University of Bristol

Supervisors: Dr Jie Zhang, Prof Bruce Drinkwater, Dr Nicolas Larrosa

Industry Partner: Sellafield

Background

Sellafield is no longer the country’s best kept nuclear secret. It is where Sellafield Ltd are tackling the legacy of our nuclear past, building capability for the future, and where they are creating a clean and safe environment for future generations. The task will take many decades and will require highly skilled scientists and engineers to tackle known and as-yet unknown challenges.

On an aging Site such as Sellafield, corrosion is a problem and will be for many decades to come. Sellafield Ltd need people with specialist skills to develop the tools and techniques that will enable us to assess structures and infrastructure so that we can make informed critical decisions such as plant renewal through to facility life extensions.

Objectives

  • Understand the failure mechanics of nuclear waste storage containers
  • Explore a range of ultrasonic sensing methods and understand their application to the inspection of nuclear waste storage containers
  • Investigate data analysis approaches to enable the NDT data to be used to make predictions of the current state of the nuclear waste storage containers and potentially predict remaining life
  • Produce a strategy for the non-destructive monitoring of nuclear waste storage containers

Details of the Project

Work package 1: The initial part of the project will involve detailed literature survey and discussions with Sellafield Ltd teams to determine relevant conditions and areas where defects/anomalies have been encountered or are thought to be susceptible, as well as current inspection techniques used. The literature will be also used to determine and identify relevant failure modes and the potential NDT techniques used for inspection and monitoring of real relevant components (typically in flat plate, bended plate, welded plate and non-contact NDT techniques), identify 1-2 inspection challenges, and propose possible technique solutions for investigation.

Work package 2: Following the initial studies in WP1, this work package will involve sub-tasks each of which will address the systematic development of improved NDE methods for the characterization of a specific failure mode, for example SCC, fatigue and/or pitting. The NDE approaches will be used to evaluate the structural integrity of the candidate components under the relevant material and environment conditions (e.g. microstructure, residual stresses, relative humidity, Cl– content).  The severity of relevant defect characteristics (e.g. size and shape), for example, fatigue cracks, SCC, and corrosion pits will be monitored from initiation to propagation. We will try to answer questions like what is the role of time/diffusion on defect evolution? Are short-term tests representative? How do the defect geometry changes affect structural integrity assessment for specific structures? Multiple sensors will be used in this stage, including ultrasound sensors, potential drop sensor, digital image correlation cameras. The material microstructures will be analysed using traditional microscopy.

Work package 3: The next stage in the project will be to consolidate the separate NDT challenges into an overall strategy addressing advanced ultrasonic sensor techniques, multiple failure modes and with associated background documentation and validation procedures. For each challenge, the solution will be firstly developed in lab condition, then investigate the feasibility to use it on site.

Work package 4: The final stage in the project will be completion of the doctoral studies by witting up the Thesis.