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:
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:
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.
DBD’s deliverables were to deliver a dynamic process and control simulator.
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.
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.
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.
The application of the D2O process realised the following benefits to the 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 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:
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.