US Best Estimate Transient Analysis Licensing

The ECCS Acceptance Criteria, applied to LOCA are defined in 10 CFR 50.46. Loss of coolant means makeup flow up to DEG of largest pipe in reactor coolant boundary. The ECCS Acceptance Criteria postulated in 10 CFR 50.46 are Max cladding temperature < 22000F, Max cladding oxidation < 0.17 times cladding thickness before oxidation, Maximum hydrogen generation < 0.01 times the amount generated if all metal in clad were to react, Cooling geometry and Long term cooling. Two Types of Analysis are now allowed. The first one is the using Appendix K, which give advantages of Advances in Analysis Methodology and necessity of Additional Experimental Information. The second one is the Best estimate approach using uncertainty. An ECCS evaluation model may be developed in conformance with the required and acceptable features of appendix K ECCS Evaluation models. According of Appendix K a prescriptive description of analysis models and methodology is implemented, including heat sources swelling and rupture of fuel cladding, blowdown phenomena and post Blowdown Phenomena. The required documentation used in this process are related to the description of each evaluation model, complete listing of each computer program, demonstration of solution convergence via nodding and time-step studies, sensitivity studies (pump operation, parameter variation) and predictions compared to experiments. The evaluation model must include sufficient supporting justification to show that the analytical technique realistically describes the behaviour of the reactor system during a loss-of-coolant accident. Comparisons to applicable experimental data must be made and uncertainties in the analysis method and inputs must be identified and assessed so that the uncertainty in the calculated results can be estimated. This uncertainty must be accounted for, so that, when the calculated ECCS cooling performance is compared to the (acceptance) criteria, there is a high level of probability that the criteria would not be exceeded, The previous sentence presented in 10 CFR 50.46, give the definition for the Best estimate analyses