Theoretical study of flashing and water hammer in a supercritical water cycle during pressure drop

Physical-chemical Background of the Potential Phase Transitions during Loss of Coolant Accidents in the Supercritical Water Loops of Various Generation IV Nuclear Reactor Types

“…For the expansion calculations, existing designs are replaced with a simplified supercritical loop [6]. The pressure of the fluid is always considered constant (24.5 MPa or 25 MPa), while the temperature changes between maximal and minimal working temperatures of the actual designs (see Table 1).…”

“…For supercritical water used as working / moderator fluid for reactors, one of the advantage -compared to pressurized water -that under normal conditions, phase transitions can be avoided. It has already been shown that although it is true for normal conditions, by accidents causing pressure loss, sudden phase transitions like flash boiling or steam collapse can be induced [6]. This differs from the pressurized water case, where only flash boiling can be caused directly by these kinds of accidents.…”

“…there is no separate liquid and steam, at least not in normal working conditions. But as it has already been discussed [6], during accidents associated with fast pressure drop, phase transitions might happen even in supercritical loops. While in pressurized water reactors (PWR), accidents with pressure drops can cause only fast liquid-to-vapour phase transition (flashing), in SCWRs the reverse might be also possible (fast vapourto-liquid transition).…”

“…An additional and quite important approximation for the calculations is the use of a simple supercritical loop, instead of the real reactor design [6]. The working pressure and the maximal / minimal working temperatures used in the calculations match the values used in various real designs (see Table 1, data are taken from various references [10][11][12][13][14]), while internal pressure is always taken as atmospheric (0.1 MPa).…”

Condensed Matters Under Negative Pressure

“…Moreover, there are several natural or industrial examples where the negative pressure plays important role (from flash boiling during loss of coolant accidents in nuclear power plants through the eruption of mud volcanoes to the transport of sap in trees) [4,9].…”