Integrated Management Program for CANDU® Steam Generator Cleanliness

Abstract

The status of steam generators (SG) is a key factor for plant performance, high plant availability, possible life time extension and important to NPP safety. The major safety function of SG is well-known as being a barrier between the radioactive primary side and the non-radioactive secondary side. Any degradation mechanism, which impairs this barrier function, is a significant safety concern. The main reason for steam generator tube failure is known to be the accumulation of deposits contributing to formation of locally aggressive conditions. Furthermore, deposits on the primary as well as secondary side of SG tubes reduce the heat transfer performance. An SG cleanliness management program based on optimized water chemistry and mechanical and chemical cleaning processes is, therefore, mandatory to ensure high plant performance regarding efficiency as well as component integrity. AREVA has developed an integrated management program for SG cleanliness. This program consists in principle of a closed cycle process with the following steps: A. Assessment of the current SG condition based on water chemistry data, inspection results and heat transfer data; B, Identification of measures based on assessment results and adjusted to plant operator’s needs and requirements to improve the current status or even counteract on identified serious issues; C, Implementation of identified improvements or countermeasures. The measures identified in step B include, on the one hand, possible changes in the water chemistry (including additives) and material concept. These changes aim to minimize unfavorable conditions to reduce the effort for later remedial measures. On the other hand, primary or secondary side mechanical or chemical cleaning measures may be recommended. Due to the interdisciplinary and unitary nature of the program, a harmonization between all involved sector and specialists is required. Therefore, it is especially important to minimize the interfaces among the participating parties. The current paper presents the complete unitary and field-proved management program ranging from SG assessment, water chemistry improvements to primary side (e.g. mechanical cleaning by SIVABLAST) and secondary side SG cleaning (e.g. using AREVA’s customized chemical cleaning (C3) concept)