P. Goyal

Thermal Analysis of Spent Fuel Transportation Cask

Spent fuel transportation casks are required to meet among others (test conditions), the regulatory thermal test conditions in order to demonstrate their ability to withstand specified accidental fire conditions during transport. This paper describes the transient thermal analysis performed with the above intention for a transportation cask. The analysis was carried out using COMSOL Multiphysics code employing the Finite Element Method (FEM). The computation covers normal transport condition, and half an hour fire test at 800°C. The objective of the analysis was to determine the maximum outer surface temperature for normal transport conditions and to assess the extent of melting of lead during fire period.

Modeling and analysis of condensation induced water hammer

Abstract Direct contact of steam and subcooled water under certain situations may cause immense steam condensation at the two-phase interface and can lead to the generation of fast and violent pressure surges which is often termed as condensation induced water hammer (CIWH) or direct contact condensation (DCC) driven water hammer. The present work aims at the exploration of the underlying physics of the CIWH phenomenon in a horizontal two-phase flow scenario using a dedicated 1D, compressible in-house code which is formulated based on the two-fluid modeling approach (six-equation based model). The developed code is verified against the benchmark two-phase shock tube problem (Reimann problem) and it is observed that it is capable to capture the shock wave, rarefaction wave and contact discontinuity satisfactorily. A comparative assessment between present in-house code, RELAP5 and WAHA3 against the PMK-2 CIWH experimental data shows that the pressure peak amplitude predicted by our in-house code is more accurate in comparison to WAHA3 and RELAP5 simulation. In this work, emphasis is also given on the detailed investigation to study the effect of inlet water subcooling (20–80 °C), water inflow rate (corresponding  = 0.1 and 0.7) on the pressure peak amplitude (along with its occurrence time and location), phase distribution, temperature history and interfacial condensation rate during CIWH. Observation reveals that with the decrease in inlet water temperature, pressure peak magnitude increases. It is also found that the pressure peak amplitude increases with the increase in inlet water flow rate.

Flow accelerated corrosion study in feeder pipes

Abstract The Indian Pressurized Heavy Water Reactor (PHWR) core consists of a number of horizontal channels containing nuclear fuel bundles. Parallel coolant channels are connected to Inlet and Outlet header through feeder pipes. Coolant from Reactor Inlet Header is distributed to the coolant channels and after removing heat combines at Reactor Outlet Header. Due to space constraints the feeder pipes are joined to the channel with one or two elbows close to the end fittings of the coolant channels. The carbon steel feeder pipes carry high temperature fluid at higher velocity and are liable to undergo Flow Accelerated Corrosion (FAC). In the recent inspection it has been found that feeders having double elbow are more susceptible to FAC on the intrados of second elbow. But it was found that in some of the elbows maximum thinning due to FAC was observed on the intrados of the first elbow. Hence to resolve this, effect of first bend orientation with respect of upstream direction has been studied. Two different approaches are used for predicting the FAC rate from calculated value of wall shear stress by CFD. One method is based on evaluating of wear rate using Colburn analogy and the other using an empirical equation between wear rate and shear stress. In Colburn analogy, mass transfer coefficient is evaluated by knowing shear stress and equilibrium concentration. For a case study, wall shear stress obtained from k-∊ turbulence model was compared with k-ω SST turbulence model and no appreciable change in the wall shear stress has been found. Hence for subsequent analysis k-∊ turbulence model was chosen because large mesh size near to the surface (first layer thickness) is permitted due to higher y+ value.

CFD analysis of a hydraulic valve for cavitating flow

Abstract A successful design of high pressure hydraulic valves requires a thorough analysis of both velocity and pressure fields, with the aim of improving the geometry to avoid cavitation. Cavitation behavior prediction of hydraulic valves and its associated performance drop is of high interest for the manufacturers and for the users. The paper presents a CFD analysis of the flow inside a high pressure hydraulic valve. First, the analysis was carried out without using cavitation model (single phase). It was observed that absolute pressure was going below the vapor pressure. Hence, it was required to turn on the cavitation model. This model enables formation of vapor from liquid when the pressure drops below the vaporization pressure. Since the cavitation bubble grows in a liquid at low temperature, the latent heat of evaporation can be neglected and the system can be considered isothermal. Under these conditions the pressure inside the bubble remains practically constant and the growth of the bubble radius can be approximated by the simplified Rayleigh equation. For typical poppet valve geometry, ½ of computational domain is assumed, with pressure inlet and outlet boundary conditions, and a steady flow solution is computed. Because of the highly complex geometry of the hydraulic valve, the computational domain was meshed using unstructured grids using tetrahedral cells only. The paper presents a numerical investigation of the flow inside a hydraulic valve using commercial CFD code CFD-ACE. The aim of the study is to provide a good basis for future designing of the hydraulic valve. The result indicated the cavitation zones which in turn suggest needs of modification of present geometry.

Thermal plume behaviour in the Kadra reservoir at Kaiga atomic power station - Part 2: studies for the case of four and six units in operation

Abstract A computational model was developed earlier for 2 units of Nuclear Power Plants (NPPs) operational at Kaiga Atomic Power Station (KAPS) to understand the thermal plume behaviour in the Kadra reservoir wherein the hot water from the plant condensers is discharged. The model was successfully validated against the site data. The same model has now been extended for analyzing the thermal plume bahaviour in case of 4 NPP units as well as 6 NPP units operational at the same site. The present paper briefly describes details of the studies along with the results of earlier study to understand the overall behavior of thermal plume in Kadra reservoir.

CFD simulation of thermal discharge behaviour in the Kadra reservoir at the Kaiga atomic power station: Part 1: Validation for 2 power plant units in operation

Abstract The thermal pollution arising out of discharge of hot water from the power plant condensers into the natural water bodies such as rivers, lakes, reservoirs, oceans etc. has been a serious concern to environmentalists ever since the plants started operating world over. In the past forty to fifty years, the methods of calculations for predicting the velocity and temperature fields in the affected regions of the stagnant/flowing water bodies have undergone a significant improvement. Currently, use of Computational Fluid Dynamics (CFD) codes for performing these calculations is gaining popularity. However, several factors such as the assumed computational domain and its discretisation, the boundary conditions used, representation of hydrodynamic characteristics (laminar/turbulent, buoyant/non-buoyant), etc. have a strong influence on the accuracy of predictions by such a model. A CFD code STAR-CD has been used for analyzing the thermal plume behaviour in the Kadra reservoir at Kaiga Atomic Power Station (KAPS). The predictions from these calculations of two units in operation have been found to be in good agreement with the site data made available from earlier studies. The present paper briefly describes the model developed using STAR-CD and results obtained for the Kadra reservoir at KAPS.

Calculation of moderator circulation in IPHWR using a porosity approach

Abstract In the present configuration of the calandria for the 700 MWe Kakrapara Nuclear Power Plant, moderator inlet diffusers are directed upwards and the outlet is from the bottom of the calandria. Moderator circulation patterns and temperature distribution needs to be predicted to ensure adequate cooling margin for all channels. This study consists of two steps: at first, an optimized calculation scheme is obtained by comparison of the predicted results with the experimental data and by evaluating the fluid flow and temperature distribution. Then, in the second step, the analysis for the real 700 MWe IPHWR moderator under normal operating conditions has been performed with the optimized scheme. The present paper describes the methodology used for predicting the circulation pattern and temperature distribution in the moderator during normal operation using CFD code CFD-ACE+. The matrix of the calandria tubes in the core region is simplified to a porous media in which the momentum resistance model is used for pressure loss. The buoyancy effects due to internal heating and jet momentum effects through inlet nozzles have been considered in the analysis. The results show that the maximum temperature observed in the calandria is within the design limits during normal operation.

Simulation model of a nuclear power plant turbine

Abstract A computer code “TURDYN” has been developed for prediction of high pressure and low pressure turbine torque under thermodynamic transient conditions. The model is based on the conservation laws of mass and energy. All the important components of turbine systems, e. g. high pressure turbine, low pressure turbine, feed heaters, reheater, moisture separator have been considered. The dynamic equations are solved simultaneously to obtain the stage pressure at various load conditions. The details of the mathematical formulation of the model and open loop responses for specific disturbances are presented.