Deposition via electrokinetic phenomena and mitigation techniques for fission and fusion nuclear power plant cooling loops

The deposition of corrosion products within nuclear reactor cooling loops can reduce the safety and efficiency of plant operation. In particular, when coolant accelerates electrokinetic mechanisms are thought to promote formation of localised deposits. The experimental research presented in this thesis examines the electrokinetic phenomena affecting this deposition and explores novel techniques to monitor and reduce its undesirable impact. Regarding the electrokinetic deposition of corrosion products under accelerated flow, investigations were undertaken into the generation and behaviour of electrokinetic streaming currents. Streaming currents were produced and measured in pure and lithiated water flowing through 316 Stainless-Steel (316 SS) tubes and streaming current magnitude was shown to increase exponentially with increasing pH from 7 to 10.5, relating to an exponential increase in 316 stainless-steel zeta potential (more negative). In relation to cooling for future experimental fusion reactors, such as ITER, the effect of an applied 0.3 Tesla magnetic field on streaming current magnitude was studied, with results suggesting a deflection of streaming current with potential to promote localised corrosion under non-accelerating conditions. The Zeta Potential (ZP) of magnetite (a major constituent of Steam Generator (SG) deposits) was measured over a temperature range 25-250oC in ammonia, pHRT 9.6 solution, with the resulting trend suggesting a change from negative to positive ZP at 300oC. ZP is the key parameter controlling electrostatic interactions in particle dispersions and can be used to optimise water chemistry and reduce deposition rates. The work produced design and methodology recommendations for a future experimental test rig to allow accurate ZP measurements up to 300oC+ (PWR SG conditions). The novel use of hydrodynamic cavitation to reduce CRUD build up around primary side constrictions was explored using micro-orifices containing corrosion products deposited under flow accelerated conditions. A global reduction in deposit was measured after 5 minutes hydrodynamic cavitation exposure, in addition to a steady and repeatable increase in orifice diameter with exposure time. After 30 hours, the micro-orifice surfaces exhibited no damage characteristics, suggesting that cavitating flow regimes may be used for short time periods within SGs to reduce deposit build up within and around constrictions, without damaging the stainless-steel components. The new technique could reduce the use of chemical and mechanical cleaning, which are respectively expensive and intrusive. Finally, the validity of existing discharge prediction methods for micro-orifice creeping flow was extended for microfluidics applications with thick micro-orifices. Previous research has shown that careful monitoring of pressure drop across an orifice can enable real-time calculation of deposit build-up rate (BUR), and these measurements could further be applied to assess the cleaning of constrictions via hydrodynamic cavitation in a nuclear environment. Accurate prediction methods for micro-orifice discharge are vital to test these ideas on a miniature scale, which has been demonstrated as a feasible alternative to large scale, expensive test rigs.