Permanent ultrasonic monitoring of parts of operational nuclear power stations that can currently only be monitored when the plants are shut down will provide increased confidence in operating safety, more efficient operation with lower costs and reductions in exposure to harmful radiation for maintenance personnel. The PUMA project will seek to overcome the technical challenges that have so far prevented the attainment of these highly desirable goals. Using the experience and expertise of the consortium members, it will develop and test ultrasonic phased array sensors capable of detecting cracks shortly after they first occur and monitoring them continuously thereafter. This will allow planned repairs to be undertaken before there is any risk of failure, while avoiding unnecessary interuptions to plant operation. This capability will revolutionise in-service inspection in the nuclear power and other major industries and open up worldwide opportunites for UK inspection businesses.