Vol.:(0123456789) 1 3 Journal of the Brazilian Society of Mechanical Sciences and Engineering (2020) 42:131 https://doi.org/10.1007/s40430-020-2211-z TECHNICAL PAPER Numerical analysis of parallel‑channel density wave instabilities in a supercritical water reactor Raghvendra Upadhyay 3  · Neetesh Singh Raghuvanshi 2  · Goutam Dutta 1 Received: 8 October 2019 / Accepted: 30 January 2020 / Published online: 17 February 2020 © The Brazilian Society of Mechanical Sciences and Engineering 2020 Abstract Supercritical water reactor (SCWR), a possible generation IV nuclear reactor, is expected to be more efcient and economical than the existing reactors. However, the possibility of thermal–hydraulic (TH) instabilities poses a challenge to its develop- ment. A generic pressure vessel (PV) SCWR concept, similar to the US SCWR design, is investigated at present for density wave oscillations (DWOs). An existing TH model, which was used earlier for the single-channel analysis, is extended here for the analysis of parallel channels. The TH model accounts for the regional heterogeneity in power distribution. The TH model is validated with the existing numerical results to access its capability to simulate the parallel-channel density wave instabilities (DWIs) in a supercritical water (SCW) system. Then, the TH model is used to capture the core-wide as well as regional modes of parallel-channel DWIs in the PV SCWR. The marginal stability thresholds are obtained for both the modes of DWOs and are compared. Subsequently, the aforementioned stability thresholds are compared with those obtained from the single-channel model as well, with the purpose to quantify the diference in stability thresholds obtained from the single- and parallel-channel analysis. Keywords Pressure vessel SCWR  · Core-wide and regional oscillations · Channel-to-channel interactions · Stability thresholds · Efect of parallel channels List of symbols A Area, m 2 a Acoustic speed, m/s c p Specifc heat capacity, J/kg K e Specifc internal energy, J/kg e f Specifc fow energy, J/kg D h Hydraulic diameter, m g Gravitational acceleration, m/s 2 H Height, m h Specifc enthalpy, J/kg k Thermal conductivity, W/mK L Length, m L H Heated length, m N Relative power P Perimeter, m p Pressure, Pa  Q Power, W q  Heat fux, W/m 2 R Total number of radial channels r rth radial channel T Temperature, ◦ C t Time, s u Axial velocity, m/s W Mass fow rate, kg/s z Axial location, m Greek letters  Dirac-delta operator  Dynamic viscosity (Pa s)  Shear stress, N/m 2  Density of a fuid, kg/m 3 Subscripts ex Exit i singular point in Inlet Technical Editor: Erick de Moraes Franklin, Ph.D. * Goutam Dutta goutam.dutta@iitjammu.ac.in 1 Indian Institute of Technology Jammu, Jagti Campus, Nagrota Bypass Road, Jammu, Jammu & Kashmir (UT) 181221, India 2 Indian Institute of Information Technology Design & Manufacturing Jabalpur, Dumna Airport Road, Khamaria, Jabalpur, Madhya Pradesh 482005, India 3 Terna Engineering College, Plot No. 2, Sector 22, Phase 2, Nerul (w), Navi Mumbai, Maharashtra 400706, India