ML19321A566
| ML19321A566 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 06/26/1980 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | Colt S AFFILIATION NOT ASSIGNED |
| Shared Package | |
| ML19321A567 | List: |
| References | |
| NUDOCS 8007230626 | |
| Download: ML19321A566 (10) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION j,
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JUN 2 9 GEO Ms. Sylvia Colt 83 Horatio Street New York, NY 10014
Dear Ms. Colt:
This is in reply to your letter of April 5,1979, about nuclear energy.
I am sorry for the long delay in responding, but we have been very busy with the aftemath of the Three Mile Island accident.
After the accident at Three Mile Island, the Nuclear Regulatory Comission de-cided not to license new nuclear power plants until criteria for improved safety had been developed. The NRC has found that actions recommended by its own staff and by the President's Comission on the Accident at Three Mile Island in the areas of human factors, operational safety, emergency planning, nuclear power plant design and siting, health effects, and public information are necessary and feasible. Interim measures have been taken, and an Action Plan has been devel-oped to include other safety improvements, detailed criteria for their implemen-tation, and various implementation deadlines. Meanwhile, in order to avoid unnecessary delays, the NRC has approved the issuance of licenses for three nuclear power units to load fuel and, under specified conditions, to operate at low power levels for testing.
Every effort is being made to protect the public health and safety at all nuclear power plants that are currently in operation or that may start operating in the future. Any plants that are found to be unsafe will not be allowed to operate.
You asked for infomation on the process of producing nuclear energy.
Encicsed are excerpts on this subject from a report on " Energy Alternatives: A Ccmpara-tive Analysis."
Sincercly, AktS a
Harold R. Denton, Director Office of Nuclear Reactor Regulation
Enclosure:
As stated THIS DOCUMENT CONTAINS POOR QUAUTY PAGES 80.07230 M.
N-W i
Altertiatives:
A Comparative Analy. sis E')( c tER P TS Prep. red for c o e
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CHAPTER 6 THE NUCLEAR ENERGY--FISSION RESOURCE SYSTEM
6.1 INTRODUCTION
other atoms, causing them to fission, and thus create a " chain reactien." 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-tions are altered to make the reaction ating plant went into operation at In a nuclear reactor, the controlled cease.
Shippingport, Pennsylvania in 1957. The chain reaction creates heat, which can be use of nuclear power as an energy source convertedtoelectrgealenergy.
grew out of nuclear weapons development Three isotopes fission readily and are during World War II. With the creation of usua y referre as fissile fuels:
the Atomic Energy Commission (AEC) following U-235. Pu-239 (Plutonium-239), and U-233, the war came an explicit effort by the gov-when an ate = fissiens, the twe newly formed ernment to fund and develop the commercial at ms are ca led fission products or fission use of nuclear energy. The major rationale fragments. Since the splitting can occur behind this development has been the assump-1" * **#i**Y f dif *#*"t **Y**
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- tion of a large supply of nuclear resources
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. that could one day be substituted for the s r nt am, cesium, dine, kryptoru xeran.
more limited fossil fuel ' sources.
etc.
The nuclear fuels and = cst of these The development of nuclear fission as ssion products are radicactive, thereby an energy source has been strongly influ-
"9 Y~E#0 **
9 enced by the complex technologies and the prcblems that are unique to the nuclear hazards from radioactivity. The complexity pnwer industry.
of the technologies has required continuous
- research and. development, and as a result, 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 isotepes of an suited in a major role for the federal gov-element exhibit sb=ilar chemical properties e rnment 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-233, Uranium-235, and Uranium-238. All con-Nuclear.,ission 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 bor 7:d-v ed with low-energy neutrons. Fertile 1.
a particle)..The neutrons can than react with. bombarded by a neutron, becomes fissile.
term that describes a material Which, when 6-1 2:
~
. 6.2. LIGHT WATER FIACTOR (LWR) SYSTEM 6.2.1 Introduction The light water reactor gets its name from the use of ordinary water (terms light water ) to transfer heat from the fission-ing of uranium to a steam turbine. The pri-mary energy sources for the LWR is U-235,
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and there are 10 major activities in the LWR fuel cycle as indicated in Figure 6-1:
ex- !
t P1 oration for uranium; mining of uranium ore and reclamation; milling of uranium ore to Produce yellowcake (U 0 )t Production 38 of uranium hexaf'louride '(UF ) ; enrichment 6
to produce a higher concentration of U-235; fuel fabrication: use of the LWR to produce electricity; reprocessing of used fuel to recover the remaining U-235 and Pu-239 3
radioactive waste management; and transpor-tation of radioactive materials at various stages in the LWR system.
.Light water is pure H O (two hydrogen atoms plus one oxygen atom) 2 Heavy water is deuterium oxide, D 0 (two deuterium atems 2
plus one oxygen atem). Deuterium is a heavy isotope of hydrogen.
The product of a milling process that converts are containing 0.2-percent U 038 in-to "yellowcake" containing approximately 80-percent U Cg.
3
- 6. 2. 5.4 Fuel Fabrication The fuel fabrication step eenverts the enriched UF n
0 Pellets and then en-l 6
2 cases them in lon'g metal tubes known as cladding. From 50 to 200 of the cladding tubes are positioned in a grid to form a fuel assembly. Several of these fuel asse=blies are shipped to an LWR each year.
- 6. 7. ri 4
Radioactive Waste Management n
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Reprocessing
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v G.?.1 6.2.4 6. 2. 'i.1 6.2.
5.2 6.?.r.1 6.2.5.4 6.'.6 Fuel Electricity,
Exploration
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6 UF Milling Enrichment LWR Reclamation Fabrication Product. ion U
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G.2.C Processing Domestic Uranium E..'. 9 Transportation Lines Resources involves Transportation
Does Not involve Transportation l'i q u re 6-1.
Li gh t Water Reactor Fuel Cycle M L i
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.m reactor cannot explode like s bomb. A dif-ferent type of fuel and different 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-tured by Babcock and Wilcox, Combustion
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Engineering, and Westinghouse.
I 6.2.6.1.1 Boiling Water Reactors Figure 6-9 is a simplified schematic of a boiling water reactor. In this type 7
of reactor, water is pumped in a closed i.
6.2.6 Light Water Reactors cycle frem 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 ilar in nature to the fossil-fueled power the water flowing around the fuel assemblies.
i plants described in Chapter 12 except that The water boils and a mixture of steam and I
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 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 t) the f rom the fissioning of U-235 at:ms, with turbine-generator (s).
The turbine exhaust a small contribution from the fissioning is condensed and returned to the reactor of U-238 atoms. However, as the reactor pressure vessel to co=plete the cycle.
(See operates, a fissile at m (Pu-239) is pro-Chapter 12 for a more complete description duced from U-238.
For each gram of U-235 ef stern pcwer plants).
consumed in LWR fuel, as much as 0.6 gram Because the energy supplied to the wate.
is formed. Generally more than half of the from the hot fuel is transported directly Ij plutonium formed undergoes fission in the (a2 stets) 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.1.1-2).
LWR's typical-1,000 pounds per s uare inah (psi), with a ly employ partial refueling annually, with steam temperature of 545*F (AEC, 1974d: Vol.
somewhere between one-fourth and one-third IV, p. A.1.1-18). Neutron-absorbing control of the fuel assaiblies being removed and rods, operated by hydraulic drives located I
replaced with fresh fuel each year. Spent below the vessel, are used to centrol the fuel assemblies are stored underwater at the rate of the fission chain reacticn (and thus power plant for a period of five to six the heat output).
months to allow their radioactivity level One major concern wi'.h light water to 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 trem a high-A. l.1-lO. Since the his
.eal origin of pressure steam pipe rupture). If ao safety nuclear power is from nuclear weapons, it messures were in effect, such events would is important to point out that a nuclear cause the core to overheat and melt, and 6-28 a
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11oi1ing Water React or Source:
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m large amounts of high-level radioactivity by preventing any large pressure 1 might be released to the environment.
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To This pressure injectien poc1 also prevent such catastrophes, reactor systems rvos include emergency core cooling systems as a potential source of water fe: 3e emergency core spraying system im 1974f:
(ECCS's) to prevent meltfmwns and contain-Vol. IV, p. A. l.1-21).
ment systems for prevent:ng th e release of The " secondary" centain=ent I
radioactivity in the 77 cm is event of any type of the bu11 ding that hcuses the reac accident.
-nf its primary containment system (ne: p.0wn Although provisions differ from plant in Figure 6-9).
to plant, all BWR's have multiple provi-Reactor building 3 3re con-struc ced of poured-in-place, reirfer:cd cen-sions.for cooling the core fuel in an crete and have sealed joints and 2nte:1c:4ed emergency. Typical ECOS 's involve either double-door entries. Under accidens condi-a high-pressure core spray system (early
- tions, or both core sprays and a high-pres-the normal building ventiLi;1cn syr-BWR 's) tem would shutdown, and the builttng would sure coolant-injecticn system (latest SWR's) to assure adequate cooling of the core in be exhaust-ventilated by two parallel stand-by systems.
the event cf reactor system depressurization These ventilating sys tems in-corporate effluent gas treatment devices.
(AEC, 1974d Vol. IV. pp. A. l.1-2 0),
including high-efficiency particulate To prevent such accidents frem releas-ing radioactivity and other pollutants to cleaners and solid absorbents for trnpping radioactive halogens (particularly iodine) the environment. BWR designs generally pro-vide both " primary" and " secondary" contain-that might have leaked from the pri=ary centainment system (AEC, 1973: 1-24).
i ment. The primary containment 1
system, shown in Figure 6-9 as the " containment structure,"
6.2.6.1.2 Pressurired Water Reacter is a steel pressure vessel surrounded by re-s infcreed cencrete and designed to withstand Figure 6-10 is a si=plified schematic the peak transient pressures that of a pressurized water reactor.
The pri-might occur mary difference between a ?WR sad a SWR in the most severe of the postulated less-is that all PWR's empicy a dual coolant of-coolant accidents. The primary contain-syste for transferring energy fr:
ment the systa= employs a "drywell," which en-closes the entire reactor vessel and its reactor systems. In the dual coolant sys-tem, the pri=ary 10cp is water that recirculation pumps and piping. The drywell is pu= ped through the core and the heat is connected to a lover-level, pressure sup-ex-ch anger.
pression chamber in which a large poci of The secondary loop is water that 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 from the re.ctor to the turbine-generators (the 600 F by the nuclear core in the pressure 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 from the reactor system would be released high-pressure water is piped cut of the 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 co=pletely condensed, there-bine.
The secondary stream is then con-densed and the water is pc= ped back to the 6-30 E
Pressurized water reactor (PWR) containment structure steam steam line sum 2=
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Pressurized Water Reactor Source:
Atomic Industrial Forum, Incorporated.
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.a steam generat:r to begin the cycle over.
- o For example, in scme plants, the contain-steam is generated in the primary locp and ment space is kept slightly below at=o-the water is returned to the core from the spheric pressure so that leakage through steam generator to start the primary cycle the
- ntaineert walls wculd, at most tires.
over. As in SWR's, the nuclear chain re-be inward fren the surroundings. Other action is controlled thr: ugh the use of systers have doutie barriers against escape neutron-absorbing rods; however, in PWR's, of material from the ccntainment space.
In additienal centrol can be ettained through addition, to condense the steam resulting the dissolution of such variable-concen-frc= 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 (AE, 1973: 1-17).
primary system coolant.
The PWR ECC5's censist of several in-6.2.6.2 Ene.rgy Efficiencies i
i dependent s ub sy st em s, 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 cutput to total heat energy produced.
LWR's l
PWR ECCS 's vary f ram plant to plant (de-(beth SWR 's and PWR 's) have energy efficien-j pending on the vendor of the steam supply cies around 32 percent, as ccmpared to 39 i
system), all modern PWR plants employ heth to 40 percent for modern foss:1-fueled plants I
accumulator injection systems and pump (see Chaptar 1:1. The reas n f:: this 1:wer j
in3ection systems. Accu =ulater injection efficiency is that LWR plants can cnly cper-systems are called passive systems because ate at a raximum steam temperature of arcund f
they operate autematically without acti-600*r while fcssil plants can operate at f
vaticn of pumps, motor driven valves, or 1,000 F or higher.
other equipment. The systems consist of pressur: zed tanks of cool borated water which are connected througr. check valves to the reacter vessel. Should the primary coolant system lose pressure, the check valves would open and a large volume of 6
water would be rapidly discharged into the reactor vessel and core. Two pu=p injection (active) systems are also incorporated in PWR ECCS's.
One is a low-pressure system I
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to provide coolant af ter the above mentioned accumulator tanks are empty, and the other is a high-pressure systen designed to func-tion if the break is small and the primary coolant pressure remains too high to acti-9i vate the passive systems (AEC, 1973: 1-14).
k The containment structure for PWR's t
I is of reinforced cencrete with a steel liner and is stressed to withstand the maximum expected temperature and pressure if all the water in the primary system was expelled into the contain=ent. However, containment sys-tem designs vary widely frem plant to plant.
l 6-39 L
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