Steam suppression pools

Partiele fluxes to the bubble walls can be resisted by the evaporation of water vapour into the bubble as it rises through the pool and loses hydrostatie head. This resistance by evaporation becomes more signifieant as the pool temperature increases toward saturation. Circulation of gases within a rising bubble that leads to inertial impaction of particles can be damped by accumulation of surface-active impurities on the bubble surface. 

Aerosol removal from bubbles is very dependent on bubble size. Removal is more efficient from smaller bubbles. Fortunately, bubbles rising in a suppression pool disintegrate to a eommon size of about 0.5 cm regardless of how they are injected into the pool [A-9]. 

Aerosol removal processes that oceur when a bubble rises through a suppression pool vary in efficiency with particle size. As with sprays, very fine and very large particles are efficiently removed. There is a partiele size that is minimally affeeted by the deeontamination processes. Aerosols that emerge from a suppression pool have sizes narrowly distributed around the minimally affected particle size (also called the maximum penetration size). These residual aerosols also resist removal by many other deeontamination proeesses so they can be quite persistent in the atmosphere. 

Aerosols are removed during the proeess of formation of bubbles in the suppression pool as well as during bubble rise through the pool. Partieles in the gas jet that forms the bubble can impact the developing bubble wall or diffuse to the bubble surface. Recent analyses suggest that particle removal during bubble formation may be comparable with particle removal during bubble rise [A-9]. 

Aerosol removal by suppression pools has reeeived quite a lot of experimental and analytical attention. Computer models of the removal proeess inelude the SPARC model [A-lOa], the BUSCA model [A-10b], and the proprietary model SUPRA [A-lOe]. Exeellent experimental studies have been eondueted [A-11] and additional studies are underway in Europe and Japan [A-9a, b]. 

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Flooded release pathways created by coolant addition were responsible for the relatively modest radionuclide releases to the containment during the Three Mile Island accident. Gas flows through flooded pathways are broken into bubbles. Radioactive vapours and aerosols are removed from the bubbles by processes that are quite like those that occur in steam suppression pools. These removal processes are also discussed in Chapter V. 

A-8a. K. Fischer and W. Hafher, Retention of Aerosols in Water Pools, BF-V38.070-01, Battelle Engineering Corp., Frankfurt am Main, Germany, March 1994, and A-8b. D.A. Powers, A Simplified Model of Decontamination by BWR Steam Suppression Pools,... 

Experimental programs that are intended to validate the models of aerosol removal by steam suppression pools and other water pools. 

General In comparison with design information on blowdown drums and cyclone separators, there is very httle information in the open technical hterature on the design of quench tanks in the Chernies industry. What is available deSs with the design of quench tanks (Sso called suppression pools) for condensation of steam or steam-water mixtures from nuclear reactor safety vSves. Information and criteria from quench tanks in the nuclear industry can be used for the design of quench tanks in the chemicS industry. There have been sev-... 

Below the Chernobyl reactor were water pools meant to capture and condense any steam released from a pipe break or any other failure in the containment rooms. A system of relief valves and ducts led from the containment rooms to these suppression pools. RBMK s were built in pairs ... 

Relevant only for a small fuel time constant and under low pressure Various modes of dynamic flow redistribution Occurs with steam injection into vapor suppression pools Very-low-frequency periodic process (-0.1 Hz)... 

Reactor 2, Steam separators 3. Inlet header 4. Main circulation pump 5. Outlet header 6. Pressure suppression pool 7, ECCS vessels 8, ECCS pumps for cooling damaged half of reactor 9. Heat exchangers 10. Clean condensate container 11. ECCS pumps for cooling undamaged half of reactor 12. De-aerator 13. Feed pump,... 

The RBMK reactor design had a complex containment system. Varions parts of the plant had containment structures around them designed to prevent the release of steam to the environment. If a part of the plant failed, the steam would be contained and diverted to the suppression pools where the steam would condense and any radioactivity would be trapped in the water. 

The blow-down of steam to the suppression pool passes through vertical concrete pathways to horizontal openings between drywell and wetwell. 

As in the case of large-capacity plants, the reactor is depressurized by discharging steam to the pressure suppression pool via safety-relief valves actuated by diverse pilot valves of both active and passive design. A further diverse means for pressure relief is provide by rupture disks. Once the reactor pressure has been sufficiently reduced, water is able to flow by gravity into the RPV from an elevated pool, the core flooding pool. 

Steam condensing Containment spray Suppression pool cooling High-pressure core spray (HPCS) system Low-pressure core spray (LPCS) system Automatic depressurization... 

In the unlikely event that the RHR shutdown suction line is unavailable during reactor shutdown to cool reactor water and during the period when the LPCI function of the RHR system and/or the LPCS system pumps are injecting water into the reactor vessel, safety/relief valves used for automatic depressurization can be used to pass water from the reactor vessel to the suppression pool via valve discharge lines. For this to occur, the reactor vessel floods to a level above the vessel main steam line nozzles, selected safety/relief valves are opened from the control room to pass reactor water to the suppression pool. 

Condensation occurs in many industrial applications including in nuclear reactor where condensation occurs in the suppression pool when steam is injected and in turbine condensers. Condensation is classified into the following classes (1) surface filmwise condensation, where the vapor condenses in drops which grow by further condensation and... 

During the evolution of the BWRs, three m or types of contaiiunents were built Mark 1 (page 3-16), Mark 11, and the Mark 111 (page 3-18). Unlike the Mark HI, that consists of a primary containment and a dry well, the Mark 1 and Mark n designs consist of a drywell and a wetwell (suppression pool). All three containment designs use the principle of pressure suppression for LOCAs. The primary containment is designed to condense steam and to contain fission products released from a LOCA so that offsite radiation doses specified are not exceeded and to provide a heat sink and water source for certain safety related equipment. 

The Mark 111 primary containment consists of drywell which is a cylindrical, reinforced concrete structure with a removable head and suppression pool. The drywell and wetwell are connected via the weir wall and the horizontal vents. The suppression pool contains a large volume of water for rapidly condensing steam directed to it. A leak-tight, cylindrical, steel containment vessel surrounds the drywell and the suppression pool to prevent gaseous and particulate fission products from escaping to the enviromnent. The containment system has water spray system at top of the drywell that activates when the containment pressure increases from a set point. 

The suppression pool contains borated water to provide a diverse backup to the gravity-driven control rods. Core cooling and decay heat removal is assured, with water returned to the reactor vessel and steam produced by decay heat vented to the suppression pool. The containment overpressure relief periodically opens to vent steam from the suppression pool. There is a three-day supply of water available to accept decay heat. No operator action is required during this time. For longer periods the suppression pool is manually refilled. Emergency diesel generators and core cooling pumps are not required. 

The steam which in a loss-of-coolant accident is released from the primary system may lead to a pressure increase inside the containment and to a pressure difference between the drywell and the condensation chamber. As a consequence, a steam-air mixture is transported to the pressure suppression pool where the steam is condensed. Simultaneously, fission products which might be carried with the steam are retained in the water volume of the pool, thus efficiently reducing airborne radioactivity. 

For BWRs, the radiologically representative design basis accidents have not been defined as precisely as for PWRs. However, the possible events are phenomenologically quite similar (with the exception of the steam generator tube rupture accident, which does not apply for BWRs) and there are no significant differences to be expected in radionuclide behavior. Consequently, equivalent requirements are applied to the design of both PWR and BWR plants. This means that in most cases the radiochemistry principles discussed in what follows will apply mutatis mutandis to boiling water reactors as well. In the event of a loss-of-coolant accident, the BWR pressure suppression pool represents an effective retention system the behavior of the fission products in this pool will be discussed in Section 7.3.2.4. 

In BWRs, the steam-water mixture escaping from the primary system in a LOCA event is directed to the pressure suppression pool (see Section 2.) where the steam is condensed in the large water volume. Simultaneously, radionuclides carried by the escaping steam are to the most part retained in the water phase the processes occurring in the pool will be discussed in more detail in Section 7.3.2.4. 

In the event of a transient, there is no direct contact between the reactor pressure vessel and the containment, so that the steam-gas flow escaping from the reactor pressure vessel, as well as the volatile fission products and the aerosols carried by it, are transported through the relief line to the pressure suppression pool. When it passes through the water volume of this pool, the overwhelming fraction of the aerosols is retained (as well as iodide), while a small fraction of elemental iodine can potentially escape from the water phase due to its volatility... 

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