Analyses of the Warm Pre-Stressing Effect in SMILE Experiments

The integrity of the reactor pressure vessel (RPV) has to be demonstrated under the most severe type of loadings that can occur during the plant lifetime. The selection of the pressurized thermal shock (PTS) transients is questionable since no account is made of potential beneficial effect of the load history. If one considers a crack close to the inner wall of the vessel, the loading at elevated temperature will open the crack, then cooling will tend to close the crack and if a load is applied at low temperature, the fracture resistance of the cracked component will be much higher than predicted using toughness values at this temperature. This is known as the warm pre-stress (WPS) effect and has been well documented since decades ([1], [2]). A 3-year European Research & Development programme (SMILE) has been launched in January 2002 as part of the 5^th Framework Programme of the European Atomic Energy Community (EURATOM) to comfort this phenomenon and develop methods of analysis for 3D configurations liable to experience significant local yielding [3]. This paper analyzes the WPS type experiments performed in SMILE on C(T) specimens and on the mock-up which consists in a hollow cylinder containing a total circumferential crack on the inner wall. The predictions, based on an extended version of the BEREMIN model appear to be good but slightly conservative.