Indo-UK Civil Nuclear Collaboration April 07, 2016

Background There have been three phases in which projects have been jointly pursued. These projects are funded by EPSRC for UK. From Indian side, no extra funding is being sought from DAE as the work is in line with our mandate. Phase-1: V&V of CHF and CFD Experiments related to dryout modeling, effect of heat flux on entrainment and deposition rates. Experiments for counter-current natural circulation in a pipe Phase 2: Thermal hydraulics of boiling and passive systems (ongoing) Development of phenomenological tool for dryout prediction. This is a continuation of the CHF V&V. Experiments and simulation of boiling Development of simulation techniques for flow under supercritical conditions Phase-3: New reactor design from a safety system perspective, passivity and grace time Single phase buoyancy driven flows In-vessel retention Premature oscillation induced CHF 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 EPSRC funding timelines

Scopes and significance of the projects related to annular flow Relation to DAE mandate What we get from UK collaborators What UK collaborators get from us V&V of CHF and CFD Phenomenological tool development for dryout analysis Dryout is one of the criterion which determines the power limit for all BWRs. AHWR is a Natural circulation cooled boiling water type of reactor. Dryout prediction is essential for our rod cluster. Technical expertise in development of techniques for film flow rate and film thickness measurement. Joint analysis of annular flow phenomena and CCNC. Data for both model validation and development. Mutual benefits: Experimental facilities, Lectures by Professors from Imperial College, visits by Indian collaborators to UK, models and joint papers.

Joint papers [1] A. Dasgupta, D. Chandraker, S. Walker, and P. Vijayan, "An Assessment of the Correlations for Entrainment and Deposition Rates in Annular Flow for Dryout Prediction," in Multiphase Science and Technology (submitted), ed, 2016. [2] A. Dasgupta, D. Chandraker, B. Suhasith, A. K. Nayak, S. P. Walker, G. Hewitt, et al., "Experimental investigation on dominant waves in upward air-water two-phase flow in churn and annular regimes," in Experimental Thermal and Fluid Science (Submitted), ed, 2016. [3] A. Dasgupta, D. Chandraker, A. K. Nayak, P. Vijayan, A. Rama Rao, and S. P. Walker, "Development and validation of a model for predicting direct heat transfer from the fuel to droplets in the post dryout regime," in Advances in Thermal Hydraulics 2016 (ATH 16), ed. New Orleans: American Nuclear Society, 2016. [4] F. Sebilleau, A. K. Kansal, R. I. Issa, S. P. Walker, and N. K. Maheshwari, "CFD and experimental analysis of single phase buoyancy driven counter-current flow in a pipe," in NURETH16, ed. Chicago, 2015. [5] L. Sanmiguel Gimeno, S. P. Walker, G. Hewitt, J. Le Corre, A. Dasgupta, and M. Ahmad, "Validation and cross-verification of three mechanistic codes for annular two-phase flow simulation and dryout prediction," in NURETH 16, ed. Chicago, 2015. [6] A. Dasgupta, P. Kulkarni, G. Gorade, D. Chandraker, A. K. Nayak, S. P. Walker, et al., "Rewetting and Quenching of a Heated Rod: Physical Phenomena, Heat Transfer and the Effect of Nano-Fluids," in 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, ed. Chicago, 2015. [7] A. Dasgupta, D. Chandraker, B. Suhasithb, R. Reddy, R. Rajalakshmia, G. Hewitt, et al., "Wave structures and behavior in churn and annular flows in vertical tubes," in Multiphase Science and Technology (submitted), ed, 2015. [8] A. Dasgupta, D. Chandraker, A. K. Nayak, P. Vijayan, S. Kshirasagar, B. R. Reddy, et al., "Visualization of large waves in churn and annular two-phase flow," in Proceedings of the 23rd National Heat and Mass Transfer Conference and 1st International ISHMT-ASTFE Heat and Mass Transfer Conference IHMTC2015, ed. Thiruvananthapuram, India, 2015. [9] D. Chandraker, D. Kaushik, A. Dasgupta, A. K. Nayak, S. P. Walker, P. K. Vijayan, et al., "Validation of the Dryout Modelling Code, FIDOM," in Nuclear Engineering and Design (to appear), ed, 2015. [10] F. Sebilleau, A. K. Kansal, R. Issa, and S. P. Walker, "CFD Analysis of Single Phase Counter-Current Buoyancy Driven Flows and its Applications to Passive Reactor Design," in ICONE22, ed. Prague: ASME, 2014.

Achievements (Dryout and CHF) We have developed two facilities viz. Air-water and steam-water facilities for annular flow studies. Advanced techniques and instrumentation have been developed for measurement of film flow rate and film thickness in annular flow. Experiments have been performed under conditions which have been investigated earlier in literature. Our data are in-line with earlier measurements Experiments have also been conducted in parameter space where data are scarce/unavailable and models/correlations for annular flow have been validated. In-house code annular flow and dryout modeling SCADOP has been verified against UK code GRAMP and the results are seen to be close to each other. Regions of Heat Transfer

Glimpses – Air-water facility

Glimpses- Steam-water facility CHIL Extraction chamber Presently only film flow rate measurements are possible. It is planned to also put film thickness sensor in the loop. If successful, this will be the first such high temperature-high pressure measurement in the world. Design pressure: 100 bar Design temp.: 300 oC Mass flux: 600 – 2000 kg/m2s

Conductance Sensor & Signal Conditioning Electronics Module Development of high temperature conductance probe for film thickness measurements in Steam-Water Annular flow studies Need: Required for measurement of liquid film thickness during annular flow regime in two-phase flow process for generating experimental data related to mechanistic modeling of dry out relevant to BWR conditions in AHWR CHF & Instability studies Loop (CHIL). Sensor simulation Results Basic Principle : Works on the difference in conductivity between the liquid phase and gaseous phase. Salient Features: The conductance probe consists of two concentric ring electrodes flush mounted on the pipe wall over which the film is passing. Concentric ring electrodes give average film thickness measurement. Modeling, simulation studies to obtain optimum design parameters, fabrication of sensor and electronics, calibration and testing are completed in house. Conductance Sensor & Signal Conditioning Electronics Module

Few representative results- Air-water Entrained fraction and film thickness in adiabatic air-water flows have been obtained and used to validate the in-house codes. Visualization studies have led to new measurements for disturbance wave velocities in annular and churn flow. New technique has been suggested for demarcation of churn and annular flow regimes New understanding has been obtained for the criterion for onset of entrainment in annular flows. Film flow rate Onset of entrainment Identification of flow regime Film thickness

Representative results- Steam-water Experiments have been conducted at different powers to determine the reduction in film flow rate as dryout is approached. Extrapolation of the data also gives an alternate method for estimation of dryout power The present film flow data (at low power) are at qualities near to transition to annular flow. Very few such data are available in literature. Measured film flow rate

Future work for continuing projects and challenges We presently have a model for reasonable (as inferred from comparisons against literature and other codes like GRAMP) prediction of dryout. Deposition and entrainment rates are essential ingredients for the model. The effect of heat flux on these is not very well studied in literature. Scheme for the determination of this effect has been worked out jointly with Imperial College London. These experiments are planned in CHIL. The major challenge is related to the time consuming nature of the experiments, viz., getting at least 10 stable data points for one measurement of film flow rate. Also, determining the effect of heat flux involves moving of bus-bars

Phase 3 projects Premature Oscillation Induced CHF This is a continuation of the dryout related work with emphasis on the effect of flow oscillations. Some theoretical studies have been carried out in past in BARC. The present project aims to conduct experiments by inducing flow oscillations using VFD. New reactor design from a safety system perspective, passivity and grace time This involves two parts: One is concerned with buoyant plumes in pipes. This is a continuation of CCNC studies already carried out. The other is regarding in-vessel retention which is relevant to sever accident management in PHWRs.

Description of the Loop CHF and Instability Loop (CHIL) is an experimental loop set up with the objectives of studying natural circulation stability characteristics and Critical Heat Flux (CHF) under oscillatory flow conditions. CHF (steady and oscillatory flow) experiments will be performed by employing forced circulation of water through an electrically heated test section which has an inner diameter of 10.5 mm and wall thickness of 1.1 mm. A canned motor pump (3.7 kW) is used for forced circulation the facility. The power to the pump is fed through a Variable frequency Drive (VFD). The VFD is also used to provide programmed oscillatory frequency to the pump resulting in oscillatory flow variation in the loop. CHF and Instability Loop (CHIL)

EFFECT OF FREQUENCY AND AMPLITUDE ON CRITICAL POWER Experimental Program Premature CHF (degradation factor) under flow oscillation To study the reduction in the CHF value due to flow oscillations, critical power ratio (degradation factor) with oscillations and without oscillations (CPOF/CPNOF) is calculated at different frequencies and amplitudes. In base case CHF occurs at 53 kW. CPOF/CPNOF variation with frequency at different amplitudes is shown in Fig. It is seen that for low frequency CPOF/CPNOF value remains constant but with higher frequency it increases. Operating parameters: Pressure (bar) Mass Flux Inlet liquid Subcooling ( C) Amplitude Frequency 70 500 20 10%, 20%, 30% 0.1, 0.5,1,5 10 700 1000 EFFECT OF FREQUENCY AND AMPLITUDE ON CRITICAL POWER

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