Use of Guided Wave Inspections to Monitor the Integrity of Nuclear Power Station Boilers

Abstract

Owing to potential concerns about creep occurring in the mid-part of the central tubular spines of nuclear plant boilers, as a precautionary measure TWI and its subsidiary, Plant Integrity Ltd, were contracted in 2002/2003 to develop a test procedure to check the integrity of the spines using their Teletest ultrasonic guided wave testing (GWT) system. At that time, both the thickness and complexity of the component were beyond the normal operating window of the Teletest equipment, which was designed for testing pipelines. To validate the operation and capabilities of the method, a full-scale mock-up component was produced. Field testing was commenced in 2003. The eight boilers around a reactor were tested when it was shut down for a statutory outage, which occurs on a 3-year cycle for each reactor.

Periodic tests have been carried out on all 32 spines at statutory outages since 2003. Up to 2013, all spines produced consistent responses. However, in September 2013, one spine at Heysham 1 Power Station, Reactor 1 produced a significantly different response. The application of guided wave testing enabled a significant failure in a nuclear power plant to be avoided.

• Investigation of the factors affecting the responses from flaws in the affected region enabled a capability to be established and this contributed to the production of a successful safety case for return to service of the plants affected.

• Special tooling and data gathering equipment have enabled continued monitoring.

• GWT is now an integral part of the ongoing assessment of integrity of the spines.

V-1672-15