performed after properties in the reactor core were altered resulting in changes to the neutron beam characteristics
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call