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정한섭(Hansub Chung),김홍덕(Hongduk Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Wall thinning by flow accelerated corrosion is the active degradation mechanism of A-106 carbon steel feeders of CANDUs. The primary variables affecting FAC are water chemistry, temperature, chemistry of the carbon steel and thermal hydraulics determining the mass transfer coefficient. The thermal hydraulics play the key role in distributing extent of wall thinning depending on locations and channels. The initial thickness of each feeder distributes heavily depending on locations after bending, so that the gap between the maximum and the minimum thickness is as high as 4mm for a given feeder. Distribution of the thinning rate is an important concern for the long-term management of feeders. Cracking is the other degradation mechanism of feeders. It is clearly understood that the cracking is affected by the bending or weld residual stress, though the underlying mechanism is not clear.
CANDU 압력관 건전성평가 절차의 보수성에 대한 검토
정한섭(Hansub Chung),김홍덕(Hongduk Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Excessive conservatism may be embodied in the integrity assessment procedure for PTs of CANDUs, as guided in the CSA N285.8-05 code. Four sources of conservatism are suggested as (1) the effect of thermal history on DHC, (2) the effect of manufacturing variables on properties of PTs, (3) poor definition or limited availability of databases regarding the aging degradation trends and probability density functions of important material properties, and (4) the simplified equations defining threshold condition for the initiation of DHC at the volumetric flaws. It is suggested that both extensive review of databases available and extensive calculation case studies are required to remove the potential excessive conservatism.