ML19309A592

Forwards Excerpts from Univ of Ok Rept, Energy Alternatives:Comparative Analysis, in Response to Request for Info on Nuclear Energy

ML19309A592
Person / Time
Issue date:	02/14/1980
From:	Harold Denton Office of Nuclear Reactor Regulation
To:	Ritch D AFFILIATION NOT ASSIGNED
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UNITED STATES e

o NUCLEAR REGULATORY COMMISSION

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February 14, 1980 Mr. Donny Ritch i

P. O. Box 803 Montgomery, Texas 77356

Dear Mr. Ritch:

Your letter to the Nuclear Regulatory Commission asked for information about nuclear energy.

Enclosed are excerpts from a report on " Energy Alternatives: A Comparative Analysis" prepared for a number of Government agencies. These excerpts describe light water reactors used for power generation.

Sincerely,

,/

Harold P., Denton, Director Office of Nuclear Reactor Regulation

Enclosure:

As stated

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Energy Alternatives:

i A Comparative l

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EXCERPTS

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Prepared for c o e

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i Depart ent fte ter r ce of R earch an Deve opment Oc f Ene gy &

oficy ty o Ok$a ome Norma,

ahc$a nly May 1975

f CHAPTER 6 THE NUCLEAR ENERGY--FISSION RESOURCE SYSTEM other atoms, causing them to fission, and 6.1 IttrRODUCTION thus create a " chain reaction." The term 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, the an energy source has a history of less than chain reaction will continue until condi-20 years; the first electric power gener-ns are anend to mah Ge macdon ating plant went into operaticn at Shippingport, Pennsylvania in 1957. The use of nuclear power as an energy source

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grew out of nuclear weapons development Three isotopes fission r dily and are during World War II. With the creation of the Atomic Energy Commission (AEC) following

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the war came an explicit effort by the gov-We two newly fomed en an a m ss ms, ernment to fund and develop the ccrmnercial atoms are called fission products or fission use of nuclear energy. The major rationale fragments. Since the splitting can occur behind this development has been the assump-Y

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tion of a large supply of nuclear resources fission products are formed; for example, that could one day be substituted for the arn a, ces e, i dine, k @ on, xenon, more limited fossil fuel sources, The nuclear fuels and most of these etc.

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 Problems that are unique to the nuclear

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i im urds from radioactivity. The complexity f

of the ochnologies has required continuous l

research aad development, and as a result, development nosts 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 suited in a major role for the federal gov-element exhibit similar chemical properties ernment in the development of nuclear energy.

but dif ferent physical properties because of their different atomic weight. For ex-6.1.2 Basics of Nuclear Energy ample, uranium has three isotopes, Uranium-

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Nuclear fission is the process Vaereby tain' 92 protons b'ut a dif ferent number cf 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 nucle:.r clear fuels that will fission when bombard-e w-energy neu mns.

FeMe is a particle). The neutrons can then react with term that describes a material which, When b mbarded by a neutron, becomes fissile.

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c reactor cannot explode like a bomb. A dif-ferent type of fuel and dif ferent fuel con-figuration are used in a reactor.

There are currently two different types of U.S. LWR's:

the boiling water reactor (BWR) manufactured by General Electric and the pressurized water reactor (PWR) manufac-l tured by Babcock and Wilcox, Combustion Engineering, and Westinghouse.

6.2.6.1.1 Boiling Water Reactors Figure 6-9 is a simplified schematic of a boiling water reactor. In this type of reactor, water is pumped in a closed I

5.2.6 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 sim-transferred through the metal cladding to g

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

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the nuclear steam supply system replaces water flows out the top of the core and the conventional fuel boiler and the nuclear through steam separators in the top of the g

fuel core replaces the fossil fuel supply.

pressure vessel. The separators clean and In LWR's, the heat energy comes basically

" dry" the steam before it is piped to the 5

from the fissioning of U-235 atoms, with turbine-generator (s). The turbine exhaust f

a small contribution from the fissioning is condensed and returned to the reactor f

of U-238 atoms. However, as the reactor pressure vessel to complete the cycle.

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operaten, a fissile atom (pu-239) is pro-Chapter 12 for a more complete description 1j duced from U-238.

For each gram of U-235 of steam power plants).

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consumed in LWR fuel, as much as 0.6 gram Because the energy supplied to the water

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plutonium formed undergoes fission in the (as steam) to the turbine, the BWR system 1

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core, thus contributing significantly to is termed a " direct cycle" system The pres-

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the energy produced in the power plant (AEC, sure in a typical BWR is maintained at about k

1974d: Vol. IV, p. A. l.1-2).

LWR's typical-1,000 pounds per square inch (psi), with a j

ly employ partial refueling annually, with steam temperature of 545 F (AEC, 1974d: Vol.

somewhere between one-fourth and one-third IV, p. A. l.1-18). Neutron-absorbing control of the fuel assemblies being removed and rods, operated by hydraulic drives located 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 t

a power plant for a period of five to six the heat output).

months to allow their radioactivity level one major concern with light water ta decrease prior 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 from nuclear weapons, it measures were in effect, such events would is important to point out that a nuclear cause the core to overheat and melt, and 6-28 I

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larg'e 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, 1974d:

(ECCS 's) to prevent meltdowns and contain-Vol. IV, p. A.1.1-21),

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-tem 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 c,orporate 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-containment 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 amploy a daal 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

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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 stema lines from 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 from 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 6-30 k

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_1 steam generator to begin the cycle over. No For example, in some plants, the contain-steam is generated in the primary loop and the water is returned to the core from the ment space is kept slightly below atmo-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-action is controlled through the use of be inward from the surroundings.

Other systems have double barriers against escape neutron-absorbing rodst however, in PWR's, additional control can be obtained through of material from the containment space.

In the dissolution of such variable-concen-addition, to condense the steam resulting tration neutron-absorbing chemicals as boron from a major break of the primary system, (which may also serve other purposes) either cold-water sprays or st'ored ice is in the provided (AEC, 1973: 1-17).

primary system coolant.

The PWR ECCS's consist of several in-6.2.6.2 Energy Efficiencies dependent subsystems, each characterized by redundancy of equipment and flow path, The overall energy efficiency for the Although the arrangements and designs of power plant is the ratio of electric energy output to total heat energy produced.

PWR ECCS's vary from plant to plant (de-LWR's pending on the vendor of the steam supply (both BWR's and PWR's) have energy ef ficien-cies around 32 percent, system), all modern PWR plants employ both as compared to 38 accumul'ator injection systems and pump to 40 percent for modern fossil-fueled plants (see Chapter 12).

injection systems. Accumulator injection The reason for this lower systems are called passive systems because efficiency is that LWR plants can only oper-they operate automatically without acti-ate at a maximum steam temperature of around vation of pumps, motor driven valves, 600 F While fossil plants can operate at 1,000 F or higher.

or other equipment. The systems consist of pressurized tanks of cool borated water which are connected through check valves to the reactor vessel. Should the prbnan coolant system lose pressure, the check valves would open and a large volume of water would be rapidly discharged into the 7M-reactor vessel and core. Two pump injecti (active) systems are also incorporated in PWR ECCS's.

One is a low-pressure system to provide coolant af ter the Maove mention accumulatte tanks are empty, and the other is a high-pressure system designed to fune tion if the break is small and the primary coolant pressure remains too high to acti-vate the passive systems (AEC, 1973: 1-14)

The containment structure for PWR's is of reinforced concrete with a steel lin and is stressed to withstand the maximum expected temperature and pressure if all d water in the primary system was expelled in the containment.

However, containment sys-tem designs vary widely from plant to plant 6-3; w

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