A preliminary evaluation of unprotected loss-of-flow accident for a prototype fast-breeder reactor

Abstract

Core disruptive accident (CDA) In-vessel retention (IVR) Sodium-cooled fast reactor (SFR) Unprotected loss of flow (ULOF) SAS4A SIMMER-III/IV a b s t r a c t In the original licensing application for the prototype fast-breeder reactor, MONJU, the event progression during an unprotected loss of flow (ULOF), which is one of the technically inconceivable events postulated beyond design basis, was evaluated. Through this evaluation, it was confirmed that radiological consequences could be suitably limited even if mechanical energy was released. Following the Fukushima-Daiichi accident, a new nuclear safety regulation has become effective in Japan. The conformity of MONJU to this new regulation should hence be investigated. The objectives of the present study are to conduct a preliminary evaluation of ULOF for MONJU, reflecting the knowledge obtained after the original licensing application through CABRI experiments and EAGLE projects, and to gain the prospect of in-vessel retention for the conformity of MONJU to the new regulation. The preliminary evaluation in the present study showed that no significant mechanical energy release would take place, and that thermal failure of the reactor vessel could be avoided by the stable cooling of disrupted-core materials. This result suggests that the prospect of invessel retention against ULOF, which lies within the bounds of the original licensing evaluation and conforms to the new nuclear safety regulation, will be gained.

Preliminary analysis of the post-disassembly expansion phase and structural response under unprotected loss of flow accident in prototype sodium cooled fast reactor

“…3. The calculation geometry of the reactor core is the same as that adopted in the transition phase analysis (Suzuki et al, 2015), where subassemblies of reactor core, radial blanket and neutron shielding were modeled as independent channels (region 1, 2, 3 and 11 of Fig. 3).…”

“…Material distribution as well as temperature distribution in the core region is given by the result of transition phase analysis (Suzuki et al, 2015). The axial and radial power distribution and power history are also given by the transition phase analysis.…”

“…30MJ: evaluation for MONJU with reasonable conservativeness based on up-to-date experimental knowledge and analytical method (Suzuki et al, 2015). 500MJ: a hypothetical bounding case for safety assessment.…”

“…Recent evaluation of ULOF sequences performed in JAEA , (Suzuki et al, 2015) using up-to-date analytical tools revealed that the existence of many inherent mechanisms mitigating the positive reactivity insertion prevented the mechanical energy release due to power excursion in the initiating phase, even though the uncertainties of these mechanisms were considered conservatively. In contrast to the initiating phase, if the conservative assumption such that suppression of molten fuel discharge from disrupted core through control rod guide Onoda, Matsuba, Tobita and Suzuki, Mechanical Engineering Journal, Vol.4, No.3 (2017) [DOI: 10.1299/mej.…”

“…In the new regulatory requirements, measures against severe accidents and the evaluation of their effectiveness are required. In accordance with the requirements, a preliminary evaluation against ULOF was conducted for MONJU in JAEA (Suzuki et al, 2015) reflecting the latest knowledge. In this evaluation, the newly obtained knowledge and improvements of analysis tools fairly reduced the energy production during the neutronic power excursion compared to that estimated in the first licensing.…”