Publications

Assessment of Silicon Carbide Cladding for High Performance Light Water Reactors

MIT-NFC-TR-098 (November 2007)

Abstract

A proposal for using silicon carbide duplex as fuel cladding in light water reactors is investigated. The cladding consists of a monolithic inner layer surrounded by a tightly wound fiber-matrix composite. The monolithic layer retains the volatile fission products while the composite adds strength.

Empirical models were developed to describe the physical properties of the composite as a function of operating temperature and neutron fluence. The FRAPCON steady-state thermo-mechanical fuel rod modeling code was used to examine the performance of SiC cladding at high fuel burnup and high power density. A comparison of the behavior of the SiC cladding to the conventional zircaloy cladding demonstrated that the SiC has superior resistance to creep and mechanical degradation due to radiation or oxidation. However, the lower thermal conductivity of the SiC is an issue, which resulted in significantly increased peak fuel temperatures. Mixed UO2-PuO2 fuel was also examined in place of traditional UO2 pellets, since this may better resemble transmutation fuels of the future. It was found that the use of plutonium-bearing mixed-oxide fuels further exacerbates the high fuel temperatures.

The performance of SiC cladding was also investigated under reactor transient conditions and compared to the existing regulatory limits for zircaloy cladding. Both the Loss of Flow Accident (LOFA) and the Large-Break Loss of Cooling Accident (LBLOCA) were studied using the RELAP thermal-hydraulics code. During LOFA SiC cladding was found to have a lower, but still acceptable, minimum departure from nucleate boiling ratio. For the LBLOCA, the peak SiC cladding temperature remains lower than the regulatory limit between initiation of the break and establishment of stable safety injection coolant flow.