Radiant energy – Invisible radiant energy responsive electric signalling – Including a radiant energy responsive gas discharge device
Reexamination Certificate
1999-05-07
2002-04-02
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Including a radiant energy responsive gas discharge device
C250S394000, C250S376000
Reexamination Certificate
active
06365901
ABSTRACT:
The present invention concerns improvements in and relating to monitoring and/or detecting and particularly, but not exclusively, to monitoring items such as pipes, for alpha source contamination.
Any item which passes time within the active area of a nuclear facility may become contaminated by radioactive material from within that area. As a result, before the item can be removed and subsequently re-used, disposed of or recycled, its potential contamination needs to be evaluated.
The absence of contamination may allow an item to be re-released. The higher grade of waste items are categorised as, the greater the storage/disposal costs which apply to their decommissioning.
It is therefore important to check the level of contamination in order to appropriately and cost effectively dispose of the item.
Detection and monitoring of alpha contamination of such items presents a number of difficulties, principally due to the short distance over which alpha particles can be detected. Alpha particles are stopped by tens of micrometers of solid material and within a few centimetres in air. Detectors further away in these distances cannot detect the alpha contamination.
In certain scenarios this, therefore, makes the detection of the alpha contamination very difficult, calling for close proximity scanning of the article with a detector.
In other scenarios, such detection is physically impossible as the inside surfaces of, for example, pipes, scaffolding and ducts are simply not accessible to such detectors and yet the detectors cannot monitor the alpha contamination through the walls of such items.
With any it can be useful to be able to locate the position of a source of contamination. Such information may allow more accurately controlled subsequent decontamination to take place or may also allow the item to be cut into one or more pieces some of which are substantially free from contamination and may thus be more easily disposed of.
The present invention aims to provide apparatus and methods for the monitoring of items for alpha contamination, and also to provide information relating to the position of the alpha contamination within or on the item. Systems for evaluating the position of other forms of contamination are also provided.
According to a first aspect of the invention we provide a system for monitoring alpha emitting sources on an item/location, the item/location being in contact with a medium, alpha emissions generating ions in the medium, the system comprising an instrument having a detecting chamber, the detecting chamber being provided with one or more electrodes for discharging ions, the instrument further being provided with means to monitor ions discharged on the electrode(s) to generate discharge with time data, the system being provided with means for moving the medium from in proximity to the item/location through the detecting chamber in a controlled manner, the discharge monitoring means monitoring the discharge occurring with time, the instrument being provided with processing means for converting the discharge with time data into alpha source position on the item/location data.
The item(s) to be monitored may be or include tools, pipes, pumps, filters, cables, beams, rods and the like, but particularly elongate items. The locations may include surfaces in general, such as floors, walls, ceilings, soil, rubble, material on a conveyor, and include parts of, or surfaces of items, such as glove boxes, tanks, vessels and the like.
Preferably the item is mounted or supported so as to maximise the surface area exposed, for instance to the medium flow.
The item or location may be introduced within the detecting chamber.
The item or location may be monitored in-situ. The item or location may be connected to the detecting chamber by medium conveying means, such as a pipe or conduit. The conveying means may be temporarily connected to the item or location. The conveying means may be provided as a part of the instrument. The conveying means, item or location and detecting chamber may define a closed circuit.
The medium may be a fluid, such as a liquid, but is preferably a gas. The gas may be a mixture, such as air, or may be in substantially single gas form, such as argon.
The detecting chamber may comprise an elongate chamber. The detecting chamber may have a circular or rectilinear cross-section.
The detecting chamber may be provided with an inlet and an outlet, the electrodes being provided between the inlet and the outlet. The inlet and/or outlet may connect to the surrounding environment for the instrument, for instance to give an open circuit instrument. The inlet and/or outlet may connect the instrument to the item or location, for instance through intermediate fluid conveying means, for instance to give a closed circuit.
Preferably means are provided within the system to remove extraneous ions and/or particulate matter. The ions and/or particles may be removed by a filter. A filter may be provided between downstream of the electrodes. The filter may, for instance be provided in the medium conveying means prior to the item or location. A filter is preferably provided in this way in a sealed system.
Particularly in an open system, a filter may be provided between the inlet from the surrounding environment and the item or location and/or detecting chamber. A filter may be provided between the detecting chamber and the outlet to the surrounding environment.
The detecting chamber may be openable to introduce or remove an item or location, for instance for an open circuit. The detecting chamber may comprise a sealable chamber, for instance for a closed circuit. The seal may be broken to make the chamber accessible to introduce and/or remove an item to be monitored.
Preferably the item or location is positioned upstream in the medium flow relative to the electrodes, where medium flow is used to move the ions.
The instrument may be provided with a single electrode. The instrument may be provided with a charged element or plate, such as an electret.
Preferably the detecting chamber is provided with a plurality of electrodes, the electrodes being spaced from one another. The electrodes may be configured with a first outer electrode and a second outer electrode and none or one or more intermediate electrodes provided there between.
The electrodes are preferably arranged parallel to the direction of medium flow. Preferably the medium flow passes through the spacing between the electrodes.
One or more, and preferably all, of the electrodes may be planar. Preferably the electrodes are provided parallel to one another. Preferably the electrodes are provided in opposition, for instance, an outer electrode being opposed by one electrode, an intermediate electrode being opposed by two electrodes. The spacing between the electrodes is preferably the same between each pair of opposing electrodes. The spacing between the outer electrodes and the detector chamber is preferably the same as between opposing electrodes.
The electrodes may be continuous, such as a plate, or discontinuous, such as a grid.
An applied, preferably externally generated, potential may be employed. The electrical potential is preferably provided by an external power source. An electrostatic potential may be employed, for instance from a charged plate or element, such as an electret.
Potentials of between 10 V and 1000 V may be provided.
The means for monitoring ions discharged and/or collected on the electrode(s) may comprise electrostatic charge monitoring means. More preferably the means for monitoring ions discharged on the electrode(s) comprise current indicating means and more preferably current measuring means. Preferably a single current measuring means is used. Preferably the combined current of all the electrodes connected to the current measuring means is measured. An electrometer, and most preferably a ground referenced electrometer is preferred for this purpose.
The means for moving the medium may comprise a piston provided in a bore in fluid connection with the detector chamber. The piston may be provi
Bounds John Alan
Dockray Thomas
Luff Craig Janson
Macarthur Duncan Whittemore
Orr Christopher Henry
British Nuclear Fuels PLC
Hannaher Constantine
Israel Andrew
Workman & Nydegger & Seeley
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