Thermal-hydraulic tests with out-of pile test facility for BOCA development

Kitagishi, Shigeru  ; Aoyama, Masashi; Tobita, Masahiro; Inaba, Yoshitomo  ; Yamaura, Takayuki 

For the up-graded use and the lifetime extension of LWRs, the JMTR has a plan of power ramping tests on new design LWR fuels. The purpose of the power ramping tests is to evaluate the fuel behavior during power ramping condition using a capsule inserted into the OSF-1. The design and fabrication of the natural convection capsule used in the power ramping tests has been carried out based on BOCA, which had experience on power ramping tests of 88 BWR fuels. The outer cladding diameter of 88 BWR fuels is 12 mm. On the other hand, for a high power, the outer cladding diameter of the new design LWR fuel is changed to 9.5 mm. And, there is potential for transition from nucleate boiling to film boiling because the heat flux of the peak linear power 600 W/cm in the tests approaches the critical heat flux. In this study, prior to the irradiation tests of the fuels, the out-of pile test facility, which had a heater pin instead of a test fuel pin, was designed and fabricated to simulate the capsules used in power ramping tests, and thermal-hydraulic tests were carried out using the out-of pile test facility. In addition, in order to investigate the thermal-hydraulic behavior in the capsule, the out-of pile tests were simulated numerically using the improved analysis code ACE-3D. From these experimental and analytical results, it was found that the power ramping tests with fuels with their outer cladding diameters of 9.5 mm are able to be realized up to linear power 600 W/cm in JMTR.