The Ageing of Materials and Structures by Klaas Breugel Dessi Koleva & Ton Beek

Author:Klaas Breugel, Dessi Koleva & Ton Beek
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

For off-normal and accident conditions, the maximum cladding temperature should not exceed 570 ℃ (1058 ℉).

Casks for HBF may have cladding walls that have become relatively thin from in-reactor formation of oxides or zirconium hydride. For design-basis accidents, where the structural integrity of the cladding is evaluated, one should specify the maximum cladding-oxide thickness and the expected thickness of the hydride layer (or rim), which may not be uniform. Cladding-stress calculations should use an effective cladding thickness that is reduced by those amounts and that has been justified by the use of oxide-thickness measurements and valid computer codes.

The guidance in ISG-11, Rev. 3, for storage of HBF for an initial period of 20 years, was based on short-term laboratory test data and analysis, which may not be applicable to the storage of HBF beyond 20 years. A major concern addressed in ISG-11 was the potential detrimental effect of hydride reorientation on cladding integrity. Because of the presence of radial hydrides, HBF cladding could exhibit a ductile-to-brittle transition temperature (DBTT) that could influence the retrievability of HBF assemblies and result in operational-safety problems for HBF that has cooled below the DBTT (i.e. ≈200 ℃ or 392 ℉) [5, 6]. Figure 2 shows the ductility comparison for high-burnup M5® cladding, as-irradiated versus following simulated-vacuum drying—that is, cooling at 5 ℃/h from 400 ℃ at peak hoop stresses of 90, 110, and 140 MPa, with the corresponding DBTT of <20, 70, and 80 ℃, respectively.

Fig. 2Ductility comparison for high-burnup M5® cladding, as-irradiated versus simulated-vacuum drying (i.e. cooling at 5 ℃/h from 40 ℃ at peak hoop stresses of 90, 110 and 140 MPa)

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