Investigations into surface treatment methods for reduction of recontamination of BWR reactor systems

This contribution deals with surface treatment methods for prevention of a quick recontamination of systems and components of BWR plants after decontamination treatments. The following methods were selected: (1) Platinum deposition (Low Temperature NobleChem process LTNC^TM); (2) Application of a self-assembling monolayer SAM (patent application of AREVA pending), and, (3) Platinum deposition followed by the application of a SAM. The methods were applied to carbon steel surfaces representative for decontaminations with the AREVA process CORD^® CS (reference condition for the tests). Their effectiveness is tested by in-plant exposure of tube samples in the mitigation monitoring system MMS of the BWR Cofrentes. The dose rate reduction effect of the surface treatments after six months exposure is 50% for the SAM coating, 40% for the Pt + SAM treated sample and 30% for the Pt treatment. The measured dose rates are dominated by Co-60. Comparison of the data with data of the BWRs Cooper and River Bend yields a similar dose rate reduction effect of Pt treatments for carbon steel and stainless steel test samples. The results provide an excellent basis for the continuation of the joint R and D program of the operator of the BWR Cofrentes and AREVA. Based on the status reached after six months of in-plant exposure, the preferred treatment options are a SAM treatment of the carbon steel piping sections for recontamination reduction and a Pt treatment of the stainless steel components for additional SCC mitigation. Exposure conditions in BWR systems are much more hostile for organic films than those in PWR primary systems. The data and experience gathered at the BWR Cofrentes with SAM coatings are therefore applicable also to PWR primary systems. (author)