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WO1995010840A1 - Separation thermique du tritium et appareil prevu a cet effet - Google Patents

Separation thermique du tritium et appareil prevu a cet effet Download PDF

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Publication number
WO1995010840A1
WO1995010840A1 PCT/GB1994/002201 GB9402201W WO9510840A1 WO 1995010840 A1 WO1995010840 A1 WO 1995010840A1 GB 9402201 W GB9402201 W GB 9402201W WO 9510840 A1 WO9510840 A1 WO 9510840A1
Authority
WO
WIPO (PCT)
Prior art keywords
sample
tritium
gas
humidified
chamber
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/GB1994/002201
Other languages
English (en)
Inventor
Geoffrey Vincent Atkins
Paulo Pacenti
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
European Economic Community
Original Assignee
European Economic Community
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by European Economic Community filed Critical European Economic Community
Publication of WO1995010840A1 publication Critical patent/WO1995010840A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/28—Treating solids
    • G21F9/34—Disposal of solid waste
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/02—Treating gases
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/28—Treating solids
    • G21F9/30—Processing
    • G21F9/32—Processing by incineration

Definitions

  • This invention relates to thermal separation of tritium from nominally-radioactive material.
  • the present invention is concerned especially, though not exclusively, with methods and apparatus for thermal separation of tritium from samples of potentially-radioactive waste material. These methods and apparatus are required, for example, for radioactive-contamination assessment of waste material, and in particular for the declassification of the waste to a non-radioactive status in compliance with limits established by regulatory bodies.
  • Separation techniques previously used involve combustion of the material.
  • oxygen as oxygen itself, or in air
  • Tritium is released as tritium gas or as tritiated water vapour, but in some cases the sample commences aerobic (oxygen related) degradation prior to the ignition point, so that decomposition products, which may not be completely combusted upon exit from the heated section of the apparatus, are released as well.
  • the present inventors have developed a method for thermal separation of tritium that has a number of advantages over the known methods of separation for radioactive materials. This method is particularly useful for determining the amount of tritium in a bulk sample of material and therefore determining its status for the purposes of disposal.
  • a method for thermal separation of tritium from nominally-radioactive material comprises stripping tritium from said material into a stream of humidified gas.
  • the humidified gas is passed over and/or through said nominally-radioactive material which is positioned in a heated chamber or furnace.
  • Tritium in the sample of material generally in the form of tritiated water, is stripped into the humidified gas either by simple transfer of the tritiated water to the gas or by isotope exchange between the water vapour in the gas and the tritium in the sample.
  • the gas used, at least initially, in this first aspect of the invention is inert and may be, for example, nitrogen that is supplied, humidified and heated to pass over and/or through the material.
  • the supply of metered, humidified inert gas may be maintained to complete the stripping process without combustion of the test material.
  • the supply of nitrogen may be replaced by a metered supply of humidified air (or oxygen) to allow controlled combustion of the sample.
  • the sample material and the inert humidified gas may be heated to a temperature of about 200 to 400°C.
  • the humidified gas is pre-heated to the appropriate temperature before coming into direct contact with the sample. This may be achieved by using the heat from the furnace to heat the gas, for example by passing the gas around the outside walls of the furnace before passing therein.
  • the humidified gas loaded with tritiated water after being in contact with the sample of radioactive material, exits the furnace.
  • the furnace For determination of the amount of tritium in the sample, it may be passed through condensing means and the condensate collected and subjected to scintillation counting.
  • the passage of an inert humidified gas over and/or through the sample for a pre-determined period of time without combustion may be sufficient to determine the tritium content thereof and is useful in situations where it is preferable if the sample material is not destroyed.
  • the method of the first aspect of the invention may include the additional step of replacing the flow of inert humidified gas with a metered supply of humidified air or oxygen once the desired pre-combustion temperature has been reached.
  • the sample may then undergo combustion at a rate which is determined by the flow rate of the humidified air or oxygen. This controlled combustion is in contrast to prior art methods where air or oxygen are added to the sample in excess and there is thus no control over the rate of combustion.
  • the tritium loaded gas may be passed through the condensing means and the condensate collected for scintillation counting in conjunction with that from the inert gas stage.
  • the temperature of the sample is measured independently of the temperature of the body of the furnace or chamber and the apparatus for carrying out the method of the invention, which is described hereinafter, has means for so doing. Knowing the temperature of the sample allows the real time of combustion at the required temperature to be determined.
  • the sample is introduced into the upper part of the furnace. Any air which may have entered therewith is removed by purging at least the furnace chamber, if not the rest of the apparatus with nitrogen before lowering the sample into the hottest part of the furnace.
  • the controlled combustion step alone, without prior exposure to a humidified inert gas may be sufficient for stripping tritium for a nominally-radioactive material in some applications.
  • the invention provides a method for thermal separation of tritium from a sample of a nominally-radioactive material by controlled combustion which comprises stripping tritium from said material into a stream of humidified oxygen or air, the rate of combustion being controlled by the flow rate of said humidified air or oxygen stream.
  • Tritium is found as contaminant mainly in the form of tritiated water on waste materials of tritium extraction plants and other nuclear facilities.
  • Experimental work using the methods of the first and second aspects of the present invention has demonstrated that a useful percentage of the total tritium content can be separated from the material using a lower temperature than required for the known, uncontrolled-combustion techniques. Condensation of the tritium-bearing water vapour from the gas stream and measurement of tritium in the condensate, enables the concentration of tritium per unit mass of the material to be determined.
  • the method has been found to enable extraction from the material of a reproducible percentage of the total tritium content.
  • This enables the total concentration to be calculated from the measurement of tritium in the condensate, using a scaling factor, and avoids the high-temperature requirements and other disadvantages of the known extraction methods.
  • Data obtained in this way from a sample taken from a body of waste material can be utilised, in conjunction with determination of the concentrations of other forms of radioactivity in that material, for comparison with regulatory requirements for declassification of the waste as radioactive.
  • declassification is given by way of an exemption order under provisions of the Radioactive Substances Act.
  • the samples used are typically less than 1.5 grams in weight.
  • the sample-size restriction applicable makes such techniques unsuitable for batches of mixed, radioactive waste where larger, more representative quantities of each contributing material type should be included to create a truly representative sample.
  • the known methods attempt to give almost complete extraction and capture of the tritium present, and unlike the method of the present invention are not readily applicable to determining the classification of waste material using appropriately representative samples of, for example, 10 to 20 grams in weight.
  • the invention provides an apparatus for the thermal separation of tritium from a sample of a nominally-radioactive material which comprises a chamber for receipt of said sample, means for heating said chamber to a pre-determined temperature, means for supplying a humidified gas into said chamber, means for heating said gas to said pre-determined temperature before entry into said chamber, means for exiting said humidified gas from said chamber and means for condensing the water vapour in said humidified gas on exiting said chamber.
  • the heated chamber will be a furnace and in a preferred embodiment the furnace also pre-heats the humidified gas.
  • the furnace chamber is double-walled, the space between the inner and outer wall forming a passage through which, in use, the humidified gas must pass before entry into the chamber thereby pre-heating the gas to the temperature of the chamber before presentation to the sample.
  • the means for supplying humidified gas is capable of switching the supply from humidified inert gas to humidified oxygen or air, the gases being humidified by passage through a water bubbler or the like.
  • the sample is introduced into the furnace chamber in a holder, for example, a wire basket, which contains the sample throughout the stripping procedure.
  • a holder for example, a wire basket, which contains the sample throughout the stripping procedure.
  • a holder is suitable for 10 to 20 grams of material.
  • the sample holder may include a temperature sensing means such as a thermocouple.
  • the condensing means is preferably a temperature controlled condensing vessel which incorporates a condensing coil and a reservoir for collection of the condensate. Preferably, it also incorporates within the vessel the initial portion of the exhaust gas exit tube which may be mounted vertically from the reservoir. These components are all maintained at the same temperature during the processing cycle minimising the possibility of re-evaporation of trapped tritiated water.
  • FIG. 1 is a schematic illustration of the apparatus using the thermal separation method of the invention.
  • Figures 2 and 3 are longitudinal sections of a furnace forming part of the apparatus of Figure 1 and illustrating, respectively, successive stages of operation of the apparatus in the thermal separation method of the invention.
  • a vertical-tube furnace 6, into which the sample is inserted within a wire-mesh basket 9, is arranged to be supplied with nitrogen from a pressurised source 1, or with pressurised air from a source 20, according to the setting of a valve 5.
  • the nitrogen or air supplied through the valve 5 passes via a flow meter 3, and hence through a heated distilled-water bubbler 4 to become laden with water vapour, before entering furnace 6.
  • the humidified gas enters an outer stainless-steel tube 7 of two concentric tubes 7 and 8 of the furnace 6, to pass downwardly between them and become heated to several hundred degrees Celsius before entering the inner tube 8 through holes 81 in its wall.
  • the heated gas entering the tube 8 rises within the tube 8 to come into contact with the sample in the basket 9; the pre-heating of the gas within the tube 7 ensures that the sample is not cooled by it.
  • the basket 9 is provided at its base with a thermocouple 9a for measuring the temperature in the immediate vicinity of the sample. Exchange of tritium from the sample to the water vapour occurs at the basket 9, and the gases then rise to the top of the furnace 6 to exit through glass tubing 10.
  • the tubing 10 is heated by a heating jacket 11 to avoid early condensation from the gases, and includes a filter 12 for capturing any solids expelled from the furnace 6.
  • the gases pass from the filter unit 12 into the condensing coil 131 of a condensing vessel 13.
  • the coil 131 is cooled by a coolant that is supplied and recirculated through the vessel 13 by a pump 18 of a refrigeration unit 17.
  • the condensate collects within a reservoir 132 at the base of the condensing coil 131 and within the thermal environment of the vessel 13 and may be drained off into a vial 14 for submission to a liquid scintillation counter, via a tap 133.
  • Gases exit the condensing coil 131 at low temperature (for example at 4 to 5 degrees Celsius) , and this minimises tritium losses; such losses can be checked by analysis of the contents of a water bubbler 41.
  • a facility is provided, using an inlet 26, for flushing the condensing coil 131 internally with distilled water or the same cocktail of chemicals used for scintillation counting.
  • a small pressure depression is maintained inside the apparatus during operation, by use of a vacuum pump 16 acting on the point where gases exit the condensing vessel 13. This assists in avoiding the possibility of external contamination during operation and sample changing.
  • the apparatus is first purged with nitrogen to ensure that there is no combustion when the sample (for example 15 grams) is initially introduced into the inner tube 8 in the wire basket 9 as illustrated in Figure 2.
  • the supply of metered, humidified nitrogen is maintained as the sample is introduced fully into the furnace 6 along the tube 8, as illustrated in Figure 3, and retained there to complete the stripping process without combustion of the test material.
  • the resultant tritiated water condensed inside the condensing coil 131 and as subsequently drained from the reservoir 132 into the vial 14, is submitted to liquid scintillation counting.
  • the valve 5 may be operated to replace the nitrogen by air, after (but only after) the sample has acquired a desired pre-combustion temperature.
  • the supply of metered, humidified air to the furnace 6 allows controlled combustion of the sample to take place; combustion is controlled especially in that the time of combustion at the required temperature is known, the temperature of the sample itself being known independently of the temperature of the heating chamber due to the thermocouple 9a on the basket 9.
  • the tritium extracted from within the sample in this way is taken up into the water vapour so as to be added into the condensate collected in the reservoir 132 during the flow of humidified nitrogen. This condensate is drained into the vial 14 as before, and submitted to liquid scintillation counting.
  • the condensate collected in the vial 14 in both cases represents a percentage of the total tritium content of the test material.
  • the method gives substantially consistent results using a sensitive scintillation counter that gives a good counting accuracy.
  • the level of consistency is such as to enable the tritium concentration of the bulk material to be calculated using a previously-derived scaling-factor; the appropriate scaling-factor is determined by calibrating the apparatus using a sample from material having a known total tritium content.
  • the calculated value has an accuracy that is adequate for determing whether the material is significantly above or below the relevant regulatory classification threshold.
  • item 2 is a differential manometer; items 15, 21, 24, 25 and 28 are valves; item 27 is an electrical heater for the bubbler 4; item 23 is a gas-flow meter; and items 22 and 19 are, respectively, an electrical switch for the pump 16 and an electrical transformer for furnace heating-current.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Environmental & Geological Engineering (AREA)
  • Measurement Of Radiation (AREA)
  • Sampling And Sample Adjustment (AREA)

Abstract

L'invention se rapporte à un procédé et à un appareil conçu pour séparer thermiquement le tritium d'un échantillon de matière nominalement radioactive, ce procédé consistant à retirer le tritium de cette matière dans un flux de gaz humidifié. L'échantillon de matière est placé dans un four et le gaz humidifié y est introduit pour qu'il puisse passer sur et/ou dans l'échantillon. Tout tritium se trouvant dans l'échantillon est transféré dans le gaz qui passe. Le gaz humidifié est ensuite refroidi et le condensat d'eau soumis au comptage des scintillations. Selon un mode de réalisation de l'invention, le gaz humidifié est à l'origine un gaz inerte qui, après une période prédéterminée, est remplacé par de l'air humidifié ou de l'oxygène, ce qui permet une combustion régulée de l'échantillon.
PCT/GB1994/002201 1993-10-08 1994-10-10 Separation thermique du tritium et appareil prevu a cet effet Ceased WO1995010840A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB939320806A GB9320806D0 (en) 1993-10-08 1993-10-08 Thermal separation
GB9320806.4 1993-10-08

Publications (1)

Publication Number Publication Date
WO1995010840A1 true WO1995010840A1 (fr) 1995-04-20

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PCT/GB1994/002201 Ceased WO1995010840A1 (fr) 1993-10-08 1994-10-10 Separation thermique du tritium et appareil prevu a cet effet

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GB (1) GB9320806D0 (fr)
WO (1) WO1995010840A1 (fr)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2384330A1 (fr) * 1977-03-16 1978-10-13 Hoechst Ag Procede pour retenir du tritium
JPS5559831A (en) * 1978-10-31 1980-05-06 Showa Denko Kk Removing method of tritium in gas
JPS56143977A (en) * 1980-04-10 1981-11-10 Fuji Electric Co Ltd Tritium water vapor capturing device
US5298196A (en) * 1992-05-18 1994-03-29 The United States Of America As Represented By The United States Department Of Energy Method and apparatus for extracting tritium and preparing radioactive waste for disposal

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2384330A1 (fr) * 1977-03-16 1978-10-13 Hoechst Ag Procede pour retenir du tritium
JPS5559831A (en) * 1978-10-31 1980-05-06 Showa Denko Kk Removing method of tritium in gas
JPS56143977A (en) * 1980-04-10 1981-11-10 Fuji Electric Co Ltd Tritium water vapor capturing device
US5298196A (en) * 1992-05-18 1994-03-29 The United States Of America As Represented By The United States Department Of Energy Method and apparatus for extracting tritium and preparing radioactive waste for disposal

Non-Patent Citations (6)

* Cited by examiner, † Cited by third party
Title
21ST NUCLEAR SCIENCE SYMPOSIUM;14TH SCINTILLATION AND SEMICONDUCTOR COUNTER SYMPOSIUM; 6TH NUCLEAR POWER SYSTEMS SYMPOSIUM, WASHINGTON, DC, USA, 11-13 DEC. 1974, ISSN 0018-9499, IEEE TRANSACTIONS ON NUCLEAR SCIENCE, FEB. 1975, USA, PAGE(S) 676 - 680 *
DATABASE INIS INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA), VIENNA, AT; TERRANI, S. ET AL: "Sampling device for tritium assessment in solid waste materials." *
DATABASE INSPEC INSTITUTE OF ELECTRICAL ENGINEERS, STEVENAGE, GB; OSBORNE R V: "Central tritium monitor for CANDU nuclear power stations" *
DATABASE WPI Section Ch Week 8024, Derwent World Patents Index; Class E36, AN 80-42445C *
PATENT ABSTRACTS OF JAPAN vol. 006, no. 022 (P - 101) 9 February 1982 (1982-02-09) *
RADIOACTIVE WASTE MANAGEMENT AND ENVIRONMENTAL RESTORATION (1994) V. 18(4) P. 295-302. CODEN: RWMREG ISSN: 1065-609X, SWITZERLAND *

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Publication number Publication date
GB9320806D0 (en) 1993-12-01

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