Location: Sellafield UK

Customer: Doosan Power Systems Ltd

Project Summary

NVE supplied 33 Power Fluidic Pulse Jet Mixing (PJM) Systems to mobilize Stored Radioactive Waste from the First Generation Magnox Storage Pond (FGMS) at Sellafield. The PJM’s are to be used to mitigate hydrogen build-up in the waste, maintain a level sludge bed during filling, and mix the waste prior to final retrieval and recovery. The scope of work included design, manufacture, inspection and testing, packaging, and delivery of the major fluidic components for mixing the waste in the storage tanks in the proposed facility at Sellafield, known as SPP1 buffer store.

Background

The First Generation Magnox Fuel Storage Pond (FGMSP) at Sellafield is an aging facility, containing a significant quantity of Corroded Magnox Sludge (CMS) arising from the corrosion of magnesium alloy clad Magnox reactor fuel in storage. CMS contains primarily magnesium and uranium corrosion products and is known to be capable of developing high yield strength over time in a settled and dewatered state. Approximately 1200 m3 of CMS will be retrieved from various areas of the FGMSP and hydraulically transferred into 3 Bulk Storage Vessels (BSVs), each approximately 30m long x 3m wide x 7m deep and in a purpose built Buffer storage facility on site. The sludge will be stored in the BSV’s for several years before transfer to a new processing plant for immobilization in a containerized concrete matrix product for long term storage and, ultimately, geological disposal.

A critical need for the FGMSP clean-up program and the NDA mission is to manage the CMS bed in the BSV’s during initial sludge transfer, interim storage, and final mobilization and transfer of the CMS from the BSV’s for processing at the end of the storage period. The bed of CMS in each BSV will be up to 4.8m deep and is expected to consolidate with time and depth, thereby increasing the yield strength of the sludge to a value up to 75kPa– the consistency of modelling clay.

The project objective was to design, manufacture, inspect, test, and deliver a PJM system for the BSV’s which would be robust and reliable enough to meet all operational requirements of the plant under the challenging properties of the CMS sludge.

Project Description

The PJM system for the BSVs was comprised of 11 pulse tubes per vessel, each with a nominal volume of approximately 4.5m3. An internal diameter of 1100mm with an overall height of 5270mm was selected for each PJM based on empirical guidelines verified by extensive testing. Spacing of the pulse tubes is indicated in the Figure below.

Operations in the buffer storage vessels take place in three distinct phases:

• Filling
• Storage
• Retrieval

Each stage has specific requirements relating to the PJM system.

The requirement to be able to operate the PJMs and return the sludge to a mobile condition to facilitate final sludge retrieval was paramount. The operational strategy in relation to the high yield stress sludges requires the following:

• Capability to maximize available storage volume in the BSVs by operation of the PJMs to level the bed of sludge.
• Start-up and operation of the PJMs in a high yield stress material (should it develop).
• Provision of contingencies and recovery options into the system to cope with un-planned circumstances.

For each PJM, NVE supplied a separate dedicated set of skid-mounted process controls. Detailed design of the PJM system for the BSVs proceeded in parallel with technology underpinning work.

Challenges and Solutions

The project required the design, manufacture, inspection and test, and delivery of a mixing system for the BSV’s which would be robust and reliable enough to meet all operational requirements of the plant under the challenging properties of the CMS sludge. NVE delivered a key enabling technology (PJM system) for this project that could not be provided by “off the shelf” solutions available in industry.

This application of PJM technology was unique and extremely demanding. In addition, the fast track requirements of this project meant that NVE were required to develop the detailed design and build the equipment in parallel with technology underpinning work. This required constant and open dialogue between SL, prime contractor, and NVE technical teams to manage risk and jointly develop and apply innovative solutions to technical challenges as they arose. Execution of the project required the successful collaboration of a multinational team of US and UK based companies.

Through this project, NVE was able to provide a turnkey service to a fast track schedule and supply PJM technology to address this major waste clean-up concern, which was of highest priority to NDA, NMP and Sellafield Limited.

Benefits Achieved

• Designed and built an innovative PJM system to meet sludge mixing requirements that could not be provided by “off the shelf” solutions available in industry
• Provided essential technology for the construction and commissioning of a high integrity facility to receive and safely store highly challenging and hazardous radioactive waste
• Achieved turnkey delivery of plant and equipment to meet demanding customer schedule for overall facility construction and commissioning
• Allowed Sellafield Limited to address a legacy waste problem of national importance

Customer Feedback

“Remediation of the FGMSP is of the highest priority to NDA, NMP and Sellafield Limited. Given the significant inventory of highly radioactive sludge that resides in this facility, the construction and commissioning of a high integrity facility which can receive and safely store this Material is of national importance. The sludges present a broad range of extremely challenging technical and engineering issues.

NVE have worked tirelessly, over a number of years, with a whole range of stakeholders to address concerns and build confidence in the ability of their PJM technology to mobilize extremely dense sludges.

The way the NVE team have worked with stakeholders on such a time critical, innovative, and hypersensitive project is a credit to all involved. It has been a privilege to work with the team to overcome the technical challenges involved in this project while also realizing a significant turnaround in stakeholder views and opinions”

— George Andrews, Director NES Limited, former Sellafield Limited Ponds & Silos Superintendent