Monitoring of the Structural Integrity of Reactor Circuit (RAKEMON): RAKEMON summary report

Developing techniques and monitoring systems that can be used to monitor the structural integrity of the primary circuit components is quite essential. Basic pilot monitoring system was developed and constructed during 2007 and 2008. In 2009 and 2010 pilot monitoring system was further developed and monitoring tests were performed with austenitic stainless steel (316LN) pipe. The final aim was to develop measurement systems both for detection and analysis of macroscopic flaws and microscopic changes in the material that are often preceding the macroscopic failure. It is also necessary to develop inspection techniques that can be applied to reactor circuit components where the access is restricted and decreasing the reliability of inspection. The geometry and the material properties of the component to be inspected must always be considered when an ultrasonic test is planned. Ultrasonic inspection simulations for difficult geometries (nozzles) and anisotropic weld metals were done with simulation program CIVA (versions 8, 9 and 10). Fibre optical monitoring methods have been developing rapidly in recent years and nowadays there are already fibres that can resist radiation. Also methods for correcting measurement errors arising from radiation induced attenuation have been developed. The potential of using fibre optical monitoring technology in nuclear environments was evaluated in 2008. It was noticed that metal embedded fibres are in strong compression and polymer coating is eliminated. Therefore it could be possible that drift in Bragg wavelength due to volumetric changes and radiation induced hydrogen evolution from the polymer coating on the fibre could be eliminated with metal embedded fibres. Closed cracks are very dangerous because they can stay undetected for many inspection cycles due to inspection restrictions related to closed cracks. A new ultrasonic method has been developed for these closed cracks. The subharmonic ultrasonic inspection is developed at Tohoku University Japan and it seems to be very promising for these dangerous closed cracks. Steam generators are one part in the PWR type nuclear power plant that can be restricting the lifetime of the plant. Inside the steam generators there is known to be magnetite deposition on tubing and between tubes. The inspection data of steam generators contain also additional information than flaw indications. Recently eddy current data has been applied to show locations of magnetite deposition on tubing. Improvement of eddy current analysis, e.g., concerning magnetite deposition on tubing and between tubes, and flaw sizing was started in 2009 by performing literature review. Also an experimental study on detecting magnetite deposition between tubes was made in 2010. Understanding the variations in the local environmental condition facilitating iron deposition in steam generators should be improved. Pertinence of water chemistry based predictions, NDE monitoring results concerning iron deposition and plant observations and experience were studied and documented as literature reviews during 2009 and 2010.