Computational Fluid Dynamics Analysis and Structural Safety Assessment of a Mitigation Device to Minimize Consequence of a Containment Bypass Nuclear Accident

Abstract

The thermally-induced steam generator tube rupture (TI-SGTR) accident is principal contributor to mean early and latent cancer fatality among the containment bypass accidents. To mitigate the consequence of a TI-SGTR accident, use of a bypass mitigation device has been proposed. This study investigated the feasibility of using the proposed bypass mitigation device based on computational fluid dynamics (CFD) analysis and structural safety assessment using a commercial simulation software (Fluent). As TI-SGTR accident may occur if main steam safety valve (MSSV) for preventing over pressurization is stuck-open in SBO scenario, the analysis included the modeling of the flow of dry steam from MSSV to the capturing pipe of the mitigation system. According to CFD analysis results, after passing MSSV, the inlet pressure was decreased to the atmospheric pressure. The structural safety analysis was based on evaluating the equivalent stress distribution of the capturing pipe. Under three inlet pressure conditions, the largest concentrated stress on the capturing pipe was found to be less than 10% to tensile strength of the steel. For the concrete support, the safety margins may not be sufficient for 8.7 MPa inlet pressure condition. The thermal-mechanical analysis was performed for the period of 15 minutes indicated that the effect of thermal expansion is small and that the resulting strain does not pose a concern. The results of this study can also be utilized to study externally released flow through MSSV or to identify directions for supplementing or reinforcing the migration system.

Feasibility Study of Using Bi-mna Metal–Organic Frameworks as Adsorbents for Radioiodine Capture at High Temperature

“…For example, in an unmitigated thermally induced steam generator tube rupture accident, the temperature at the interface between the steam generator and the hot stream may reach well above 600–800 K. , The steam containing radioactive materials may pass through the failed steam generator tube under these temperature conditions. Although the steam temperature gradually decreases while traveling through the pipelines before being released into the environment, the temperature can still reach above 600 K when being released outside in this accident scenario …”

“…However, radioiodine also can be released from a nuclear power plant (NPP) during a severe accident but under harsher conditions. − Iodine is a major contributor to the radioactivity and dose if released into the environment during a nuclear severe accident. 131 I decays rapidly ( t 1/2 = 8.02 d) with high radiation.…”

“…Although the steam temperature gradually decreases while traveling through the pipelines before being released into the environment, the temperature can still reach above 600 K when being released outside in this accident scenario. 33 Generally, the captured radioactive steam would pass through a series of aerosol filtration systems. 38,39 This would result in lowering of the temperature of the radioactive steam before reaching iodine filters.…”

“…Nonetheless, the temperature conditions for iodine capture are still expected to be much higher than those of the reprocessing plants. Although expected to be lower than 600 K by the time radioactive iodine reaches the gaseous filtration system (accounting for the cooling effect when the radioactive gas is released outside), 33 effects of other variables such as relative humidity on the iodine capture efficiency would be of little concern as the steam would still likely be in a dry or superheated state at such a high temperature.…”