Boiler Spine Recovery

Project Description and Services Provided

The Advanced Gas Reactors at Heysham 1 and Hartlepool reactors are of the same design and uses a unique design of pod boiler. During a routine inspection of the boilers at Heysham, EDF Energy observed an anomaly result from a test on one of the boilers which checks the structure the central supporting spine. This test could indicate a potential failure of a circumferential weld and subsequently all 4 units were turned off to allow detailed inspection and verification that there were no other defects in any critical plant structures.

With all the units shutdown, a large part of the UK’s electrical generating output was lost and also a loss of income for EDF Energy.

A multiorganization workstream was started to understand the issue at Heysham, verify the condition of the Heysham Boiler and develop a solution to ensure the plants could be safely returned to service, ensuring the issue would not develop on the other boilers. Amentum were able to provide initial on site inspections and support, expertise in remote Engineering, materials, modelling, safety cases and rigs.

Initially two inspection campaigns were undertaken:

• Firstly via vessel entry campaign to access an area as close to the area of concern as possible and to deploy visual and radiography equipment, which found a crack in the weld.

• Secondly specialist remote tooling was developed that could be deployed from outside the reactor, to perform radiography of the other 31 boilers.

Only one boiler had suffered a failure due to thermal fatigue cracking, it was decided to perform modifications on all remaining 31 pod boilers, which involved installing insulation around the weld area to reduce the temperature, removing the main cause of failure. The faulty boiler at Heysham was safely isolated.

Challenges

Access to the spine location was through two access penetrations 100mm in diameter, 12m above the area to be inspected and required inserting tooling through a narrow (<4 mm in places) gap.

The solution to provide heat shielding in the area around the weld by remotely install 12 off cover plates between the boiler spine and inner shroud, which blocked the hot gas, had never been delivered remotely before.

No as build drawings were available, with modifications and obsolescent instrumentation cabling being in the way of the inspection and installation path.

Access was constrained around the pod boiler instrumentation penetrations. Inside the boiler closure, further restrictions and doglegs made access difficult.

Solutions and Outcome

Amentum developed the equipment and process to undertake radiographic inspection of the boilers to further understand the problem and deployed it on station, including vessel entry with partner organisations.

We also identified, tested and prepared an insulation, that could be used to fill an annular void and protect the structure from further exposure to high temperatures which met all the requirements for lifetime use.

Amentum developed remote operations equipment and processes to install two types of plugs in to eight 70mm gas bleed holes and four 8mm construction holes per boiler. The plugs and insulation were deployed remotely from the pile cap which is approximately 12m above the plug locations and 8m above the top of the annulus.

The tooling was certified on our full-scale mock-ups at our birchwood park site. Once certified we provided training materials to aid in the development of the solutions and to train technicians before they went sent to site to perform the inspections and modifications on plant.

We deployed over 100 people from Amentum and our partner organisations to install the plugs and insulation in conditions that replicated those on station. We installed the plugs and insulation in 31 boilers working 24 hrs a day for 8 months meeting the client’s challenging timescale.

Benefits

All four units were successfully visually inspected and non destructive tested, all serviceable boilers were plugged and insulated. The units were retuned to service and continue to operate. The insulation is inspected during their outages and no further defects have been detected.

Hartlepool Reactor 1 & 2

• 192 Plugs deployed and signed off from EDF quality and assurance.
• 297 litres of Insulation media deployed across sixteen boiler pods.
• 100% visual inspections of welds, gas bleed holes, tapped holes and back out inspections.
• Eddy current inspections of all sixteen boiler pods on both penetration.
• 1 Thermocouple installed on 2A2 to support the safety justification for the ONR.
• Both units returned to service

Heysham Reactor 1 & 2

• 180 Plugs deployed and signed off from EDF quality and assurance.
• 259 litres of Insulation media deployed across Fifteen boiler pods.
• 100% visual inspections of welds, gas bleed holes, tapped holes and back out inspections.
• Eddy current inspections of all sixteen boiler pods on both penetration.
• 1 Thermocouple installed on 1B1 to support the safety justification for the ONR.
• Both units returned to service