Nuclear pressurized water reactors

Small amounts of silver are used annually in such diverse applications as a backing for mirrors, and in control rods for pressurized water nuclear reactors Miscellaneous uses like this account for only a small fraction of total silver consumption. 

Figure 18.7 A pressurized water nuclear reactor. The control rods are made of a material such as cadmium or boron, which absorbs neutrons effectively. The fuel rods contain uranium oxide enriched in U-235.

Pressurised water nuclear reactors require metals that will have a high degree of corrosion resistance to pure water at around 300°C. Laboratory testing of materials for this application have included potentiostatic polarisation experiments designed to clarify the active-passive behaviour of alloys as well as to establish corrosion rates. Since pressure vessels are used for this work, it is necessary to provide sealed insulated leads through the autoclave head . 

The phrase "nuclear power" covers a number of technologies for producing electric power other than by burning a fossil fuel. Nuclear fission in pressurized water-moderated reactors—light water reactors— represents the enrrent teehnology for nuclear power. Down the line are fast breeder reactors. On the distant horizon is nnclear fusion. 

This model shows a pressurized, light-water nuclear reactor, the type most often used to generate electrical energy in the United States. Note that each of the three water systems is isolated from the others for safety reasons. 

It has been proposed that some of the natural uranium needed to fuel a pressurized-water nuclear power plant be obtained by extracting uranium from seawater used to cool the plant. If the seawater temperature rise is lO C and the reactor and fuel-cycle conditions are as given in Frg. 3.31, how many kilograms of uranium per year could be recovered at 80 percent yield from cooling water What fraction is this of the armual fuel requirement of the reactor ... 

Kahn, B., Blanchard, R. L., Kolde, H. E., Krieger, H. L., Gold, S., Brinck, W. L., Averett, W. J., Smith, D. B., and Martin, A. 1971. Radiological Surveillance Studies at a Pressurized Water Nuclear Power Reactor. US Environmental Protection Agency Report RD71-1. Washington, DC EPA. 

Source Duffey, R. et al.. Supercritical water-cooled pressure channel nuclear reactors Review and status, Proceedings of GLOBAL, Paper No. 020, Tsukuba, Japan, October 9-13,2005. With permission. 

Under normal operating conditions, the water-steam circuit (or secondary circuit) of pressurized water nuclear power reactors is completely free of radionuclides. Activated corrosion products and tritium, which have been reported in very low activity concentrations from the water-steam circuits of some high-temperature reactors and which are caused by the neutron Held reaching into the steam generator or by diffusion through intact steam generator heating tubes, do not appear at the PWR secondary side. 

In the unalloyed form, zirconium is used for the construction of chemical equipment. Of much higher importance are however the zirconium alloys, from which especially the types zircaloy-2 (1.5 % Sn, 0.1 IS Fe, 0.1 % Cr, 0.05 % Ni) and zircaloy-4 (1.5 % Sn, 0.1 % Cr, 0.2 % Fe) are of interest. They are used as fuel cladding materials in pressure and boiling water nuclear reactors and for structural elements in the reactor core. 

Accordingly, Inspection and Enforcement Bulletin No. 83-04" was issued on March 11, 1983, to all pressurized water nuclear power reactor facilities holding an operating license except those with Westinghouse DB type breakers for action and to other nuclear power reactor facilities for information. The Bulletin described the San Onofre events and mentioned that similar events involving the General Electric AK-2 type breakers had previously occurred at Arkansas Unit 1, Crystal River Unit 3, Oconee Units 1 and 3, Three Mile Island Unit 1, St. Lucie Unit 1, and Rancho Seco Unit 1. Licensees were to (a) take actions similar to those required by Bulletin No. 83-01, (b)... 

Reviews of high temperature water and steam cooled fast reactor concepts from the 1950s to the mid 1990s are described in Appendix B grouped as supercritical pressure water cooled reactors nuclear super heaters and steam cooled fast reactors. 

In service inspections of French nuclear Pressure Water Reactor (PWR) vessels are carried out automatically in complete immersion from the inside by means of ultrasonic focused probes working in the pulse echo mode. Concern has been expressed about the capabilities of performing non destructive evaluation of the Outer Surface Defects (OSD), i.e. defects located in the vicinity of the outer surface of the inspected components. OSD are insonified by both a "direct" field that passes through the inner surface (water/steel) of the component containing the defect and a "secondary" field reflected from the outer surface. Consequently, the Bscan images, containing the signatures of such defects, are complicated and their interpretation is a difficult task. 

Liquid Metals. If operating temperatures rise above 250—300°C, where many organic fluids decompose and water exerts high vapor pressure, hquid metals have found some use, eg, mercury for limited appHcation in turbines sodium, especially its low melting eutectic with 23 wt % potassium, as a hydrauhc fluid and coolant in nuclear reactors and potassium, mbidium, cesium, and gallium in some special uses. 

Niobium is also important in nonferrous metallurgy. Addition of niobium to tirconium reduces the corrosion resistance somewhat but increases the mechanical strength. Because niobium has a low thermal-neutron cross section, it can be alloyed with tirconium for use in the cladding of nuclear fuel rods. A Zr—l%Nb [11107-78-1] alloy has been used as primary cladding in the countries of the former USSR and in Canada. A Zr—2.5 wt % Nb alloy has been used to replace Zircaloy-2 as the cladding in Candu-PHW (pressurized hot water) reactors and has resulted in a 20% reduction in wall thickness of cladding (63) (see Nuclear reactors). 

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). 

As of 1994 there were 105 operating commercial nuclear power stations in the United States (1) (see Power generation). AH of these faciUties were light, ie, hydrogen—water reactors. Seventy-one were pressurized water reactors (PWRs) the remainder were boiling water reactors (BWRs). 

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. 

Because of its low neutron absorption, zirconium is an attractive stmctural material and fuel cladding for nuclear power reactors, but it has low strength and highly variable corrosion behavior. However, ZircaHoy-2, with a nominal composition of 1.5 wt % tin, 0.12 wt % iron, 0.05 wt % nickel, 0.10 wt % chromium, and the remainder zirconium, can be used ia all nuclear power reactors that employ pressurized water as coolant and moderator (see... 

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