In-vessel ITER tubing failure rates for selected materials and coolants

Abstract

Several materialshave been suggestedfor fabricationof ITER in-vesselcoolanttubing: beryllium, copper, Inconel,niobium,stainlesssteel, titanium,and vanadium. This report " generates failureratesforthe materialsto identifythe best performerfrom an operational safetyandavailability perspective.Coolanttypesconsidered in thisreport are heliumgas,. liquidlithium,liquidsodium,and water. Failurerates forthe materialsare generatedby includingthe influenceof ITER'soperatingenvironmentand anticipatedtubingfailure mechanisms withindustrial operatingexperience failurerates. The analysesdefine tubing failure mechanismsfor ITER as: intergranularattack, flow erosion, helium induced swelling, hydrogen damage,neutronirradiationembrittlement, cyclicfatigue, and thermal cycling. K-factors,multipliers, are developedto modeleach failuremechanismand are appliedto industrial operatingexperiencefailure ratesto generatetubingfailure ratesfor ITER. The generatedfailurerates identifythe best performerby its expectedreliability. Withan averageleakagefailurerateof 3.1e-10 (m-hr) "1andan averagerupturefailure rate of3.le-11 (m-hr) "1, titaniumprovedto I:,) the best performerof the tubingmaterials. The failurerates generatedinthis reportare intendedto serveas comparisonreferencesfor designsafetyand optimization studies.Actualmaterialtestingand analysesare required to validatethefailure rates.

Selected Component Failure Rate Values from Fusion Safety Assessment Tasks

“…In the external LOCA cases, the event leads to the in-vessel tubes being burned out in short time frames [< 60 s of continued plasma operation (see Marshall et al, 1994)], and this is a situation where the radioactive inventories in the vessel (tritium, dust, plasma disruption volatilized materials from the walls, and possibly water chemical reaction volatilized materials from the walls) can escape after air pressure equalization. The details of the plasma shutdown system are not defined at this time.…”

“…Double Walled Vacuum Vessel. An early estimate of vacuum vessel wall integrity suggested the extremely unlikely events range of 1E-04 to 1E-06/year (Cadwallader, 1994). Considering a recent survey of pressure vessel failure rates shows an overall failure rate of 5.1E-05/year, with these failure mode distributions: inspection faults (57%), leakage faults (28.5%), wall deformation without breach (10%), and disruptive failures (ruptures, 4.5%) (Davenport, 1991).…”

“…Buende states that using conventional weld technology will not give very high availability, and that advanced welding methods are needed for fusion reactors. Using Buende's input and assuming stringent quality control and electron beam welding gives a weld failure rate of 1.8E-07/hour-meter (Cadwallader, 1994), where meters denotes the meters of length of weld and hours denotes calendar hours. This failure rate is for small leaks; the failure rate for large leaks is a factor of 10 lower, and for weld ruptures the failure rate is a factor of 100 lower (Buende, 1991).…”

“…The upper bound failure rate for small weld leaks is set at 2E-06/meter-hour. If the welds are double welded with two complete welds per joint, then the failure rate can be reduced by a factor of 10, which is the same factor as applied to double walled piping (see Marshall and Cadwallader, 1994).…”

“…Since the bellows are double walled for ITER (FDR, 1997), these average failure rates can be reduced by a factor of 10 for actual leakage to the surrounding environment. The factor of ten is adopted for the bellows walls based on the discussion of double walled piping in Marshall and Cadwallader (1994). Therefore, the ITER bellows failure rates are 5E-07/hour for small external leakage (error factor of 10) and 6E-08/hour for large external leakage (error factor of 10).…”