A numerical investigation of nuclear coupled density wave oscillations

Space and temporal evolution of density wave oscillations in multi-phase flow channels of boiling water reactors

“…1) It is assumed that the pressure at the upper plenum is known and is constant along time. This is a consequence of the assumption that there is not accumulation of steam and water in the upper plenum (UP) and this condition lead, as proved by Prassad et al [2], to constant pressure in the upper plenum. March-Leuba [1] also considered this same boundary condition, but they assume that the UP pressure is mantained constant by the pressure regulator.…”

“…The problem of two phase flow instabilities it is found in a big variety of energy and chemical engineering systems such as the channels of Boiling Water Reactors (BWR), conventional steam boilers, and phase change heat exchangers used in the chemical industry. Among the different instability types the most important for the nuclear engineering field is the density wave oscillation mechanism (DWO), which is due to a multiple regenerative feedback between the mass flow rate, the steam generation rate, and the pressure drop [1,2]. This phenomenon is especially interesting in BWR because there is a coupling via the void and Doppler reactivity feedbacks between the void fraction, and the fuel temperature with the core power.…”

Simulating investigations on the start-up of the open natural circulation system

“…Increasing the inlet subcooling can make the system more stable at the medium and high subcoolings but more unstable at the small subcoolings (Boure et al, 1973). Prasad et al (1995) considered that increasing the exit resistance can reduce the stability region of the system, but increasing the inlet resistance will make the system more stable. van Bragt and van der Hagen (1998) found that increasing the riser length will destabilize the system in Type-I region and stabilize the system in Type-II region.…”

Heat transfer, flow regime and instability of a nano- and micro-porous structure evaporator in a two-phase thermosyphon loop

“…Prasad et al [22] developed a numerical model of boiling-water reactor for simulation of instabilities and found that increasing the mass flow rate or decreasing the power input does not necessarily stabilize the boiling at low Froud number.…”

“…Aritomi et al [20] and Chiang et al [21] described three types of instabilities, geysering, natural circulation oscillations and density wave oscillations. Prasad et al [22] classified the instabilities in two-phase flow with natural circulation as dynamic and static. Static instabilities referred to steady state characteristics of the system like boiling crises, flow pattern transition and excursion, whereas the dynamic stabilities were caused by feedback mechanisms such as density wave oscillations which were generated when the flow rate, vapor generation rate and pressure drop in boiling channel interact at a specific condition.…”