Heat transport auxiliary systems

During normal operation, the main circulator transports hot helium at 1266°F (686°C) from the bottom of the core to the steam generator which, in turn, produces superheated steam at I005°F (541 °C) and 2500 psia. The cold helium at 496°F (258°C) is returned to the top of the reactor core. During normal shutdown and refueling, the non-safety auxiliary shutdown heat removal system removes core afterheat if the main heat transport system is not operational. 

A scheme of the 4S-LMR main heat transport system with the indication of heat removal path in normal operation and in accidents is given in Fig. XV-11. The reactor incorporates redundant passive decay heat removal systems. Specifically, a reactor vessel auxiliary cooling system (RVACS) is adopted in which the natural convection airflow removes the decay heat radiated through the guard vessel. The heat removal capability depends on the thermal radiation area. A specific (per thermal power) heat radiation area of small reactors is larger than that of medium sized or large reactors. It is expected that about 1% of the nominal power could be removed with the RVACS. 

The rated thermal output of MONJU [5.63, 5.64] is transported through the primary heat transport system (PHTS) and intermediate heat transport system (IHTS) loops to the steam generators. Shutdown heat removal is normally by forced circulation (FC) provided by pony motors associated with each of the loop pumps. Heat is rejected to air at the air blast heat exchanger of the intermediate reactor auxiliary cooling system (ACS) which branches off from each IHTS loop. Thus the auxiliary cooling system (ACS) of the Monju reactor is coupled with the secondary system which also has the role as decay heat removal system. 

SOFC technology, on the other hand, offers interesting options to improve the effectiveness of CHP units. The reasons are many the prospects for high efficiency, low emissions, low noise, scalability, reliabihty, and, finally, potentially low cost. However, the main attractiveness in CHP is the high system efficiency even for small units and at part load operation [14]. Among the most interesting applications are stationary distributed power generation (incl. CHP), small residential combined heat and power units (micro CHP), various transport apphcations (auxiliary power units, APU), and medium-sized portable systems up to 5 kWei-... 

Results from MELCOR (Version 1.8.0) calculations of three accident sequences in a W-PWR 900 Mwe three loop plant are presented. The scenarios considered include an AB sequence and two V type events a rupture of the Low Pressure Coolant Injection System in the auxiliary building, and the rupture of ten steam generator tubes in all cases without the intervention of the active emergency core cooling systems. Emphasis is put on the release and transport of core materials. It has been found that deposition of vapors from the most volatile species is high within the core structures. Later in the accident, revaporization induced by decay heat takes place, at times in coincidence with the production of steam due to core slumping, what may change the nature and composition of source terms. 

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