Pressurized water loop

Fig. 21. Schematic of a pressurized-water-loop reactor coolant system.

Thornton, E. W. Activity transport mechanisms in water cooled reactors. Report IAEA TECDOC-667 Coolant Technology of Water Cooled Reactors, Vol. 3 Activity Transport Mechanisms in Water Cooled Reactors., Vienna, 1992, p. 9—51 Walker, S. M., Thornton, E. W. Reanalysis of oxide solubility data. Proc. 5. BNES Conf Water Chemistry of Nuclear Reactor Systems, Bournemouth, UK, 1989, Vol. 1, p. 89—95 Walton, G. N., Hesford, E. The migration of activated corrosion products in high-pressure water loops. Proc. Conf Corrosion of Reactor Materials, Salzburg 1962, Vol. 2, p. 547-556... 

Fuel bundles were used in the Severe Fuel Damage (SFD) tests which were conducted in the US Power Burst Facility (PBF), a reactor which consists of a driver core and a pressurized water loop into which the test assembly was inserted. 

Fig. 1. Pressurized water reactor (PWR) coolant system having U-tube steam generators typical of the 3—4 loops in nuclear power plants. PWR plants having once-through steam generators contain two reactor coolant pump-steam generator loops. CVCS = chemical and volume-control system.

Most nuclear reactors use a heat exchanger to transfer heat from a primary coolant loop through the reactor core to a secondary loop that suppHes steam (qv) to a turbine (see HeaT-EXCHANGETECHNOLOGy). The pressurized water reactor is the most common example. The boiling water reactor, however, generates steam in the core. 

Fig. 4. Cutaway view of the Model 412 four-loop pressurized water reactor vessel (46). Courtesy of Westinghouse Electric Corp.

PWRs operate differendy from BWRs. In PWRs, no boiling takes place in the primary heat-transfer loop. Instead, only heating of highly pressurized water occurs. In a separate heat-exchanger vessel, heat is transferred from the pressurized water circuit to a secondary water circuit that operates at a lower pressure and therefore enables boiling. Because of thermal transfer limitations, ultimate steam conditions in PWR power plants ate similar to those in BWR plants. For this reason, materials used in nuclear plant steam turbines and piping must be more resistant to erosion and thermal stresses than those used in conventional units. 

To prevent from hydro-chemical clogging the systems should be designed so there is no entrance of air to the ground water loop. Hence, the loop should be perfectly air tight and constantly under pressure. 

The HTTR is an experimental helium-cooled 30 MW(t) reactor. The HTTR is not designed for electrical power production, but its high temperature process heat capability makes it worthy of inclusion here. Construction started in March 1991 [47] and first criticality is expected in 1998 [48]. The prismatic graphite core of the HTTR is contained in a steel pressure vessel 13.3 m in height and 5.5 m in diameter. The reactor outlet coolant temperature is 850°C under normal rated operation and 950°C under high temperature test operation. The HTTR has a primary helium coolant loop with an intermediate helium-helium heat exchanger and a pressurized water cooler in parallel. The reactor is thus capable of providing... 

The mechanical contractor is usually also responsible for providing adequate pressurized water supply, drainage (with special provisions for low-level areas of the closed-loop water system), bypasses, an electrical supply (typically 110 V, 1 phase, but also 3 phase where temporary pumps are required), HVAC system air purge vents, as well as other facilities, such as site access, toilets, security, and equipment handling systems. 

Secondary Cooler The secondary cooler takes the exit gases from the oxidation unit at 140°C and cools them down to 65°C, a suitable temperature for entry into the absorption column. It is a shell and tube-type heat exchanger constructed of SS304L. The cooling medium is circulating warm water from the warm-water loop. The inlet temperature is 50°C and the exit temperature is about 80°C. The design pressure for this unit is about 1200 kPa. 

The control of the separation section is presented in Figure 10.11. Although the flowsheet seems complex, the control is rather simple. The separation must deliver recycle and product streams with the required purity acetic acid (from C-3), vinyl acetate (from C-5) and water (from C-6). Because the distillate streams are recycled within the separation section, their composition is less important. Therefore, columns C-3, C-5 and C-6 are operated at constant reflux, while boilup rates are used to control some temperatures in the lower sections of the column. For the absorption columns C-l and C-4, the flow rates of the absorbent (acetic acid) are kept constant The concentration of C02 in the recycle stream is controlled by changing the amount of gas sent to the C02 removal unit The additional level, temperature and pressure control loops are standard. 

Energy produced in the reactor is carried away by means of a coolant such as pressurized water, liquid sodium, or carbon dioxide gas. The circulating coolant absorbs heat in the reactor once outside the reactor, it is allowed to boil or the heat it contains is used to boil water in a secondary loop. Steam produced in either of these ways is then piped into the electrical generating unit, where it turns the blades of a turbine. The turbine, in turn, turns a generator that produces electrical energy. 

Water Loop Water pump reservoir Knock-out drum, condensers High-pressure rail system Water deionization filter Water pump reservoir Knock-out drum, condensers High-pressure rail system Water deionization filter... 

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