GB2432668A

GB2432668A - Improvements in and to monitoring iodine gas removal

Info

Publication number: GB2432668A
Application number: GB0524184A
Authority: GB
Inventors: Simon Perrin
Original assignee: Bil Solutions Ltd
Current assignee: Bil Solutions Ltd
Priority date: 2005-11-28
Filing date: 2005-11-28
Publication date: 2007-05-30
Anticipated expiration: 2025-11-28
Also published as: GB0524184D0; GB2432668B

Abstract

A method of monitoring an iodine containing gas removal function is provided which is easier to deploy due to the materials used. The method comprises introducing non-radioactive methyl iodide as a test gas into a medium at a first location in a gas stream, providing a sampling material for the test gas at a second location downstream of the first location, providing a sampling material for the test gas at a third location downstream of the iodine gas removal function, the iodine gas removal function providing for the at least partial removal of the gas from the medium and the function being provided between the first location and the third location, detecting the amount of the test gas collected by the second location sampling material and detecting the amount of test gas collected from the third location sampling material so as to monitor the effectiveness of the iodine containing gas removal function in removing gas.

Description

IMPROVEMENTS IN AND TO MONITORING

This invention concerns improvements in and relating to monitoring, particularly, but not exclusively in relation to gas adsorption plant.

There is a need to test the efficiency and availability of gas adsorption plant in many instances. In the nuclear energy business, such plant are provided for gas streams which might contain radioactive gases so as to prevent their release to the atmosphere. At present such adsorption plant are tested using radioactive methyl iodide, with detection using gamma spectroscopy. There are problems associated with this approach.

According to a first aspect of the present invention we provide a method of monitoring an iodine containing gas removal function of a nuclear power generating facility, the method comprising introducing non-radioactive methyl iodide as a test gas into a medium at a first location in a gas stream; providing a sampling material for the test gas at a second location downstream of the first location; providing a sampling material for the test gas at a third location downstream of the iodine gas removal function; the iodine gas removal function providing for the at least partial removal of the gas * from the medium and the function being provided between the first location and the third location; detecting the amount of the test gas collected by the second location sampling material * S.*** and detecting the amount of test gas collected from the third location sampling material so as * to monitor the effectiveness of the iodine containing gas removal function in removing gas. Is.. I. *s * . 0 * S

According to a second aspect of the present invention we provide a method of monitoring a gas removal function, the method comprising introducing a test gas into a medium at a first location; providing a sampling material for the test gas at a second location; providing a sampling material for the test gas at a third location; the gas removal function providing for the at least partial removal of the gas from the medium and the function being provided between the first location and the third location; detecting the amount of the test gas collected by the second location sampling material and detecting the amount of test gas collected from the third location sampling material so as to monitor the effectiveness of the gas removal function in removing gas.

The method niar be a method of monitoring an iodine gas removal function of a nuclear power generating facility. The test gas may be non-radioactive methyl iodide. The test gas may be introduced into a gas stream. The sampling material for the test gas ny be provided at a second location downstream of the first location. The sampling material for the test gas may be provided at a third location downstream of the iodine gas removal function.

The method may provide for to monitoring the effectiveness of the iodine gas removal function in removing gas.

According to a third aspect of the present invention we provide a method of monitoring a function, the method comprising introducing a gas into a medium at a first location; providing a sampling material for the gas at a second location; providing a sampling material for the gas at a third location; : the function providing for the at least partial removal of the gas from the medium and *: : the function being provided between the first location and the third location; * detecting the presence, prefably a characteristic, of the gas from the second location * sampling material and detecting said presence, preferably said characteristic of the gas from Slits, * the third location sampling material so as to monitor the function. I...

* Preferably the function is a gas removal function. Preferably the gas introduced is a test gas. Preferably the amount of the test gas collected by the second location sampling material is detected. Preferably the amount of test gas collected from the third location sampling material is detected. Preferably the method provides for monitoring the effectiveness of the gas removal function in removing gas.

The method may be a method of monitoring an iodine gas removal function of a nuclear power generating facility. The test gas n$y be non-radioactive methyl iodide. The test gas may be introduced into a gas stream. The sampling material for the test gas may be provided at a second location downstream of the first location. The sampling material for the test gas may be provided at a third location downstream of the iodine gas removal function.

The first and/or second and/or third aspects of the invention may include any of the features, options or possibilities set out elsewhere in this application, including the following.

The function may emove iodine and/or iodine containing species from gases. The function may remove 12131 and/or j131 containing species from gases.

The function may remove one or more species in a gas stream as a result of a nuclear reactor blowdown and/or as a result of a nuclear fuel rod failure.

The function may be part of a facility using and/or handling and/or processing nuclear material. The function may be part of a nuclear reactor.

The function may be provided by carbon. The carbon may be provided with potassium iodide and/or fri-ethylene diamine.

The gas may be introduced as a fixed volume of gas. The gas may be introduced in a non-continuous manner before and/or during the monitoring. The gas may be injected. The * :* gas may be introduced as a pulse of gas within the medium. The medium may be the gas *: : : :* stream, for instance the off gas from a nuclear reactor.

The sampling material may be a carbon, for instance an activated carbon. The carbon * may be of high purity. The sampling material may have a controlled porosity. The sampling * * material may have a controlled pore size and/or range of pore sizes and/or distribution of pore *:.* sizes. The sampling material may have a controlled pore size and/or range of pore sizes * and/or distribution of pore sizes within the <3nm range and/or 3nm to SOnm range and/or >SOnm range. The sampling material may have an open area of between 30% and 60%. The sampling material may have an internal surface area of greater than 400 m2 g'. The pore size distribution may be controlled within a distribution, potentially a bimodal or trimodal pore size distribution.

The sampling material may be provided as a cylindrical unit, for instance as a monolith. The sampling material may be provided within a stainless steel outer casing. The sampling material may be provided with a sealable container. The container may be provided with an inlet and/or an outlet. Preferably the inlet and/or outlet can be opened or closed.

The sampling material may be provided as particles or beads.

The sampling material may provide for highly efficient absorption of methyl iodide.

The sampling material and/or other material may allow the separation of the methyl iodide from carbon dioxide and/or water vapour and/or other components which may be present in the medium and/or gas stream.

The second location may be connected to the medium and/or gas stream in one configuration, for instance to allow the gas to contact the sampling material. The second location may be disconnected from the medium and/or gas stream in a second configuration, for instance to allow introduction of the sampling material and/or removal of the sampling material.

The second location may be upstream of the third location. The second location may be upstream of the function. The function may be downstream of the second location.

The third location may be connected to the medium and/or gas stream in one configuration, for instance to allow the gas to contact the sampling material. The third location may be disconnected from the medium and/or gas stream in a second configuration, for instance to allow introduction of the sampling material and/or removal of the sampling material.

*: :: The third location may be downstream of the second location. The third location may be downstream of the first location.

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* The function may be provided between the second location and the third location.

The presence, preferably characteristic, of the gas may be detected by gas *:.* chromatography. The amount of the gas may be detennined by gas chromatography. The * amount of gas collected by the second location sampling material may be compared with the amount of gas collected by the third location sampling material. The ratio of the amount of gas collected by the second location sampling material to the amount of gas collected by the third location sampling material may be calculated.

The sampling material may be disconnected from the medium and/or gas stream before the presence, preferably characteristic of the gas is detected. The detection may be remotely located compared with the second location and/or third location. The detection may be provided off-line from the medium and/or gas stream.

The monitoring of the function may establish whether the function has a capability above and/or below a predetermined level. Monitoring which reveals that the function has a capability below a predetermined level may result in further action. The further action may include replacement of part or all of the function, for instance through replacement of the material providing the function.

The method may provide for the provision of a first unit of sampling material at the second location for a first time period, preferably after introduction of the test gas, and the provision of one or more further units of sampling material at the second location at one or more other times. A first unit of sampling material at the second location for a first time period, with a second unit provided at the second location for a second time period and with a third unit of sampling material at the second location at a third time. The first and/or second and/or third time periods may be between 10 and 300 minutes, more preferably between 20 and 180 minutes. The first time period may be 30 minutes +1-10 minutes. The second time period may be 60 minutes +1-20 minutes. The third time period may be 120 minutes +1-30 minutes.

The method may provide for the provision of a first unit of sampling material at the third location for a first time period and the provision of one or more further units of : sampling material at the third location at one or more other times. A first unit of sampling : :: * material at the third location for a first time period, with a second unit provided at the third location for a second time period and with a third unit of sampling material at the third SSe...

: location at a third time. The first and/or second and/or third time periods may be between 10 I.,.

* and 300 minutes, more preferably between 20 and 180 minutes. The first time period may be 25. 30 minutes +1-10 minutes. The second time period may be 60 minutes +1-20 minutes. The S...

. third time period may be 120 minutes +1-30 minutes.

Preferably the first and/or second and/or third units of sampling material are provided at the second and third locations for the same time periods as each other.

According to a fourth aspect of the present invention we provide a transportable assembly, the assembly including: a plurality of units containing a sampling material including carbon; a volume of non-radioactive methyl iodide; and a gas chromatography instrument.

According to a fifth aspect of the present invention we provide a transportable assembly, the assembly including: a plurality of units containing a sampling material; a volume of gas; and a gas chromatography instrument.

Preferably the sampling material includes carbon. Preferably the gas is methyl iodide.

The fourth and/or fifth aspects of the invention may include any of the features, options or possibilities set out elsewhere in this document, including those of the first and/or second and/or third aspects and/or from the following.

The transportable assembly may be part of a vehicle. The transportable assembly may be a permanent part of a vehicle. The transportable assembly may be connectable to a vehicle, for instance for carriage and/or towing.

The assembly may include at least 6 units containing a sampling material and more 2J: preferably at least 12 units.

*: : : :* The methyl iodide may be provided in a container, for instance a sealed and/or pressurised container.

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* : The gas chromatography instrument may be configured and/or set up and/or calibrated Si....

* to detect methyl iodide.

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* Various embodiments of the invention will now be described, by way of example only.

In limited circumstances relating to nuclear reactors there is a need to release gas to the atmosphere. A key feature in this respect is the presence of a filter to remove certain components of the gas stream before it is released to the atmosphere. In particular iodine absorption plant are used to remove j131 in the event of reactor blowdowns or in the event of a fuel rod failure. The adsorption plant commonly uses potassium iodide impregnated charcoal as the absorber.

As with all operations involved in the nuclear industry there is a need to monitor the adsorption plant's effectiveness.

The existing approach to this involves the creation of methyl iodide containing j131 to provide a radioactive test gas. This is then taken to the test site and a volume of the test gas is then released into the gas stream upstream of the adsorption plant and two sampling points.

Sampling units, which include granular activated carbon, are fed gas from the gas stream, with the gas taken from sampling points upstream and downstream of the adsorption plant to be tested.

After a period of time the packs are removed and analysed. The analysis determines by radiological measurement, gamma spectrometry, the amount of test gas absorbed by each of the packs. Gamma spectrometry is extremely useful in this respect as it allows read detection of even the very low levels of methyl iodide taken up in tests such as this. The results give a measure of the effectiveness of the adsorption plant in removing the radioactive gas between the two sampling points.

The use of methyl iodide as the test gas has been widely accepted by the regulatory authorities as an appropriate test gas because it is the most difficult of the species encountered Q: in actual use to remove. Furthermore, the isotope of concern for removal from the gas stream : : : :* is the same isotope as is involved in the test gas in such a case.

However, there are problems with this test gas. Firstly, the test gas has to be produced S..,..

at an appropriately licensed site and transported in a suitably protected manner (Type A * transport package) to the site where it is going to be used, because it is radioactive. Secondly, the half life of the i13I involved is only 8.04 days and so any delay in its transportation and use :* of over 2 to 4 days renders the test gas useless and necessitate another being ordered, transported and used. Problems also arise from physical changes in the test gas which occur with time, making it harder to vaporise and so harder to inject. The limited amount of test gas also limits the number and usefulness of the measurements that can be taken.

In the present invention, non-radioactive iodine is used in the methyl iodide which forms the test gas. As a result, the gas can be manufactured and transported with less restrictions and hence cost. Furthermore, greater volumes of test gas can be made available for the testing process. The adoption of non-radioactive methyl iodide is possible because of the improved ability to capture and detect the methyl iodide discussed below.

During testing, test gas is introduced to the gas stream upstream of a first sampling point, adsorption plant and second sampling point. The first and second sampling points provide a flow of gas to a unit containing a sampling material in each case. The sampling material removes the non-radioactive methyl iodide from the gas for later analysis. A first unit of sampling material is provided at each location and used for 30 minutes after the introduction of the test gas. The first unit is replaced with a second unit for the next 60 minutes, with a third unit used for the 120 minutes after that.

The units contain a different form of sampling material to that which has been used previously. The sampling material provides for the effective collection of the non-radioactive methyl iodide as it flows past, but importantly also provides for the release of the non- radioactive methyl iodide, under controlled conditions to allow the analysis described below.

To achieve this, the invention replaces the loose filled plastic cartridges contained rough edge granular, uncontrolled pore size carbon with an improved sampling material. The sampling material is a high purity carbon with controlled microporous (>3nm), mesoporous (3-SOnm) and macroporous (>SOnm) structure. An open area of between 30% and 60% may be provided. The internal surface area is generally greater than 400 m2 g'. The pore :* distribution is closely controlled within a distribution, potentially a bimodal or triniodal pore ** * distribution. The sampling matenal is provided as a cylrndncal monolith which is received within a stainless steel outer casing. Other shapes are possible, and the material could be I.....

* provided as bead structures instead. . . Such matenals provide for highly efficient adsorption of non-radioactive methyl *2'.* iodide. Themselves, or in conjunction with other materials, they allow the separation of the * * non-radioactive methyl iodide of interest from carbon dioxide, water vapour and other components which may be present in the gas stream.

To analyse the units of sampling material, they are individually connected to a gas chromatography instrument and subjected to an electric current. Due to resistance heating, this causes the sampling material to release the test gas into a nitrogen gas stream for detection.

Detection of the non-radioactive methyl iodide is achieved using gas chromatography which provides a quantitative indication of the amount present. The ratio of the amount in the upstream sample to the downstream sample is used to provide a decontamination factor.

As well as the benefits previously mentioned, the invention provides for benefits in terms of lowering the radiological dose to which operators are exposed when testing nuclear facilities. The technique also provides the ability to conduct repeat tests in a short time frame and allows the removal of the need for a non-active leakage test prior to the use of the test gas. The technique is also possible on sites where active testing is not allowed. Generally speaking, the same benefits can be obtained, but at lower cost compared with the prior art approach. * S. * S I I.. S S... * . I...

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Claims

CLAIMS

I. A a method of monitoring an iodine containing gas removal function of a nuclear power generating facility, the method comprising introducing non-radioactive methyl iodide as a test gas into a medium at a first location in a gas stream; providing a sampling material for the test gas at a second location downstream of the first location; providing a sampling material for the test gas at a third location downstream of the iodine gas removal function; the iodine gas removal function providing for the at least partial removal of the gas from the medium and the function being provided between the first location and the third location; detecting the amount of the test gas collected by the second location sampling material and detecting the amount of test gas collected from the third location sampling material so as to monitor the effectiveness of the iodine containing gas removal function in removing gas.

2. A method according to claim 1 in which the test gas is introduced before monitoring.

3. A method according to any preceding claim in which the sampling material is an .* activated carbon. Is * S I..

4. A method according to any preceding claim in which the sampling material has a S...., : controlled pore size and/or range of pore sizes and/or distribution of pore sizes.

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** 5. A method according to any preceding claim in which the sampling material has an open area of between 30% and 60%.

6. A method according to any preceding claim in which the sampling material is provided with a sealable container, the container being provided with an inlet and an outlet.

7. A method according to any preceding claim in which the presence, preferably characteristic, of the gas is detected by gas chromatography. -8. A method according to any preceding claim in which the amount of the gas is determined by gas chromatography.

9. A method according to any preceding claim in which the amount of gas collected by the second location sampling material is compared with the amount of gas collected by the third location sampling material, the ratio of the amount of gas collected by the second location sampling material to the amount of gas collected by the third location sampling material being calculated.

10. A method according to any preceding claim in which the method provides for the provision of a first unit of sampling material at the second location for a first time period and the provision of one or more further units of sampling material at the second location at one or more other times.

11. A transportable assembly, the assembly including: a plurality of units containing a sampling material including carbon; a volume of non-radioactive methyl iodide; and * a gas chromatography instrument. I... * * * S..

12. A transportable assembly according to claim 11 in which the transportable assembly is S'S...

* : part of a vehicle.

* USSSI * . * 13. A transportable assembly according to claim 11 or claim 12 in which the assembly I 55.

* : includes at least 6 units containing a sampling material.