ML19263F411
| ML19263F411 | |
| Person / Time | |
|---|---|
| Issue date: | 12/20/1979 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | Happer F AFFILIATION NOT ASSIGNED |
| References | |
| NUDOCS 8001280150 | |
| Download: ML19263F411 (11) | |
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UNITED STATES
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WASHINGTON,0. C. 20555 DEC 2 01979 Mr. Forbes Hopper 133 Taconic Road Greenwich, Connecticut 06830
Dear Mr. Hopper:
This is in reply to your letter of November 27, 1979, requesting information on the functioning of a nuclear power plant.
Enclosed are excerpts from a report of May 1975 on " Energy Alternatives:
A Comparative Analysis," prepared by the Science and Public Policy Program at the University of Oklahoma for a number of agencies of the Federal Government. These excerpts deal with light water reactors of the types currently used in nuclear power plants.
It should be noted that cost information given in the report is out-of-date.
Sincerely, i
I Harold R. Denton, Director Office of Nuclear Reactor Regulation
Enclosures:
As stated i
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CHAPIER 6 THE NUCLEAR ENERGY--FISSION RESOURCE SYSTEM other atoms, causing them to fission, and 6.1 INIRODUCTION thus create a " chain reaction." The term 1
6.1.1 History of Nuclear Energy
" nuclear criticality" is used to describe Commercial use of nuclear fission as a sustaining chain reaction: that is, th e an energy source has a history of less than chain reaction will continue until condi-20 yearst the first electric power gener-ating plant went into operation at Shippingport, Pennsylvania in 1957. The chain reaction creates heat, which can be use of nuclear power as an energy source converted to elect al ene m.
grew out of nuclear weapons development Three isotopes fission r dily and are during World War II. With the creation of
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the Atemic Energy Commission (AEC) following the war came an explicit effort by the gov-
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When an atom fissions, the two newly formed ernment to fund and develop the cermercial atoms a u called Hssion prod e s or nasion use of nuclear energy. The major rationale fragments. Since the splitting can occur behind this development has been the assump-i" * ""#i'*Y f diff*#*"* **Y
- "#i tion of a large supply of nuclear resources fissi n products are formed; for example, that could one day be substituted for the str neium, cesium, i dine, krypton, xenon, more limited fossil fuel sources.
etc. The nuclear fuels and most of these The development of nuclear fission as fission products are radioactive, thereby an energy source has been strongly influ-creating fuel and fuel by-product handling enced by the complex technologies and the pr blems that are unique to the nuclear hazards from radioactivity. The complexity power industry.
of the technologies has required continuous Radioactivity (or " radioactive decay")
research and development, and as a result, can be described as the spontaneous development costs have been higher than the private sector has been willing to bear.
Together with the need for regulating radio-Isotopes are atoms that contain the active materials, the level of cost has re-same number of protons but a different num-ber of neutrons. Two or more isotopes of an sulted in a major role for the federal gov-element exhibit similar chemical properties ernment in the development of nuclear energy.
but different physical properties because of their different atomic weight. For ex-6.1.2 Basics of Nuclear Energy ample, uranium has three isotopes, Uranium-233, Uranium-235, and Uranium-238. All con-Nuclear fission is the process whereby tain 92 protons but a different number of certain heavy atoms split into two dissimi-neutrons.
lar atoms and, in doing so, release energy Fissile is a term that describes nu-and one or several neutrons (a basic nuclear clear fuels that will fission when bombard-
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particle). The neutrons can then react with term that describes a material which, when bombarded by a neutron, becomes fissile.
1817 186 6-1
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described, including information on en-of uranium hexaflouride (UF ) - enrichment 6
ergy ef ficiencies, environmental impacts, to produce a higher concentration of U-235; fuel fabrication; use of the LWR to produce and economics.
The presentation of the environmental electricity; reprocessing of used fuel to residual data di ffers from the presentations recover the remaining U-235 and Pu-239:
in other chapters. In the LWR section, the radioactive waste management; and transpor-amount of residuals for each process is tation of radioactive materials at various based on a 1,000-Mwe nuclear plant operatLg stages in the LWR system, for one year at a load factor of 80 percent.
Each process (such as milling, enrichment, 6.2.2 Resource Base etc.) must produce a certain " quantity" of product material to be used by the model 6.2.2.1 Characteristics of the Resource 1,000-Mwe plant. The residuals listed in Uranium is one of the elements and the tables are based on this " quantity."
occurs in nature as a compound. About 95 Another difference is that the LWR tables percent of the uranium mined in the U.S.
include the residuals frorn secondary power exists as uranium oxide (known as uraninite sources. For example, the majority of the or pitchblende). Most of the remaining sulfur oxides (50,) residuals listed for five percent exists in uranium hydrous the enrichment process are emissions from silicate compounds (known as coffinite) or the Tennessee valley Authority coal-fire potassium uranium vanadate (known as carno-tite) (Singleton, 1968:11). Uranium con-plants.
The residual assumptions used in the sists of three naturally occurring isotopes HTGR and the LMFBR sections differ from in the following proportions:
99.29 percent those used in tl.e LWR.
The necessary infor-U-238, 0.71 percent U-235, and a trace of mation to understand these residuals is giv-U-234.
U-235 is used to fuel the LWR.
A en in the appropriate HTGR and LMFBR sections. ton of uranium-bearing ore contains, on the average, four to five pounds of uranium 6.2 LIGHT WATER REACTOR (LWR) SYSTEM oxide from which 0.024 to 0.030 pound of U-235 can be obtained.
Most of the uranium mined in the U.S.
6.2.1 Introduction The light water reactor gets its name is found in three types of deposits: petri-frczn the use of ordinary water (tems light fied rivers, veins, and ancient conglomer-water ) to transfer heat from the fission-ates. Ancient conglomerates are old stream ing of uranium to a steam turbine. The pri-channel deposits that were formed more than mary energy sources for the LWR is U-235, one-half million years ago. (Singletoa,1968:
and there are 10 major activities in the LWR 22).
The dif ference between petrified riv-ex-ers and veins is that the host sandstone fuel cycle as indicated in Figure 6-1:
pioration for uranium; mining of uranium ore containing the uranium lies horizontally and reclamation; milling of uranium ore to in the first and vertically in the second.
(U 0 ) I production These sandstone formations provide 95 per-produce yellowcake 38
_I cent of the ore mined in the U.S.
.Light water is pure H O (two hydroge9 6.2.2.2 Quantity of the Resources atoms plus one oxygen atom)2 Heavy water is deuterium oxide, D20 (two deuterium atoms Uranium resources and reserves are plus one oxygen atom). Deuterium is a heavy normally discussed in terms of quantities isotope of hydrogen.
The product of a milling process that Unless preceded by " metric," " ton" will converts are containing 0.2-percent U 038 in-refer to a short ton (2,000 pounds). A to "yellowcake" containing approximately 80-metric ton is 2,205 pounds.
percent U C3 8-6-3 1817 187
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occurring and would have very little effect reactor cannot explode like a bomb. A dif-if they did (AEC, 1974c: E-4 and E-5).
forent type of fuel and different fuel con-figuration are used in a reactor.
6.2.5.4.4 Economic Considerations There are currently two dif ferent types The cost of fabricating the fuel assem-of U.S. LWR'st the boiling wat9r reactor blies was estLaated in 1972 to be approxi-(BWR) manufactured by General Elo-tric and mately $70 per kilogram of contained ura-the pressurized water reactor (PWR) manufac-nium. This cost represents approximately tured by Babcock and Wilcox, Combustion 0.4 mill per kwh, about 20 percent of the Engineering, and Westinghouse.
total fuel processing costs of 1.93 mills per kwh or only four percent of the total 6.2.6.1.1 Boiling Water Reactors power generation costs of 9.0 to 11.0 mills Figure 6-9 is a simplified schematic per kwh (NPC, 1973: 28).
of a boiling water reactor. In this type of reactor, water is pumped in a closed 6.2.6 Light Water Reactors cycle from the condenser to the nuclear reactor. In the reactor core, heat generat-6.2.6.1 Technologies ed by the fissioning uranium pellets is A nuclear-electric power plant is skm-transferred through the metal cladding to ilar in nature to the fossil-fueled power the water flowing around the fuel assemblies.
plants described in Chapter 12 except that The water boils and a mixture of steam and the nuclear steam supply system replaces water flows out the top of the core and the conventional fuel boiler and the nuclear through stern separators in the top of the fuel core replaces the fossil fuel supply.
pressure vessel. The separators clean and In LVA's, the heat energy comes basically
" dry" the steam before it is piped to the from the fissioning of U-235 atoms, with turbine-generator (s). The turbine exhaust a small contribution from the fissioning 16 condensed and returned to the reactor of U-238 atoms. However, as the reactor preksure vessel to complete the cycle.
(See operates, a fissile atom (Pu-239) is pro-Chaptsr 12 for a more complete description duced from U-238.
For each gram of U-235 of stean power plants).
consumed in LWR fuel, as much as 0.6 gram Because the energy supplied to the water is formed. Generally more than half of the from the hot fuel is transported directly plutonium formed undergoes fission in the (as steam) to the turbine, the BWR system core, thus contributing significantly to is termed a " direct cycle" system The pres-the energy produced in the power plant (AEC, sure in a typical BWR is maintained at about 1974d: Vol. IV, p. A.l.1-2).
LWR's typical-1,000 pounds per square inch (psi), with a ly employ partial refueling annually, with steam temperature of 545 F (AEC, 1974d: Vol.
scmewhere between ene-fourth and one-third IV, p. A. l.1-18). Neutron-absorbing control of the fuel asse=blies being removed and rods, operated by hydraulic drives lv sted replaced with fresh fuel each year. Spent below the vessel, are used to control the fuel assemblies are stored underwater at the rate of the fission chain reaction (and thus power plant for a period of' five to six the heat output).
months to allow th 2ir radioactivity level One major concern with light water to decrease prio: to shipment to a fuel re-reactors is an accidental depressurization processing plant (AEC, 1974d: Vol. IV, p.
or coolant loss (e.g.,
resulting from a high-A. l.1-15). Since the historical origin of pressure steam pipe rupture). If no safety nuclear power is frem nuclear weapons, it measures were in effect, such events would is important to point out that a nuclear cause the core to overhe e a It, and I
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- large amounts of high-level radioactivity by preventing any large pressure buildup, might be released to the environment. To This pressure injection pool also serves prevent such catastrophes, reactor systems as a potential source of water for the include emergency core cooling systems emergency core spraying system (AEC, 1974dr (ECCS ' s) to prevent meltdowns and contain-Vol. IV, p. A. l.1-21).
ment systems for preventing the release of The " secondary" containment system is radioactivity in the event of any type of the building that houses the reactor and accident.
its primary containment system (not shown Although provisions differ from plant in Figure 6-9).
Reactor buildings are con-to plant, all BWR's have multiple provi-structed of poured-in-place, reinforced con-sions for cooling the core fuel in an crete and have sealed joints and interlocked emergency. Typical ECCS's involve either double-door entries. Under accident condi-a high-pressure core spray system (early tions, the normal building ventilation sys-BWR's) or both core sprays and a high-pres-tess would shutdown, and the building would sure coolant-injection system (latest BWR's) be exhaust-ventilated by two parallel stand-to assure adequate cooling of the core in by systems. These ventilating systems in-the event of reactor system depressurization corporate effluent gas treatment devices, (AEC, 1974d: Vol. IV, pp. A. l.1-20).
including high-efficiency particulate To prevent such accidents from releas-cleaners and solid absorbents for trapping ing radioactivity and other pollutants to radioactive halogens (particularly iodine) the environment, BWR designs generally pro-that might have leaked from the primary vide both " primary" and " secondary" contain-contain.aent system (AEC, 1973: 1-24).
ment. The primary containment system, shown in Figure 6-9 as the " containment structure,"
6.2.6.1.2 Pressurized Water Reactors is a steel pressure vessel surrounded by re-Figure 6-10 is a simplified schematic inforced concrete and designed to withstand of a pressurized water reactor. The pri-the peak transient pressures that might occur mary difference between a PWR and a BWR in the most severe of the postulated loss-is that all PWR's employ a dual coolant of-coolant accidents. The primary contain-system for transferring energy from the ment system employs a "drywell," which en-reactor systems. In the dual coolant sys-closes the entire reactor vessel and its tem, the primary loop is water that is recirculation pumps and piping. The drywell pumped through the core and the heat ex-is connected to a lower-level, pressure sup-changer. The secondary loop is water that pression chamber in which a large pool of is pumped through the heat exchanger and water is stored. In the event of an acci-the turbine. The water is heated to about dent, valves in the main steam lines frczn 600 F by the nuclear core in the pressure the reactor to the turbine-generators (the vessel,but pressure is sufficiently high
" isolation valves" in Figure 6-9) would (about 2,250 psi) to prevent boiling. The close automatically and any steam escaping high-pressure water is piped out of the frcm the reactor system would be released reactor vessel into usually two or more into the drywell. The resulting increase
" steam generators" that form a basic heat in drywell pressure would force the air-exchanger. The primary heat is transferred steam mixture in the drywell down into and to the secondary stream. The secondary through the large pool of water where the stream boils, providing steam for the tur-steam would be completely condensed, there-bine. The secondary stream is then con-densed and the water is pumped back to the l817 191
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steam generator to begin the cycle over. No For example, in some plants, the contain-steam is generated in the primary loop and ment space is kept slightly below atmo-the water is returned to the core from the spheric pressure so that leakage through steam generator to start the primary cycle the containment walls would, at most times, over. As in BWR's, the nuclear chain re-be inward from the surroundings. Other action is centrolled through the use of systems have double barriers against escape neutron-absorbing rods t however, in PWR's, of material from the containment space.
In additional control can be obtained through addition, to condense the steam resulting the dissolution of such variable-concen-from a major break of the primary system, tration neutron-absorbing chemicals as boron either cold-water sprays or stored ice is (which may also serve other purposes) in the provided (AEC, 1973: 1-17).
primary system coolant.
The PWR ECCS's consist of several in-5.2.6.2 Energy Efficiencies dependent subsystems, each characterized The overall energy efficiency for the by redundancy of equipment and flow path, power plant is the ratio of electric energy Although the arrangements and designs of output to total heat energy produced.
LWR's PWR ECCS's vary from plant to plant (de-(both BWR's and PWR's) have energy efficien-pending on the vendor of the steam supply cies around 32 percent, as ccmpared to 38 system), all modern PWR plants employ both to 40 percent for modern fossil-fueled plants accumulator injection systems and pump (see Chapter 12).
The reason for this lower injection systems. Accumulator injection efficiency is that LWR plants can only oper- {
systems are called passive systems because ate at a maximum steam te=perature of around they operate automatically without acti-600 F while fossil plants can operate at vation of pumps, motor driven valves, or 1,000 F or higher.
a other equipment. The systems consist of pressurized tanks of cool borated water 6.2.6.3 Environmental Considerations which are connected through check valves to the reactor vessel. Should the primary 6.2.6.3.1 Chronic Residuals coolant system lose pressure, the check The main residuals from LWR's are waste valves would open and a large volu=e of heat and radioactive emissions. For a 1,000-water would be rapidly discharged into the Mwe plant operating at a 75-percent load reactor vessel and core. Two pump injection factor, a 32-percent efficient nuclear plant 12 (active) systems are also incorporated in would emit 47.6x10 Btu's of waste heat PWR ECCS's.
One is a low-pressure system annually. For comparison, a 38-percent to provide coolant af ter the above mentioned efficient fossil plant would emit 36.5x10 accumulator tanks are empty, and the other Btu's of waste heat.
For a description of is a high-pressure system designed to func-the cooling mechanisms and water required tion if the break is small and the primary to dissipate this waste heat, see the sec-coolant pressure remains too high to acti-tion on cooling in Chapter 12.
vate the passive systems (AEC, 1973: 1-14).
Table 6-12 gives the annual chronic The containment structure for PWR's radioactive emissions for both types of is of reinforced concrete with a steel liner LWR's.
These data are based on a 1,000-Mwe and is stressed to withstand the maximum plant operating at a 100-percent load factor.
expected te=perature and pressure if all the The PWR emits a larger quantity of water in the primary system was expelled into tritium (the heaviest hydrogen isotope which the containment. However, containment sys-is radioactive) than does the SWR.
The tem designs vary widely frem plant to plant.
tritium is created as a direct product of 6-3?
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Requests info re the const & functioning of nuclear power
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