An Analysis of Transient Behavior of a Metallic Fuel FBR during Initiating Phase of Core Disruptive Accident

Abstract

The transient behavior during an initiating phase of CDA (core disruptive accident), was analyzed for a metallic fuel reactor, which is expected to realize high breeding ratio and low fuel cycle cost. In the present study, SAS3D code was modified for applying to the metallic fuel reactor. Unique phenomena of the metallic fuel reactor such as eutectic formation were modeled and material properties of the metallic fuel were installed. Assuming flow decay half-time of 5 s, the ULOF (unprotected loss of flow) transient was analyzed for a 1,600 MW thermal power, pool-type fast reactor at the beginning of cycle. During the transient, the fuel melting and the eutectic formation quickly occurred after the coolant voiding, then, the fuel pin failed. The molten fuel was released into the coolant channel and was dispersed outside the core. Therefore, the reactor did not reach prompt-criticality. The peak power was only two times of the initial reactor power and the pin failure region was about half of the inner core. These results were largely smaller than those of a similar MOX fuel reactor. By the present study, it was found for a metallic fuel reactor that the ULOF transient quickly proceeds after the coolant boiling and becomes very mild.