Pressurized water reactors containment isolation system

The Emergency Core Cooling System uses high pressure gas to inject ordinary water into the fuel channels, followed by pumped recirculation and cooling of water within the reactor building. The containment system includes the reactor building and the containment isolation system. 

The vacuum line is isolated from the forepump, and a liquid-nitrogen bath is put around trap D. The fluorine metering system is partially evacuated with the water aspirator, as discussed above. Then the vacuum line is completely evacuated with the forepump. Fluorine is allowed to expand slowly into the metal system by means of the needle valve 3. As the pressure increases above atmospheric, some fluorine is allowed to bleed into the vacuum line and storage bulbs until a pressure of 650-700 mm. is reached. First needle valve 1 on the metal system and then the fluorine control valve 3 are quickly closed. (Some fluorine may escape from the blowout manometer during this operation.) Approximately a 10% excess of fluorine (0.023 mole in this case) is condensed into the metal pressure reactor containing the thionyl fluoride. The amount of fluorine used is measured by the pressure drop in a calibrated volume in the pressure range of approximately 700-400 mm., since fluorine has a vapor pressure of approximately 400 mm. at —196°. 

The hydrogen gas from the chemical reaction increases the pressure within the vessel. When the pressure within the SG reaches a predetermined higher level, the rupture disks burst and the sodium within the SG drains rapidly into a sodium dump tank. For such large sodium/water reaction events, it is also necessary to seal off the reactor/SG system for the purpose of containment isolation. An SG isolation system (SGIS) is provided to terminate a sodium/water reaction (by rapidly removing the water from the SG) and to isolate the water side with safety-related isolation valves which serve a safety-grade barrier for the purpose of containment isolation. 

The letdown flow outside containment isolation valve is a normally closed, fail closed, air-operated globe valve that isolates letdown to the liquid radwaste system. This valve automatically opens and closes on a plant control system signal from the pressuriser level control system or a containment isolation signal from the protection and safety monitoring system. Ibis valve operates in the same fashion as the letdown flow inside containment isolation valve. The letdown flow outside containment isolation valve eloses more quickly than inside containment letdown flow isolation valve to limit seat wear of inside containment isolation valve. This valve operator has a flow restricting orifice in the air line, so it opens more slowly than inside containment letdown flow isolation valve. In addition, during brief periods of shutdown, when the reactor coolant system is water solid, this valve throttles to maintain the reactor coolant system pressure. Manual control is also provided in the main control room and at the remote shutdown workstation. 

Figure 16.1 Schematic of economic simplified boiling water reactor with many different cooling systems (Saha et al., 2013). DPV, Depressurization Valve IC, Isolation Condenser SRV, Safety Relief Valve PCC, Passive Containment Cooling RPV, Reactor Pressure Vessel BiMAC, Basemat Internal Melt Arrest and Coolability (Device)...

Nuclear Boiler Assembly. This assembly consists of the equipment and instrumentation necessary to produce, contain, and control the steam required by the turbine-generator. The principal components of the nuclear boiler are (1) reactor vessel and internals—reactor pressure vessel, jet pumps for reactor water circulation, steam separators and dryers, and core support structure (2) reactor water recirculation system—pumps, valves, and piping used in providing and controlling core flow (3) main steam lines—main steam safety and relief valves, piping, and pipe supports from reactor pressure vessel up to and including the isolation valves outside of the primary containment barrier (4) control rod drive system—control rods, control rod drive mechanisms and hydraulic system for insertion and withdrawal of the control rods and (5) nuclear fuel and in-core instrumentation,... 

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