Over the past few decades, there has been significant research towards the development of the Best Estimate Plus Uncertainty (BEPU) approach to replace with conservative methods for reactor safety analysis and licensing. This approach relies on Best Estimate (BE) models and codes to simulate phenomena occurring in the Nuclear Power Plant (NPP) while quantifying the associated uncertainties. Wall-to-fluid friction pressure drop, as a part of 116 Thermal-Hydraulic Phenomena (THP), is categorized as Basic Phenomena (BP) that can affect the general behavior of thermal-hydraulic (TH) system. The final objective of this work is to demonstrate the errors in pressure drop calculation in system thermal-hydraulic (SYS TH) code. Likewise, the error for single-phase pressure drops in RELAP5 correlation that eventually will affect two-phase pressure drops, was investigated as first step in this research. The findings reveal that the errors are significant in very low Reynolds numbers (𝑅𝑒<50) for both sub-cooled water and super-heated steam in RELAP5 3.2mz and in special cases also in RELAP5 3Di. As mentioned, for some cases a comparison between RELAP5 mod3.2mz and 3D was performed to assess the behavior of different SYS TH codes in the case of pressure drops. Another key point that needs to be addressed is consideration of the associated effects of the chemistry and wall material in pressure drops since the highest value of uncertainty in friction pressure drop is due to uncertainties in value of the roughness iinot to mention that SYS TH codes are not able to predict the effects of corrosion. Additionally, until the time that new experiments are done, for turbulent regime, only Colebrook implicit equation with iterative procedure must be used as a reference for all friction factor calculations. In summary, the uncertainties associated with pressure drop calculations as a single phenomenon in TH SYS code (particularly in low Re number e.g. natural circulation) have the potential to impact the application of the BE TH SYS code in the BEPU. This may affect the safety analysis both for conventional and non-conventional LWRs (i.e. CAREM, NuScale, SMART, IRIS, etc
Wall-to-Fluid Friction Pressure Drop Phenomenon Impact on BEPU Investigations
Yousefi H.
Investigation
;Zingales V.;Cai Q.Methodology
;D'Auria Francesco
Supervision
2024-01-01
Abstract
Over the past few decades, there has been significant research towards the development of the Best Estimate Plus Uncertainty (BEPU) approach to replace with conservative methods for reactor safety analysis and licensing. This approach relies on Best Estimate (BE) models and codes to simulate phenomena occurring in the Nuclear Power Plant (NPP) while quantifying the associated uncertainties. Wall-to-fluid friction pressure drop, as a part of 116 Thermal-Hydraulic Phenomena (THP), is categorized as Basic Phenomena (BP) that can affect the general behavior of thermal-hydraulic (TH) system. The final objective of this work is to demonstrate the errors in pressure drop calculation in system thermal-hydraulic (SYS TH) code. Likewise, the error for single-phase pressure drops in RELAP5 correlation that eventually will affect two-phase pressure drops, was investigated as first step in this research. The findings reveal that the errors are significant in very low Reynolds numbers (𝑅𝑒<50) for both sub-cooled water and super-heated steam in RELAP5 3.2mz and in special cases also in RELAP5 3Di. As mentioned, for some cases a comparison between RELAP5 mod3.2mz and 3D was performed to assess the behavior of different SYS TH codes in the case of pressure drops. Another key point that needs to be addressed is consideration of the associated effects of the chemistry and wall material in pressure drops since the highest value of uncertainty in friction pressure drop is due to uncertainties in value of the roughness iinot to mention that SYS TH codes are not able to predict the effects of corrosion. Additionally, until the time that new experiments are done, for turbulent regime, only Colebrook implicit equation with iterative procedure must be used as a reference for all friction factor calculations. In summary, the uncertainties associated with pressure drop calculations as a single phenomenon in TH SYS code (particularly in low Re number e.g. natural circulation) have the potential to impact the application of the BE TH SYS code in the BEPU. This may affect the safety analysis both for conventional and non-conventional LWRs (i.e. CAREM, NuScale, SMART, IRIS, etcI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
