25/01/2007

  1. WASTE MONITORING
  2. POTENTIAL DAMAGE
  3. PIT CORROSION
  • It is difficult to be detected by any sensors. Sensors could only detect ‘local cracking’ rather than any cracks on the packages.
  • It is not feasible to place many sensors around the package as it could occur at any surface of the package.
  • STRESS CORROSION
  • Rather than detecting corrosions around the packages, it is easier to detect stresses by detecting change in strain.

2.1.3.SWELLING

  • It is more significant for the package to expand radially, especially at the mid height. Hence, it is more sensible to position sensors to detect strains in this direction.
  • A strap attached with a strain gauge strapped around the package (including 3m3 drums and boxes)
  • Swelling would not be monitored in dummy packages.
  • DROPPING
  • It is assumed that dropping could only occur during lifting and transportations.
  • It is more sensible to detect them from the lifting crane/machines.
  • Possibly, a few strain gauges attached to the ‘Grab’ which could detect a sudden drop in weight.
  • CRACKING
  • Cracking is difficult to be detected. Only localised cracking can be detected.
  • Most feasible way of checking is via strain, but it’s very difficult to represent the condition of the packages.
  • Cracking is best detected using 3D mapping placed in the inspection cell.
  • It is not feasible to perform 3D mapping in storage vault due to expensive equipments.
  • MONITORING IN VAULTS
  • ‘DUMMY’ PACKAGES
  • Do not contain radioactive waste
  • Function is to monitorcorrosion, humidity and temperature, thus giving an indication as to the immediate environmental conditions.
  • It is found that ‘dummy packages’ and ‘parking bay’ would only reduce effective storing capacity by no more than 5%.

2.2.2SENSORS ON ‘REAL’ PACKAGES

  • Packages containing radioactive waste.
  • Function is to monitorcorrosion, humidity and strain thus, giving an indication as to the immediate environmental conditions.
  • Unlike the dummy package, the condition of this package is critical.
  • Strain of the package is measured so any internal pressure increase can be monitored. (This would be due to build up of gases inside the package)

2.2.3SAMPLING LAYOUT

  • From N/077 Volume 2, (DRG No. :E/DRG/0040010) (see Appendix 1), it is stated that horizontal spacing between stillages would be 230mm while spacing between 3m3 packages is 350mm.
  • The following table illustrates the number of packages or stillages that can be stored in a vault.A margin of 1.1m between the packages and vault wall exists throughout.

Packages type / No. in a stack / No. across the vault / No. along the vault / Total
stillages / 7 / 7 / 155 / 7595
3m3 packages / 7 / 7 / 146 / 7154
  • A ‘block’ refers to the number of packages or stillages in an arrangement of 7 by 7 by 7.
  • It is thought that 16 dummies and 12 real packages with sensors will be placed in a block of packages. The following figure illustrates the arrangement of dummy packages and packages with sensors within a block.

  • Imagine the larger box to be a block of 7 by 7 by 7 stillages, while the smaller box represents a 3 by 3 by 3 cube in a block. All 16 nodes represent positions of all dummy packages. Packages with sensors will be positioned at each face of both cubes. Hence a total of 16 dummy packages and 12 sensor packages
  • A sensor package is a real package with a sticker affixed to it.

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  • The following tables show the number of dummy packages, sensor packages and parking bay (Refer to Logistics Report) in a vault for different numbers of parking bays.

Type / Real Packages / Sensor Packages / Dummies / ‘ParkingBay’ (1 every 1 block) / Total Space
500L drums / 29376 / 276 / 304 / 700 / 30380
3m3 packages / 6694 / 265 / 292 / 168 / 7154
Type / Real Packages / Sensor Packages / Dummies / ‘ParkingBay’ (1 every 2 blocks) / Total Space
500L drums / 29740 / 276 / 304 / 336 / 30380
3m3 packages / 6785 / 265 / 292 / 77 / 7154
  • From the table above, it is shown that for a vault that stores 3m3 packages only, approximately 8% of the packages can be monitored via dummy or sensor packages or. approximately 2% of the 500L drums if they were the only packages present.
  • The quality of sampling of both vaults is arguably the same. This is because the spacing between each sensor is approximately the same, which is no further than 6m apart.
  • From the tables above, it is also noted that dummy packages and parking bays reduce the storage capacity of the vault by no more than 7%.

2.2.1.2Different Sampling Layouts

Please refer to Appendix 1, Figures 1 and 2.

a) Dummies within a stack

b) Dummies along sides of the vault

c) Dummies at entry/exit of vault.

d) ‘Sticker’ on real packages. ‘Box in a box’ layout. (Sticker houses the sensors, RFID tag for remote access to data and a battery to provide power).

e) Combination of b) and d).

*It was initially envisaged that a ‘sticker’ would be attached to every real package. However, with battery life estimated at one year, replacing the each battery this frequently would be expensive and cause congestion within the PGRC. A further idea was to affix a ‘sticker’ to every package and bring the power source to each package. However, this was thought to be too complex in practice given the number of packages in a vault.

2.2.4SENSORS

Each sticker will need a battery with associated charge level sensor. A reading of ‘charge level’ will be transmitted via the RFID system, with the readings of the other parameters described below. The assumed life of the battery is 1 year. Batteries will be replaced and recharged.

2.2.4.1 CORROSION

  • Three areas on a 3m3 drum have been identified as possible regions for corrosion analysis. See Appendix 1, Figure 3

2.2.4.2 HUMIDITY

  • It is thought that most moisture will collect on the underside of a package i.e. between the package and the stillage.
  • It was argued that a high humidity was simply indicating a high likelihood of corrosion. Thus, a humidity sensor is essentially a corrosion sensor.
  • It was considered that the humidity could be used to double check the condition of the package, if the corrosion sensors malfunction.

For the dummy package, it was proposed that the original package design be modified to house the humidity sensor. (See Appendix 1 Figure 4.) However, it was deemed more sensible to use the standard package design and to locate the humidity sensor on the side of a package.This would be as near to the base as reasonably possible and thus near to the probable location of moisture.

  • The humidity sensor must not be so near the base of the package such that it would be damaged during the lifting/transportation of the package.

2.2.4.3 RADIATION

  • Radiation level will be measured and recorded prior the entry to the PGRC in the Inlet Cell.
  • It is assumed that the radiation level in the storage vault would slowly decrease over time. (but never increase).
  • It is also assumed that radiation level in the storage vault will be measured from time to time to ensure that the condition of the storage vault is safe. Hence, there is no need to detect the radiation level of on individual packages, be they ‘real’ or ‘dummy’.
  • Radiation sensors also proved to be very expensive approximately £1000 each.

2.2.4.4 STRAIN

  • Mentioned above, swelling (2.1.3) is likely to happen radially. Hence radial expansion will be measured.
  • Strain will be measured by strapping a metal strap around packages, including 3m3 drums and boxes. The metal strap will then be attached to a strain gauge.

2.2.4.5 TEMPERATURE

  • Nirex specify that the ambient temperature of all areas of the PGRC must not exceed 50°c.
  • Temperature sensors are fitted to both dummy and real packages.

2.2.4RFID

  • RFID tags can be classified into active tags and passive tags. Active tags have a longer range (up to 100m) but require power. Passive tags however has a shorter range (only a few feet), but doesn’t require additional power.
  • Every package will have an RFID tag so its location can be tracked.
  • Initially, sensor packages and dummy packages are to be equipped with passive tags. But this is requires ‘signal boosters’, which may add to complications.
  • Sensor packages and dummy packages with batteries will equipped with an active tag. Other packages will be equipped with passive tags.
  • Having active tags, sensor packages and dummy packages can transmit data back to the transceiver, by conducting an ‘RFID sweep’.
  • All data will be read and reviewed by personnel in the Control Centre.
  • High frequency RFID will be used, due to its fast data transfer. Low frequency RFID which is more penetrative is normally being used if the tag is shielded by other materials.
  • An RFID transceiverwill be mounted on the lifting crane to perform an RFID sweep along the vault and to identify other packages during lifting.
  • As the ‘sticker’ is located on the outside of the package, the radiowaves will only need to pass through air and the metal stillages if the RFID power source is on the crane.(See Figure 7). If the ‘sticker’ is within the package, the stainless steel drum would reflect most of the signal, while the concrete within will dissipates its energy.
  • The RFID tag should located on the surface where it could be detected easily, but not damaged by the grabber during lifting procedure.

2.2.2.DIRECT VIEWING & CCTV

  • Camera will be able to tilt, pan and zoom and be mounted on a robotic crawler.
  • It is assumed that robotic crawlers could have access to every package, no matter its location within the vault.
  • Crawler will be controlled remotely.
  • Crawler will measure local temperature and transmit this to Control Centre.
  • Sufficient spacing between stacks to allow access of mobile CCTV.
  • Minimise blind spots by flexibility of mobile CCTV.
  • Direct viewing probably not feasible to be performed in the vault, due to arrangements of packages and need for lighting.
  • Mobile CCTV is still the primary method for inspecting packages in the vault. .
  • Lights will be installed on the mobile crawler.

2.2.6WELDED COUPON

  • A welded coupon is a piece of metal of the same material as the package welded on the surface of the package.
  • The function of the coupon is as an indicator for corrosion, especially around the welded area.
  • It is predicted that corrosion will be most likely to happen around the welded areas. Hence, visual inspection around the welded areas should be conducted via mobile crawler.
  • The coupons should be coloured green to make corrosion distinctive for visual inspection.
  • The coupons will be positioned at a standard and accessible location on the package.

2.2.6STILLAGES

  • It is assumed that no creep will occur in a stillage due to the weight of stillages on top of it. The idea of putting 6 or 7 stillages on top of each other, (in a ‘stack’), was put forward in the design brief supplied by Nirex.
  • Corrosion of stillages will be monitored. It is assumed that other parameters such as temperature, humidity etc. will not significantly affect the functionality of a stillage.

2.2.7OTHERS

  • It is preferable to have wider spacing between each stack. This is to accommodate other forms of lifting, if packages/stillages are severely damaged.
  • Preventive measures of dropping packages/stillages on other stacks should be looked into. A lattice of horizontal and vertical steel beams could be located in the space between stacks. This would ensure a ‘domino effect’ would not occur throughout the whole vault should a package be dropped. However, the design of a storage vault is not within the design brief so this problem is not discussed further in this report.

WASTE MONITORING SEQUENCE

  1. RFID sweep of the whole vault.
  2. Any problem packages identified from the received data will be assessed by the mobile CCTV, before being taken to the Inspection Cell.
  3. A total of 4 packages will be inspected. Of these 4, packages identified as damaged will be sent to the inspection cell.
  4. If no problem packages are identified, 4 real packages are randomly selected and taken to the Inspection Cell. A further 10 real packages would be randomly selected and then inspected with the mobile CCTV.

Appendix 1

Arrangement of Dummies in a Block

Figure 1 – ‘Box in a box’ layout

Figure 2 – Possible location of dummy packages (along the walls)

Figure 3 – possible regions for corrosion analysis

Figure 4 – Dummy package (modified package design to house humidity sensor inside the base)

Figure 5 – Dummy package (using standard package design)

Figure 6 – Sensor Package

Figure 7 – Radiowaves of RFID only pass through air and metal stillages

Figure 8 - N/077 Volume 2, (DRG No. :E/DRG/0040010)

Figure 9: Strain Gauge on a wall

Figure 10: A radioactive resistant robotic crawler with mounted CCTVs

Figure 11: Humidity Sensors

Figure 12: A typical RFID sticker to be placed on every package

Figure 13: Corrosion in welded area

Figure14: Corrosion sensors which detects corrosion in gas pipes

REFERENCES

RFID Journal, 2002-2007

  • WPS/640: Guidance on monitoring Waste packages during storage (Nirex online), September 2005
  • WPS/700: 500 litre drum waste package specification: Explanatory Materials and Design Guidelines, October 2005
  • WPS320/01, July 2005
  • WPS 310/01, July 2005