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Case Studies

Sellafield

Emergency Preparedness & Resilience Architecture

Sellafield

The outcome of the process assessment either confirms that adequate arrangements are in place and/or suggests improvements to enhance the ability of individual plants and processes, and Sites as a whole, to withstand low probability/high consequence accident scenarios. Typical examples could include, a prolonged full Site Black Out (SBO), a significant seismic event, flood, or a malicious act.

The RESEP, was developed to be a structured, deterministic, and consistent approach to applying the stress tests at the Sellafield site. The RESEP is a staged assessment process, and includes the following:

  • Progression of events from individual plants and processes to the whole site, including domino effects
  • Searching for 'cliff edge' effects and development of timelines for critical mitigating response actions
  • Assessment of infrastructure requirements both on and off-site

An essential part of the process is to identify the Critical Safety Function (CSF) for each plant using the principles of nuclear safety. This allows attention to be firmly focused on the actions essential to sustain the CSF. The existing emergency arrangements are assessed to identify the logistics i.e. time, resources, tools, access, plant conditions etc., required to implement and then sustain each of the backup systems. Two timelines are produced for each plant/process:

  • A pessimistic timeline where any backup that depended upon external help to implement was disallowed
  • An optimistic timeline where Site help was allowed, if required, to implement and maintain the backup systems.Structuring the RESEP process in this way ensures the essential services i.e. power, water, steam etc., the extent of Site help required, and the adequacy and duration provided by the declared backup systems to protect the CSFs are clearly identified.It has been deployed on a complex nuclear chemical site with multiple facilities, processes and working patterns. RESEP can be applied to new/future operations and or existing sites/ facilities to identify additional safeguards which may have arisen as a result of changes in the risk perception, changing legislation, regulation, etc.

DBD Defined Deliverables

  • Although developed for the nuclear industry it is easily transferable to non-nuclear high hazard processes.
  • Leading and managing the development of emergency preparedness including “hard engineering” and “command and control decision making” from design through inactive and active commissioning, to handover to operations
  • Managing implementation of the Resilience Evaluation Process (RESEP) including defining plant/process CSF’s
  • Production of bespoke facility/project response timelines
  • Resilience Options Diagram (ROD), to clearly identify the optimum time for deployment of backup systems including options and any potential consequences of deploying the backup options for example hazard to operators.
  • Production of Severe Accident Management Strategy Option Diagrams (SAMSOD) for use in Emergency Control Centres to support event response decision making

Client Deliverables

  • A report prepared for each high consequence plant/process detailing the effectiveness of each of the backup systems with recommendations for improvements for any shortfall or gap found
  • A report prepared on the overall effectiveness of emergency management processes
  • A report on the reliability of the Sites infrastructure

The Results/Client Benefits

  • Robust, auditable, documented review process supported by the UK Nuclear Regulator.
  • Fit-for-purpose emergency arrangements Visual tool to aid informed decision making during a severe accident.
  • An emergency plan with both operational and safety case requirements fully integrated.
  • Provision of Emergency Preparedness Intelligent Customer capability.
  • The ability to proactively manage a severe accident.

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Simulation & Modelling

Dynamic Process & Control Simulation

Sellafield

DBD is leading a team, possessing specialist simulation expertise, to develop and implement a model that simulates the full core and ancillary plant. The simulation enables the process design to be checked and validated, to provide a vital plant commissioning baseline and operator training tool.

  • Dynamic Process Simulation for process design and control system verification
  • Gas process modelling of evaporator off gas at vacuum conditions via two stage steam ejector condensers
  • Modelling of two phase flow multi-component in pipework carrying steam, air and steam condensate with change of phase
  • Built, run and verified in stages to give client early feedback of results
  • Early capture of design and operational issues prior to plant construction phase
  • Long term aim to interface with actual control system to support commissioning and operations phases

DBD Deliverables

DBD’s deliverables were to deliver a dynamic process and control simulator.

The Results

DBD delivered a dynamic process and control simulator to our client, a major construction company. The simulator models a new Highly Active Evaporator at Sellafield, UK. The model was based on design documentation as the plant was still being constructed. The purpose of the model was to verify that the control system definition and philosophy will correctly and efficiently control the plant during its cyclic and batch sequential operation.

The simulator models the process and control system. It also has fully navigable 'control room' screens of the complete process plant, including auxiliary equipment and services (See Figure 1). This allows the designers to operate the plant before it is built or commissioned, allowing offline controller tuning, corrections to the control system and verification of the design. It has brought the design to life and in many cases the operation of the plant has not conformed to the designer’s vision. This feedback means that the control system can be tuned or corrected to ensure that a round of design iteration is removed from the expensive commissioning stage.

An example is of a main vessel level control that is designed to control a feed flowrate. The model showed that the process volumetric holdup caused sufficient time lag in the feedback control loop, resulting in setpoint overshoot and triggering of alarms/trips as well as unstable operation during startup.

The model was built in phases, with the core of the process being modelled first. This demonstrates how DBD applied their process knowledge to decide which parts of the plant, process and control, are of most benefit to the client at the current stage of the project lifecycle.

 Evap D Simulator

Figure 1 – Example Screen from the Simulator

The simulator has completed a full Factory Acceptance Test (FAT) and the model output has been compared to the expectations of the client’s design and operational team.

On the whole, the simulator provided the client with the confidence that the process design was fit-for-purpose. However, the simulator found many discrepancies (some hazardous) and suggested some enhancements to the control system definition. These have now been corrected at the design stage.

The model paid for itself many times over by discovering a significant discrepancy in the process design that may otherwise have been found during commissioning. This discrepancy would have meant the plant throughput not being achieved and therefore the functional specification requirements not being met. It has been conservatively predicted that a delay of 2-3 months to commissioning testing would have resulted (at a cost of £6m to £9m). Due to DBD’s efforts it was found in design stage so remedial action could be taken at low cost.

The simulator platform was partly chosen due to the ability to support the plant operations after the design stage is completed. The simulation looks like a control room DCS (e.g. with trends, alarms etc) and so plant operators were immediately comfortable with the visual side. The plant operator was keen to use the simulator for operator training, taking advantage of the fault injection system and scenario handling capability. The simulator can, in the future, be used to test plant modifications prior to implementation on plant.

The simulator was built with a ‘generic’ control room interface but when the actual plant control system is delivered and approved, the simulator will be merged so that it can provide offline operator training and control system testing with a high degree of realism.

Client Benefits

  • Identification of discrepancies during the design stage, enabling remedial action to be taken at a low cost and preventing delays to the commissioning schedule
  • A saving to the overall project budget of between £6M to £9M through the identification of a key design issue that was able to be redesigned prior to the commencement of manufacture of the main evaporator
  • Longer-term benefits to control system testing and plant operator training

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D20

Decision Making & Optioneering Prioritisation

Confidential Client

DBD worked in close collaboration with the Client to set the criteria, which tied to Government and Regulator strategic goals. After scoring each project against each of the criteria in an initial screening, weightings were applied to reflect the different objectives and priorities of each stakeholder. The options were then down-selected to the options that would be carried through to study phase.

On presenting the study outputs to the Client, DBD was able to show the results from different perspectives, e.g. projects by site, by stakeholder owner or by total benefit against the criteria. These differing viewpoints allowed the decision-makers in the Client team to determine the high priority tasks that scored consistently high across all criteria. Through this assessment the original portfolio of projects was changed for projects that provided more benefits in risk reduction across a number of the Client’s sites.

In addition, DBD was able to easily apply risk scenarios to the output to test that the scorings were robust and to check the “must-do” list of projects was complete.  This process allowed a full audit trail of the decision making process to the Client, showing how each of the prioritised projects provided the Client with multiple benefits against their success criteria.  It also allowed changes in budget or workload to be easily re-assessed.

Client Benefits

The application of the D2O process realised the following benefits to the Client:

  • Reduced need for data collection: Effort is placed on the real differentiators without need for a huge quantity of “bottom up” data on everything
  • Reduced overall complexity: Total combination with just 30 tasks is in excess of 1bn. This was eventually reduced to 6 different portfolios
  • Helped stakeholders reach consensus: Analysis was based on inputs from 3 different stakeholders
  • Highly responsive to changes: If there were risks or emergencies the process would take them into account and provide updated outputs very quickly with the minimum of effort
  • Identified better project portfolio: Assessment of the benefits of the projects against the key success criteria identified a better project portfolio

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Design

Risk-Focused Design Review

Confidential Client

DBD was subsequently requested to develop a review process which focused on establishing whether the quality of design and the levels of uncertainty and risk on a project were in line with the asserted level of maturity.

The DBD Risk Focused Design Review (RFDR) process has been developed in-house to address a significant issue which occurs on many major engineering projects. That is despite seemingly robust QA systems supported by audits and decision gate processes latent risks continue to arise and impact on project performance.

DBD Deliverables

DBD produced a Business Case which was used by the client to initiate the project. DBD then produced a report setting out in detail the process proposed and a further report describing in detail the criteria to be used in reviewing projects. The process was designed to fit into the Client’s existing arrangements and organisation structure. The process was then applied by DBD to three projects following which the Client decided to formally implement the process. DBD then wrote the supporting Operating Procedure and Work Instructions, produced a Training Package and undertook the initial training of the Client’s nominated Reviewers.

Key features of the approach are as follows:

  • The Design is examined at specific points with a focus relevant to the stage reached in the design process. Each point is in advance of a particular decision associated with, for example, the start of a new activity and/or step change in resource commitment.
  • At each point evidence is sought to support the asserted maturity of the project. A key issue will be to ensure that the various safety “threads” continue to flow through from APPRAISE and into EXECUTE. Evidence is gained by examination of relevant documentation, discussion with the project team and focused questioning. Reviews are undertaken by personnel experienced in the design and delivery of major projects
  • A consistent set of criteria are used, grouped by focus area, against which the design is reviewed and scored

The Results

Following implementation some 15 Major Project reviews have been undertaken over a period of two years and the process continues to be applied. It is fully embedded in the Client’s Management System. It is not viewed as a process for catching projects out but one which adds value and provides valued assurance to project teams at key points in the progress of design and engineering.

Client Benefits

  • Increased confidence in project decision making
  • Reduced level of recycling of decisions and avoidance of abortive work
  • Some specific issues identified with certain projects leading to corrective actions being taken and in some cases a timely re-think on particular aspects of design

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