Comprehensive and consistent interpretation of local fault experiments and application to hypothetical local overpower accident in Monju

Abstract

Experimental studies on local fault (LF) accidents in fast breeder reactors have been performed in many countries because LFs have been historically considered as one of the possible causes of severe accidents. Comprehensive and consistent interpretations of in-pile and out-of-pile experiments related to LF were arrived at in this study based on state-of-the-art review and data analysis techniques. Safety margins for a hypothetical local overpower accident, which was evaluated as a LF accident in the licensing document of the construction permit for a prototype fast breeder reactor called Monju, were also studied. Based on comprehensive interpretations of the latest experimental database, including those performed after the permission of Monju construction, it was clarified that the evaluation of the hypothetical local overpower accident in the Monju licensing was sufficiently conservative. Furthermore, it incorporated adequate safety margins in terms of failure thresholds of the fuel pin, molten fuel ejection, fuel sweep-out behavior after molten fuel ejection, and pin-to-pin failure propagation. Moreover, these comprehensive interpretations are valid and applicable to the safety evaluation of LF accidents of other fast breeder reactors with various fuel and core designs.

Feasibility study mixed oxide fuel tests in the impulse graphite reactor

“…In the safety analysis of fast sodium reactors, local destruction of fuel elements are considered as possible initiating events for severe accidents [1]. The destruction (cracking) of the fuel at nominal operating conditions occurs due to thermal stresses and gas swelling as one of the significant burnout effects.…”

“…Local destruction of fuel can cause destruction of neighboring fuel elements if conditions for their cooling are violated. One of the reasons for the deterioration of the cooling conditions for fuel elements is a blockage of the flow area of the coolant caused by the release of fuel outside the fuel elements in case of overheating [1]. Such a situation may arise as a result of errors in loading fuel elements with fuel pellets with a higher than required content of fissile isotopes.…”

Updating of adventitious fuel pin failure frequency in sodium-cooled fast reactors and probabilistic risk assessment on consequent severe accident in Monju

“…Fuel-element-failure-propagation (FEFP) was considered to be of greater importance in safety evaluation of SFRs because fuel elements are generally densely arranged in the fuel subassemblies (FSAs) in this type of reactors and power densities are higher compared with those in light water reactors (LWRs) [1]. Therefore, probabilistic risk assessments (PRAs) [2][3][4], deterministic safety analyses and experimental studies on LF accidents have been performed in many countries historically.…”

Validation study of SAS4A code for the unprotected loss-of-flow accident in an SFR

“…designed to precisely model the IP event progressions and was developed by the experimental knowledge obtained from various in-pile experiments in the French CABRI (Heusener et al, 1990;Haessler et al, 1990;Sato et al, 2004;Fukano et al, 2009;Fukano et al, 2010) and U.S. TREAT (Wright et al, 1990;Fukano, 2013) reactors. This paper describes the study on the validation methods and the results of the validation in a typical SFR in order to improve the reliability of SAS4A.…”