A. Inoue et al., VOID FRACTION DISTRIBUTION IN BWR FUEL ASSEMBLY AND EVALUATION OF SUBCHANNEL CODE, Journal of Nuclear Science and Technology, 32(7), 1995, pp. 629-640
Void fraction measurement tests for BWR fuel assemblies have been cond
ucted as part of a Japanese national project. The aim was to verify th
e current BWR void fraction prediction method. Void fraction was measu
red using an X-ray CT scanner. This paper describes typical results of
void fraction distribution measurements and compares subchannel-avera
ged void fraction data with current subchannel analysis codes. The sub
channel analysis codes COBRA/BWR and THERMIT-2 were used in this compa
rison. The agreement between data for an actual BWR fuel assembly with
two unheated rods was good, but in the case of many unheated rods, th
e codes were unable to predict well large void fraction gradient in th
e radial direction observed in the measured data over the unheated rod
region. The prediction errors of COBRA/BWR and THERMIT-2 for the subc
hannel-averaged void fraction were [A] (average of difference between
measurement and calculation)=-1.1%, sigma(standard deviation)=5.3% and
[A]=-2.2%, sigma= 6.3%, respectively.