VPT Rad performs all neutron
displacement damage irradiations in a Low-Enriched, open-pool, water moderated, thermal
neutron reactor. It utilizes flat-plate type fuel, and having a maximum thermal energy
output of up to 1 MW. The Fast Neutron Irradiator (FNI) faces one side of the reactor
core, its design produces a geometrical planar beam of fast neutrons that is
approximately uniform over an area of 12 in × 20 in. Lead and thermal neutron absorbing
compounds are combined to filter out both fission gammas and thermal neutrons. The ratio
of fast-to-thermal neutrons is approximately 400:1, with a gamma exposure of less than
150 rad (Si) for a 1E12 n/cm2 (1 MeV Si equivalent) exposure. The FNI can accommodate a
sample or samples with size up to 30 cm in diameter and 15-cm thick including packaging
materials. The minimum neutron fluence rate is 1E6 n/cm2-s. The maximum neutron fluence
rate is approximately 1.0 E11 n/cm2-s. (both values are 1 MeV Si
equivalent).
The neutron fluence rate is determined
using the previously-measured neutron radiation field for the FNI, performed in
accordance with ASTM standards (ASTM F1190 &), and correlated to the measured
reactor power level. The neutron dose is timed to meet the customer-specified fluence
for the irradiation. Neutron dosimetry meeting ASTM standards (ASTM E265) is utilized to
track and make sure that irradiations meet the required minimum. The facility retains
source-suitability with the Defense Logistics Agency (DLA) Laboratory Suitability
Program for ASTM Test Method 1017. The DUTS are typically irradiation in an unbiased
condition as per TM1017. If bias conditions are required, they can be maintained via dry
thimbles connected to the irradiation volume.