Zircaloy Performance in Light-Water Reactors

Roberts, John; Gelhaus, F.E.

doi:10.1520/stp36670s

Cited by 5 publications

(3 citation statements)

References 6 publications

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“…These differences are most likely related to the approaches used in the stress analysis of fuel pellet cracks, which form the basis for the classical PCI methods used in Falcon and RODEX-4. 3-D Bison-CASL stress concentration factor, as a function of MPS defect width, compared to values from literature [3,14].…”

Section: -D Five Pellet Model With Mps Defectmentioning

confidence: 99%

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confidence: 99%

“…2-D Stress concentration factor using the same geometric models, e.g. crack length, MPS shape, and 90 degree model, as a function of MPS defect width compared to values from the literature[3].…”

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confidence: 99%

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Evaluation of missing pellet surface geometry on cladding stress distribution and magnitude

Capps

Montgomery

Sunderland

et al. 2016

Nuclear Engineering and Design

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INTRODUCTIONPellet cladding interaction (PCI) in light water reactor (LWR) fuel is a coupled thermal-chemicalmechanical process that can lead to cladding breach and release of radioactive fission products into the coolant under certain conditions of operating history, power change, and fuel rod design characteristics [1][2][3][4]. Reactor operating restrictions, which limit power maneuvering, have been established to mitigate PCI, but they restrain operational flexibility and lead to loss of power generation. The Consortium for the Advanced Simulation of Light water reactors (CASL) has selected PCI as a key challenge problem and is developing an advanced, 3-dimensional fuel rod simulation capability (referred to as Bison-CASL) to evaluate fuel performance in general and provide PCI failure assessments in particular. With an advanced fuel rod modeling capability that considers the underlying mechanisms leading to cladding failure, fuel designers and engineers can investigate improved fuel concepts for PCI-resistance and better quantify margins to PCI for operating existing fuel rod designs.. PCI failures generally occur following an increase in the local power over a short period of time, and in fuel that has been previously exposed to irradiation. Classical PCI is driven by the localized strains in the vicinity of a pellet crack, as well as the presence of a chemical species, such as iodine, that drive stress corrosion-induced cracking of the cladding [5]. Fuel pellet cracks that form in brittle ceramic pellets by large temperature gradients, are believed important in the PCI failure mechanism [5]. During a local power increase, pellet expansion produces a high contact force between the fuel pellet and cladding material, when a reduced or eliminated residual pellet-clad gap is present because of previous irradiation. Furthermore, during the rapid thermal expansion of the pellet, the fuel cracks can further open, which transfers tangential shear forces onto the cladding. These tangential shear forces are a function of the equilibrium pellet-clad gap or residual contact pressure at the start of the power increase, the power level at gap closure, the interfacial friction, and the maximum local power.Non-classical PCI failure is associated with the presence of a missing pellet surface (MPS) defect [5]. These MPS defects form through mishandling or the manufacturing process, where the pellet is chipped leaving a flaw on the outer surface. The presence of an MPS defect during a localized power ramp can cause severe bending moments in the clad in the vicinity of the MPS when the fuel undergoes rapid thermal expansion due to this increase in local power. Furthermore, the localized region near the MPS also experiences a different temperature distribution compared to when the MPS is not present. The result is a localized hot spot in the fuel and cold spot in the clad.Both classical and non-classical PCI are significantly influenced by the geometry of fuel pellet flaws (i.e pellet cracks and MPS). The purpose of the current...

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Section: -D Five Pellet Model With Mps Defectmentioning

confidence: 99%

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mentioning

confidence: 99%