Location: Sellafield UK

Customer: Sellafield Ltd

Project Summary

NuVision Engineering designed, fabricated, installed, commissioned, and operated Pulse Jet Mixer (PJM) test rigs to underpin the operating parameters of a full-scale PJM sludge mobilization system to be installed in a major sludge storage facility at Sellafield site. The completed test rigs were operated to demonstrate and refine the solution to one of the most challenging issues in the UK cleanup program today: the mobilization of large quantities of radioactive sludge, which has challenging properties like modeling clay and has proved to be beyond the capability of any other mixing technology.

Background

Approximately 1200 m³ of Corroded Magnox Sludge (CMS) needed to be retrieved from various areas of the First-Generation Magnox Fuel Storage Pond (FGMSP) at Sellafield and hydraulically transferred into 3 Bulk Storage Vessels (BSVs), approximately 30m long x 3m wide x 7m deep each, in the purpose built SPP-1 Buffer Storage facility on site. The sludge would be stored in the BSVs for several years before being transferred to a new processing plant for immobilization in a containerized concrete matrix product for long term storage and, ultimately, geological disposal.

The bed of CMS in each BSV was up to 4.8m deep and 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 proposed operational strategy in relation to the high yield stress sludges required the following:

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

Strong safety, schedule, and regulatory drivers required that NVE proceed with design and build of the PJM systems in parallel with technology underpinning work to confirm the system design and performance characteristics. The project identified that representative scale test rigs were required to further underpin the performance of the proposed PJM system and establish guidance for scale up of observed performance to the full-scale system in the BSVs. NVE was awarded this turnkey contract by SL to design, build, and operate new test rigs at ¼ and ½ scales.

Project Description

The completed rigs were commissioned in December 2011 and were operated by NVE under SL direction to further confirm and refine PJM design features and operational performance. The test facility was located at the NIS Facility in Chorley in the UK. Under Phase 1 of this contract, NuVision Engineering, with its subcontract partners NSG Environmental Ltd and Nuclear Technologies plc, designed, fabricated, installed, and commissioned two scale test rigs to underpin the operating parameters of the full-scale sludge mobilization system currently under construction.

The heart of the test rig system was comprised of 2 sets of 3 PJMs (¼ and ½ scale) and test tanks. The entire mobilization system equipment was designed in modular form and was skid mounted for ease of transport. The principle modules were:

• Test Tank & Pulse Tubes
• Jet Pump & Valve Skid
• Prescon® Control System

The test tank and pulse tubes were fully instrumented and equipped with ancillary features for flushing and cleaning between test campaigns. The rig featured the innovative use of sonar instruments for sludge bed mapping and load cells to investigate forces on the PJM support structure. Large quantities of simulant material were required for the extensive series of test campaigns, therefore the test rig featured simulant preparation facilities for storage of raw materials, preparation, transportation, and disposal. A ventilation system was included for control of airborne dust arising from simulant handling. The completed test facility was located at the NIS Facility in Chorley in the UK.

Phase 2 (operations) commenced in January 2012 and lasted 3 years. Multiple operational campaigns were conducted to investigate the performance of the PJM’s under various conditions, principally:

1. Capability to maximize available storage volume by operation of the PJMs to level the bed of sludge.
2. Start-up and operation of the PJMs in a high yield stress simulant material.
3. Testing of contingencies and recovery options to cope with unforeseen circumstances.

Under Phase 3, the rigs were decommissioned.

Challenges and Solutions

The greatest challenge addressed by this project was to prove PJM technology for the mobilization of large quantities of sludge, which has challenging properties like modeling clay and which has proved to be beyond the capability of any other mixing technology.

Execution of the project required the successful collaboration of a multinational team of US and UK based companies. NVE carefully assembled, coordinated, and managed a team of subcontractors in the US and UK with the complementary skills and resources necessary to achieve the project aims and objectives. In addition, fundamental to the success of the project has been the need for NVE to work in close collaboration with SL and prime contractor technical teams under the parallel but interfacing contract to supply the PJM systems. NVE worked diligently with SL to analyze, interpret, and apply the information gained through this project and incorporate this into the evolving PJM system design. This requires 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 arise. The success of this overall collaboration has been a key enabling factor in allowing the FGMSP remediation program to proceed.

Benefits Achieved

• Delivered a key enabling technology need for the mitigation of the FGMSP at Sellafield that could not be provided by “off the shelf” solutions available in industry.
• Allowed a fast track program for one of the highest priority projects in the NDA portfolio to proceed with manageable technical and commercial risk.
• Delivered a program of work to provide sound and defensible answers to stakeholder and regulator concerns and challenges to the project.

Customer Feedback

“The results from the initial (NuVision) high priority trials; later PJM trials and studies; and modifications incorporated at DP2; enabled TUP to change the focus of the project strategy from identifying modifications to the Buffer design to making best use of the available installed equipment and features.

The early fears that high yield strength sludge’s may prevent the PJMs from functioning now appear very pessimistic with the addition of the water injection system and the incorporation of a system to purge the pulse tube of sludge following operation. At DP2 the question generally shifted from: “Will the PJMs work?” to “How well will the PJMs work” and further to “The PJMs will work, how can we best operate them to maximize mobilization over the range of potential material properties?”

NuVision trials to date have been extremely successful, leading to plant modifications and providing confidence that the sludge can be managed through filling and storage to ensure final retrieval”.

— C Birchall (SPP-1 Technical Manager), Sellafield Limited