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Introduction
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The |SAS| computer code is developed by Argonne National
Laboratory for thermal, hydraulic, and neutronic analysis of power and
flow transients in liquid-metal-cooled nuclear reactors (LMRs). SAS4A
was developed to analyze severe core disruption accidents with coolant
boiling and fuel melting and relocation, initiated by a very low
probability coincidence of an accident precursor and failure of one or
more safety systems. SASSYS‑1, originally developed to address
loss-of-decay-heat-removal accidents, has evolved into a tool for margin
assessment in design basis accident (DBA) analysis and for consequence
assessment in beyond-design-basis accident (BDBA) analysis.

SAS4A contains detailed, mechanistic models of transient thermal,
hydraulic, neutronic, and mechanical phenomena to describe the response
of the reactor core, its coolant, fuel elements, and structural members
to accident conditions. The core channel models in SAS4A provide the
capability to analyze the initial phase of core disruptive accidents,
through coolant heat-up and boiling, fuel element failure, and fuel
melting and relocation. Originally developed to analyze oxide fuel clad
with stainless steel, the models in SAS4A have been extended and
specialized to metallic fuel with advanced alloy cladding.

SASSYS‑1 provides the capability to perform a detailed thermal/hydraulic
simulation of the primary and secondary sodium coolant circuits and the
balance-of-plant steam/water circuit. These sodium and steam circuit
models include component models for heat exchangers, pumps, valves,
turbines, and condensers, and thermal/hydraulic models of pipes and
plena. SASSYS‑1 also contains a plant protection and control system
modeling capability, which provides digital representations of reactor,
pump, and valve controllers and their response to input signal changes.

.. toctree::
	:maxdepth: 2

	background
	version5
	doc_overview
	references