An improved critical power correlation for tight-lattice rod bundles

Developing critical power correlation is indispensable for R&D of Innovative Water Reactor for Flexible Fuel Cycle, which adopts a triangular tight-lattice fuel rod configuration and axially double-humped heated profile. In this research, the critical power correlation for tight-lattice rod bundles is improved by using two sets of different tightness 37-rod bundle data derived at Japan Atomic Energy Agency (JAEA), with an aim to predict critical power in different tightness bundles with high accuracy. Deduction for the correlation forms of critical heat flux - critical quality type for spot dryout mechanism and critical quality - annular flow length type for complete dryout one is given out. To account for the changed transverse power peaking effect when the peaking location changes, power peaking on non-peripheral rods, LPF1, is introduced in the development of the critical power correlation. The standard deviation of Experimental Critical Power Ratio to JAEA data is 3.24%. To Bettis Atomic Power Laboratory data, this value is 9.2%. The applicable range of the correlation is: rod number 20 or 37, gap width between rods from 1.0 to 2.29 mm, mass velocity from 150 to 1,500 kg/m(2)s, pressure from 2 to 11 MPa, inlet subcooling from 50 to 1 K, and transverse power peaking from 1 to 1.1.