Several inherent and passive systems have been adopted in Indian innovative reactor, AHWR. Analyses have been performed to prove design concepts of these systems. Experiments and further analyses of these systems are being carried out rigorously. Several major areas of R & D have been identified for detailed study and the required development activities are in progress.

Extensive work has been carried out in the area of natural circulation. A transparent rectangular loop has been installed to study natural circulation. The stability of natural circulation with different heater and cooler orientations has been studied in the loop. Start-up procedure and instability studies are being carried out at high pressure natural circulation loop (HPNCL). Flow pattern transition instability studies using neutron radiography have been conducted at APSARA reactor in flow pattern transition instability loop (FPTIL). Integral behaviour experiments are being conducted in an integral test loop (ITL). The ITL (Fig. III-5) was commissioned in 2005 in BARC. The performance of isolation condensers for reactor decay heat removal is being evaluated in the ITL. A parallel channel experimental facility is set up in BARC to investigate parallel channel instability. Void coefficient of reactivity has been simulated in the loop. The pre-test single channel stability and parallel channel stability analyses by RELAP 5 and other in house codes have been carried out for the ITL and parallel channel loop. Two-phase low flow pressure drop experiments are being conducted in 3 MW boiling
water loop (BWL) across the various components of coolant channel. Earlier single phase and two phase (air-water) pressure drop experiments were performed on simulated full scale fuel bundle of AHWR in flow test facility at low pressure.

Thermal stratification inside a water pool is being investigated. One dimensional theoretical model and computer code for solving two dimensional Navier-Stokes equations have been developed to study the stratification phenomena in the water pool. Other generalized computer codes available are also being used for this purpose.

An experimental set up to study phenomena associated with passive containment isolation is being set

up.

The effect of non-condensable gas on steam condensation inside a vertical tube has been investigated experimentally. A comparison of local heat transfer coefficient determined by theoretical model with experimental data has been carried out. An experimental facility to investigate the effect of non condensable gas on condensation of steam on the outer surfaces of tubes of passive external condensers has been commissioned and experiments are in progress.