The potential of high-frequency forced pulsed water jet for nuclear decommissioning - 15367

Forced Pulse Water Jetting (FPWJ) has been demonstrated in other works as a credible and consistent method for removing coatings or otherwise preparing surfaces across numerous industries. Its applicability to the nuclear industry as a powerful tool for decommissioning and waste treatment has only recently being recognized and underpinning study is required before any deployment can be considered. Use of FPWJ within the nuclear sector for decommissioning and waste treatment, requires a different degree of surface finish to achieve a decontamination effect or an assured performance. This necessitates a greater erosion of the base metal than in other industries. The addition of a Forced Pulse Modulation Unit (FPMU) to a high pressure water jetting system offers performance shifts akin to the differences between High Pressure (HP) and Ultra High Pressure (UHP) water jets. Trials have been undertaken in a controlled environment to establish the number of cycles to achieve a given mass loss and or depth of penetration that would otherwise provide decontamination of mostly flat or simple geometry surfaces using a robotic arm for consistency and safety. It has also been shown that metalwork can be readily penetrated without risk of explosion, for example to allow draining of a gas cylinder. Most nuclear facilities have a plethora of pipe systems spanning various diameters. A considerable portion of the UK Sellafield site has 2 inch bore pipe. The FPMU technology is being adapted to consider applications in enclosed systems, such as decontamination of pipes. Exploratory works to date show there to be many physical attributes that influence performance that include, standoff of the jet, established propagated forced pulse jet length, interference from resultant water spray and angle of attack. Comparatively small changes to these parameters can have a profound effect on performance. The process is capable of removing 10's microns to several mms of metal progressively and repeatedly. This enables a credible potential treatment of plant and equipment at Intermediate Level Waste and High Level Waste thresholds. In considering this as a treatment method, a balance between performance, cost and environmental impact of effluents must be made and will be studied further during future active trials. (authors)