The Boiling Water Reactor

An example of a modern boiling water reactor is the General Electric reactor of the BWR/6 type which is scheduled for construction at Grand Gulf, about 25 miles south of Vicksburg, Mississippi. The first reactor of the two-unit station is expected to achieve commercial operation in 1982 and the second in 1986. Each reactor will have a net output of 1250 MWe. 

The layout of the core and pressure vessel is shown in Fig. 9.6. The core, steam separators, and driers are enclosed within a low alloy steel pressure vessel of diameter approximately 6.4 m and height 22 m, with a removable head. The wall thickness is nominally 6 in. (152 mm). The core is made up of 

After passing through the core, the coolant steam-water mixture enters the bank of centrifugal steam separators mounted above the core, where the water is separated out by vortex action and flows down to join the recirculation flow through the annulus. The steam passes upwards into the steam driers in which the moisture is further reduced, and thence to the turbine. The steam leaving the core is at a temperature of 286°C, at a pressure of 1040 psi (73 kg cm The total thermal output from the core is 3833 MWt. Recirculation flow control is used to provide automatic load following power changes of up to 25% of full power can be accommodated in this way. 

The core is made up of a total of 800 fuel assemblies, arranged to form an array of roughly circular cross section, as shown in Fig. 9.8. Each of the assemblies consists of an 8 x 8 square array of fuel pins, with zircaloy-2 cladding, surrounded by a square-shaped channel of zircaloy-4. The assembly has tie plates at both ends, the lower of which has a nosepiece which fits into the fuel support and distributes the coolant flow to the rods. The use 

The containment is of the pressure suppression type, in which a large volume of water is used to cause a rapid reduction of pressure by condensation of steam in the event of a loss of coolant accident. The protection against release of radioactivity into the atmosphere comprises three separate barriers a concrete dry well around the reactor vessel, a water 

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A variety of nuclear reactor designs is possible using different combinations of components and process features for different purposes (see Nuclear REACTORS, reactor types). Two versions of the lightwater reactors were favored the pressurized water reactor (PWR) and the boiling water reactor (BWR). Each requites enrichment of uranium in U. To assure safety, careful control of coolant conditions is requited (see Nuclearreactors, water CHEMISTRY OF LIGHTWATER REACTORS NuCLEAR REACTORS, SAFETY IN NUCLEAR FACILITIES). 

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. 

In the secondary loop, a feed water pump circulates water through a heat exchanger where the primary and secondary loops exchange heat. The water in the secondary loop is turned to steam here and feeds a turbine, where electricity is generated. In the boiling-water reactor, there is only one loop, and as a result, the overall efficiencies are higher at the added expense... 

For example, one of the earliest types of nuclear reactors is the boiling water reactor (BWR) in which the reactor core is surrounded by ordinary water. As the reactor operates, the water is heated, begins to boil, and changes to steam. The steam produced is piped out of the reactor vessel and delivered (usually) to a turbine and generator, where electrical power is produced. 

The boiling-water reactor is the other type of power reactor in common use in the United States that uses H2O as coolant and moderator. In this type the water in the reactor is at a lower pressure, around 70 bar (1000 Ib/in ), so that it boils and is partially converted to steam as it flows through the reactor. Coolant leaving the reactor is separated into water, which is recycled, and steam, which is sent directly to the turbine as illustrated in Fig. 1.9. Comparison with Fig. 1.8 shows that the boiling-water system differs from the pressurized-water system in having no external steam generator, the reactor itself providing this function. 

Also the boiling water reactor is the basis for an innovative design with passive safety installations, sized approx. 1300 MW(e) for the evolutionary type designed by General Electric in cooperation with Hitachi/Toshiba and approx. 600 MW(e) for the passively safe reactor. Of the former type, two units have commenced commercial operation in Japan since 1996 [86]. 

We illustrate the general principles of thermal reactors by a short description of the two most inqx)itant power reactor types the pressurized water reactor (PWR) and the boiling water reactor (BWR). They are further discussed in Chapter 20. 

Two types of light water reactors, namely, the boiling water reactor (BWR) and the pressurized water reactor (PWR) are in use in the United States of America. The fuel for these reactors consists of long bundles of 2-4 wt% of enriched uranium dioxide fuel pellets stacked in zirconium-alloy cladding tubes. 

This section provides a comparison of power reactors built in the UK with the Soviet RBMK. But it is worth recollecting that, elsewhere in the world, other types of power reactors are in use. The most widely built reactor is the Pressurised Water Reactor (PWR) but the second is the Boiling Water Reactor (BWR), a light water reactor in which, like the RBMK, steam is generated in the core and passed to the turbines in a direct cycle. Light (i.e. ordinary) water is used as coolant and moderator. The Canadian industry has developed the CANDU series of reactors, with limited export to India, etc., which have many pressure tubes to retain the coolant, as in the British SCHWR and Soviet RBMK, but are heavy-water-cooled and moderated. 

Except for the fact that the mode of reactor cooling has been changed from forced circulation to natural circulation (reactor water recirculation pumps have been eliminated), all other sterns and components employed for plant operation are based on the extensive upeiating expel leiice gained fiom the boiling water reactor plants currently in service in Germany as well as on the proven system and component designs implemented in these plants. 

Development of the boiling water reactor (BWR) was carried out by the ANL. Following the operation of several experimental reactors in Idaho, the experimental BWR (EBWR) was constructed in Illinois. The EBWR was the first BWR power plant to be built. The plant was initially operated at 5 Megawatts electric (MWe) and 20 Megawatts thermal (MWt). The reactor was operated from 1957 to 1967 at power levels up to 100 MWt. 

The purpose of this chapter is to provide a general insight into the manufacture of fuels used in nuclear reactors. The primary focus will be on uranium dioxide (UO2) fuels for light water reactors (LWRs), including both the pressurized water reactor (PWR) and the boiling water reactor (BWR). Many of the details relating to the fuel for these reactors are also presented in Sections 1.2 and 1.3 of this handbook. Some of the information from those chapters will be repeated for clarity. 

Lin, C. C., Pao, C. R Wiley, J. S., DeHollander,W. R. A mathematical model of corrosion product transport in the boiling water reactor primary system. Nucl. Technology 54, 253-265 (1981)... 

The Benefit of Hydrogen Addition to the Boiling Water Reactor Environment on Stress Crack Initiation and Growth in Type 304 Stainless Steel J. Eng. Mater. Technol. (Trans. ASME) 108 (1986) 1, S. 10-19 piO] Hettiarachchi, S. et al. 

The LWR is further classified into the pressurized water reactor (PWR) which operates at about 150 atm and 318°C with a thermal efficiency of about 34%. The other type of reactor is the boiling water reactor (BWR) which operates at 70 atm pressure and 278°C with a thermal efficiency of 33%. These reactors require fuel with enriched to about 3% to have a sufficient neutron flux for the chain reaction. The fuel, as UO2, is in the form of pellets enclosed in a zirconium alloy, Zircaloy-2. 

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