OVERVIEW
Cavendish Nuclear's fast neutron detector based Plutonium Hold-Up Measurement System (PHUMS) is a lightweight, compact and portable assay system with the flexibility to measure the nuclear material content of a wide range of objects including process cells, facilities, gloveboxes, pipes and drums to inform Post Operation Clean Out strategies.
AT A GLANCE
• The ultimate tool for informing Post Operation Clean Out strategy, decommissioning, waste management and security applications • Unique, modular, mobile design for the in-situ assay of a wide range of object sizes and shapes • Calculates both plutonium mass and distribution • Determines information for use in pre- commencement safety cases • State of the art fast neutron counting technology • Novel analytical methods including likelihood expectation and clustering techniques • Optional High Resolution Gamma Spectrometry system for Pu isotopics analysis
THE PRODUCT IN DETAIL
The PHUMS is an innovative and novel analysis method that combines the latest in fast neutron detection technology with advanced analysis techniques to allow characterisation of extended environments such as a process cell or facility, or glovebox line, as well as discrete objects such as individual gloveboxes or drums. Fast neutron measurements can be conducted quickly and easily with minimal disruption to the environment within which the detectors are deployed. The number of detectors and the duration and number of measurements taken can be tailored to suit the object under investigation and its environment to ensure optimum measurement coverage. Using the Cavendish Nuclear developed fast neutron detection system it is possible to determine both the mass and distribution of nuclear material within the item being measured. Each fast neutron detector is pre- calibrated prior to deployment to ensure that it is operating optimally and the response of the detector is fully determined before deployment. Multiple detectors can be deployed to minimise measurement times and thereby reduce operator dose uptake whilst still ensuring adequate coverage of the item being investigated. The measurement data available for analysis is extensive, enabling neutron energy spectrum information. total fast neutron count rates, fast to thermal neutron ratio, and the ratio of spontaneous fission neutrons to (a,n) neutrons to be determined. This extensive dataset makes Cavendish Nuclear’s fast neutron detection capability unique and an ideal way to inform Post Operation Clean Out (POCO) strategy. Most characterisation methodologies do not allow for robust uncertainties to be fully determined as, typically, only one of the many valid solutions is calculated. However, by combining “likelihood expectation” strategies with novel clustering methods a near complete set of solutions is found. This permits a best estimate plutonium mass to be determined with much more robust uncertainties. As PHUMS does not rely on background shielding Model showing detector position around gloveboxes within a process cell of the detectors, the analytical modelling • Perform likelihood expectation. can be set up so that the detectors are thought of as being within • Generate neutron emission. the environment and not just around an • Generate plutonium mass and object. This approach makes the PHUMS uncertainty ideal for characterisation of entire cells • Typically takes between 10 minutes or facilities and several hours dependent upon The analysis consists of three phases: 1) Measurement Phase • Measurements taken throughout cell for > 5 minutes. The duration and number of measurements is chosen to give optimum coverage. • Typically takes between 1 and 5 days dependent upon cell / facility size. 2) Modelling Phase • MCNP model created for scene / environment. • Generate point set. • Determine build up and transmission factors. • Time depends on complexity of model but does not need repeating for subsequent deployments in same location. 3) Solution Phase • Construct response matrix. • Subdivide point set complexity. An optional high resolution gamma spectrometry (HRGS) system may be deployed to supplement the fast neutron measurements in order to determine plutonium isotopic composition. PHUMS trials have been successfully undertaken in a range of different environments validating the suitability of the system as a plutonium hold-up characterisation method suitable for use in POCO strategy development. In a number of cases it has been possible to verify results by comparison with deployments of existing well proven hold-up characterisation methods such as Cavendish Nuclear’s DISPIM (Decommissioning In-Situ Plutonium Imaging Monitor) system.
FOR MORE INFORMATION, CONTACT:
Jonathan Britton - Product & Services Manager, Cavendish Nuclear, 106 Dalton Avenue, Birchwood, Warrington, Cheshire  WA3 6YD +44 (0)1925 377800  instrumentservices@cavendishnuclear.com