Effects of pressure tube deformation on reactivity and power in CANDU6 reactors with 3-dimensional consideration

On average, about a 1% power reduction occurs every year in a CANDU6 reactor. Among many other components, the major contributor to this 1% reduction is known to be the pressure tube. In addition, among four phenomena regarding a pressure tube deformation, namely, the expansion in the radial and axial directions, sagging, and thinning, radial expansion and axial sagging are the most dominant factors for pressure tube aging. By using a finite element based code, SHAFE, a 3-dimensional problem including radial expansion and axial sagging, can be solved through a proper boundary treatment capability. Until now, the 2- dimensional problem regarding radial expansion solely was solved with the HELIOS code many times. Thus, the effects from radial expansion are quite well known to many persons because of a lack of analysis tools for 3-dimensional unstructured mesh. By introducing the results from combined modeling which deals with radial expansion and axial sagging, the effects from sagging can be quantified. In this paper, the multiplication factor and pin power distribution results of the SHAFE code will be introduced for the pressure tube problem. (author)