Title: AEROSOL MODELING OF HYPOTHETICAL LMFBR ACCIDENTS.

The expansion characteristics of the detonation products of a high-explosive energy source used to simulate the pressure-volume change relationships for sodium-vapor expansions during hypothetical core disruptive accidents in a Fast Test Reactor were determined experimentally. Rigid cylinder-piston experiments performed at two scales (ratio 1:3) were undertaken to determine a pressure-volume relationship as a function of source mass and expansion environment. Some of these measurements were compared with code calculations for the source.

Six experiments were performed to evaluate the structural response of an above core structure (ACS) to increasingly energetic hypothetical core disruptive accidents (HCDA). The tests were performed in a thickwall 1/20-scale model of a liquid metal fast breeder reactor (LMFBR) demonstration plant to provide information on ACS displacement as a function of HCDA energy so that computer codes such as SIMMER might include ACS displacement when calculating core release energetics. The 1/20-scale ACS models include a 5-kg aluminum block with dimensions that simulate the overall geometry of the ACS and the four columns that support the ACS over the coremore » of the reactor. Each column includes an 8-in-long, 0.7-in-diameter 0.050-in-wall Ni 200 tubular section that experiences all of the deformation upon HCDA loading. The columns are supported by a rigid structure that simulates the geometrical constraints provided by the cover of the reactor.« less

Analyses have been performed to evaluate the effect of certain engineered safety features on reducing the risk of hypothetical core disruptive accidents in LMFBRs. Consideration has been limited to accidents which are assumed to result in the core meltthrough of the reactor vessel. The consequences of such accidents have been compared for two principal plant designs: one which does not include any specific provisions to accommodate such an accident, and the other which includes an ex-vessel core catcher and a reactor cavity liner system (hot liner). The general characteristics of the plant design which was studied are representative of amore » small demonstration plant similar to the FFTF. The approach to risk analysis which is based on the development of accident event trees that was used in this study is essentially the same as that used in the Reactor Safety Study (WASH-1400). The scope of the present study was quite restricted, however; the evaluation of the likelihood of an accident that could result in the meltthrough of the primary system was not undertaken. Thus, insight into the potential risk was obtained only on a relative basis. The consequences of the various accident sequences considered were evaluated in terms of the fraction of the reactor inventory of radioactive materials released to the environment as a function of time.« less

This article discusses salient aspects of severe-accident-related recriticality modeling and analysis in the Advanced Neutron Source (ANS) reactor. The development of an analytical capability that uses the KENO5A-SCALE system is described, including evaluation of suitable nuclear cross-section sets to account for the effects of system geometry, mixture temperature, material dispersion, and other thermal-hydraulic conditions. Benchmarking and validation efforts conducted with KENO5-SCALE and other neutronic codes and compared with critical experiment data are described. Potential deviations and biases resulting from the use of the 16-group Hansen-Roach library are shown. A comprehensive test matrix of calculations to determine the reactivity of variousmore » hypothetical configurations that might arise, along with the effects of various parameters on that reactivity, is described. Strong dependencies on geometry, material constituents, and thermal-hydraulic conditions are also discussed as well as the introduction of designed mitigative features.« less