Modeling of residual stresses in core shroud structures

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Description

A BWR core shroud is a cylindrical shell that surrounds the reactor core. Feedwater for the reactor is introduced into the annulus between the reactor vessel wall and the shroud. The shroud separates the feedwater from the cooling water flowing up through the reactor core. The shroud also supports the top guide which provides lateral support to the fuel assemblies and maintains core geometry during operational transients and postulated accidents to permit control rod insertion and provides the refloodable volume needed to ensure safe shutdown and cooling of the core during postulated accident conditions. Core shrouds were fabricated from welded ... continued below

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14 p.

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Zhang, J.; Dong, P.; Brust, F. W.; Mayfield, M.; McNeil, M. & Shack, W. J. October 1997.

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Description

A BWR core shroud is a cylindrical shell that surrounds the reactor core. Feedwater for the reactor is introduced into the annulus between the reactor vessel wall and the shroud. The shroud separates the feedwater from the cooling water flowing up through the reactor core. The shroud also supports the top guide which provides lateral support to the fuel assemblies and maintains core geometry during operational transients and postulated accidents to permit control rod insertion and provides the refloodable volume needed to ensure safe shutdown and cooling of the core during postulated accident conditions. Core shrouds were fabricated from welded Type 304 or 304L stainless steel plates and are supported at the top and bottom by forged ring support structures. In 1990, cracking was reported in the core shroud of a non-U.S. BWR. The cracks were located in the heat-affected zone (HAZ) of a circumferential core shroud weld. Subsequent inspections in U.S. BWRs have revealed the presence of numerous flaw indications in some BWR core shrouds, primarily in weld HAZs. In several instances, this cracking was quite extensive, with the cracks extending 75% or more around the circumference of some welds. However, because the applied stresses on the shroud are low during operation and postulated accidents and because of the high fracture toughness of stainless steel, adequate structural margins can be preserved even in the presence of extensive cracking. Although assessments by the USNRC staff of the potential significance of this cracking have shown that core shroud cracking does not pose a high degree of risk in the short term, the staff concluded that the cracking was a safety concern for the long term because of the uncertainties associated with the behavior of core shrouds with complete 360{degrees} through-wall cracks under accident conditions and because it could eliminate a layer of defense-in-depth.

Physical Description

14 p.

Notes

INIS; OSTI as DE97054152

Source

  • 14. international conference on structural mechanics in reactor technology (SMIRT), Lyon (France), 17-22 Aug 1997

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  • Other: DE97054152
  • Report No.: ANL/ET/CP--94374
  • Report No.: CONF-970826--
  • Grant Number: W-31-109-ENG-38
  • Office of Scientific & Technical Information Report Number: 561142
  • Archival Resource Key: ark:/67531/metadc699334

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  • October 1997

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  • Aug. 14, 2015, 8:43 a.m.

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  • Feb. 9, 2016, 4:47 p.m.

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Zhang, J.; Dong, P.; Brust, F. W.; Mayfield, M.; McNeil, M. & Shack, W. J. Modeling of residual stresses in core shroud structures, article, October 1997; Illinois. (digital.library.unt.edu/ark:/67531/metadc699334/: accessed September 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.