Framatome ANP - AREVA

FeaturesAdhesive Bonding Technique Usedfor Preventive Maintenance at IkataImprovement of the fuel canalat Ikata 1 in Japan using adhesivelybonded steel patches was completed inlate 2002. This marked the completionof six preventive maintenance projectsto improve the stainless steel linersof the spent fuel pools and fuel canalsat Ikata’s three PWR units.Framatome ANP’s Coating andAdhesive Technology group hasdeveloped a wide range of innovativetechniques using organic materialsfor nuclear applications. Adhesivebonding, for example, is a fast,inexpensive and low-dose alternativeto the conventional repair techniqueof welding, and even enables repairs tobe carried out underwater. Coatings,on the other hand, have been usedto develop accident-resistant plasticliners for concrete containments asa substitute for steel containments.HistoryDuring reracking work in 2000 in“Pit B,” a spent fuel storage poolat Ikata 3, chloride-induced weldcorrosion was discovered at twolocations. These were repaired in theconventional manner by welding.However, the plant operator, ShikokuElectric Power Corporation (SEPCO),wished to go a step further by ensuringthat the leak-tight integrity of the poolABOVE:General view of “Pit B” weldsafter improvementRIGHT:Detailed view of adhesivebonded steel patches atfuel canal cornersliner would nevertheless be guaranteedif such damage should later recur whenspent fuel was being stored in the pool.For this reason SEPCO was interestedin a prophylactic measure whichwould provide suitable protectionat reasonable cost for the remainderof the plant’s service life. Thanksto Framatome ANP’s impressiveportfolio of references, SEPCO chosethe company’s adhesive bondingtechnique, first deployed more than10 years ago for fuel pool repair andpreventive maintenance at a Germannuclear power plant. Since thenthe technique has been deployed withgreat success to repair steel fuel poolliners at a number of European plants.Improvement ProjectsCover Fuel Pools andFuel CanalsIn the summer of 2000, only threemonths after the correspondingfeasibility study had been commissioned,adhesively bonded steel patches wereapplied over a total of 600 meters ofwelds on the walls and floor of Pit B atIkata 3. In Pit A which, unlike Pit B,already contained fuel assemblies,adhesively bonded steel patches wereinstalled over a total of 900 meters ofwelds in December 2001 after the poolhad been decontaminated. FramatomeANP additionally submitted a studybased on improvement of the fuelpools in Ikata 1 and 2 (which arealmost completely full of spent fuelassemblies) using the same techniqueunderwater.Other activities included installingadhesively bonded steel patches overthe welds in the reactor cavity atIkata 3 as well as in the fuel canalsof Units 1, 2 and 3. Only thosesections of the welds that were mostat risk were improved; for example,all fuel canal corner joints. Despiteconsiderable spatial constraints –16 Advanced Nuclear Power N O 7 April 2003