Probabilistic assessment of reactor pressure vessel integrity under pressurised thermal shock

A deterministic fracture mechanics analysis does not address the uncertaint ies involved in material properties, magnitudes of loads, location and size of the flaws, etc. However, in a real life situations such uncertainties c an affect significantly the conclusions drawn out of a deterministic analys is. The principles of probabilistic fracture mechanics may be used to ascer tain the effects of such uncertainties. A computer code PARISH (Probabilist ic Assessment of Reactor Integrity under pressurised thermal SHock) has bee n developed based on principles of PFM for analysing a reactor vessel subje cted to pressurised thermal shock. The code assumes a crack in the reactor vessel of random dimension depending upon Marshall flaw depth cumulative di stribution function. The applied SIF at the tip of this crack is computed e ither using closed form solution or a precomputed data base. The material K -IC is then calculated using the crack tip temperature and RTNDT The value of RTNDT depends on the initial value of RTNDT and the increase in the valu e of RTNDT depending upon the fluence, copper content and nickel content. A Gaussian distribution is assumed for these parameters. If the applied SIF is more than the material K-IC, the crack is assumed to propagate. The crac k can be arrested only if the applied SIF is less than the material K-Ia at that location. The material K-Ia again depends upon the RTNDT, which in tu rn depends upon the fluence, copper content and nickel content of the mater ial at that location. The vessel failure is assumed if the crack propagates by the 75% of the thickness. Such procedure is repeated for large number o f cracks (of the order of one million). Using Monte-Carlo simulation, proba bilities of no crack initiation, crack initiation and vessel failure are ca lculated. The present probabilities are conditional in the sense that the t ransient is assumed to occur. The case studies are presented involving a nu clear reactor vessel subjected to two different kinds of pressurised therma l shocks. (C) 1999 Elsevier Science Ltd. All rights reserved.