[en] In the proposed Indian Advanced Heavy Water Reactor (AHWR) the coolant recirculation in the primary system is achieved by two-phase natural circulation. The two-phase steam-water mixture from the reactor core is separated in steam drum by gravity. Gravity separation of phases may lead to undesirable phenomena - carryover and carryunder. Carryover is the entrainment of liquid droplets in the vapor phase.Carryover needs to be minimized to avoid erosion corrosion of turbine blades. Carryunder is the entrainment of vapor bubbles with liquid flowing back to reactor core. Significant carryunder may in turn lead to reduced flow resulting in reduced CHF margin and stability in the coolant channel. An Air-Water Loop (AWL) has been designed to carry out the experiments relevant to AHWR steam drum. The design features and scaling philosophy is described in this report. (author)

[en] Air-Water Loop (AWL) is an experimental facility aimed at the simulation of two-phase flow phenomenon relevant to steam drum of Advanced Heavy Water Reactor (AHWR). AWL consists of scaled down model of AHWR steam drum, operating with air-water mixture. Scaling has been performed such that the superficial velocities of both phases in the model are identical to that in the prototype. The required boundary flow, i.e. two phase air-water flow at drum inlet is generated using two-phase natural circulation loop formed by pipe channels connected between the drum and a water tank. Air is injected at the bottom of channels and is separated in the drum. Steady state experiments have been performed in AWL at various operating levels in drum and air injection flow rates. The experimental data has been validated using a numerical model developed based on momentum balance in channels. This paper describes the geometry of the experimental facility, details of two-phase natural circulation experiments carried out and validation of experimental data. (author)

[en] In the present work investigations on the start-up and various operational procedures of the natural circulation based Advanced Heavy Water Reactor (AHWR) have been carried out. A transient computer code RELAP5/MOD3.2 has been utilized for the purpose. Operational procedures such as stage-wise pressurized start-up, power raising, power set back and normal reactor trip have been simulated to study the flow stability during the transient. Options for improving the economy of the processes have been also considered. Stable operating procedures are arrived at with simulation calculations. (author)

[en] Steam and water mixture is separated purely due to gravity in the steam drum of Advanced Heavy Water Reactor (AHWR). The elimination of mechanical separators leads to simplification of design however steam drum needs to be designed so that the entrainment of water droplets in the steam (carryover) is limited to an acceptable level. Experimental investigations on carryover have been carried out in a scaled down facility known as Air-Water Loop (AWL). AWL is aimed at the simulation of two-phase flow phenomenon relevant to steam drum of AHWR. AWL consists of scaled down model of AHWR steam drum, operating with air-water mixture. The entrainment (water droplets) out of steam drum has been physically measured. The entrainment is function of droplet size distribution at the interface, air velocity, balance of drag and buoyancy forces upon the droplets during the motion through air space above the interface. Among these the droplet size distribution is unknown and critical parameter. Using high speed photography and shadowgraph technique droplet size distribution was obtained. This paper describes the entrainment measurement and its comparison with correlations from literature, droplet size distribution and its analysis in details. (author)

[en] Core heat removal by natural circulation under the operating as well as accidental conditions is one of the several passive safety features of the Advanced Heavy Water Reactor (AHWR) being developed in India. Integral Test Loop (ITL) is an experimental test facility which simulates the Main Heat Transport System and safety systems of AHWR. Several experiments have been carried out to validate the thermal-hydraulic design features of AHWR such as flow stability during startup, LOCA and performance of Isolation Condensers to remove decay heat using natural circulation. This paper presents an overview of these experimental studies. (author)

No abstract available

[en] RELAP 5 and CATHARE are the two best estimate codes used for design and safety analysis of Light water reactors. Although the basic models for solving the conservation equations are same for both the codes however the constitutive relationships which are empirical models may be different in both the codes, which can have significant influence on the predictions of the different phenomenon involved in water cooled reactors. Natural circulation is extensively used as the mode of heat removal in many reactors not only during the accidental conditions but also during the normal power operation An attempt has been made here to compare the predictions of natural circulation behavior of an experimental test facility using both the codes. The steady state and transient natural circulation flow behavior of the test facility for power raising process has been predicted by the codes and compared with each other as well as with the experimental data available. (author)

[en] High Temperature Reactors (HTR) and solar thermal power plants use molten salt as a coolant, as it has low melting point and high boiling point, enabling us to operate the system at low pressure. Molten fluoride salt and molten nitrate salt are proposed as a candidate coolant for High Temperature Reactors (HTR) and solar power plant respectively. BARC is developing a 600 MWth pebble bed high temperature reactor, cooled by natural circulation of fluoride salt and capable of supplying process heat at 1000°C to facilitate hydrogen production by splitting water. Beside this, BARC is also developing a 2MWe solar power tower system using molten nitrate salt. With these requirements, a Molten Salt Natural Circulation Loop (MSNCL) has been designed, fabricated, installed and commissioned in Hall-7, BARC for thermal hydraulic, instrumentation development and material compatibility related studies. Steady state natural circulation experiments with molten nitrate salt (mixture of NaNO₃ and KNO₃ in 60:40 ratio) have been carried out in the loop at different power level. Various transients viz. startup of natural circulation, step power change, loss of heat sink and heater trip has also been studied in the loop. A well known steady state correlation given by Vijayan et. al. has been compared with experimental data. In-house developed code LeBENC has also been validated against all steady state and transient experimental results. The detailed description of MSNCL, steady state and transient experimental results and validation of in-house developed code LeBENC have been described in this report. (author)

[en] Highlights: • A scaled down model for horizontal steam drum of Advanced Heavy Water Reactor was designed. • Steady State two-phase natural circulation experiments were carried out. • A numerical model developed for prediction of experimental results. • Validation performed using empirical models for void fraction and pressure drop. - Abstract: Advanced Heavy Water Reactor (AHWR) is a vertical pressure tube type boiling water reactor that relies on two-phase natural circulation for heat removal from the nuclear core under normal operating as well as accidental conditions. In case of AHWR, the two-phase flow generated in the core is transported by vertical riser pipes to horizontal steam drums at the top. These horizontal steam drums provide sufficient surface area for the separation of steam water mixture purely based on gravity i.e. due to density difference between steam and water. To investigate this gravity separation phenomenon, an experimental facility known as Air-Water Loop has been designed. The facility has a scaled geometry of AHWR steam drum operating with Air-Water mixture as a working fluid. The required flow conditions for the experimental simulations are generated using air-water two-phase natural circulation in this facility. Steady state natural circulation experiments were performed where measurements on recirculation flow rates, two-phase and single phase pressure drop in various sections of the loop have been carried out. The present paper aims to describe the design aspects of the facility, pre-test calculations, steady state two-phase natural circulation experiments and assessment of measured experimental data. The experimental measurements have been predicted using a numerical model that considers various void fraction and pressure drop correlations from the literature for estimation of measured parameters.

[en] Highlights: • Experiments with air-water shows near surface entrainment of the order of 400–600%. • Droplets generated at interface follow Upper Limit Log Normal (ULLN) distribution. • Within the operating range, maximum droplet diameter measured was of 2.7 mm size. • Kataoka & Ishii correlation predicts higher entrainment rates when compared to CFD. - Abstract: Advanced Heavy Water Reactor (AHWR) being developed in India is a vertical pressure tube type boiling water reactor. In case of AHWR the steam-water two-phase flow from the core is separated in horizontal steam drums purely due to gravity i.e. density difference between the steam and water. This simple principle eliminates the need for mechanical separators and associated system pressure drop. However, the separation efficiency is affected by the entrainment phenomenon, i.e. conveyance of water droplets by the separated steam out of the drum i.e. carryover. Carryover estimation for new equipment with existing empirical correlations may not be reliable and experimental investigations in relevant geometries are necessary. In the present work carryover process has been investigated in a test facility known as Air-Water Loop (AWL). The facility aims at simulation of gravity separation of two-phase flows relevant to AHWR steam drum, using air-water mixture. During the experiments, carryover at operating levels closer to exit has been measured. AWL also has a facility for optical measurements using high speed camera. Measurements on droplet size distribution have been carried out with shadowgraph technique at different operating levels. The present work also involves the analysis of carryover using 3-D Euler-Lagrangian simulations with OpenFOAM based solver.