Numéro : 2007 - Year : 1986
Defects appeared in service on tubes of a steam generator of the advanced stokehold prototype (CAP), lessons from the metallurgical and thermohydraulic analysis
Ecole Nationale Supérieure de Mécanique et d'Aérotechnique, Poitiers
J.Y. ROBERGE, Ingénieur Technicien d'Etudes et Fabrication Etablissement des Constructions et Armes Navales ( ECAN) , Indret
The nuclear reactor C.A.P. is a small power pressuriled water reactor exploited at CADARACHE site by TECH~JICATOME company.
Its steam generator is of vertical U tube recirculating type with Alloy 600 tubing ; this steam generator has presented tubes failures which some has led to leakages between primary and secondary side.
After pulling some tubes out of the steam generator, ECAN d'INDRET has performed metallurgical tests on samples.
The results of these tests conclude that defects were due to local concentration of aggressive chemical species which induce corrosion. Analysis of thermal-hydraulics conditions on the secondary side of the steam generator showed that liquid deficient regions could appear at tube support plate contact and subsequently concentration near this region could occur.
A new geometry of tube support plate has been drawn to prevent dry-out in the new steam generator.
Feedwater treatment of operating C.A.P. steam generator has been modified to eliminate phosphates which acid concentration was suspected to be the major cause of tubes failures.