The N2072 Passive Neutron Decommissioning Piece Monitor is a high efficiency passive neutron counter designed for the measurement of plutonium contaminated size reduced pieces arising from the decommissioning of nuclear plant and equipment. The system can also be used to measure plutonium bearing material in storage containers.
The N2072 performs passive neutron counting of the correlated neutrons arising from spontaneous fission of the even Pu nuclides, principally 240Pu. The measurement chamber can be installed outside of any Modular Containment System or similar exclusion zone. This can be adjacent to a convenient baggage port through which size reduced pieces are introduced for measurement. A closure plug is provided for the top of the measurement chamber.
Plant measured isotopic ratios can be used by the software in order to convert 240Pueffective mass to total Pu mass. Alternatively a suitable germanium gamma-ray detector can be conveniently installed through the base polyethylene shield plug to interrogate the sample and determine the Pu isotopic ratios independently using PC-FRAM or other isotopic code.
The neutron detection system consists of 72 3He tubes arranged in two concentric rings of 36 tubes embedded in a polyethylene moderator; 18 sets of 4 tubes are connected to a high voltage junction box containing an Amptek charge sensitive amplifier/discriminator circuit and connections for high voltage, low voltage and signal cables. The detectors are embedded in a polyethylene moderator, which includes a thickness of 230 mm back shielding for operation in relatively high neutron background environments. The outer surface is covered in stainless steel cladding. The internal and external moderator surfaces are covered in cadmium to prevent thermalised neutrons from re-entering the sample measurement cavity.
The N2072 can be used with either a Multiplicity Shift Register with INCC-32 software or the N2000 Universal Neutron Counter with A2000-15 LVDS. In either case the system can be operated in conventional shift register coincidence counting (reals) mode (with a calibration function), multiplicity counting list mode, or totals counting mode.
The chamber is portable and housed on a robust trolley with locking castors for safety and stability.