Success criteria analysis in support of probabilistic risk assessment for nuclear power plants: application on SGTR accident

Success criteria analysis(SCA) bridges the gap between deterministic and probabilistic approaches for risk assessment of complex systems. To develop a risk model,SCA evaluates systems behaviour in response to postulated accidents using deterministic approach to provide required information for the probabilistic model. A systematic framework is proposed in this article for extracting the front line systems success criteria. In this regard, available approaches are critically reviewed and technical challenges are discussed. Application of the proposed methodology is demonstrated on a typical Westinghouse-type nuclear power plant. Steam generator tube rupture is selected as the postulated accident. The methodology is comprehensive and general; therefore, it can be implemented on the other types of plants and complex systems.

Thermo-Hydraulic Characteristics of Non-Isothermal Batch Transportation Pipeline System with Different Inlet Oil Temperature

The batch transportation process of several kinds of crude oil is accomplished by an entire coupled pipeline system,which exhibits complex thermo-hydraulic characteristics.Based on the coupled characteristics among soil,pipelines and devices(including pumps,heating furnaces and valves),a coupled simulation model of batch transportation for the crude oil pipeline system is established,and a novel coupled simulation algorithm is proposed.The simulation results are in good agreement with the field data of an actual crude oil pipeline system.In addition,based on the numerical simulation,thermo-hydraulic characteristics of pipeline system are investigated,and some new thermo-hydraulic characteristics are obtained.In the batch transportation process with constant flowrate,the change trends of temperature at the outlet of each pipeline segment are hysteretic and the change ranges of temperature become small along mileage.And the adjustment of devices influences thermohydraulic characteristics to some extent.In the batch transportation process with variable flowrate,the complex thermo-hydraulic characteristics are exhibited,which are induced by the comprehensive influence of the changes of oil type,flowrate and absorbed/released heat.Compared with the transportation process with constant flowrate,the high-viscosity oil exhibits similar minimum temperature and lower maximum pressure in the transportation process with variable flowrate,which means that the higher transportation safety of pipeline system is obtained.This study can provide a scientific reference for making the safer batch transportation scheme of crude oil pipeline system.

A COUPLED THERMO-HYDRAULIC MODEL FOR STEAM FLOW IN PIPE NETWORKS

This article aims to establish a coupled thermo-hydraulic mathematical model for steam network by adopting a set of equations, i.e., the continuity equation, motion equation, energy equation, state equation and enthalpy equation and considering the interaction of hydraulic and thermal working conditions. The model is simplified according to steam flow features in pipe networks. The unsteady flow model is simplified to a steady one with considering engineering practice and the solution to the governing equations are obtained by using the standard fourth-order Runge-Kutta method. Many factors of steam flow are generally considered, such as condensability, change of state, friction and heat transfer in the model. It is concluded that coupled iteration can be employed in steam network thermo-hydraulic computation. The numerical results with the model are basically in accordance with practical operation data.

Transient Behaviors of Thermo-Hydraulic and Thermal Stratification in the Pressurizer Surgeline for the Nuclear Power Plant

In pressurized water reactor(PWR)system,the surgeline plays an important role in bonding the pressurizer and the primary circle.Some considerable problems,including the thermo-hydraulics,the thermal stratification and the accompanying thermal stress under transient conditions,pose risks to the surgeline integrity.Herein,a fully-coupled flow-heat-thermo-elasticity model was developed to investigate the transient behavior of thermo-hydraulic parameters and the thermal stratification phenomenon in PWR.To evaluate the nonuniformity of the stratified flow,a stratification degree indicatorζis introduced.It is found that during the outsurge flow,the increase of temperature variation will enlarge the temperature gradient on the wall,corresponding to a more serious deformation.In the cases of positive temperature variation,the higher temperature variation causes higher stratification degreeζ,and vice versa.The mass flow rate m and the stratification degree are in negative correlation.The local deformation can reach 1.802 cm under a 50 K temperature variation,while its location varies from case to case.More attention should be paid to the regulation between the highest deformation location and the surgeline thermo-hydraulic parameters.

MODELING ON THE CYCLIC OPERATION OF STANDING COLUMN WELLS UNDER REGIONAL GROUNDWATER FLOW

Coupled hydrogeological-thermal simulation of the Standing Column Well （SCW） system is essential to provide an optimized configuration and operation schedule for boreholes on the site. This paper presents numerical investigations and thermo-hydraulic evaluation of standing column well system operating under cyclic flow regime. A three-dimensional numerical model for groundwater flow and heat transport is used to analyze the heat exchange in the ground. The model includes the effects of convective and conductive heat transfer, heat loss to the adjacent confining strata, and hydraulic anisotropy. The operation scenario consists of cyclic injection and recovery and four periods per year to simulate the seasonal temperature conditions. For different parameters of the system, performances have been evaluated in terms of variations in recovery temperature. The calculated temperatures at the producing pipe are relatively constant within a certain range through the year and fluctuating quarterly a year. Pipe-to-pipe distance, injection/production rate, ground thickness, and permeability considered in the model are shown to impact the predicted temperature profiles at each stage and the recovery water temperature. The influence of pressure gradient, which determines the velocity of regional groundwater flow, is most substantial.

Heat transfer and fluid flow analysis of an artificially roughened solar air heater： a CFD based investigation

In this paper, the effect of rib （circular sectioned） spacing on average Nusselt number and friction factor in an artificially roughened solar air heater （duct aspect ratio, AR= 5：1） is studied by adopting the computational fluid dynamics （CFD） approach. Numerical solutions are obtained using commercial software ANSYS FLUENT v12.1. The computations based on the finite volume method with the semi-implicit method for pressure-linked equations （SIMPLE） algorithm have been conducted. Circular sectioned transverse ribs are applied at the underside of the top of the duct, i.e., on the absorber plate. The rib-height-to-hydraulic diameter ratio （e/D） is 0.042. The rib-pitch-to-fib-height （P/e） ratios studied are 7.14, 10.71, 14.29 and 17.86. For each rib spacing simulations are executed at six different relevant Reynolds numbers from 3800 to 18000. The thermo-hydraulic performance parameter for P/e = 10.71 is found to be the best for the investigated range of parameters at a Reynolds number of 15000.