ORTEC - Antech Model 2200 Passive Neutron Drum Monitor

ANTECH Model 2203
Very High Efficiency Neutron Counter (VHEnC)

Modular construction based on the well-proven ANTECH 'decagon' design for the neutron counting of 200 litre waste drums.
Multiple neutron measurement methods include: neutron totals counting mode for very low level measurements, neutron coincidence counting to reach lower level detection thresholds and neutron multiplicity counting to perform matrix correction where sufficient Pu mass is present in the chamber.
The system can also be operated as an absolute neutron multiplicity system, independent of calibration for intermediate level waste.
Removable internal cadmium filters allow detection efficiency to be varied in accordance with the measurement requirement.
Very high detection efficiency, typically 36% with Cd filters deployed and between 41% and 45% with the internal Cd liner removed.
Semi-automatic drum loading and unloading.

nda4.gif (19603 bytes) The ANTECH Model 2203 Very High Efficiency Neutron Counter (vHENC) has a typical detection efficiency of 36% with Cd filters deployed and between 41% and 45% with the internal Cd liner removed. It is used for the determination of the plutonium mass in intermediate and low level waste in 200 litre drums.

The operation of the instrument is based on passive neutron counting of the correlated neutrons arising from spontaneous fission of the even Pu nuclides, principally ²⁴⁰Pu. The neutron detection system consists of 16 polyethylene modules each containing ten, 6 atmosphere 1-inch ³He tubes. The tubes are connected using HN connectors to a junction box at the top of the vertical modules or on the end of the horizontal modules. The junction boxes are hermetically sealed and contain not only the high voltage distribution and charge collection circuitry, but also the AMPTEK model A-111 charge sensitive amplifiers. The detector modules are housed inside an outer shielding of 270 mm thickness of polyethylene.

Cadmium thermal neutron filters are installed and surround the high energy neutron detector modules. Where the cadmium is exposed, it is clad in aluminium. Removable cadmium on the internal face of the vertical modules and the internal face of both the bottom and top modules facilitates changing the configuration of the drum monitor to a higher efficiency unfiltered configuration.

The vHENC is coupled with an Advanced Multiplicity Shift Register (AMSR-150) that uses an optimised version of the LANL INCC code based on super-HENC technology for cosmic-ray reduction. This involves both multiplicity distribution truncation and veto counting of adjacent detectors to reduce the cosmic-ray generated coincidence background.

The vHENC is available with ‘Add-a-Source’ Cf-252 based matrix correction capability, as an option. This is a well established technique for matrix correction and is appropriate where low count rates and small quantities of material are present in the measurement chamber. 'Add-a-Source' complements matrix correction by neutron multiplicity counting. The system consists of typically an 80 mCi ²⁵²Cf source deployed on a ‘Teleflex’ cable with associated shielding, motor drive and control.

The vHENC can be operated in conventional shift register coincidence counting (reals) mode (with a calibration function), the absolute multiplicity counting mode (histogram function) or totals counting mode. Plant measured isotopic ratios can be used by the software to convert ²⁴⁰Pu_effective mass to total Pu mass.

Specifications

160 He-3 detector tubes, 25.4 mm x 1.0 m at 6 Atmospheres
Detection efficiency typically 36% with Cd filters deployed and between 41% and 45% with the internal Cd liner removed
Operating Voltage: ~1650 volts
Die-away time: <40 ms
Minimum detection limit of between 1.3–15 mg ²⁴⁰Pu_effective in coincidence (reals) mode equivalent to between ~20 and 250 mg total Pu (military grade)
Weight: 3500 kg approx
Dimensions: (L x W x H) 3.3 m x 1.8 m x 2.1 m

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