[en] A somewhat simplified two-dimensional linear elastic fracture mechanics model of the beltline of a RPV is presented. The fracture mechanics model used tends to be conservative in the sense that it ignores possible beneficial effects of warm prestressing and cladding. For LEFM studies that require a large number of analyses on the same geometry but with different loads and material toughnesses, the superposition principle is an accurate and simple method to determine K₁, provided that K₁ due to a unit load (called K* in this paper), acting on an arbitrary point on the crack surface is known. The details of the superposition principle and the procedure used for determining K* have been presented. It is believed that the error in the K₁ - values so determined is less than 3.5%. Once these K* - are determined for a specific geometry, then the determination of K₁ for the same geometry can be made accurately and in a manner that permits parametric studies involving thousands of individual analyses. An example of the use of the simplified model for a parametric analysis is also presented. 35 refs., 11 figs., 1 tab