Patent ID: 6141397
Filing Date: 2000-10-31
Classification: G21C,Y02E

Abstract:
A core of a boiling water reactor including fuel assemblies each comprising a plurality of fuel rods having a fuel effective length L, at least one water rod, an upper tie plate for holding upper end portions of said fuel rods and said water rod, a lower tie plate including a fuel holding portion to hold lower end portions of said fuel rods and said water rod, and a channel box surrounding an outer periphery of said fuel rods tied up into a bundle; and fuel support pieces for supporting said lower tie plates of said fuel assemblies, wherein:said fuel support piece includes a first coolant passage formed therein and having an orifice with an inner diameter of at least 5.6 cm;said fuel holding portion has a plurality of through holes for introducing a coolant in said lower tie plate to a second coolant passage defined between said fuel rods above said fuel holding portion, a total cross-sectional area S1 of all said through holes being smaller than a total cross-sectional area S2 of said second coolant passage;said water rod includes a rising passage opened to a space in said lower tie plate below said fuel holding portion and introducing upward the coolant introduced to said rising passage, and a falling passage communicated with said rising passage and introducing downward the coolant introduced through said rising passage, said falling passage having a coolant outlet opened to said second coolant passage above said fuel holding portion;the relationship of 0.2.ltoreq.r.ltoreq.0.4 holds on an assumption that a ratio S1/S2 of said total cross-sectional area S1 to said total cross-sectional area S2 is r; anda height h from an upper surface of said fuel holding portion to said coolant outlet is set to satisfy at least one of relationship (a), (b) and (c) of:(a) -2.1r.sup.2 +2.2r-0.3.ltoreq.(h/L)<-2.2r.sup.2 +1.8r+0.04;(b) -4.2r.sup.2 +3.4r-0.4.ltoreq.(h/L)<-0.53r.sup.2 +0.5r+0.46; and(c) -4.2r.sup.2 +3.4r-0.4.ltoreq.(h/L)<-2.2r.sup.2 +1.8r+0.04.