Evaluation of the Potential for Containment Bypass due to Steam Generator Tube Rupture in VVER-1000/V320 Reactor during Extended SBO sequence using SCDAP/RELAP5 code

A severe accident-induced of a Steam Generator (SG) tube releases radioactivity from the Reactor Coolant System (RCS) into the SG secondary coolant system from where it may escape to the environment through the pressure relief valves and an environmental release in this manner is called “Containment Bypass”. This study aims to evaluate the potential for “Containment Bypass” in VVER/V320 reactor during extended Station Blackout (SBO) scenarios that challenge the tubes by primarily involving a natural circulation of superheated steam inside the piping loop and then induce creep rupture tube failure. Assessments are made of SCDAP/RELAP5 code capabilities for predicting the plant behavior during an SBO event and estimates are made of the uncertainties associated with the SCDAP/RELAP5 predictions for key fluid and components condition and for the SG tube failure margins.

Improvement Methods for Supply Performance in Emergency Interconnection Plans

When operating a water supply network (WSN), pipe failures and water service interruptions are inevitable. A large-scale water service interruption decreases the reliability of a WSN; therefore, an emergency interconnection plan (EIP) is adopted to prevent it. To establish an EIP involving emergency interconnection pipes, in most cases, only the operation plan is considered. However, it is required to evaluate possible interconnected supply areas (PISAs) from the EIP to achieve the purpose of the EIP. It is obvious that PISA is dependent on the structure of the WSN, elevation difference between the adjacent interconnected blocks, size and location of the emergency interconnection pipes, and inline pumping station. In this study, we categorized the reasons resulting in insufficient PISA from the EIP and suggested improvement methods such as increasing the pipe diameter, new pumping stations, adding emergency interconnection pipes, and adding pressure relief valves. To quantify the effect of the improvement methods on the performance of the EIP, we applied them to a real WSN and estimated the emergency supply rate for each improvement method by using Pressure Driven Analysis (PDA) was used as the hydraulic simulation tool. Consequently, each improvement method increased the PISA and the emergency supply rate on the network. Thus, the suggested method will be used in the design and operation of EIPs to improve their performance.

Modeling of impact of the poppet element on its seat body in pressure relief valves

This article deals with modeling of the impact between the moving elements and their seats bodies in pressure relief valves. Four different impact models, such as the Kelvin–Voigt, the Maxwell, the standard-solid and the Hunt–Crossley models, are considered. A comprehensive dynamic model of the studied valve, considering the four models, is deduced. The simulation results show that the Kelvin–Voigt model cannot be used to represent the impact in pressure relief valves because, by the end of impact period, the model results in a tensile force, which is physically impossible in rigid bodies impacting. In the Maxwell model, a considerable number of discontinuities appeared in the impact force, which causes the poppet element to make a number of rebounds with the seat body during the impact period. However, in the standard-solid model, the poppet element barely rebounds. In the Hunt–Crossley nonlinear model, a certain penetration distance between the poppet element and the seat body occurs, which is certainly unrealistic in rigid bodies impacting. The validation of the impact models showed that the Maxwell model is the suitable impact model that can be used to represent the impact in pressure relief valves. However, the validation of the proposed dynamic model proved that the impact has no significant effect on the dynamic performance of pressure relief valves. The main reason behind this is that the impact occurs when the operating pressure has fallen down (the valve is out of operation).

Failure Assessment of Spring-Operated Pressure Relief Valve Proof Test Data for Extending Time-in-Service

The proof test results of 1669 Spring-Operated Pressure Relief Valves (SOPRV), which were previously installed in active processes, were analyzed with respect to proof test ratio (R), time-in-service (TIS), set pressure (SP), working fluid (WF), material composition of the SOPRV and, if an SOPRV failed-to-open (FTO), the root cause of failure in the FTO failure mode if available. Many of these SOPRV had accumulated TIS in excess of the normal maximum of five years yet proof testing indicated that most would have functioned properly. This paper examines the results of the analysis and provides guidelines under which it is appropriate to consider extending TIS for individual SOPRV.