11
DRAFT
TECHNICAL NOTELOGISTICS
Prepared by: / Name / Sam BillingChecked by: / Name
Approved by: / Name
DOCUMENT INFORMATION
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Date:
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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.
11
DRAFT
Summary
This document demonstrates the logistics of the integration of inspection cell and overpacking cell into the PGRC.
Package traffic throughout the whole system is illustrated, and the logistics are broken down into two key phases. Phase 1 is the emplacement period during which packages are located in the vaults. Phase 2 is the monitoring period in which the packages are monitored and cyclic inspection processes are performed. The roles of the various cells during these phases are highlighted.
The role of proven technology in the designs of the transport systems is highlighted, with emphasis on using existing operational designs. Improvements to the transfer tunnel design are demonstrated to cope with the increased package flow.
Maintenance procedures and frequency for cells and transfer tunnel is considered with reference to existing Nirex specifications. Logistics and design are assessed from a safety perspective.
Finally the integration with the existing ventilation system is demonstrated.
Contents Table
1. Package Traffic 3
2. Package Flow 5
2.1 Phase 1 5
2.2 Phase 2 5
3. Location 7
4. Lifting/moving equipment 8
4.1 Cranes 8
4.2 Transfer Tunnel 10
5. Maintenance 12
5.1 Vaults 12
5.2 Transfer Tunnel 13
5.3 Inspection Cell and Repacking Cell 14
6. Ventilation 15
7. Safety 16
7.1 Inspection and Repacking Cells 16
1. Package Traffic
In the reference case there is a total of 202000 packages. However, due to there being four 500 litre drums per stillage, the total is reduced to 73000. Of this total UILW accounts for 71000 packages all of which will pass through the inlet cell. For the proposed 50 year emplacement period this gives an average of 1420 packages passing through the inlet cell each year (N077 V1).
Figure 1: Package flow into repository at emplacement phase
This figure equates to around 4 packages per day (24hrs), giving a 6 hour time frame in which an individual package must be emplaced in the vault via the transfer tunnel and inspection cell. Due to the process in which the vaults are filled (one at a time), each inspection cell must have the capability to deal with 16 packages per day in the case of 4 stillages, or 13 packages per day in the case of 3 stillages and one larger container (it is assumed a larger container will present greater handling/inspection difficulties) during the emplacement phase.
During this emplacement phase the inspection cell is unlikely to be used to its full capabilities (reworking etc). Furthermore the reworking element is likely only to be used in the case of dropped packages. These cells will only begin to function fully in the monitoring phase following the emplacement phase, when packages will undergo scheduled full inspection, possible requested inspection, and reworking or overpacking dependant on condition.
During the monitoring phase the inspection cells will have the capability to perform 4 inspections per day. Therefore, in a worst case scenario of a vault containing only four drum stillages, running at full capacity each package will be inspected every 18 years (not taking into account requested inspections).
The inspection selection will be a scheduled, cyclic process where the first into the vault is first inspected. This however is open to review as it is suggested ‘higher threat’ containers should be inspected more frequently.
Repacking will occur only in cases of severe defects therefore will be fairly infrequent. However the likely case is that defects will increase in number and severity with time, therefore it is suggested the repacking cell should have the capability to meet the worst case scenario; if all inspected packages require overpacking, 44 packages will require repacking per day. This is an unlikely case, however due to the simplicity of the overpacking process, this target could be met. It should also be considered that if this limit was approached, further repacking cells could be built adjacent to the existing cell, or it may prove more economically viable to ‘back-fill’.
2. Package Flow
Figure 2: Package flow diagram
With reference to figure 2, package flow to the vault is shown in black. Package flow with defects is highlighted blue. The life of any individual package can be separated into to phases;
2.1 Phase 1
Packages initially enter the repository through the inlet cell. Here the package is prepared for storage in the vault. It is between here and the vault that the first stage of inspection is performed. The package will be transferred into its designated vault via the transfer tunnel, however before emplacement it will be transferred from the transfer tunnel to the inspection cell assigned to that vault via the emplacement crane. Here the package will be examined, and data of that particular package will be stored for future inspection comparison (see …). The package will then be transferred into the vault for long term storage and further monitoring.
2.2 Phase 2
During its time in storage the package will undergo further inspection. This will be carried out due to scheduled inspection or requested inspection which can arise from vault monitoring (see ….) or external party demands. The package will be transferred to the inspection cell via the emplacement crane. The package is then inspected for defects (see …); if defects are present the package will require either minor reworking (performed in the inspection cell) or transfer to the repacking cell. If the defects are easily reparable reworking will be performed in the inspection cell, the package will then be re-inspected and transferred back to the vault via the emplacement crane. If the defect is too severe for the rework capabilities of the inspection cell, it will be transferred to the repacking cell via the emplacement crane and the transfer tunnel. Once the package is repaired or over-packed it is returned to the vault via the transfer tunnel and the emplacement crane.
Phase 1 will only occur once for any one particular package. Phase two will occur numerous times although reworking is unlikely so the process will only be partial.
3. Location
The location of the inspection cells and repacking cell is optimised to suit the current PGRC and logistics.
The inspection cell is located at the front (transfer tunnel side) of each vault. This gives optimum package flow capabilities and integrates with current personnel areas to allow visual inspection. It also allows for efficient transfer between inspection cell and transfer tunnel in the case of a package requiring repacking.
The overpacking cell is located adjacent to the inlet cell, at the centre of the vault. This optimises transfer times and locates it near a personnel area, making visual inspection and maintenance possible. The location is also near ventilation outlets, allowing particulates to be removed from the cell efficiently.
For further information on location see…
4. Lifting/moving equipment
4.1 Cranes
Existing proven technology designs will be used for all cranes in the repository. In the vault the overhead crane has the facility to lift stillages, 3m3 boxes and 3m3 drums. Existing overhead crane designs are illustrated bellow.
Figure 3: Overhead crane at Sellafield
Figure 4: Twist lock crane
Figure 5: Stillage showing twist lock insertion points
Accurate crane positioning is of high importance. This is achieved using high precision crane winding and traversing carriage along with an optical encoding system. Examples of these systems are illustrated below. (corwym89)
Figure 6: Crane traverser at Sellafield
Figure 7: Optical encoding system for crane positioning
Figure 8: Toothed belt encoder system for crane positioning
4.2 Transfer Tunnel
The transfer tunnel will transport waste packages between;
- Inlet cell and vault (emplacement phase)
- Vault and vault (vault maintenance)
- Vault and overpacking cell (monitoring phase)
At the inlet cell the package is loaded onto the bogie. On transfer to the vault the bogie would stop beneath a shield plug, or slide door at the location of the vault. The package would then be removed from the bogie using the emplacement crane. The operation for vault to vault transfer would follow the same procedure. On transfer to the inspection cell the bogie will enter the inspection cell via a shield door, the package will be removed, the bogie will leave the overpacking area and the shield door will close behind.
The bogie will require an encoding system to ensure it is positioned correctly to enable crane lifting operations. This will be done using existing techniques.
The transfer tunnel will be designed to the specifications stated in corwm89. It will utilise proven technology demonstrated at previous storage sites such as Sellafield.
Figure 9: Transfer tunnel bogie at Sellafield
5. Maintenance
Maintenance of the following areas will be required throughout the life of the repository;
- Vaults
- Transfer tunnel
- Inspection cell
- Overpacking cell
5.1 Vaults
Vault maintenance has already been discus in corwm126. Reviewing these procedures is necessary with reference to the transfer tunnel, inspection and overpacking cells. Degradation rate of transport routes and cells is likely to be comparable with that of the vault.
The vaults will degrade with time. This is likely to occur roughly every 100 years.
It will be established nearer the time whether vault replacement or refurbishment is the most viable option.
Taken from ‘Nirex Generic Repository Studies, Care and Maintenance, corwm126’;
“The process of vault refurbishment would involve the removal of all waste and the clean up of any residual contamination before construction personnel could begin work. The principal tasks within the vault would necessitate the following procedures.
1. Decontamination.
2. Re-establishment of construction services (including ventilation) and routes.
3. Staged removal and replacement of the sprayed concrete roof support systems, the installation of additional roof bolts and installation of replacement in situ monitoring systems.
4. Staged removal and replacement of the sidewall sprayed concrete, crane rails and corbels, the installation of additional roof bolts and installation of replacement in situ monitoring systems.
5. Removal and replacement of the concrete floor, peripheral backfill and drainage systems.
6. Re-establishment of emplacement services and routes.”
This is a large and costly operation and vault replacement may prove a more economic option. In the case of a new vault the benefit of hindsight and experience may allow design improvements to be realised. In either case the package transfer process would be largely the same; packages would be moved between vaults in exactly the same way they came in (corwm126).
5.2 Transfer Tunnel
The transfer tunnel cannot be replaced without significant construction in all areas; therefore it is important it is maintained frequently. The current concept design incorporates two transfer tunnels as shown below;
Figure 10: Transfer tunnel layout
Design has evolved slightly – to be updated in final report
Between transfer tunnels 1 and 2 there is a shield wall. The tunnels are also separately shielded from the inlet cell and repacking cell. This allows an individual tunnel, or section of tunnel to be maintained whilst other sections remain in use. Transfer tunnel will be used most frequently as it is the primary transfer route for packages travelling to the vaults from the inlet cell. In the case of maintenance of this tunnel, transfer tunnel 2, which is primarily used for transport of defected packages to the repacking cell, will be used for inlet – vault transfer.
In the case of transfer tunnel refurbishment the same procedure as stated in vault refurbishment (corwm126) will be followed, however this is unlikely due to the size of the structure.
5.3 Inspection Cell and Overpacking Cell
It is estimated that refurbishment or replacement of these cells will be necessary at the same frequency as the vaults. The same procedure will be used (corwm126).
Maintenance of these cells, especially the inspection cell, will be more frequent than that of the vaults due to higher frequency usage. Equipment will require regular maintenance; this will be done either remotely or by suited personnel.
6. Ventilation
The ventilation system for the PGRC is illustrated bellow.
Figure 11: PGRC ventilation system
Integration of the inspection cell and overpacking cell with this system is fairly complex. Both cells have facilities involving the use of particulates which could contaminate waste packages, causing defects. Therefore airflow from these cells should not meet other flows before the return side, and in the case of the vaults, after the outlet. The inspection cell is located at the front of each vault; this proves difficult to integrate from a view to optimising ventilation, therefore it is proposed the inspection cells require a separate ventilation outlet which bypasses the vault and rejoins the airflow at the end of the vault. This would be very simple to engineer; ventilation pipes along the vault wall would suffice.
The overpacking cell is located adjacent to the inlet cell. This is very close to the construction return therefore it is suggested the overpacking return should feed into the construction return before leaving the repository.
In both cells pressure differentials would be maintained to ensure that any air transfer was from the inactive to active areas (N/079)
7. Safety
From N/079;
“Nirex has set out the Nuclear Design Safety Principles (NDSPs) which it has adopted for a phased disposal facility. The aim in producing that document is to apply recognised engineering and design principles for the safe operation of nuclear plant. The application of those principles within a systematic framework is intended to ensure that: