Framatome ANP - AREVA

the fuel canals in Ikata 1 and 2are particularly hard to access andare very narrow – all six projectswere completed well ahead of thespecified deadlines.Materials for All NeedsIn spent fuel pools, adhesively bondedsteel patches are exposed over theplant’s remaining service life to highlevels of radiation from the spent fuelstored in the pools. Also, patches onthe pool floors have to withstand severemechanical loading induced by the fuelstorage racks and the fuel assembliesthey contain. The cumulative dose forthese areas was calculated to be around16 MGy. The selected adhesive –Framatome ANP EP 130 – has averified radiation resistance of 20 MGy,thus providing a sufficient safetymargin. For the materials employedin the reactor cavity and fuel canals,however, the main criterion was thatthey must adhere strongly to theelectropolished steel liner plates,without mechanical surfacetreatment beforehand (to preventthe ingress of foreign materials suchas blasting agents). For this reasonFramatome ANP recommended useof Framatome ANP SG 460 –a material with a radiationresistance that is lower than thatof Framatome ANP EP 130 but isstill several times higher than theplant lifetime dose anticipated atthese locations.Framatome ANP EP 130 isan epoxy-based material whileFramatome ANP SG 460 issilicon-based. In both cases, a thicklayer of adhesive (approx. 4 mm)was applied to either the liner orthe steel patch. Once all patcheshad been properly positioned, acontinuous pressure was applied tothe patches until the adhesive hadfully cured. Then the work wascompleted by finish-machining allthe joints and edges.Contractual SetupEach of the six improvement projectswas performed by a consortiumcomprising Yonden EngineeringCompany, Inc. (responsible for detailedengineering, supply of steel patches,provision of maintenance personneland performance of work in situ)and Framatome ANP (basicengineering, supply of adhesives,technical expertise, training and qualitymanagement). Marubeni UtilityServices, Framatome ANP’s agentin Japan, provided interpreters andcoordinated all activities. ■Advantages ofFramatome ANP’sadhesive bondingtechniques comparedto welding repair:• The techniques are faster,less expensive and resultin lower doses• Exact locations of existing leaksdo not have to beprecisely pinpointedbecause large areas can becovered using adhesivelybonded patches• The structure of the existingmaterial is not altered; i.e. thereis no material oxidation orsensitization and no changein component dimensions• Use of organic materials forrepairs prevents any furtherpropagation of corrosion• Framatome ANP’s patches andadhesives have been qualifiedand approved by the competentauthorities in Germany, Spainand Switzerland, not only forpreventative maintenance butalso for repair• The materials available cansatisfy nearly all requirementsAdvanced Nuclear Power N O 7 April 2003 17