Воробева Нуцлеар Реацтор Тыпес (Леарн то реад бы реадинг) 2010

Heat extraction: Heavy water (D20) at high pressure is heated by passing over the fuel in the pressure tubes. It is pumped to а steam generator where it boils light water (Н20) in а separate circuit; the steam drives а turbine coupled to an electric generator.

Exercises

Ex. 1. Answer the following questions:

1. What kind of reactor is the CANDU? 2. What is the advantage of heavy water as a moderator? What is its disadvantage? 3. What is the arrangement of the CANDU core? 4. In what way is heat removed? 5. Where is steam raised? 6. What .are the advantages of the individual pressure tube structure of the CANDU? 7. What kind of fuel is used in the CANDU? What makes it possible to use natural uranium as a fuel? 8. In what way is control maintained? 9. What core-cooling systems are provided for in the CANDU? 10. What are the components of the containment building?

Ex. 2. Translate the attributive groups:

Ex. 3. Translate. Pay attention to the underlined words.

1. This chapter will describe the reactor currently available in Canada. 2. That figure actually presents the pressurized heavy-water design that is presently available. 3. Instead of light water this design makes

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use of heavy water both as coolant and as a moderator. 4. The fuel of a Candu is very similar to that of an LWR. 5. The primary coolant system is similar to that of a PWR except that the pressure vessel is replaced by a lattice of individual pressure tubes. 6. The important distinction between an LWR and a HWR is that the moderator of the latter is heavy water. 7. The reactor is refueled only a little at a time as opposed to the abrupt once-yearly operation. 8. The Candu uses heavy water rather than light water as the moderator. 9. The structure can be maintained at a negative pressure with respect to the external surroundings. 10. The irradiated bundle also contains plutonium as a result of neutron capture by 238U. Because of the lower absorption and because the heavy water is somewhat less effective moderator, it is feasible to have larger separations between bundles than in an LWR. 12. The neutron multiplication factor is increased unless substantial control is used. 13. The Candu does not need much control since the fissile load remains essentially constant.

Ex. 4. State the meaning of "as".

1.He works as an engineer.

2.As you know, …

3.As the t° rises, …

4.As the problem is too difficult, …

1. As you know in the Candu heavy water is used as the moderator. 2. A basic feature of the Candu is use of natural uranium as the fuel. 3. As mentioned above the vault serves as shielding and maintains the calandria at a constant t°. 4. The fast reactor has a high breeding ratio, as nuclear physics shows. 5. The calandria is constructed of much thinner steel than the pressure walls for LWR as operating t°s are in the range 110-160 °F. 6. As the reactor runs, fission product poisons are accumulated. 7. As the coolant rises through the core, it boils, resulting in lower coolant densities. 8. The water in the vessel boils as it rises through the core. 9. Although current Candus use heavy water, not only as the moderator, but also as the coolant, other cooling fluids are possible. 10. The strength of graphite increases as the t° rises. 11. As nuclear power develops, changes in the nuclear fuel cycle may occur. 12. The check valves open as soon as the primary system pressure drops much below 1000 psi. 13. Control of the reactor is maintained by a number of variable neutron absorbers as well as a number of adjusting rods.

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Ex. 5. Give the 3 forms:

Ex. 6. Find the predicate. Translate.

1. Neutrons and protons do attract each other through the nuclear force. 2. The liquid-drop model does lead to a good qualitative understanding of the fission phenomenon. 3. A fission chain reaction does introduce some special aspects to the reactor. 4. It is the fissile material that yields most fissions and hence energy. 5. Uranium resources are not unlimited either. 6. Surrounding this core is a blanket of uranium. 7. Enclosed in a containment structure is the primary coolant system. 8. Connected to this shutdown system is an emergency-core-cooling supply of light water. 9. Complicated as it is, the boundary layer is the most basic and the most variable element in the cooling system. 10. Not only does the reaction rate affect the amount of heat generated, but the heat also affects the reaction rate. 11. Only during the 1970s have serious attempts been made to predict the probability of reactor accidents. 12. Had the alchemists known this property of uranium, they might have tried to turn metals into gold. 13. Little did they know that uranium changed by natural radioactivity into a whole family of other elements. 14. An emergency-core-cooling supply of light water may be injected should the basic system fail. 15. The answer to this question is not known. Nor is it known how best to prevent manufacture of weapons. 16. The backup systems become operative should some sort of abnormality occur. 17. Should the containment be ruptured due to overpressure, volatile radionuclides could escape into the environment. 18. Were it possible to reduce control, the conversion ratio would rise.

Ex. 7. Make the sentences emphatic, using “it is ... that (which, who)”.

1. The Candu reactor uses heavy water. 2. The lower pressure removes the necessity of a single pressure vessel. 3.The fissile load remains essentially constant. 4. Decreased control improves conver-

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sion. 5. The Candu reactor operates on natural uranium. 6. The fissile material yields energy. 7. A supply of light water is connected to the shutdown system. 8. The primary coolant system is enclosed in a containment structure.

Ex. 8. Give a free translation.

В Канаде для АЭС разработаны тяжеловодные реакторы канального типа, называемые Candu. В Candu тяжелая вода используется и как замедлитель, и как теплоноситель. Candu загружается природным ураном в оболочке из циркалоя. Это обстоятельство исключает необходимость в дорогостоящем процессе обогащения урана.

Другим достоинством системы Candu является то, что перегрузка в нем выполняется непрерывно во время работы (on power), причем две загрузочные машиныработаютодновременно.

То, что системы охлаждения обсуждаемого реактора спроектированы так, чтобы обеспечивать аварийное охлаждение каждого отдельного канала, представляет собой еще одно преимущество данной системы. Очевидно, к основным недостаткам Candu следует отнести высокую цену тяжелой воды, которая диктуется чрезвычайно дорогим процессомее производства.

READING 5-B

SGHWR Steam Generating Heavy Water Reactor

Thermal Reactor - Heavy Water Moderated

Indicative data for а reactor of 600 MW(e) size:

Uranium enrichment 2.24 % U235. Coolant outlet temperature 272 °С. Pressure 900 psi. Thermal efficiency 32 %. Core dimensions 6.5 m dia × × 3.7 m high.

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world. The Nazi government was greatly interested in fission experiments and hence, in obtaining heavy water. When the nazis invaded Paris in June 1940, they tried to confiscate the heavy water the French scientists had. But they could not find it, it was not in Paris. The heavy water had been taken to the unoccupied part of France. There it was stored in the underground vaults of a bank in containers marked “Product L.”

With the nazis occupying all of France, it was not safe to leave the water there. And one night two scientists hid Product L in a cell of a prison.

After a series of adventures, the men arrived in Bordeaux with the 40 gallons of heavy water. The English ship “Broompark” was waiting to take the water to England, even then it was not safe. Through spies the nazis learnt where the water was. But there were 3 ships leaving Bordeaux that day and the nazis didn’t know which was to carry the heavy water. They sank two of the ships but it was “the Broompark”" that escaped. The heavy water was made use of for important research carried on by Frederic Joliot and other physicists from Allied countries through war years.

READING 5-D

Economics

Nuclear power reactors are expensive to build but relatively cheap to operate. Their economic competitiveness thus depends on keeping construction to schedule so that capital costs do not blow out, and then operating them at reasonably high capacity over many years. By way of contrast, gas-fired power plants are very cheap and quick to build, but relatively very expensive to operate due to the cost of their fuel. With rising gas prices, and the high cost of moving coal long distances, nuclear plants are generally competitive with both gas and coal in most parts of the world, and becoming more so.

• While discussing Economics make use of the following vocabulary:

Expensive (quick) to build; cheap (expensive) to operate; economic competitiveness; keeping construction to schedule; capital costs; operating at high capacity; gas-fired power plants; due to; With rising gas prices; moving coal long distances; competitive with both gas and coal.

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UNIT VI

HIGH-TEMPERATURE GAS-COOLED REACTORS

READING 6-A

High-Temperature Gas-Cooled Reactor (HTGR)

The HTGR core consists of a massive pile of hexagonal graphite blocks, each containing fueled regions, the whole structure being cooled by pressurized helium gas. The graphite serves as the neutron moderator. The fuel itself consists of highly-enriched uranium as the fissile material and thorium 232 as the fertile. These materials, in the form of the dioxide or carbide, are present as small fuel kernels with ceramic coatings, so that both fuel and its “cladding” are ceramic. The final fuel will be composed of two particle types, one containing uranium enriched to 93 % 235U, the other containing the thorium. As the reactor runs, fissile - 233U would build up in the latter particles. The fuel particles are bound into fuel rods (with graphite as the binder) which are incorporated into the basic block or element. These elements are stacked. A basic refueling region consists of a central stack, which has two vertical control rod channels, and the six adjacent stacks (without such channels). The central stack has an additional channel into which boron balls can be poured as a reserve shutdown system. All of the fuel elements have holes through which the coolant flows.

The core and the other NSSS components are contained in a “prestressed-concrete reactor vessel” (PCRV) which has steel-lined cavities for each component. The reactor is fueled through penetrations above the central stack of each refueling region; this same penetration also serves for the drive for the control rod pair penetrating that stack. There are additional penetrations for piping and removal plugs for servicing (and even replacement) of steam generators, circulators, etc. The vessel is prestressed with vertical steel tendons and with circumferential wire wrapping. The PCRV and its contents are extremely massive (100,000,000 Ib); and indeed the core itself is more massive, by about one order of magnitude, than the core of an LWR. The PCRV is surrounded by a containment building much like that of a PWR.

The helium gas, at a pressure of 700 psi, is pumped downward through the core, and exits with a temperature of 1370 °F. The gas then passes into one of the 4 or 6 (depending on the plant size) heat exchangers, raising

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steam as usual. Above each steam generator is a circulator which pumps the helium. The higher reactor operating temperature, which is permitted by the gaseous form of the coolant and the good high-temperature characteristics of the core, provides steam which can be converted to electrical energy with an efficiency of 39 %, substantially greater than in a water-cooled reactor. Moreover, the potential exists, with development of helium-driven turbo generators, to raise this efficiency even more.

The accident response of an HTGR is noticeably different than that of a water-cooled reactor, principally because of the mass of the core, were shutdown to occur with complete loss of cooling, no damage to the fuel would occur for about half an hour (as compared with the roughly 1 min of an LWR). The fuel particle, due to its ceramic coating, is much less susceptible to melting than a metal-clad fuel rod. And, due to the, heat capacity of the core, it takes much longer to reach elevated temperatures. Moreover, the core’s structural strength is provided by graphite, whose strength improves as the temperature rises.

To make a complete loss of coolant incredible, flow restrictors are incorporated around PGRV penetrations to reduce helium loss should the vessel integrity be violated there. As a result, helium is always presumed to be in the system. Should all the primary cooling loops become unavailable, which is difficult to predict since they are largely independent, the two or three loops of the auxiliary cooling system are activated. These are sized to be sufficient for safe shutdown.

Exercises

Ex. 1. Answer the questions.

1. What reactor is referred to as a HTGR? 2. What is the structure of the core? 3. What fuel is used in the reactor? 4.What is the structure of the fuel element? 5. What is the basic refueling region? 6. In what way is refueling accomplished? 7. What is the containment system of the reactor? 8. What makes it possible to achieve a higher efficiency with this type of reactor? 9. What factors influence the accident response of the HTGR? 10. Summing up, what are advantages of the HTGR? 11. Are there any emergency systems here?

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Ex. 2. Translate the following attributive groups:

Ex. 3. Translate. Pay attention to “that”.

1. In principle it is possible to build a reactor that produces more fissile material that it destroys. 2. The fuel of a Candu is similar to that of an LWR. 3. The pins are somewhat smaller and simpler than those of LWRs. 4. Unlike the typical PWR fuel bundle, that of the BWR has an outer sheath. 5. The slow neutron cross-section for Pu239 is larger than that for U235. 6. Otherwise, the fuel design is similar to that of an LM FBR. 7. The neutrons from fusion are much more energetic than those from fission. 8. The important distinction between an LWR and a HWR is that the moderator of the latter is heavy water.

Ex. 4. Translate the sentences.

1. The HTGR core consists of a massive pile of hexagonal graphite blocks, each containing fueled regions, the whole structure being cooled by pressurized helium gas. 2. The initial fuel will be composed of two particle types, one containing enriched uranium, the other containing thorium. 3. Helium is always presumed to be in the system. 4. Were shutdown to occur, no damage to the fuel would occur for about half an hour, as compared with 1 min of an LWR. 5. Should the vessel integrity be violated, flow restrictors are incorporated to reduce helium loss. 6. Should all the primary cooling loops become unavailable, the two or three loops of the auxiliary cooling system are activated. 7. As the reactor runs, fissile U233 would build up. 8. Boron carbide balls can be used as a reserve shutdown system. 9. These elements are stacked as indicated in Fig. 10. Graphite serves as the neutron moderator. 11. The PCRV is surrounded by a containment building much like that of a PWR. 12. The core is more massive, by about one order of magnitude, than that of an LWR. 13. Both the fuel

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and its cladding are ceramic. 14. Neither the conversion nor the breeding ratio is a complete characterization. 15. The accident response is different than that of a water-cooled reactor, principally because of the mass of the core. 16. The gas passes into one of the 4 or 6 heat exchangers depending on the plant size. 17. The fuel particle is less susceptible to melting due to its ceramic coating. 18. An increase in the amount of water or other moderator means greater losses due to capture.

Ex. 5. Find the predicate. Translate.

1. A few years ago a new particle was discovered and given the designation “tau”. 2. In both systems accuracy is also affected by conductivity. The lower the conductivity, the less the accuracy. 3. Since the neutron has no electric charge it is not influenced by a uniform magnetic field. 4. A brief discussion of the basic phenomena was followed by preliminary development of expressions for heat and mass transfer. 5.The method described is the most accurate and should be followed in this case. 6. These questions are not easily answered. 7. A deviation of operating parameters from their normal values is referred to as a “transient”. 8. The sudden formation of steam and expulsion of the coolant from the primary system is often referred to as blowdown. 9. The conversion ratio may be strongly influenced by simple design and operational factors. 10. The stability of the atom is accounted for by the electric attraction within the atom. 11. The control system of the reactor can be relied upon. 12. The problems of safety and reliability of nuclear reactors are dealt with in many research laboratories. 13. The disposal of nuclear wastes is given detailed consideration in this paper. 14. At present chemical methods of fuel reprocessing are made use of. 15. Advantage was taken of the fast reaction rate. 16. Care must be taken in measuring radioactivity. 17. With enough correction the exact situation can be approached.

Ex. 6. Use the following word combinations in Passive constructions:

1) to remove radioactive materials; 2) to rupture the pipe; 3) to specify the limits; 4) to incorporate data; 5) to insert bundles into the channels; 6) to reduce the content; 7) to irradiate the fuel; 8) to a just the pressure; 9) to release steam; 10) to damage the core; 11) to affect

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