Outlet Feeder Research Articles

CANDU6 single channel CCP analysis on pressure tube deformation effects with multi-physics coupled calculation

Though pressure tube deformation rigorously and simultaneously affects channel coolability and neutronics behavior, the two effects have never been coupled with each other. In this study, the CUPID code is coupled with the SHAFE code to obtain the Critical Channel Power (CCP) of a designated channel which has high nominal power, a high void fraction, a high flow rate, and high pressure deformation. Even though appendage modeling is not included in this study, adequate cell-wise uniform artificial form loss was sought through iteration and imposed to conserve the header to header pressure drop by considering the inlet & outlet feeder and end fitting pressure drop. Nested loops are included in CCP calculation logic; they are the channel power loop, pin power distribution update loop and flow rate optimization loop from outer loop to inner loop, in sequence. Both CUPID and SHAFE are based on the Fortran computer language; the CUPID code is converted to the Dynamic Link Library (DLL) and the SHAFE code can load the CUPID library whenever it is required. Finally, we found that a CCP decrement for a channel with large pressure tube deformation is not that much, even for a complex deformation case. In addition, the sagging effect for a CCP decrement is significantly different from the expectation before an analysis is completed.

Effect of vibrating feeder pan geometry on radiometric separator performance

The article offers justifies the optimized shape for the vibrating feeder pan of a radiometric separator, which ensures the maximum travelling speed and uniform flow of ore material in the zone of radiation and recording. Three shapes of pans are discussed: rectangular, parabolic and triangular. It is found that motion of ore material along an inclined rectangular-shape pan is straight-linear. Distribution of ore particles along the width of the channel, which governs the scatter of the motion trajectories relative to the central axis of the channel, depends on the runoff point of particles from the outlet feeder. Proposed for the description of the motion trajectory of ore particles along an inclined channel of parabolic shape, the mathematical model demonstrates the curved and pendulum-wise motion of an ore particle with the attenuating amplitude. The motion of an ore particle in an inclined pan with the triangular-shape channel features the minimized scatter of motion trajectories relative to the central axis of the channel. The analysis of ore motion along vibrating feeder pans with different shape channels is carried out in Rocky DEM environment with regard to interaction of ore particles with the pan surface and with each other. The simulation modeling has proved the conclusions on the efficiency of the triangularshape profile of the vibrating feeder pan as it ensures uniform single-row flow of ore particles along the straight-line trajectory. The triangular shape of the pan contributes to the increased travelling speed of ore particles and, accordingly, to the enhanced capacity of the separator. The radiometric separator efficiency can be increased 1.5 times by changing from the parabolicshape channels to the triangular-shape profiles of vibrating feeder pans at the other operating conditions of radiometric separators being equal.

Type II instabilities in advanced heavy water natural circulation reactors: Application to the AHWR

This paper deals with the instabilities in advanced heavy water reactors driven by natural circulation at high pressure and power conditions. This paper also study which are the design and operating parameters that have more influence on the appearance of type II instabilities. Some of the results are compared with usual BWR reactors to stablish which are the differences between both types of reactors in the development of limit cycle oscillations and the maximum amplitude values of these oscillations when some of the influential parameters on the stability are changed.This paper also explains the main characteristics of the modelling used to simulate the fuel channels, the risers or outlet feeders, the recirculation loop of this reactor, and the kinetic and heat transfer models. In addition, we compare the closure relations used in this model with the experimental correlations for the AHWR, to know the applicability of the correlations for the AHWR under natural circulation conditions.Finally, we study in this paper the influence on the decay ratio (DR) and the limit cycle amplitude of a set of design and operational parameters. Some of these parameters are: the amount of coolant direct heating by neutrons and gamma-rays, the form loss coefficient at the channel inlet, the form loss coefficient in the spacers, the phase change number Npch, the characteristic natural circulation time and the effective inertia of the recirculation loop.

FLUID–STRUCTURE-INTERACTION ANALYSIS FOR WELDED PIPES WITH FLOW-ACCELERATED CORROSION WALL THINNING

The flow-accelerated corrosion (FAC) entrance effect results in enhanced wall thinning immediately downstream of a weld if the weld connects an upstream FAC-resistant material with a downstream less resistant material. The weld regions, especially those with local repairs, are susceptible to cracking due to the high residual stresses induced by fabrication. The combined effects of the FAC entrance effect and high stresses at a weld might compromise the structural integrity of the piping and lead to a failure. Weld degradation by FAC entrance effect has been observed at nuclear and fossil power plants. This paper describes an application using fluid–structure-interaction (FSI) modelling to study the combined effects of FAC wall thinning, weld residual stresses, and in-service loads on welded structures. Simplified cases analyzed were based on CANDU outlet feeder conditions. The analysis includes the flow and mass transfer modelling of the FAC entrance effect using computational fluid dynamics (CFD) and nonlinear structural analyses of the welded structures with wall thinning and an assumed weld residual stress and strain distribution. The FSI analyses were performed using ANSYS Workbench, an integrated platform that enables the coupling of CFD and structural analysis solutions. The obtained results show that the combination of FAC, weld residual stresses, in-service loads (including the internal pressure) and (or) extreme loads could cause high stresses and affect the integrity of the welded pipes. The present work demonstrated that the FSI modelling can be used as an effective approach to assess the integrity of welded structures.

Investigation of air–water two phase flow through a venturi

Study of two phase flow characteristics is of prime importance in various modern engineering fields including nuclear. In a 700MWe Indian Pressurized Heavy Water Reactor (PHWR), limited boiling is allowed in the channels to extract more power. In this pressure tube type of reactor, the channel power computation requires the measured channel flow and outlet quality. Though the channel flow-rate can be measured at the inlet feeder to the reactor core, the channel outlet quality needs to be derived from the measured two phase pressure drop across a venturi located at the outlet feeder of the same channel. The measured pressure drop shall be correlated to the mixture density of two phase steam–water flow in the channel. In order to study the pressure drop characteristics of the specific venturi under two phase conditions, an experimental study was performed with air–water two phase flow, with same the venturi channel system as that in the prototype reactor. A series of tests were carried out by varying the air/water flow rates, in a multiphase loop. The pressure drop across the venturi was measured using a DPT (Differential Pressure Transmitter). The measured data was compared with the correlations available in literature.

Flow accelerated corrosion of carbon steel feeder pipes from pressurized heavy water reactors

Detailed investigation of a number of feeder pipes received from Rajasthan Atomic Power Station Unit 2 (RAPS#2) after en-masse feeder pipe replacement after 15.67 Effective Full Power Years (EFPYs) was carried out. Investigations included ultrasonic thickness measurement by ultrasonic testing, optical microscopy, scanning electron microscopy, chemical analysis and X-ray Diffraction (XRD). Results showed that maximum thickness reduction of the feeder had occurred downstream and close to the weld in 32 NB (1.25″/32.75mm ID) elbows. Rate of Flow Accelerated Corrosion (FAC) was measured to be higher in the lower diameter feeder pipes due to high flow velocity and turbulence. Weld regions had thinned to a lower extent than the parent material due to higher chromium content in the weld. A weld protrusion has been shown to add to the thinning due to FAC and lead to faster thinning rate at localized regions. Surface morphology of inner surface of feeder had shown different size scallop pattern over the weld and parent material. Inter-granular cracks were also observed along the weld fusion line and in the parent material in 32 NB outlet feeder elbow.

Experimental determination of flow accelerated corrosion in bend and straight sections of carbon steel primary coolant feeder pipes in pressurised heavy water reactor system

Coolant systems in nuclear power plants undergo degradation by various corrosion processes. The carbon steel feeder pipes for the primary heat transport system of pressurised heavy water reactors (PHWRs) undergo extensive wall thinning by a degradation process, known as flow accelerated corrosion (FAC). Flow accelerated corrosion occurs under certain conditions of flow, water chemistry, pipe geometry and material composition. In PHWRs, the outlet feeders carry the heavy water (D2O) coolant, which flows at velocities in the range of 10 to 20 m s−1. The requirement of high flow velocity at high temperature and pressure to simulate the exact service hydrodynamic conditions, and the long time required to enable unambiguous observations regarding the extent of FAC, makes it difficult to undertake this study in the laboratory. This paper presents the design of an FAC module that enables the relatively rapid measurement of FAC to be undertaken in simulated PHWR primary heat transport conditions. The results of corrosion rate measurements and the attempts to explain the results using a computation fluid dynamics model are presented in this paper.

Determination of rupture frequency for feeders subject to flow accelerated corrosion

Feeder pipe wall thinning due to flow accelerated corrosion (FAC) has been identified as a degradation mechanism that may affect the operating life of outlet feeder pipes. A large number of feeders are expected to require costly repair or replacement over the remaining life of the station if a conservative FAC rate is used in the deterministic structural integrity assessment. The paper presents a preliminary probabilistic framework for determining the rupture frequency of feeders subject to FAC based on commercial probabilistic fracture mechanics code WinPRAISE 2007. The obtained information can be used as inputs for developing risk-informed feeder life management plans. Darlington Unit 2 is selected to demonstrate the proposed method.

Electrochemical Corrosion Potential of Carbon Steel Feeder Pipes in a Canadian Deuterium Uranium Reactor Generating Station under Return-to-Service Conditions

Abstract One of the principle factors affecting the stress corrosion cracking (SCC) of a susceptible metal is its corrosion potential. A number of instances of cracking on the outlet feeder pipes o...

Surface structure and stability of the Larsen C ice shelf, Antarctic Peninsula

AbstractA structural glaciological description and analysis of surface morphological features of the Larsen C ice shelf, Antarctic Peninsula, is derived from satellite images spanning the period 1963–2007. The data are evaluated in two time ranges: a comparison of a 1963 satellite image photomosaic with a modern digital mosaic compiled using 2003/04 austral summer data; and an image series since 2003 showing recent evolution of the shelf. We map the ice-shelf edge, rift swarms, crevasses and crevasse traces, and linear longitudinal structures (called ‘flow stripes’ or ‘streak lines’). The latter are observed to be continuous over distances of up to 200 km from the grounding line to the ice-shelf edge, with little evidence of changes in pattern over that distance. Integrated velocity measurements along a flowline indicate that the shelf has been stable for ∼560 years in the mid-shelf area. Linear longitudinal features may be grouped into 12 units, each related to one or a small group of outlet feeder glaciers to the shelf. We observe that the boundaries between these flow units often mark rift terminations. The boundary zones originate upstream at capes, islands or other suture areas between outlet glaciers. In agreement with previous work, our findings imply that rift terminations within such suture zones indicate that they contain anomalously soft ice. We thus suggest that suture zones within the Larsen C ice shelf, and perhaps within ice shelves more generally, may act to stabilize them by reducing regional stress intensities and thus rates of rift lengthening.

PRIORITIZING FEEDERS FOR MAINTENANCE ACTIVITIES USING AHP IN NUCLEAR POWER PLANTS

The Analytic Hierarchy Process (AHP) is a powerful and flexible decision making process to help people set priorities and make the best decision when both qualitative and quantitative aspects are to be considered. In this paper, a procedure of prioritizing the outlet feeders under multiple criteria using Saaty's priority theory is presented. In priority theory, weights are assigned to the decision criteria via pair wise comparison of criteria. Seven outlet feeders (alternatives) and three decision criteria have been considered and the prioritization process is illustrated with an example case.

Modeling Two-Phase Flow in Pipe Bends

In order to have a better understanding of the interaction between the two-phase steam-water coolant in the outlet feeder pipes of the primary heat transport system of some CANDU reactors and the piping material, themalhydraulic modelling is being performed with a commercial computational fluid dynamics (CFD) code—FLUENT 6.1. The modeling has attempted to describe the results of flow visualization experiments performed in a transparent feeder pipe with air-water mixtures at temperatures below 55°C. The CFD code solves two sets of transport equations—one for each phase. Both phases are first treated separately as homogeneous. Coupling is achieved through pressure and interphase exchange coefficients. A symmetric drag model is employed to describe the interaction between the phases. The geometry and flow regime of interest are a 73 deg bend in a 5.9cm diameter pipe containing water with a Reynolds number of ∼1E5-1E6. The modeling predicted single-phase pressure drop and flow accurately. For two-phase flow with an air voidage of 5–50%, the pressure drop measurements were less well predicted. Furthermore, the observation that an air-water mixture tended to flow toward the outside of the bend while a single-phase liquid layer developed at the inside of the bend was not predicted. The CFD modeling requires further development for this type of geometry with two-phase flow of high voidage.

Failed Fuel Location in CANDU-PHW Reactors Using a Feeder Scanning Technique

A feeder-scanning technique that involves the measurement of γ-ray fields on individual fuel-channel outlet-feeder pipes has been used successfully to locate failed fuel bundles in shutdown CANDU-PHW reactors at the Pickering G.S. High-resolution spectroscopic measurements show that the excess γ-ray fields on the outlet feeders of channels containing fuel failures are due primarily to deposited fission products, all with half-lives longer than 56 hours.