Thermal–hydraulics system codes uncertainty assessment: A review of the methodologies

AP1000® Large-Break LOCA BEPU analysis with TRACE code

“…Obviously the use of such conservatism produces a large margin between the conservatively calculated value and the 'true' value. In September 1988, 10CFR50.46 allowed the use of BE codes as an alternative of conservative code models, requiring however, the identification and quantification of uncertainties when determining the safety margin leading to the called BEPU analysis (Best Estimate Plus Uncertainties), see Wilsom (2013), D'Auria et al (2012 and Pourgol-Mohammad (2009).…”

Statistical analysis of fuel failures in large break loss-of-coolant accident (LBLOCA) in EPR type nuclear power plant

“…Namely, the boundary conditions of a fuel performance code come from a system code and from a neutronics code, and those have their own uncertainties (OECD/NEA, 2009Pourgol-Mohammad, 2009). The uncertainties in the boundary conditions are taken into account by simulating the accident 59 times with the newly introduced statistical version of the system code APROS.…”

Finite mixture models for sensitivity analysis of thermal hydraulic codes for passive safety systems analysis

“…Conservative TH codes have traditionally been employed to verify that safety limits could be respected with large safety margins . Best Estimate (BE) codes have been introduced more recently to provide more realistic results and avoid over-conservatism [Zio et al 2010] [10 CFR 50.46]; their use requires the identification and quantification of the uncertainties in the code outputs coming from simplifications, approximations, round-off-errors, numerical techniques and uncertainties in the input variable values [Pourgol-Mohammad 2009]. The quantification of the uncertainties in the output can be demanding in terms of computational cost, because it requires a large number of simulations of the BE-code [de Crécy et al 2008;Di Maio et al 2014a].…”

“…To tackle this challenge, various approaches of Uncertainty Analysis (UA) have been developed, e.g., Code Scaling, Applicability, and Uncertainty (CSAU) [Boyack et al 1990] [Wilson et al 1990] [Wulf et al 1990], Automated Statistical Treatment of Uncertainty Method (ASTRUM), Integrated Methodology for Thermal-Hydraulics Uncertainty Analysis (IMTHUA) [Pourgol-Mohammad 2009], which assume that the uncertainty in the input variables follows a statistical distribution: N input sets are sampled and fed to the BE code and the corresponding N output values are calculated, which reflect the variability of the input variables onto the output. A combination of Order Statistics (OS) [Guba et al 2003] [Zio et al 2008] and Artificial Neural Networks (ANN) has been proposed to speed up computation (substituting the TH code with a simpler and faster surrogate) [Secchi et al 2008].…”