Passive Safety of the STAR-LM HLMC Natural Convection Reactor

Abstract

The STAR-LM 300 to 400 MWt class modular, factory fabricated, fully transportable, proliferation resistant, autonomous, reactor system achieves passive safety by taking advantage of the intrinsic benefits of inert lead-bismuth eutectic heavy liquid metal coolant, 100+% natural circulation heat transport, a fast neutron spectrum core utilizing high thermal conductivity transuranic nitride fuel, redundant passive air cooling of the outside of the guard/containment vessel driven by natural circulation, and seismic isolation where required by site conditions. Postulated loss-of-heat sink without scram, overcooling without scram, and unprotected transient overpower accidents are analyzed for the 300 MWt STAR-LM design using a coupled thermal hydraulics-neutron kinetics plant dynamics analysis computer code. In all cases, STAR-LM is calculated to exhibit passive safety with peak cladding and coolant temperatures remaining within the existing database for lead-bismuth eutectic coolant and ferritic steel core materials.

Development of a plant dynamics computer code for analysis of a supercritical carbon dioxide Brayton cycle energy converter coupled to a natural circulation lead-cooled fast reactor.

“…( ) (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) Second, it is assumed that the change in the outlet temperature is equal to the change in average temperature: Equation (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) is the equation for coolant temperature in the core as it is programmed in the code 1 . The coefficients for each term are calculated at the beginning of the time step at the average coolant and cladding temperatures.…”

“…To account for this fact, the coolant mass is recalculated at the beginning of each time step, but still is assumed constant during the time step in accordance with Equation (2-3). The total heat flux between cladding and coolant can be expressed in terms of the temperature difference between the coolant balk temperature and average cladding temperature divided by the thermal resistance of coolant and cladding: Note that Equation (2)(3)(4)(5)(6) assumes that the average cladding temperature occurs midway through the cladding thickness, such that half of the total cladding thermal resistance is added to the coolant thermal resistance.…”

“…Introducing the following notation for the coolant and cladding thermal resistances and the resistance between the coolant bulk temperature and average cladding temperature, the heat flux between the coolant and cladding could be re-written as shown in Equation (2)(3)(4)(5)(6)(7)(8)(9)(10). In order to write Equation (2)(3)(4)(5) in same variables (temperatures), the change in specific enthalpy can be expressed through the change in temperature: Also, in order to simplify Equation (2)(3)(4)(5), two assumptions are made.…”

“…In order to write Equation (2)(3)(4)(5) in same variables (temperatures), the change in specific enthalpy can be expressed through the change in temperature: Also, in order to simplify Equation (2)(3)(4)(5), two assumptions are made. First, it is assumed that the difference between the inlet and outlet enthalpies is equal to the difference in temperature times the specific heat calculated at the average temperature, i.e., the variation of the specific heat along the region is ignored:…”

“…Equation (2-1) applied to stationary core structures has the following forms for cladding, bond, and fuel, respectively: The fission and decay heat power, Q fis , in Equation (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) is calculated using the current value of the reactor power (see Section 4) assuming that the axial power distribution is the same as at steady-state (i.e., only the magnitude changes): Again, the coefficients in Equations (2-25)- are calculated at the beginning of the time step and are assumed to be constant during the time step.…”