The High Flux Isotope Reactor's Horizontal Beam Tubes

Cross-section showing HFIR's horizontal beam tubes

Cross-section showing HFIR's horizontal beam tubes

The reactor has four horizontal beam tubes that supply the neutrons to the neutron scattering instruments.

HB-1 and HB-3

The HB-1 and HB-3 thermal neutron beam tube designs are identical except for the length. Both are situated tangential to the reactor core so that the tubes point at reflector material and do not point directly at the fuel. An internal collimator is installed at the outboard end. This collimator is fabricated out of carbon steel and is plated with nickel. The collimator provides a 2.75-in by 5.5-in. rectangular aperture.

A rotary shutter is located outboard of each of these beam tubes. The shutter is fabricated using carbon steel and high-density concrete. The purpose of the shutter is to provide shielding when the neutron beam is not required.

Instruments on HB-1

Instruments on HB-3

HB-2

The HB-2 thermal neutron beam tube is situated radially relative to the reactor core, looking directly at the fuel. Two beryllium inserts are installed in the spherical tip of the beam tube to maximize the thermal neutron flux within the critical acceptance angle of the neutron scattering experiment equipment. The beam tube cavity outboard of the reactor vessel has a rectangular cross-section that converges vertically and diverges horizontally such that the aperture at the outboard window is a rectangle nominally 6-in tall by 10-in wide. A carbon steel collimator assembly is located just outboard of the beam tube window. This collimator assembly provides further neutron-beam collimation and houses a fast-neutron filter to increase the signal-to-noise ratio at the neutron scattering instruments.

A rotary shutter is located outboard of the outer collimator assembly. The shutter is fabricated using carbon steel and high-density concrete. High-density concrete blocks are placed around the shutter to prevent streaming. The purpose of the shutter is to provide shielding when the neutron beam is not required.

Instruments on HB-2

HB-4

The HB-4 cold neutron source beam tube is situated tangential to the reactor core so that the tube points at reflector material and does not point directly at the fuel.

A vacuum tube fits closely inside in-vessel section of the HB-4 beam tube all the way to the spherical end. The vacuum tube contains and insulates a hydrogen moderator vessel and its associated tubing. The moderator vessel contains supercritical hydrogen at 17K (nominal). Thermal neutrons scattered into the moderator vessel from the reflector are scattered and cooled by the hydrogen so that the 4-12 Å neutrons scattered down the tube are maximized.

An internal collimator is installed in the outboard end of the HB-4 tube. This collimator is fabricated out of carbon steel and is plated with nickel. The collimator provides three rectangular apertures. The outboard dimensions of the apertures are 1.61 in by 4.33 in; 2.17 in by 3.65 in; and 1.78 in by 4.33 in.

A rotary shutter is located outboard of the outer collimator assembly. The shutter is fabricated using carbon steel and high-density concrete. The purpose of the shutter is to provide shielding when the neutron beam is not required. The shutter has provisions for routing the cryogenic hydrogen transfer line, gaseous helium, and vacuum piping necessary to support the cold source.

Instruments on HB-4