DRAFT

T E C H N I C A L N O T E

WASTE PACKAGE MONITORING

Prepared by: Name Kevin Yong

Checked by: Name

Approved by: Name

DOCUMENT INFORMATION

Document Number:

Revision:

Date:

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Contractor:

Reference Number:

STATUS : DRAFT FOR DISCUSSION / PROVISIONAL / INTERIM / FINAL

PROVISONAL or INTERIM status means this Technical Note has been prepared to facilitate Nirex’s work programme and does not necessarily reflect the company’s final position.

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Conditions of PublicationThis technical note is made available under Nirex’s Transparency Policy. In line with this policy, Nirex is seeking to make information on its activities readily available, and to enable interested parties to have access to and influence on its future programmes. This document may be freely used for non-commercial purposes. However, all commercial uses, including copying and re-publication, require Nirex’s permission. All copyright, database rights and other intellectual property rights reside with Nirex. Applications for permission to use this technical note commercially should be made to the Nirex Business Development Manager.

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DOCUMENT HISTORYSTATUS REVISION DATE COMMENTS

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SUMMARY

Packages stored in the storage vault will be subjected to damages such as pit corrosion, stress corrosion, swelling, dropping and cracking. The purpose of monitoring the packages in the vault is to provide a periodic observations and measurements to determine changes in the physical condition of the packages over time.

Monitoring of waste packages will be conducted by visual inspections and electronic sensors attached on ‘Dummy Packages’ and ‘Sensor Packages’. Electronic sensors include strain gauge, humidity sensors, and thermometer and conductivity sensors for corrosion indication.

Signals and readings will be transmitted by active RFID tags to a receiver mounted on the lifting crane. Electronic sensors and the active RFID tags will be powered by batteries which last for 5 or 10 years, for ‘Sensor Packages’ and ‘Dummy Packages’ respectively.

‘Dummy Packages’ and ‘Sensor Packages’ will be distributed evenly within the vault. The number of ‘Dummy Packages’ will not affect the effective storage capacity of the vault, while still providing a good representation of other ‘Real Packages’.

Visual inspection will be the primary method of inspection, due to its reliability, instant response and cost. Visual inspection will be conducted by remote cameras mounted on robotic crawlers. Metal coupons welded on stillages or attached on metal coupons will be inspected visually to check presence of corrosion in welded regions.

Waste packages monitoring sequence will begin with a RFID sweep followed by visual inspection. Packages identified or suspected to be damaged will be retrieved to the Inspection Cell for further inspection. If no package is identified damaged, random checks will be performed on ‘Real Packages’.

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TABLE OF CONTENT

SUMMARY...............................................................................................................................iii

AIMS.........................................................................................................................................1

INTRODUCTION......................................................................................................................1

1.0POTENTIAL DAMAGE........................................................................................................1

1.1PIT CORROSION...........................................................................................................1

1.2STRESS CORROSION..................................................................................................1

1.3SWELLING OF PACKAGES...........................................................................................1

1.4DROPPING OF PACKAGES..........................................................................................2

1.5CRACKING.....................................................................................................................2

2.0MONITORING IN VAULT....................................................................................................2

2.1DUMMY PACKAGES......................................................................................................2

2.2SENSOR PACKAGES....................................................................................................3

3.0ELECTRONIC SENSORS...................................................................................................4

3.1CORROSION SENSORS...............................................................................................5

3.2HUMIDITY SENSORS....................................................................................................5

3.3RADIATION SENSORS..................................................................................................5

3.4STRAIN GAUGE.............................................................................................................6

3.5THERMOMETER............................................................................................................6

4.0‘PARKING BAY’...................................................................................................................8

5.0SAMPLING LAYOUT...........................................................................................................8

5.1BOX IN A BOX LAYOUT................................................................................................9

5.2OTHER SAMPLING LAYOUT......................................................................................10

6.0DIRECT VIEWING & CCTV...............................................................................................11

6.1WELDED COUPONS...................................................................................................11

7.0MONITORING OF STILLAGES.........................................................................................12

8.0WASTE PACKAGE MONITORING SEQUENCE..............................................................12

CONCLUSION........................................................................................................................12

REFERENCES.......................................................................................................................13

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WASTE PACKAGE MONITORING

AIMS

The purpose of monitoring the packages in the vault is to provide a periodic observations and measurements to determine changes in the physical condition of the packages over time.[1] By monitoring packages in the vault, the condition of the vault could also be predicted.

INTRODUCTION

According to Nirex’s standard and specification (WPS/640), waste monitoring is defined as “continuous or periodic observations and measurements to determine changes in the physical condition of a waste package over time.”[1]

This report proposes designs in monitoring ILW waste packages in the vault. Packages include 500L drums, 3m3 boxes and 3m3 drums. Monitoring of the vault will be mainly by mobile cameras and electronic sensors. Monitoring of the waste packages are being conducted remotely.

1. POTENTIAL DAMAGE

Packages stored in the vault are prone to be damaged mechanically or chemically. It is thought that the following damages are likely to happen. These include pit corrosion, stress corrosion, swelling of packages, dropping of packages and cracking.

A detailed report about types of corrosion is discussed in the ‘Corrosion Technical Report’.

1.1.Pit Corrosion

Pit corrosion occurs due to the presence of a pit on the surface of packages and free water. When water evaporates, it deposits salt or chlorides on the surface of the pit. Chlorides then react with the stainless steel and hence initiate corrosion. The corrosion then progresses its way towards the pit and form a progressive corrosion mechanism.

Pit corrosion can be classified as a localised corrosion. Localised corrosions are often difficult to be detected by any sensors. This is because electronic sensor only detects the presence of corrosion in its surrounding, and it would be uneconomic to position many sensors around the package, as it could occur on any surface.

1.2.Stress Corrosion

Stress corrosion occurs when a material is subjected to both tension and corrosion. Mentioned above, it is often difficult to detect corrosions of a package. Thus, it would be easier and more feasible to measure the strain of the packages, rather than detecting the presence of corrosions.

1.3.Swelling of Packages

The wasteforms in every package differs from one another. Certain radioactive wasteforms releases gases throughout its decaying time. Swelling of packages is likely to happen when the venting filter of the package are clogged. Building up of gases within the package causes the package to swell.

1.4.Dropping of Packages

Dropping of packages would only occur due to mishandling of packages, assuming that it would only occur during lifting of packages. Hence, neglecting other mechanisms such as

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seismic movements in the PGRC, which are either site specific or has negligible probability of occurring. This ranges from human error to control systems of remote handling.

It is thought that such mechanism would be easier to be detected from the lifting crane or the grabber. By placing a load cell on each crane or grabber, one could measure the weight of the package. An unforeseen decrease in the load carried by the crane or grabber indicates a packages being dropped.

Such detection method however has its drawbacks. For example, when a package was accidentally dropped on to a stack of packages and it caused the whole stack of packages to fall over. In this scenario, the sensors only assume the dropping of one package only. Hence, it is recommended that a mobile CCTV to be dispatched to the spot.

1.5.Cracking

Cracking could occur either due to corrosion or mechanical damage. Such mode of failure is difficult to be detected. Cracking occurs locally and are difficult to be predicted. Cracking could only be detected by 3D mappings.

It was also thought that it is not feasible to conduct 3D mapping within the vault. This is due to the expensive cost of the equipment and the equipment might not be able to resist radiation. Hence, 3D mapping can only be conducted through shielded window.

3D mapping can only be conducted effectively when there’s no ‘blind spots’, such as packages being stacked together. Extracting packages and mapping them individually would somehow consume too much time.

2. MONITORING IN VAULT

It was thought that monitoring in the vaults play an essential role during the 300 years of emplacement period. Through monitoring of packages, not only one could determine the condition of packages but also predict any failure of the vault control system. ‘Dummy packages’ and ‘sensor packages’ will be use in order to monitor the conditions of the packages.

2.1.Dummy Packages

‘Dummy packages’ are packages of the same dimensions and material as other packages, but they will contain inert materials, such as grout or concrete. These ‘Dummy Packages’ will be equipped with a set of electronic sensors and a battery, which has an assumed battery life of 10 years. The batteries will be placed within the package and be shielded from radiation.

The main functions of these packages are to monitor corrosion, humidity and temperature of its surrounding area. The main advantage of these ‘Dummy Packages’ is being able to handle it without remote handling.

The following figure shows a drawing a typical ‘Dummy Package’ for 500L drums.

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Figure 1: A typical ‘Sensor Package’ for 500L drum

2.2.Sensor Packages

‘Sensor Packages’ are real packages which are equipped with electronic sensors. Electronic equipments within the vault will include corrosion sensor, humidity sensor, thermocouple, strain gauge and a battery, with an assumed battery life of 5 years. Batteries will be strapped on the outside of the package and will be shielded from radiation.

The purpose of these sensor packages is to allow monitoring of the package and its surrounding area, without reducing the effective storage capacity of the vault. The diagram below illustrates the position of sensors in a ‘Sensor Package’.

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Humidity sensor

corrosion sensor

Battery shielded within package

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Figure 2: A typical ‘Sensor Package’

3. ELECTRONIC SENSORS

Due to the radioactive environment of the vault, it is difficult and not feasible to monitor packages directly. Hence, electronic sensors will have to be used. Electronic sensors somehow have its limitations such as it require powering up and its reliability.

Powering up these electronic systems is the main drawback. Replacing batteries too often would increase the work load of the inspection cell, whereas having long lived batteries would reduce its reliability.

Several methods of powering up and charging batteries have been considered not feasible. Charging or replacing batteries with robotic crawlers somehow would prove difficult and time consuming. Hence, it is suggested that a battery life indicator should be included into the system, and batteries will be replaced.

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Corrosion Sensors

Strain Gauge on metallic strap

Humidity Sensors

Battery, active RFID tag and electronic components

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From current proven technology, it is possible to design batteries which can last for at least 2 years. It is also possible to design such batteries to be small enough to be attached to the package, without affecting much of its properties. It is also assumed that these sensors will take measurements 3 times every 24 hours, rather than taking continuous readings.

3.1.Corrosion Sensors

Figure 3 A typical corrosion sensor used in gas pipes [2]

It was assumed that corrosion is most likely to happen in welded areas of the package. Hence, these corrosion sensors will be positioned at these potential areas. These regions include top side of the lid and underside of the lifting flange. Corrosion sensors will be mounted on a strap and be strapped around these areas. This is to prevent alterations of the packages itself.

Corrosion sensors worked by measuring the conductivity of the material. Stainless steel has a relatively high conductivity. The presence of chloride would result in a decrease in its conductivity and hence the presence of corrosion can be detected.

3.2.Humidity Sensors

Figure 4: A typical humidity sensor [3]

From experience of similar projects, it was found that corrosion usually occurs due to the presence of free-water. When water evaporates, it deposits chlorides and is the main corrosive agent. Hence, a humidity sensor is essential in predicting corrosion happening.

It was thought that free-water or moisture is likely to be present at the underside of the package, which also include stillages. Therefore, humidity sensors will be placed at the bottom of the package.

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Humidity sensors also act as a fail-safe sensor, if the corrosion sensors malfunction. One could determine the condition of the packages by relying on two different sensors, without having to send robotic crawlers.

3.3.Radiation Sensors

The radioactive level of each package will be measured in the inlet cell before being transferred to the vault. The radiation level of the waste packages will only decrease through time, but will never increase.

The scope of the project only deals with unshielded ILW, hence measuring radiation level is thought to be redundant. Sensors such as a Geiger-Muller tube also proved to be expensive.

3.4.Strain Gauge

Figure 5: A typical strain gauge mounted on the wall [4]

It is thought that expansions of packages are more significant or more likely to happen in the planar direction, rather than axially. The expansion of the packages will be measured by a strain gauge on a metallic strap. The metallic strap will then be strapped at mid height around the package.

This method allows the strain gauge to obtain any expansion or within the package to be detected. But the metal strap will need to be replaced, depending on its material. This is due to creeping of the material. It is also noted that strain gauges will not be mounted on ‘Dummy-Packages’ as they don’t contain any waste materials.

3.5.Thermometer

An electronic thermometer will be used to record the temperature around the sensor. This could also acts as a secondary monitoring of the vault. Although the condition of the vault will be monitored by other sensors around its wall, ceiling and roofs, but it somehow couldn’t detect hotspots among stacks of packages.

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The strain gauge on the wall gives a rough estimation of the size of a strain gauge that could be adopted.

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3.6.RFID Tags

Figure 6: A typical active RFID tag [5]

Radio Frequency Identification (RFID) is an identification technology which is commonly used in tracking something. By emitting radio waves of different frequencies, the receiver could identify each individual package.

It is good practice to be able to identify each package, without too much hassle. The usage of Radio Frequency Identification (RFID) tags proves to be reliable and simple. RFID tags can be classified as active RFID tags and passive RFID tags. The following table illustrates their differences.

Active RFID tags Passive RFID tags

Longer range up to 100m Shorter range up to 4 feets

Requires additional battery cell Doesn’t require any additional batteries

[6]

It is thought that active RFID tags will be placed in every ‘Dummy Package’ and ‘Sensor Package’. Passive RFID tags will somehow be attached on other ‘Real Packages’. With active RFID tags, signals can be sent to a receiver mounted on the lifting crane, whereas the passive RFID could provide some form of identification when packages are being lifted.

It is also preferable to use high frequency waves due to its fast data transfer. Low frequency waves are more penetrative, hence it is only being used if the signal will have to penetrate through dense materials, such as concrete and steel.

Hence the active RFID tags shall be positioned on the surface where it is not shielded. It is thought that the RFID tags shall be placed in the side of the packages. In order to allow ease in RFID scanning and ease of mounting these tags, a ‘sticker’ will be used to fix the position of the RFID tag.

The condition of the vault simply restricts the usage of passive RFID tags on ‘Dummy Packages’ and ‘Sensor Packages’. Scanning RFID tags individually will somehow consume too much time and hence an active RFID tag will be used.

Active RFID tags will be powered by the attached battery cell. After the electronic sensors had done its individual measurements, the signals will then be transmitted to a receiver mounted on the crane. Hence, by performing and ‘RFID sweep’, one could collect readings from all ‘Dummy Packages’ and ‘Sensor Packages’ fairly quickly.

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Figure 7: Passive RFID tag underneath an ‘adhesive sticker’ [7]

Other ‘Real Packages’ will however be attached with passive RFID tags or stickers. This is to allow identification while lifting packages. By equipping with a passive RFID tag, one could also keep track where a specific package is located within the PGRC.

4. ‘PARKING BAY’

Figure 8: A drawing of a ‘Parking Bay’ in a vault

In order to enhance speed in extracting packages from the bottom of a stack, a ‘Parking Bay’ was being introduced. By having empty columns in every interval, packages at the bottom of the stack can be extracted without having the crane to move packages to the end of the vault.

5. SAMPLING LAYOUT

Equipping every package with the set of proposed sensors will prove to be too expensive and uneconomic, hence monitoring of every packages in the vault is not feasible. Nirex recommended a sample survey of a subset of packages should be taken. In order to obtain a good sample of the condition in the vault, Nirex suggested a non-probabilistic method and a probabilistic method.[1]

Since the probabilistic method requires information of the vault condition which is site specific, hence this method has been abandoned. It should be noted that the probabilistic method would maximise the use of sensors.

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The position of ‘Dummy Packages’ and ‘Sensor Packages’ should be distributed evenly in order to obtain a good representation of other packages in the vault. The number of ‘Dummy Packages’ however should be kept minimal such that it doesn’t reduce the effective storage capacity of the vault.

5.1.Box-in-a-box Layout

Figure 9: A box in a box layout [8]

The arrangement for unshielded ILW packages within the vault will be 7 stillages across and 7 stillages in a stack.[9] Assume 7 stillages across by 7 stillages high by 7 stillages along the vault to be named as a block.

The diagram above illustrates the positions of ‘Dummy Packages’ in a block. The smaller cube from the diagram above has the dimension of 3 by 3 by 3 stillages apart. ‘Dummy Packages’ will be positioned in every corner of each cube, hence giving a total of 16 ‘Dummy Packages’ in a block. From the diagram above, ‘Sensor Packages’ will be positioned at every centre of each face of both cubes, hence giving a total of 12 ‘Sensor Packages’ in a block.

Through calculations, the following table illustrates the number of ‘Real Packages’, ‘Dummy Packages’, ‘Sensor Packages’ and the total space available, with the assumption that a vault will only store 1 type of package.

Type of Package

‘Real Packages’

‘Sensor Packages’

‘Dummy Packages’

‘Parking Bay’ (1 every block)

Total Space

500L Drums 29100 276 304 700 30380

3m3 drums or boxes

6429 265 292 168 7154

Type of Package

‘Real Packages’

‘Sensor Packages’

‘Dummy Packages’

‘Parking Bay’ (1 every 2

Total Space

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Distance = 3 stillages packages apartDistance = 7 stillages

packages apart

Position of ‘Dummy Packages’

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blocks)

500L Drums 29464 276 304 336 30380

3m3 drums/boxes

6520 265 292 77 7154

From the table above, it was thought that the number of ‘Parking Bay’ reduces the effective storage capacity of the vault the most. Hence, it was decided to have a ‘Parking Bay’ in every 2 blocks.

From calculations, it was also found that by introducing ‘Dummy Packages’ and ‘Parking Bays’, the effective storage capacity of the vault is reduced by 2% for 500L drums and 5% for 3m3 drums and boxes.

It was also found that 2% of the 500L drums will be monitored with electronic sensors, via ‘Dummy Packages’ and ‘Sensor Packages’, while 9% of the 3m3 boxes or drums will be monitored with electronic sensors. Although, it may seemed that the sample size being monitored for 500L drums is insufficient, it should be noted that the distances between each sets of sensors is the same as the ones for 3m3 drums or boxes. Hence, it is arguably that the quality of the sample size is the same.

By distributing both ‘Sensor Packages’ and ‘Dummy Packages’ uniformly, one could also monitor the condition of the vault. For example, if a region in a vault experience leakage of water, the sensors around the region could indicate it.

5.2.Other Sampling Layouts

Other sampling layouts have been considered. Appendix 1A shows a sampling layout where ‘Dummy Packages’ will be placed around the edge of the wall. This layout is only feasible if the packages being stored are shielded.

The advantage of such layout is ease in conducting testing in the vault, without having to retrieve packages within the block. This layout however provides a poor representation of other packages in the vault. Only being able to monitor conditions of packages near the wall, this layout had been rejected.

Another approach was to distribute more ‘Dummy Packages’ and ‘Sensor Packages’ according to the probability and criticality of failure. Such an approach maximises the usage of sensors. For example, the likelihood of packages at the bottom of a stack to be corroded is higher compared to packages at the top of the stack, hence more ‘Dummy Packages’ and ‘Sensor Packages’ will be placed at bottom of a stack.

This approach wasn’t being implemented as it was considered to be too complicated as optimising the usage of every sensor is simply impossible. It is also difficult to justify that package at the bottom of a stack to have a higher chance to fail, while package at the top of the stack has higher probability of dropping. This layout should be considered if the proposed layout should fail.

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6. DIRECT VIEWING & CCTV

Figure 10: A typical radiation resistant robotic crawler [10]

It is best practice to be able to view packages either directly or via remote cameras. Visual inspection has the advantage of being reliable, fast and cheap. Visual inspection also has the advantage of providing an independent judgement from sensors.

It was considered that direct viewing of packages in the vault will be not economic. It would be expensive to have shielded windows along the vault, and maintenance work such as cleaning windows will be an issue.

Two options were considered, either by using stationary cameras or cameras mounted on robotic crawlers. It was decided that by mounting CCTVs on robotic crawlers, one could gain flexibility in the expense of cost.

In order to optimise the usage of these crawlers, cameras must be able to zoom, pan, tilt and have adequate lightings. Robotic crawlers should also have the capability to access every package.

6.1.Welded Coupons

Figure 11: Corrosion in welded regions [11]

The lid of a package consist welded regions. It is also noted that the lid of a package will be difficult to be viewed, even by using CCTVs on robotic crawlers, due to blind spots. Therefore, a welded metal coupon was being introduced.

A welded metal coupon of the same material will be welded on every stillage and attached to every 3m3 packages. Assuming that welded regions are more susceptible to be corroded, hence it will be more likely that these welded coupons experience corrosion. By just viewing on these welded coupons, one could judge if the other welded regions of a package is corroded.

In order to allow visual inspection to be carried out easily, the welded coupons will be welded or attached at a standard and obvious location of each stillage and package. It is also suggested that the coupon could be coloured in order to contrast the change in colour of stainless steel, and also to capture one’s attention.

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CCTV mounted can pan, tilt and

zoom.

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The flow diagram below illustrates sequence of visual inspection carried out. Significant deformations will be inspected first, followed by welded coupons and filters. It was found that the filters on the lid are also likely to be corroded as being clogged.

7. MONITORING OF STILLAGES

It was assumed that stacking of stillages will not cause significant damage to the bottom stillage. If the stillage should fail or be subjected to corrosion, stillages will be inspected 4 times more frequent compared to 500L drums. Hence, there is no need for stillages to be monitored.

8. WASTE PACKAGE MONITORING SEQUENCE

The flow diagram below illustrates the monitoring sequence of waste packages in the vault. It begins by performing a ‘RFID Sweep’ on every package in the vault, thus reading measurements of ‘Dummy Packages’ and ‘Sensor Packages’. Damaged packages are then being identified; packages around it will then be re-assessed by visual inspection. Packages identified or suspected to be damaged will then be retrieved to the Inspection Cell.

If no damaged packages are identified by the ‘RFID Sweep’, 4 real packages will be selected randomly and be retrieved to the Inspection Cell for further inspection. At the same time, visual inspection will be carried out on ‘Real Packages’ via CCTVs mounted on robotic crawlers.

CONCLUSION

It was concluded that waste package monitoring plays an essential role to demonstrate package integrity during the emplacement period. It also serves a purpose of reducing the work load of the Inspection Cell. The condition of the vault could also be monitored at the same time. Waste Package monitoring is also proved feasible and could be conducted relatively fast and easy, through electronic sensors and visual inspection.

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Filter (whether it’s corroded or clogged)

Corrosion in welded areas

Other visible areas

Check for significant deformation

Welded Coupon

RFID

Sweep

Extract + transfer to Inspection Cell

Problem package assessed with mobile CCTV

4 real packages randomly selected. These are taken to Inspection Cell

Real packages randomly selected. These are inspected by mobile CCTV.

All packages confirmed safe.

Problem package(s) identified

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REFERENCES

[1] WPS/640: Guidance on monitoring waste packages during storage, September 2005

[2] Images from National Energy Technology Laboratory, U.S.A. http://www.netl.doe.gov/publications/press/2003/tl_conformablearray.html, 29th Oct 2003

[3] Images from CTL Group, http://www.ctlgroup.com/template.asp?topic=2087, 2006

[4] Photographs from Duncan Heron from Duke University, www.env.duke.edu/eos/geo41/mmo.htm, April 1984

[5] Images from Fujitsu http://www.fujitsu.com/global/news/pr/archives/month/2004/20040927-01.html , September 2004

[6] RFID Journal at www.rfidjournal.com/article/articleview/208#Anchor-33869, January 2007

[7] Images from Macau Productivity and Technology Transfer Center http://www2.cpttm.org.mo/cyberlab/rfid/intro.html.zh , January 2007

[8] Images from Donald Bren School of Information and Computer Sciences http://www.ics.uci.edu/~eppstein/junkyard/box-in-box.gif

[9] DRG No.: E/DRG/0040010, N/077 Volume 2, Generic Repository Design: Reference Case Design, July 2003 by Nirex

[10] Images from Inuktun, www.inuktun.com, January 2007

[11] Images from Corrosion Technology Testbed, Kennedy Space Centre http://corrosion.ksc.nasa.gov/filicor.htm, January 2007

Nirex Reports

WPS/700: 500 litre drum waste package specification: Explanatory Materials and Design Guidelines, October 2005

WPS320/01, Specification for 3 cubic metre drum waste package, Technical Note July 2005

WPS 310/01: Specification for 3 cubic metre box waste package, Technical Note July 2005

WPS/640: Guidance on monitoring waste packages during storage (Nirex online), September 2005

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Appendix 1A

Dummy Packages placed along the side of the storage vault.

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Real PackagesDummy Packages