Overpacking cell
Need to consider
§ The position of the overpacking cell – one central cell or two serving each side of the vaults
§ The flow of the packages and new packages in and out of the inspection cell
§ The method and equipment that will be employed to repackage the waste
§ The rate of overpacking – how long will it take to successfully complete the overpacking and the expected number of packages
The function of the overpacking cell
The primary function of the overpacking cell is to overpack packages that are deemed unsafe for transportation and storage in PGRC. These packages will have come directly from the inspection cell where they have gone through rigorous inspection techniques to determine the need to be overpacked.
The packages could have damage from corrosion that reworking has been unable to rectify or too bad to consider. Multiple corrosion locations to critical parts of the package (Reference corrosion technical report) could have made reworking of the package an unviable option. The packages could also have incurred damage that was deemed unsafe due to accidental dropping of the package. The package, depending on the size and nature of the drop, may have undergone deformation that is deemed unsafe to store.
Once the packages are deemed safe for transportation and storage they will be returned to their respective vaults. Figure 1 show the movement of packages around PGRC.
Figure 1: Movement of waste packages around PGRC
Transfer of damaged packages
The packages will come to the Overpacking Cell from the Inspection Cell via the transfer tunnel. If a 500litre drum needs to be overpacked then there is a possibility that this will occur as a single drum from the stillage and not necessary for all the entire stillage to be transported to the Overpacking Cell. This poses the issue of transporting the single drum, on the transport bogy. The lifting equipment will be configured to lift stillages and the larger packages, not for single 500 litre drums. There is a need for an additional spare stillage in the inspection cell that will act as a transportation stillage to enable the transportation of the damaged 500litre drum.
Once at the Overpacking Cell the 500 litre Drum will be removed and the stillage returned to the Inspection Cell.
Overpacking the damaged packages
The Idea behind the overpacking cell is to encapsulate the damaged package in a larger package to give sufficient protection and to allow the damaged package to be manipulated. The package will be encapsulated in cementitious grout (See later section).
The packages will be overpacked according to their size;
As can been seen above, two 500 litre drums will be packaged in a 3m3 Box. Two damaged 500 litre drum packages will fit simultaneously in a 3m3 Box and then encapsulated in a cementitious grout. The larger packages, 3m3 Box and the 3m3 Drum will be placed in larger packages than they are already housed in. The larger package will allow a 150mm envelope around the package to allow for a suitable grout encapsulation layer. This will give new package dimensions;
Wastecontainer / External dimensions (m) / Overpack dimensions (m)
3m3 Box / 1.72 x 1.72 plan x 1.225 high / 2.02 x 2.02 plan x 1.525 high
3m3 Drum / 1.72 dia x 1.225 high / 2.02 dia x 1.525 high
Table 1: Waste container sizes
Figure 2 illustrates what will happen to a 3m3 Box, with the old package being placed into a new larger 3m3 styles Box filled with grout (Need to find out where these pictures came from). Problem areas that have been highlighted with this are to the base of the new package. In order for there to be a 150mm grout cover to the bottom of the package pre-cast grout units will be placed on the bottom of the new package and the old package will then be situated on top of these. This will then allow sufficient cover to the bottom of the package and for the cementitious grout to be injected to encapsulate the rest of the package.
Overpacking cell location
A central overpacking cell location has been chosen that will service all the overpacking needs for the PGRC. Figure 3 shows the location of the overpacking cell drawn on a schematic plan drawing of the PGRC [1].
This has been chosen because (Need to explain the different locations that were considered, the positives of this one, & the possibility of building a new cell in the future) ……………
Flow diagram
The flows of activities through the overpacking cell are shown below (Could explain in more detail);
Grout stage (What type of grout, what machinery, how long to cure)
The material chosen for encapsulation of the packages is cementitous grout (Need to reference and make sure is correct).
To achieve acceptability the following properties are required of the grout [2];
§ Sufficient fluidity for up to 2.5 hours from mixing to enable infilling of package
§ Capable of being pumped and vibrated without segregation
§ Controlled heat generation during hydration to ensure product temperatures are within acceptable limits
§ Setting to occur within 24 hours
Investigate the machinery that is required, pumping concrete abilities
Lid manipulation
No welding going to take place in the hot-cell environment so lids are going to be bolted shut on the packages. Include more on this – Sam’s stuff on logistics maybe?
Function of Storage room
To store the new packages, etc…………
References
[1] Nirex Report N/077 – Generic Repository Studies, Generic Repository Design – Volumes 1 & 2
[2] Fairhall & Palmer, The encapsulation of Magnox swarf in cement in the United Kingdom, Cement & Concrete Research, Volume 22, Pg 293-298, 1992