Reactor vessel air cooling system

Fissile element enrichment is 90%. Updating of the reactor took place from 1971 to 1973 and from 1979 to 1983. The first redesign completed in 1973 envisaged increase of the reactor power up to 10 MW, and so it was titled BR-10. However, because of some problems related to reactor vessel air cooling system reactor power was limited to 8 MW level. 

There are no special decay heat removal systems other than a reactor vessel air-cooling system (RVACS) that uses natural air draft for the heat sink ... 

Reactor is very simple and robust. It has small number of components. There are no moving components except for the control (6 pieces) and safety (1 piece) element drives these drives need to be actuated only seldom. The only special safety system is the Reactor Vessel Air Cooling System (RVACS) this system is passive. 

The passive safety grade decay heat removal system is the reactor vessel air cooling system (RVACS). The steam generators (immersed in the secondary coolant pool) provide another heat rejection path for decay heat removal. 

To summarize, the asymptotic (bounding event) analyses performed have shown all bounding cases of ATWS initiators originating from a BOP disruption to be passively accommodated within safe asymptotic temperature conditions. Decay heat removal was assumed to rely on passive reactor vessel air cooling system (RVACS). Both, the innate thermo-structural reactivity feedbacks and the innate decay heat removal pathway to ambient could be non-intrusively monitored to assure their continued capability to provide safe response. Thus, no matter what happens in the BOP, the reactor might self adjust itself to a safe asymptotic... 

The design incorporates the guard vessel, which is being cooled from outside by the passive reactor vessel air cooling system (RVACS), based on natural convection of atmospheric air. 

Figure 14.21 Overall view structure design for the China LEad-Alloy—cooled Reactor-1. RVACS, reactor vessel air cooling system.

Two independent water-cooled secondary cooling systems are designed Air is used as the final heat sink by water/air heat exchangers. CLEAR-I incorporates a reactor vessel air cooling system to remove the decay heat in case the normal heat removal path is unavailable. 

AT.MR primary sodium and reactor vessel auxiliary cooling system (RVACS) air flow circuit using for heat removal. 

For heat removal from a shutdown reactor, two independent passive systems are provided, which are the reactor vessel auxiliary cooling system (RVACS) and the intermediate reactor auxiliary cooling system (IRACS). The RVACS is completely passive and removes shutdown heat from the surfaces of the guard vessel using natural circulation of air. There is no valve, vane, or damper in the flow path of the air therefore, the RVACS is always in operation, even when the reactor operates at rated power. Two stacks are provided to obtain a sufficient draft. 

The reactor vessel auxiliary cooling system (RVACS) is a system for shutdown heat removal however, to keep the fully passive features, it is continuously operating even at normal operation of the reactor. The intermediate reactor auxiliary cooling system (IRACS) is a sodium loop with an air cooler for shutdown heat removal, arranged in series with the secondary sodium loop (Fig. XIV-2). 

For all designs, active systems include a reactivity control and shutdown system based on the mechanical control rods. All designs incorporate passive air-cooled reactor vessel auxiliary cooling systems (RVACSs) or equivalents. Natural circulation based passive decay heat... 

Specifically, a reactor vessel auxiliary cooling system (RVACS) is adopted that can remove 100% of the decay heat passively, even in total loss of the normal heat sink. In the RVACS, heat generated in the core is conveyed to the reactor vessel by natural circulation of the primary coolant, is conducted across the vessel and the guard vessel and is finally transferred to the atmospheric air naturally flowing on the outer surface of the guard vessel. 

The natural air cooling system in the reactor vessel is designed so that it is capable of removing decay heat without operation of the Primary Reactor Auxiliary Cooling System (PRACS). 

Following an accident such as a loss of heat sink without scram in which the reactor power has passively decreased to a low level of afterheat typical of decay heat levels, it may be enough to simply return to power. Or it may only be required for an operator to ultimately insert the shutdown rod(s) to terminate possible fission power at low afterheat levels and render the core subcritical i.e. to ultimately shut down the reactor neutronically. Until this action is taken, the reactor would continue to generate power at a low level that is removed by the guard vessel natural convection air-cooling system and transported to the inexhaustible atmosphere heat sink. 

The reactor vessel is cooled and thermally stabilized by "cold" sodium flow supplied from the core diagrid through the gap formed by the reactor vessel and a special baffle. A closed nitrogen cooling system is provided to assure the necessary temperature conditions in the upper-support roof items (Fig. 9.20). In case of a plant black-out it is possible to cool the reactor roof by air under natural convection. 

The reactor is now cooled with liquid nitrogen and the entire system evacuated to about 0.1 mm. The cold bath is removed and the second flask (at the manifold) is cooled within a few minutes, CI3 and CIO3 distill with foaming. To remove these gases completely, the vessel is immersed in a bath at + 20°C for one half hour and vacuum is applied. As soon as no further volatiles distill, the bath temperature is raised to about 35-36°C. The Cr03(Cl04)3 now distills into the manifold and flows into the first ampoule (transparent red liquid). The manifold with the ampoules should be somewhat inclined. When sufficient compound has collected in the first ampoule, the latter is sealed off. Additional distilled product collects in the stub left from the first ampoule, and is driven into the next ampoule by heating with a hot-air blower. 

Each well extends vertically upward from the accessible area beneath the reactor vessel to the opposite of the upper portion of the reactor core. The wells are located in the inlet air stream of the Reactor Cavity Cooling System (RCCS) to assure that the neutron detectors are not exposed to undesirable temperature transients. The atmosphere in the wells is air at ambient pressure. 

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