Seascale, United Kingdom
Seascale, United Kingdom

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Grant
Agency: GTR | Branch: EPSRC | Program: | Phase: Research Grant | Award Amount: 430.42K | Year: 2012

The key challenges facing research, development and deployment of autonomous systems require principled solutions in order for scalable systems to become viable. This proposal intertwines probabilistic (Bayesian) inference, model-predictive control, distributed information networks, human-in-the-loop and multi-agent systems to an unprecedented degree. The project focuses on the principled handling of uncertainty for distributed modelling in complex environments which are highly dynamic, communication poor, observation costly and time-sensitive. We aim to develop robust, stable, computationally practical and principled approaches which naturally accommodate these real-world challenges. Our proposed framework will enable significant progress to be made in a large number of areas essential to intelligent autonomous systems, including 1) the assessment of reliability and fusion of disparate sources of data, 2) allow active data selection based on Bayesian sequential decision making under realistic time, information & computation constraints, 3) allow the advancement of Bayesian reinforcement algorithms in complex systems, and 4) extend Model predictive control (MPC) to probabilistic settings using Gaussian process non-parametric models. At the systems level, these developments will permit the design of overarching methods for 1) controlled autonomous systems which interact and collaborate, 2) integration of sensing, inference, decision making and learning in acting systems and 3) design methods for validation and verification of systems to enhance robustness and safety. The ability to meet these objectives depends on a multitude of recent technical developments. These include, 1) development of practical non-parametric algorithms for on-line learning and adaptation 2) approximate inference for Bayesian sequential decision making under constraints, 3) the development of sparse data selection and sparse representation methods for practical handling of large data sets with complex decentralised systems and 4) the implementation of and deployment on powerful modern parallel architectures such as GPUs. We aim to build on our expertise in Bayesian machine learning, multi-agent systems and control theory and by drawing together closely related developments in these complementary fields we will be able to make substantial improvements to the way artificial agents are able to learn and act, combine and select data sources intelligently, and integrate in robust ways into complex environments with multiple agents and humans in the loop.


Sutton A.,Sellafield Ltd.
ICNC 2015 - International Conference on Nuclear Criticality Safety | Year: 2015

A large number of plant operators on the Sellafield site require criticality awareness training. Historically, this training had been developed and delivered largely by the Criticality Safety team in isolation, with a heavy focus on the physics of criticality. Feedback from operators indicated that the historic training approach perhaps over emphasised the physics of criticality as an abstract concept, while potentially under emphasising more practical considerations for day to day work on the plants. This paper discusses some of the improvements that have been made to the training courses and the methods of delivery over recent years at Sellafield.


Wilson A.R.,Sellafield Ltd
ICNC 2015 - International Conference on Nuclear Criticality Safety | Year: 2015

The PP Active Feed Tank (PPAFT) is a buffer tank that is not safe by geometry and which is located between the Medium Active (MA) and Plutonium Purification (PP) cycles of the chemical separation process in the Magnox Reprocessing Plant. The PPAFT receives Pu nitrate in acid which has been conditioned ready for the extraction of Pu with TBP/OK (tri-butyl phosphate in kerosene) solvent in the PP Cycle. The criticality safety case for the PPAFT recognises that during both normal operations and potential maloperations solvent which is dissolved (TBP which is present in solution but can be released upon a change in acidity) and entrained (TBP/OK physically carried over but not in solution) will accumulate in the PPAFT. The only practicable route out for Pu in solvent in the PPAFT is the normal process route out from the base of the PPAFT to the PP cycle through intermediate vacuum lift and feed vessels. However, the dished end base of the PPAFT and the intermediate vacuum lift and feed vessels are of particularly challenging geometry. There are five neutron monitors placed around the PPAFT for the detection of Pu in solvent. The original design intent of the neutron detection system was that any single monitor should be able to reveal an accumulation of Pu in solvent before it would potentially be unsafe if fed downstream. However, over time there have been changes to the fuel feed and chemical process of the plant which have had the potential to affect the performance of the neutron monitoring system. The ability of the neutron monitoring system to function to its original intent was questioned. Work has recently been carried out to investigate the capabilities of the PPAFT neutron monitoring system for current plant conditions and to identify potential improvements while making best use of the existing neutron monitors. It was found that moving a neutron monitor from the side to the top of the PPAFT and adding alarms based on the ratio of signals from multiple neutron detectors would be effective in improving detection of Pu in solvent. This paper describes the challenges involved in detecting thin layers of Pu in solvent using neutron monitors, discusses the improvements made to the PPAFT neutron monitors and details the combination of real plant data and modelling with the shielding code MCBEND used to provide confidence in the enhanced neutron monitoring system.


Sutton A.,Sellafield Ltd.
ICNC 2015 - International Conference on Nuclear Criticality Safety | Year: 2015

A recent event in the Magnox Reprocessing Plant involved the loss of reductant feed to a contacting vessel and required the plant to be shutdown. The criticality team attended the site out-of-hours to facilitate the production of a recovery plan. This initial recovery plan involved manual dosing of the contactor with reductant but was heavily dependent upon initial information regarding the length of time the maloperation had been occurring. Key assumptions fundamental to maintaining criticality safety during the planned recovery were clearly highlighted in the assessment that was written to support the operation, which allowed informed decisions to be made regarding the adequacy of the plan, once further information emerged suggesting the fault had been ongoing for much longer than originally assumed and therefore the amount of Pu in the contactor was much higher than initially thought.


Wilson A.R.,Sellafield Ltd
ICNC 2015 - International Conference on Nuclear Criticality Safety | Year: 2015

Following a revealed sustained loss of reductant feed to the Primary Separation 4 (PS4) U/Pu separation contactor in the Magnox Reprocessing Plant in 2014 the solvent extraction cycles were safely shutdown. However, initial mass balance calculations indicated that over four times the typical mass of Pu could be present in PS4. Due to the loss of reductant feed, much of this Pu was expected to be in the solvent phase of Tributyl Phosphate and Odourless Kerosene (TBP/OK) where it would be difficult to observe with the neutron monitors located under PS4. Samples were taken of the solvent in PS4 which confirmed the presence of Pu in solvent; normally almost all of the Pu in PS4 is in the aqueous phase. The volume ratio of solvent to aqueous in the PS4 contactor is high. This meant that simply re-dosing PS4 with reductant could not be supported as a recovery option due to the potential to realise high Pu concentrations in the aqueous phase. This paper details the recovery options which were considered and the ultimate decision to recover PS4 using Gadolinium (Gd) poisoning and Gd-dosed reductant feeds. The recovery included: • The need to consider the impact of Gd poisoning on monitoring of the recovery with the PS4 neutron monitors • Close support from criticality safety personnel on the plant at all times during the recovery • Production of operator aids and short fit for purpose safety documentation to assist with the recovery. The recovery of PS4 proceeded safely and smoothly. There were no losses of Pu to raffinate streams despite the prolonged shutdown. The plant was then safely rundown to flush out residual Pu and Gd.


Wilson A.R.,Sellafield Ltd
ICNC 2015 - International Conference on Nuclear Criticality Safety | Year: 2015

THORP reprocesses fuel from Britain's Advanced Gas-cooled Reactors (AGRs) and fuel from Light Water Reactors (LWRs). The THORP dissolvers use nitric acid poisoned with Gadolinium (Gd) to ensure criticality safety. The dissolver criticality safety case uses a burnup credit approach to determine a minimum required Gd concentration. The burn up credit approach followed originates from a time when fuel receipts for THORP were ongoing and hence models a deliberately conservative and artificial fuel type to cover all potential fuel receipts. External fuel receipts have now ceased and detailed information on post irradiation U and Pu isotopics is available for all fuel scheduled for reprocessing. Work has therefore been undertaken to determine whether the burn up credit safety case could be revised to be more representative of the fuel actually remaining for reprocessing and hence to reduce further the required Gd concentration for the dissolvers. This would ultimately reduce the quantity of high active liquid waste requiring treatment and storage. The great majority of fuel remaining for reprocessing in THORP is AGR fuel, for which the typical burnup is known to be much higher than was previously assumed in the safety case. Pu and U isotopics for irradiated AGR fuel were examined with the fuel inventory code FISPIN. Modelling with the code MONK then showed that the Gd requirement for irradiated AGR fuel of a given burnup was much lower than in the previous safety case due to the change in Pu:U ratio and Pu240 in Pu for AGR fuel compared with the previous conservative assumptions. The burnup of all remaining LWR fuel was found to be high and hence lower dissolver Gd concentrations could also be tolerated for reprocessing this fuel. The work has concluded that the THORP dissolver Gd concentration can be halved for all remaining LWR and AGR fuel campaigns with a consequent cost saving of ∼£4m in Gd and high active waste processing time. Implementation of this improvement is currently ongoing on the plant.


Sutton A.,Sellafield Ltd.
ICNC 2015 - International Conference on Nuclear Criticality Safety | Year: 2015

A recent event in the Thorp Reprocessing Plant involved unconditioned feed being sent to one of the main process solvent extraction vessels. As the feed was unconditioned the fissile material was lost to the aqueous raffinate stream. The plant was tripped and shutdown in line with the baseline criticality safety case. This paper describes the recovery option that was taken to remove the Pu from the raffinate tank and safely consign it to the downstream effluent vessels. Key assumptions that were fundamental to maintaining criticality safety throughout these operations were clearly highlighted in the supporting criticality safety assessment. Key learning points that are of relevance to the wider criticality safety assessment community are pulled out at the end of this paper.


Carlisle D.,Sellafield Ltd.
Proceedings of the International Conference on Radioactive Waste Management and Environmental Remediation, ICEM | Year: 2013

The Pile Fuel Storage Pond (PFSP) was built in 1948/50 to treat materials from the Windscale Piles. Multiple operational regimes over the intervening 60 years have resulted in a complex inventory of spent nuclear fuels, solid and liquid intermediate level wastes. A coordinated programme of work, designed to retrieve and safely dispose of the pond contents, has been implemented to enable the decommissioning of the facility. The long period of passive storage operations which preceded the implementation of the programme meant that the operator was faced with a dual challenge of providing new technical capability and changing a working culture that was inappropriate for the dynamic environment required to successfully deliver the programme. It was recognised that the nature of the programme meant that implementing a standard manufacturing approach to operations would not be appropriate. In order to create a dynamic retrievals focussed working culture, the operator has vigorously embraced change programmes aimed at improving a number of working practices including encouraging innovation, managing integrated but flexible production schedules, and encouraging workface problem solving. The combined impact of beginning to resolve the technical challenges and focussing on the delivery culture has resulted in the facility making a step change towards becoming fully retrievals operations focussed. Copyright © 2013 by ASME.


Grant
Agency: GTR | Branch: Innovate UK | Program: | Phase: Collaborative Research & Development | Award Amount: 767.78K | Year: 2015

The post operational clean out (POCO) of the highly active liquor storage tanks at Sellafield site will require the removal and immobilisation of residual solids from the heel of the tanks. The solids are expected to contain high levels of molybdenum and zirconium which are insoluble fission by-products. Some of the older highly active liquor storage tanks will require washing and stripping of the compacted solids with an alkali reagent due to a lack of engineered methods of solids agitation, one of the preferred reagents is sodium carbonate solution. Both molybdenum and sodium have limited solubility in the current glass matrix used for immobilisation of high level waste (HLW) in the UK. This project aims to address this issue by developing a new and improved glass formulation and method of delivering the glass forming additives into the existing UK vitrification process. This will ultimately reduce the volume of HLW requiring final disposal and accelerate the high level hazard reduction programme at Sellafield.


Grant
Agency: GTR | Branch: Innovate UK | Program: | Phase: Collaborative Research & Development | Award Amount: 591.95K | Year: 2013

Sellafield Limited is committed to the acceleration of the decommissioning of its highest hazard legacy plants. To do that it is necessary to retrieve and process radioactive waste sludges in a safe and efficient manner. These are extremely complex and variable materials and so it is important to be able to model their behaviour in critical parts of the process, and this project develops a new and much improved way of doing that. All such models require data for their development and validation which has been unavailable. The project also develops a means of gathering the required data in a radioactive environment. The same tool will then allow the process to be monitored to provide assurance that it is operating within its design envelope and also to be optimised to get the best performance from the taxpayers investment in the treatment processes. We then expect to see applications in other industries such as water treatment and mineral processing.

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