Preliminary Analysis of a Fully Ceramic Microencapsulated Fuel Thermal–Mechanical Performance

Abstract

In this paper, a two-dimensional characteristic unit was used to simulate the thermal–mechanical performance of a fully ceramic microencapsulated (FCM) fuel pellet, and the criterion of FCM structure integrity was discussed. FCM structure integrity can be reflected though the integrity of the silicon carbide (SiC) matrix or SiC layers because of the excellent fission retention capability of SiC ceramics. The maximum temperature of the SiC matrix under normal conditions of the pressure water reactor (PWR) environment was about 1390 K, which was lower than the decomposition point of SiC. The maximum hoop stress of the SiC matrix, especially the inner part, was up to about 1200 MPa, and the hoop stress of the non-fuel region part was lower than the inner part, which can be attributed to the deformation of tristructural-isotopic (TRISO) particles. The hoop stress of the SiC layers at the end of life was only about 180 MPa, which is much lower than the strength of the chemical vapor deposition (CVD)-SiC. The failure probability of the SiC layer was lower than 9 × 10−5; thus, the integrity of SiC layers and the fission retention capability were maintained. The structure integrity of FCM fuel was broken because the SiC matrix cracked.

Effect of Structure on the Thermal-Mechanical Performance of Fully Ceramic Microencapsulated Fuel

“…The buffer layer offered the space for accommodating the fission production because of the high porosity of buffer layer. The UN kernel and buffer layer weresubtracted out when simulate the FCM TM pellet behavior because the gap appeared, and no interaction occurred between the buffer layer and the other coated layers [17,18]. Inner and outer PyC layers are designed to provide mechanically pliable layers supporting the SiC micro-pressure vessel [17].…”

“…The UN kernel and buffer layer weresubtracted out when simulate the FCM TM pellet behavior because the gap appeared, and no interaction occurred between the buffer layer and the other coated layers [17,18]. Inner and outer PyC layers are designed to provide mechanically pliable layers supporting the SiC micro-pressure vessel [17]. SiC matrix and layer in TRISO particles are expected to offer improved containment of fission production under accident condition.…”

“…where V is the characteristic volume (m 3 ), m is the Weibull modulus of SiC layer, σ 0 is the characteristic strength (MPa), and σ p is the true stress (MPa). The characteristic strength and the Weibull modulus ofSiC layer were 350MPa and five, respectively [17].…”

“…The thermal conductivity model of SiC layer was expressed [17] as (19) where R 0 and R irr are the thermal resistance (K/W) of the prior-and post-irradiated SiC layer, respectively. The thermal resistance of SiC layer before irradiation is expressed as below [17]:…”

“…The behavior of TRISO particle has been studied vastly and lots of software such as PARFUM, PASTA and STRESS3 has been developed [16]. The performance of TRISO particle can be used as input parameters for the FCMTMsimulation including internal pressure and size deformation [17,18]. The performance of TRISO-based FCMTMfuel in LWR environment was simulated by Schappel and co-workes using BISON [18].…”