Guest blog post by Euring Edward Anderson, Senior Mechanical Engineer at Sellafield Ltd.
Sellafield Ltd is responsible for the most complex nuclear site requiring remediation in Europe, spanning approximately 700 acres in the U.K.’s West Cumbria region.
Nuclear operations on the site commenced in the late 1940s and the site was adapted for nuclear sector work after World War II. The world’s first nuclear power station opened on the site in 1956.
Today, the primary mission for the Sellafield site is safe, secure site stewardship, with acceleration of risk and hazard reduction. This is an extensive piece of work which stretches out over the next 110 years.
The site consists of more than 2,200 buildings including 170 major nuclear facilities. As the site transitions from reprocessing operations, which will cease around 2020, the major focus will shift to Post Operational Clean Out (POCO), waste management and decommissioning activities.
Tanks lined with fiber-reinforced plastic (FRP) are now in use on the site and provide the following advantages:
- Strong glass-reinforced plastic (GRP) with high chemical resistance of the inner shell
- Various external resin, glass mixtures
- Pressure or Vacuum
- Max 125 degrees Celsius
- Up to 40 years design
- Can be spark tested throughout life
- Variable Geometry of tank
- Most have specialist non-destructive testing (NDT) during manufacture
In-service inspection of FRP tanks on a Nuclear Licenced Site must adhere to the following design codes and legislation:
- Nuclear Site Licence 28 & 29
- HSE Documents, HSL/2006/21 – Inspection of Thermoplastic Tanks and
- RR760 – Mechanical Integrity of Bulk Storage Tanks
- HSE Guidance Notes PM75 & PM86
- PUWER Reg 4 & 5 Maint & Operation
- 2007 Document from IChemE & HSE – Design Life
- SAFed Guidance notes IMG 01, 02 series
- EEMUA 225:2017 Edition 1 – Guidance on Above Ground Plastic Tanks
The following failure mechanisms exist for FRP tanks:
- Internal welds or delamination of wall materials
- Acid attack, leading to cracking and failure
- Blistering on older tanks by permeation of water or chemicals
- Leaching of chemicals
- Poor design or manufacture on early tanks
- Operational defects, bulging, embrittlement, split seams, vacuum etc.
Despite the guidance and regulations noted above, many FRP tanks are aged with little inspection history. The true fibre/strength condition is not known. At the same time, many inspection techniques are impractical, costly and not suitable for use on a nuclear licensed site. The high costs would outweigh the many of the benefits.
Seeking a better alternative, Sellafield is currently conducting a trial of the UTComp UltraAnalytix™ non-destructive, non-intrusive inspection system to identify FRP tank defects and determine future life of FRP tanks.
UTComp’s patented inspection method is based on 50 years of studies by NASA and several North American universities. Ultrasonic readings taken on site are analyzed off-site using complex algorithms. Rigorous testing has shown that UltraAnalytix™ can be used to detect creep, thickness loss and corrosion barrier damage.
The benefits of UTComp’s UltraAnalytix™ system are:
- Avoids cutting into tanks to evaluate strength and condition that weakens structural integrity
- Can be undertaken on live tanks, the report identifies defects that matter and allows calculations of remnant life
- Use of evidence-based algorithms for fibre condition & corrosion barrier
- Inspections and analysis of FRP assets can deliver the true condition without sacrificing safety
- Allows comparison of data
Lessons Learned in the Nuclear Industry
- Identify your FRP tanks and incorporate them in your emergency response
- Manufacturers records may not be available; an inspection history of your assets is essential. Do not make assumptions as tanks may have had a varied operational life with different process parameters or chemicals
- There is economic pressure for FRP tanks to be used beyond design life without consideration of true condition and fitness for service
- Follow the new guidance EEMUA 225, HSE PM75, IMG02 & IMG 02B, and demonstrate best practice where possible
- A tank succession programme is essential as design, build, install, commission can take up to 1 year
- New technology allows comparison of data and is worth the investment to find out if your tanks life can be extended or needs to be retired early
- FRP tank swelling is a sign of failure…take it out of service
- If you see wetting on a FRP tank…it will fail….failure can be quick
- Conduct regular visual inspection internally and externally…know your assets
Sellafield Ltd would appreciate any feedback from others who have undertaken this type of specialist NDT or have similar experience with substantiation of FRP tanks and design life composite repairs. Please contact firstname.lastname@example.org.
Euring Edward Anderson is Senior Mechanical Engineer at Sellafield Ltd. He presented findings on Substantiation of aged composite FRP tanks using new technology: lessons learned in the nuclear Industry at the 2018 BINDT Conference on Non-Destructive Testing in September 2018.