Report on result of special test of Fast Experimental Reactor "JOYO"; Reactor start-up test vithout external neutron source

Sasaki, Makoto

A 3 pcs criterion of the neutron start-up monitor at the reactor start-up is set up in order to protect the reactivity accident at the reactor start-up and confirm the normal motion of the monitor. Fast Experimental Reactor "JOYO" has one external neutron source (Sb-Be) in the core region to meet this criterion. However, the 3 cps criterion is not met after long reactor outage, because the half life time of the external neutron source is about only 2 months. In addition, the external neutron source is irradiated by another reactor before beeing put into use. Therefore, it is very convinient if the reactor can start-up without the external neutron source since in this case various potential troubles are avoided. This report describes the start-up experiment without the external neutron source in "JOYO" MK-I core. The results are as followings: (1)The reactor was able to start-u without the external neutron source. (2)The reactor was start-up due to inner neutron of the driven fuels. (3)The reactor may be able to start-up vithout the external neutron source in "JOYO" MK-II core, too.