ML20009C453

Requests Info Re NRC Ability to Review Proposed Htgrs. Scientific American Article, Gas-Cooled Nuclear Power Reactors, Dtd June 1981 Encl

ML20009C453
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Site:	Fort Saint Vrain
Issue date:	05/26/1981
From:	Ahearne J NRC COMMISSION (OCM)
To:	Dircks W NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO)
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ACTION CONTROL DATES CONTROL NO COMPL otAouNo 6/ 9/ 81 10507-

,_ Commissioner Ahearne ACKNOWLE DGM ENT DATE OF DOCUMENT 4

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INTERIM REPLY 5 /2 6 /81

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PREPARt FOR S!GNATURE

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l OTHEPt DESCHlPTION O LETTEH h5) MEMO O nEPOnT O OTHER SPECI AL INSTRUCTIONS OR REMARKS I

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Req if soneone were to propose an PRIORITY j

HTGR - are we ready to r'eview it?

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CLASSf FIED DATA OOCUMEN T/ COPY NO.

CLASSIFICATION l f

NUMDER OF PAGES CATEGOHY I

POST AL REGIST RY NO.

O N51 O no O rno ASSIGNED TO.

DATE INFORMATION HOUTING LEG AL REVIEW D FINAL U COPY 7enton, fMR S/26/81 Dircks case A55lcNED m DATt NO LEGAL OBJECTIONS I

% hut 5/27/81 Cornell Denton 4 Murley i ffhOmpsOn NOTIF Y Rehm 1.

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NNC F6R *.I EXECUTIVE DIRECTCH FOR OPERATloNS DO NOT REAf0VE Uf/S,COEY PRINCIPAL CORRESPONDENCE CONTROL d'0107210070 810612 PDR ADOCK 05000267 p.

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Bill, if someone wants to propose an llT to review it?

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>e SCIENTIFIC Established 1845 hy

{\\ June 1981 Volume 244 Number 6 I

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Gas-coo _ed Euc_ ear Power Reactor.s j

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ti Although the U.S. has only one such reactor, they ha ve served well 1

overseas. Tl ey have zin accraccir afety feature: a loss-ofcoolant accident such as the one at Three Mile Island is all but impossible t

by Harold M, Agnew 3

n Klarch,1979, the nuclear power in-simple explanation. The pressurized-plant's rated capacity is 330 megawatts

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dustry suffered a shock fra:, which light water reactor is a straightforward of electric power, or htWe, which is

-- it has not yet recovered: the acci-adaptation of the highly compact reac-about a third the output of a standard dent that disabled one of the nuclear re-tor designed to propel the first nuc! car-commercial power plant. The reactor actors at Three hlile Island. It is ironic powered submarine, the U.S.S. Nauri-has been operating at up to 70 percent of that an event that caused no discernible lus. launched in 1954. An ekctric power rated power and has recently been re-ph>sical harm to anyone crippled the scrsion of the submarine reactor, built leased by the Nuclear Regulatory Com-prospect for expanding nuc! car power at by the Westinghouse Electric Company, mission for testing at up to full power.

the sery time the nation was becoming went into service at Shippingport, Pa.,

The Fort St. Vrain demonstration generally aware of the r,eed for new do-three years later The General Electric plant was designed and built for the mestic sources of energy.

Company soon introduced a reactor de-PuoHc Service Company of Colora.

Although the experience at Three sign of its own, the boiling-water reac-do by the General Atomic Company hiite Island demonstrated to the satis-tor, in which the heat generated by nu.

as a part of the Atomic Energy Com-fmon of technically qualified people clear fissior, was carried cway from the mission's Power Reactor Demonstra-that present day water. cooled nuclear core by steam rather than by pressurized tion Program.nis followed the success-reactors offer no significant threat to the hot water.

ful operation of a 40-htWe prototype, health and safety of the general public, Peach Bottom Atomic Power Station it also showed that such accidents and In both types of reactor it is essential No.1, on the system of the Philadelphia cquipment f ailures can jeopardize the 1 that the reactor core not be uncov. Electric Company In its seven and a operability of t;.c plant and place at risk cred, even briefly, lest the temperature half years of operation, from 1967 the heavy capital insestment it repre-in the core quickly rise and melt the through 1974, the Peach Bottom reac-sents. In the extreme case an accident metal jackets around the fuel pel.;ts, ter was available for service 86 percent su,h as the one at Threc \\lile Island can as indeed probably happened at Three of the time (except for scheduled shut-threaten the financial survival of the op-51ile Island.1.ight water reactors are dow ns relr ted to the research and devel-erating utility, equipped w ith redundant safety features op nent objectives of the reactor itself).

Perhaps the principallesson of Threc

,o cope with a " loss of coolant" acci-Tu comparable figure for all U.S. nu-hide Island is that the current genera.

dent. In such accidents the emergency clear reactors is about 66 percent.

tion of nucleer power plants is vulnera-equipment is designed to flood the core The key safety features that differenti-ble to certain rare events that can lead to with water from a plentiful and assured ate the helium-cooled reactor from wa-a condition where the time available for source. W' n the normal coolant flow ter-cooled reactors are two. First, since I

responding correctly can be less than a w as interr ted at Three hiile Island, a the reactor core is cooled by a circu-minute. In such low probabihty events sequence of impu ',able events, includ-lating gas completely confined within a if the appropriate actions are not under-ing apparent operator error, interrupted massive reactor vessel, the reactor can-taken immediately, the consequences the delivery of the emergency cascade not lose its primary coolant because of a can be estremely costly even when pub.

of water for too long a time.

rupture of pipes outside the vessel. Sec-lie safety is not at issue. It is reasonable All but one of the 71 commercially ond, if the circulatier 'f the gas is in-to ask: Do we need to be content with licensed and operating nuc! car power terrupted by some mishap to all of I

nuclear reactors cf a & sign such that plants in the U.S, which currently sup-the main helium circulation system, the i

operaton must react cotrectly within a ply about iI percent of the nation's elec-temperature within the reactor core ris-3 minute in order to prevent damage to tric powcr are light water reactors. The es only slowly because the fuel elements the reactor? The answer is no.

exception is a helium cooled reactor, are embedded in a massive matrix of That being the case, how did the U.S.

the Fort St. Vrain Nucl ar Generating graphite, which serves as the moderator nuclear power inJmtry come to follow Station, which was accepted for service for slowing down neutrons and which the path it did? The dominance in the in the summer of 1979 by the Pub-can absort the heat relcased by fission U.S of the light. water rtactor has a lic Service Company of Colorado. The prodt cis after the nuclear chain reac-(..

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lilGil.1Dirl.R AIL'RE GA% COOL ED REAClOR til1GR) is mal etEclency of 38.5 percent, s.hich is comparable to the efficiene) a second. generation splem more ethcient than the 78 light. water of the best fouil-fuel plants and is higher than the 32 to 33 percs:4 at.

power reactors that now supply about il percent of U.S. electrhit).

tained by current light-w ater reactors. Because the core of the If IG R in al h IIIGH designed h3 the General Atomic Company the moder.

contains nearly 1,500 tons of graphite, which has a high capacity for ator othe material that slows neutrons in the reacto; corells graphite absorbing heat, an IITGR is much Irw likely to be dan. aged than a a6.ed the coolant h helium. In light w ater reactors ordinary (but de.

light-water reactor if there is an interruption in the flow of coolant minerahsed and conditioned) water sets es both as the moderator and or a low of coolant. It was such an interruption that caused the acci.

as the a colant..he llI GR shown would hase an output of st;0 mega.

dent at the Three Mile Island nuclea; paaer station near liarrhin.rg, u atts of electrisity (M% el, slightly leu than that of the largest pow er Pa. The reactor core and steam-generating spiem.f the II't GR are plants whhh generate 1,000 M% e or more. The llIGH has a ther.

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g. IITGR IN illE U.S. is near Denier, Colo. It is the Fort St. Vrain Nuclear Generating i

the fuel elements would reach 3.000 de.

Station, daigned by General Atomic and on ned and operated by the Public Sersice Company of Cotorado.1 he plant, uhkh has a capacity of 3J0 31We, was placed in operation three 3 ears gtces Fahrenheit and fuel failure would ago and has since supplied more than two billion kilowatt hours of electricity. On seieral oc.

J begin in as little as 50 seconds in a pres-casions the forced circulatian of coolant in the reactor core has been interrupted for periods f

surized water reactor and in less that of as much as 15 minutes without doing any detectabte harm to the core or to the fuel eternents.

two minutes in a Soiling water reac.

tor. With a helium cooled reactor, in a compara' ole event involving a system ence at the Los Alamo

• Scientific Labo. or 20 percent than the best estimates for depressurization and the total failure ratory, gathered at La Jolla, Calif., to advanced light-water fuels." He added of the helium circulation system, more consider the problem of designing a re-that HTGR's "have some safety advan-than an hour would be req iird for the actor that would be both more efficient tages. They are machines in which you temperature inside the coac o reach and inherently more " forgiving" than don't have to do a lot of things in a hurry i

3,000 degrees F. At that temperature the reactors then t.vailable. Among if something goes wrong because the l

both the coated fuel particles and graph-those present were 11. A. ilethe of Cor-core structure is a great massive pile of ite fuel elements in a helium cooled re-nell University, Freeman J. Dyson of graphite, a very high temperature and acto wonld not be attested. The fue' the Institute for Advanced S*udy, Peter stable traterial, so that if you get a pow-p.u ticles and graphite can readily with-Fortescue of the Atomic Energy Re-er dropo!I or the plant circulators go stand temperatur es of up to 4,000 de-scarch Establishment at liarwell.n En-out, [you hase time] to sit down and grees F., which would not be reached gland and Frederic de Mclimann, who think about what to da" unni at least 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> had elapsed. In was then president of General Atomic.

short, there i, ample time to institute a Out of these early deliberations, aided "J"he first series of gas cooled reactors s arict) of reasoned emergency mea-by concepts from liritain and France, L built in Britain were called Alagnox l

sures for restoring the flow of helium esolved the concept of the high-temper-reactors because the fuel rods, which coolant attre gas cooled reactor.or HTGR, test.

contained natural unenriched uranium, ed at Peach Hottom and or, a larger were clad in a magnesium alloy. The "T*he sirtues of gas cooled graphite re-scale at Fort St. Vrain. Ilecause the U.'i reactor core. incorporating many tons 1 actors base been widelv recrgnized has plentiful supplies of helium, that gas of graphite was housed in a large and elsew here in the world. In the 1950's and could be elected as a coolant instead of expensive steel pressure vessel many l

196%, w hen the U.S. had committed car %n dioxide. Helium has the impor-times bigger than the pressure vessels l

itself tolight w ater reactors,liritam and tant adsantage that it is stable to the needed for light-water reactors. Then in i

France desclopW gas-cooled graphite-high radiatic - 'lus in the reactor, does 1958 French engineers saowed that the moderated reactors, in which the cool-not become

. ioactise, is chemically steel vessel could be replaced with a ves-ant was carbon dioside rather than heli-inert and ho excellent heat transfer set of prestressed concrete that could um. Britain now has more than 40 gas-characteristics.

be constructed in sizes large enough tooled reactors in operation or under

'the attractise features of IITOR's to house the en' ire reactor system, in-l tonstructioq, France has seven and it-were summariicd by Joscrh 51. llen. ciuding the steam generators. The al), Spain and Japan have one each.

drie, chairman of the Nuclear Regulato-prestressed-concrete reactor vessel, or

\\ lore than 600 reactor > cars of operat-r) Commission, in testimony before a PCRV, is kept in compression at all ing esperience has be-n acquired with congressional subcommittee in Starch. times by a network of redundant, ten-

.ne Europcan gas cooleu teactors. Such 1980 Such reactors, he said "hase efh-sioned steel tendons that can be moni-reamrs base accounted for nearl*, a ciencies as good as the best fossil-fuel tored and retensioned or even replaced hf th of the 'otal nuclear power ;ener. plants and are substantiall> more effi-if necessart Tightness against leaks is ated in w estern Europe, Japan and the cient ihan the water-cooled reactors. ensured by a steel liner affised to the l.,

L' 5. so far.

They not only get better thermal effi-inside of the PCRV, which acts only as a

{'L The Ilritish and French efforts uere at ciency but also get better eners) utiliza-membrane seal to contain the coolant.

an early stage m 1956 when a group of tion out of each pound of uranium that Tne liner and the walls of the PCRV phy icists many of them with esperi-is mined, better, m fact, b) riobabl> 15 are cooled by water circulating through

f abes thzt are welded to the outer sur.

fuel wss urtnium oxide, a ceramic, clad raised from ab'out 30 percent to o little f:ce of the vessel.

in stainless steel, a chinge mide possible more than 40 percent.

PCRV's were subsequently edcpted by 'he cdoption of slightly enriched ura-In the U.S. the Atomic Energy Com-for all French and Ilritish gas-reactor nium. With the new fuel AGR's could mission (a predecessor agency of the systems. The high degree of safety af-operate at higher temperatures than the Department of' Energy) nurtured inter-forded by the concrete vessel contribut-Magnox fueled reactors and were able est in gas-cooled reactors in the 1950's ed to the llritish decision to construct a to " burn" more of the utanium 235 in and 1960's by supportir.g the study of second genTration of reactors known as the fuel before refueling became neces, several advanced reactor concepts. One advanced gas reactors (AGR's) near ur-sary. Wi*h higher temperatures the cffi-of the AEC's main objectives was'to re-ban sites. In this second generation the ciency of c!cctric power generation was duce the amount of uranium required HELlUM CIRCULATOR

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W e n y #y ' L ll A i m v o y , pe HELIUM I I ~ [ (t STEAM f CONDENSATE FROM TL7 BINES STEAM TO TURBINES REACIOR CORE AND %IEA*l GENERA'IORS of the llIGR from ISe reactor core at a temperature of 1,266 degrees Fahrenheit are enslosed in a manh e prestrewed concrete reactor sewel(PCRV). and enters the base of the steam generators, where le makes two pas-l'or a reattor designed to generate 860 SIWE the PCRV would be 102 ses oser an array of helical and straight steam cow /'ater boils up-fect in diameter and 95 feet high. ( A prev. urised.lig,ht-water reactor ward through the colh and is further heated as it pawes downw ard to larger capatit3 s shown at the same scate in the illustra-emerge as superheated steam with a temperature of 1,000 degrees F. i a.f slig'.el3 tion on the oppmite page.) The graphite core of the 560-SIWE IITGR and a prenure of 2 500 pounds per square inch. Not show n are three hits a cylinJeital solume 26 feet in diameter and 21 feet high. IIsli-coolant loops in which water-cooled !. cal eschangers can remose um at a peeuure of 1,050 pounds per square inch h circulated it. cough heat from circulatiny helium when the steam-ge erating loops are some 27,000 s ertisal thannek in the core b3 four primary circulator. cat of sessice. Af ter a reactor sintdown hwion prm'ucts in the core of whic h onl3 two appear in this cams section. T he helium emerg% release beat at a raie that is high initi..ly but declines esponentially.

per uai.t cf electric power; tt th:t time - ur:nium resources appear;d scarce in STEAM TO TURBINES rs!? tion to the prrject:d needs. As a re-t 'sult the study emph shed reictor con-c: pts that wefe either breeders or ad-i- v nceil converters. A breeder creates at lezst one atom of new fuel for each atom of fuelconsumed. Advanced converters i generally create from,7 to one atom of / fuel for each atom consumed. Light wa-REACTOR NSTEAM GENERATOR ~ l l tir reactors yield between.5 and.6 atom $ERE j [ of fuel for each atorr. consumed. The f I high temperature gas. cooled graphite-I moderated reactor qualifies as an ad. vanced converter. It was one of the de-signs that survived the inevitable weed-2l ing out. The ifTGR had strong support 1 frorn the utility industry because it is competitive in capital costs with light. / k wrter reactors and because it exploits a l l uranium. thorium fuel cycle with a low 1 uranium consumption and therefore low C h% l/ mT c, f, / The continuing evolution u gas reac. SKAM CONDENSATE 2 FROM TURBANES tor technology m. Europe and the Li has led to a convergence in at least A g 4 6 L - REACTOR two itn,sortant particulars for the next

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i 4 ide as a coolant and the reactor core is M charged with nuclear fuel in a unique U + system that dispenses with the need for a }!? metal cladding. The two features have ( / V been demonstrated not only a'. Peach ( x 1 9 Dottom and Fort St. Vrair hit also in LIGHT WATER two European reretors. The British op-CC9 TANT INLET J P erated a helium. cooled 20 h1W thermal l' J tett reactor in southern England from PRESSURIZED-LIGHT WATER REACTOR has been the commonest type of nuclear h 1965 to 1976. In Germany ara llTGR of Power reactor in the U.S., with 44 reactors now in operation. Another 24 reactors are of the 15 htWe (called tb> AVR)has been ge boiling-water type,in which heat is carried off from the core by steam rather than by pressur- {i -j crating electric power since 1967, w n, ith 12ed heated water. The core of a pressurized-light water reactor rated at 1,100 MM e is shown i'i r the outlet gas temperature bemg as high here. It is housed in a steel pressure vessel about 15 feet in diameter,40 feet high and from six as 950 degrees Celsius. (The tempera-to 11 inches thicia the vesselis designed to operate with an Internal pressure of 2,250 pounds per square inch. The coolant water leaves the reactor at 610 degrees F. and passes to four ture of water leaving the core of a pres-steam. generating loops, only one of nhich is shown here. Steam emerges from the generator at .i surized. light. water reactor is about 610 540 degrees F.and a pressure of 1,000 pounds. At this temperature and preuure the system's degrees F., or 321 degrees C.) A 300- thermal ei!iciency is only 32 to 33 percent, compared with 38.5 percent for an HTGR system. AlWe plant based or the AVR experi-ence is now under construction in Ger-many and is scheduled for start-up in tal investment. The reactor core is con-auxiliary cooling system is cooled with ]' 1984 or 1985. In the U.S. the Fort St. tained within a multicavity prestressed-water circulated by electrically driven Vrain reactor of 330 N1We has provided concrete reactor vessel IIelium leaves pumps that can be powered,if need be, more than two billion kilowatt hours of the core at 1,266 degrees F. (reduced by diesel generators. power since 1978 and has demonstrated from 1,494 degrecs F. at Fort St. Vrain) The combination of a stable, inert gas the fuel performance and safety charac-and passes through four primary cool-for a reactor coolant and a highiy tem-teristics of a conternporary llTGR de-ant loops, where steam is generated pera:"re-resistant graphite,: ore struc-sign. The reactor has been subjected to at a temperature of 1,000 degrees F. ture an.ews steam to be generated at the test transic7ts up to and including the and a p essure of 2,500 pounds per high temperatures and pressures found complete loss of forced coolant circula-square in:h. in the modern electric-power plants that tion with no adverse effects on the reac. IIelium is it 4cd through each cool. burn fossil fuci The net electric gener-for core or on other primary compo-ant loop by a circulator driven by an ating efficiency of the HTGR reference nents of the system. electric motor. (The Fort St. Vrain cir-design is 38.5 percent, slightly below the i On the basis of the Fort St. Vrain ex-culators are driven by steam.) The core 39.2 percent achieved at Fort St. Vrain. l perience General Atomic, in cooper-also is provided with an auxiliary cool. The small reduction was made in the I ation with Gas. Cooled Reactor Asso-ing system consisting of three loops, interest of simplifying the steam-gener. I ciates (an organization of U.S. utility each sutlicient by itself to deliver 100 ating system and to furnish still further I! companies) and the Department of En-percent of the required cooling when the creratir,g and safety margins. ergy, has developed a reference design helium in the reactor vessel is at the nor-A fundamental property of the heli-fer an IITGR of 860 htWe. The goal mal working pressure of 1,050 pounds um coolant, a confined gas that cannot has been a design that is simple and con-per square inch, or 50 percent of the possibly condense to liquid torm in the servative and that places high empha-cooling when the vessel is depressur-system, is that it follows a linear temper-sh on the safety and protection of capi. ired. The helium that passes through the ature pressure relation; therefore instru-t 59

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p- - i. -g wg sure can provid2 mdependent checks %,,9' p/nl. ' $ on cash other. Because there is no lig-M; M G Ugm.i uid: gas interface, as there is in boiling- , p %;. wn f pJ.t N[t W A water reactors (and in pressurized-witer NU Ilff? .,- f ' ~ ~~ reactors under certain. emergency con-wf [" w-q. Y.1,h. t].M@ U J' ' ditions), a single unambiguous signal-

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• p ' O pressure-always indicates the presence g~.fQ

.y 'y,G'J.,4j'?d and physical condition of the coolant. 9% . / at Q .*g1. < . Rapid depressurization of the primary cooling system can be tolerated with-i p*i. 5f.M.. y M -out concern that voids have formed and M .f [7Y [' Q,rF[c,"g% J..- e/.4 Ns L* 3 WP d left part of the core uncovered, as can .~ My happen when pressure is released from d / L _/ 'AO O, y'^ %. b' f. water that is above its atmospheric A t Hi boiling point.

1. !

p ,?f >[ [w -] The Fort St. Vrain ex perience has ver- ,fied severalimportant safety and oper-i 1 s ]. ating advantages of H1CR's. Operat. . ]' p., j. / ing and maintenance personnel have re-6 ceived exposures to radiation far below n g$ .M, j. /. - the limits established for nuclear plants. M / Fewer than 10 workers out of a total of gyp f, g~/ W.? h several hundred have received amounts l p Q p 't. of radiation that were even measurable. l Q,,f*,'D;x 4_. d I he Fort St. Vrain system has re-d 4 NcM b ,4-g sponded smoothly and gracefully to 4 load chang,:s caused either by transient kyg 5% P, my gQ* 9;;h,g M'c.fyn. e,.N.3 M)p excursions in the power-generatmg cy-Wm cle or by the temporary shutoff of equip-t L w ON ment within the plant. Because the core i of the llTGR is large and releases less heat per unit volume than light-water reactors do and because the massive l core, incorporating some 1,500 tons of i graphite, has a large capacity to absorb heat if coolant flow is reduced or inter-rupted, the reactor responds slowly to an unexpected operational upset, allow-ing the operators enough time to take appropriate action: hours rather than seconds. i At Fort St. Vrain five such upsets have interrupted the forced circulation of he-lium for extended periods without giv-ing rise to a measurable increase in the temperature of the core or harming the / / o plant or the fuel in any way. The rist of f s o damaging the reactor or the reactor core s ^ NUCLEAR FUf L p through operator error is virtually elim-inated. Thanks to the IITGR's thermal "I stability the system for bringing the ac-tivity of the reactor to a halt by the inser. D tion of neutron absorbers and the sys-tems for emergency cooling can be of simple design. There is also ample time \\ for Such systems to be actuated manual-ly if it is allowed by regulation. One con- \\ CARBON BUFFER sequence of the Three Mile Island ac-N cident is that the Nuclear Regulatory Commission now requires the full-time

1. f n on-site expert, called a DENSE CARBON shif t technical adviser, at nuclear power plants. Fort St. Vrain is the only reactor SILICON CARBIDE p

~ exempted from this rule; an expert is not DENSE CARB required to remain on the site but is on call to report within an hour. The prestressed oncrete reactor ves. I'?El. PARTICI E dn eloped for IIIGit systems b.03 ineh in diameter, about the size cf a sel is incorporated m the design as a ma-grain of sand. A crou section of the particle h enlarged 150 diameters at the top. T he nuclear jor safety feature. First, a catastrophic tuct itsett h the cr3statline-tilse material in the center. It conshts af uranium a=> carbide in which for best performance the content of the fiuionable helope uranium 235 h enriched to rupture of the PCRV is such a remote 93 percent. t.myers of carbon and silicon carbide are built up by a high-ternperature proccu. possibility that risk analysts character-60

m. e ite it as beins incredible. $s cry steel ten-

• don that gises the PCRV its strength is f"n log l,

A Og independenrynd redundant; the vessel is QUW No h' @ol i&- O >3S0% in a tonstant state of compression. Sec- [R ' ' 9 [Sc.;O Vdi. .pOl c ond, the PCRV is designed to withstand y 4 an uhimate prenure of more than twice Ww, f :

1. ' ddT gbb'ofo % Of p oh p o$Of*0 d s

l the normal operating pressure, or some b WM( tc i 2.400 pounds per square inch. Any ' NN f g ' 2 'O e O W, u,, O, N Ci[k,'O.'O hhy)NOW j . o'; O, crack in the steel liner that might result from excesshe pressure can do no.nore M' C o O \\hoO i 7[ h L W o ;,O o, g l O, Oe than give rise to a slow gas leak; such ,'d N c4{M i p leaks tend to seal themselves when the 4' 5O 0' L G[G..g Ggcge pressure is ieduced slightly. Third, total %,?p@p E c depressuritation can result only if there

p g 9

Q o c/pG r a'o n I b'O[ipg'8 ,o g Q: is a failure of one of the pipe penetra-gg Op,- tions or small service lines that pass

1. - g mgd['S f 4

o i through the wall of the PCRV. Such a 26 N WS O If ;q. y L. EgI h> pothetical failure is ar. extremely low- ~ i t probability event. Alormver, at each yg.; E ~, ;t W N. penetration site the vesset i equipped g T 5pp; with flow limiters that prevent the rapid M ^7 release of gas that could cause structur-i al damage to the core or to the cool. g mg system. b-The improved performance charac. l reristics of the llTGR also otter sev-eral ensironmental advantages over the FUEL ROD AND FUEL Ill.OCK for an IIIGR are shown respectively at the left and the current generation of reactors. Because right. The fuel rod, about 2.5 inches in length, condsts of tens of thousr.nds of fuel particles j an IITGR operates at an effkieracy of bound in a graphite matrix. Each fuel block, *hich is approximately 14 inches across and 31 r about 39 percent compared with an etti. inches high, holds 1,656 fuel rods packed in hexagonal arrays. The numerous empty channels cicncy of about 33 percent for light wa-in the block are paths for the flow of helium. The large central hole accommodates a mecha-nism for inserting the fuel blocks in the core of the reactor. The core of an 860-31% e reactor ter reactors, an 11.TGR releases about 25 will require 3,512 blocks. Each 270-pound fuel block contains on the moerage 1.54 pounds of percent len waste heat to be dissipated U-235 and 35 pounds of thorium 232. In its four-} ear residence in the reactor such a block into the surrounding environment. If the w ould31 eld eners) equisalent to 2,500 tc,ns of coal or 12,000 harrels of fuel oil If the unburned heat. in the form of hot water is reject. U.235 and the U.233 created from thorium were recosered and recycled, the energy equis. 8 ed into a nearby lake or river, concern alent of the original nuclear fuel would rise to some 11,000 tons of coal or 54,000 barrels of oil about raising temperatures to a po.nt harmful to the aquatic ecosystem is re-I duced proportienately. If cooling tow-shipped off-site with little difTiculty or tenance and refueling. For example, the crs are used to dissipate the heat, they retained on. site. The solid wastes pro. entire primary coolant, helium, is con-consume less water and can be smaller duced by an IITGR should total less fined within the prestressed-concrete re-and less expensive. If cooling ponds are than 2,000 cubic feet per year. Some 80 actor vessel. The PCRV itself provides used, an iITOR plant with about a third percent will consist of low-level waste all the necessary ;hielding for personnel, more megawatts of capacity than a (such as paper, filter elements and spent so that maintenance work can be done i bght water plant can be sited on a poad resins) that is only slightly contaminated throughout the reactor building while .j of a ghen site w ithout exceeding a spec. and can be shipped off-site in drums for the plant is in operation. Because the l itied nond temperature. Where dry cool-burial or burning with virtually no effect entire secondary steam system is essen-ing towers must be adopted to mect en-on the environment. The remaining 20 tially free of radioactivity all equipment k vironmental regulations or fit available percent will be intermediate-level waste, in the steam cycle outside the PCRV, water supplies, the loss of plant capacity consisting chiefly of reflector blocks, including the turbine-plant equipment, in hot weather will be only about half which must be periodically replaced. can be operated and maintained as it as great w ith an llTGR as it is with exist-Such waste can be shipped off site in would be in a plant fired with fossil fuel. in; nuclear power plants. As a result an shielded 55-gallon transport casks for Because the amount of steam flowing to 11 TGR plant can be situated at a remote long-term safe disposal. the turbines in an llTGR plant is only arid or semiarid site with a smaller pen-liclium parification and gas recovery about 60 percent as large as that flowing alty in cost. s> stems in porated in the standard to the turbines in a light-water power The lesel of radioactaity in nor-IITGd pla. hould reduce the radioac-plant of the same output, all the equip. mal disci.arges from all nuclear pow-tive levels in released gases to several ment associated with the steam and l cr plants is carefully monitored. An orders of magnitude below the current feed-water cycles of an llTGR plant is 11TGR plant inherently releases into the Government regulation of five milli-small and therefore casier to maintain. plant prosen streams less radioactiv-rems per Scar. Tritium (the radioactive in general, maintenance, repair and han-it) and at lower concentrations than a isotope of hydrogen) generated within dling costs are lower in an 11 FGR plant light water reactor does. In addition an the primary system of an llTGR is re-than icy are in light water plants be-IITGR incorporates features that will moved in the helium purification sys-cause helium, unlike water, is inert, non-3 ensure that releases of radioactivity tem by an oxidizer that conserts the trit-radioacthe and noncorrosive. i from the plant to the environment are ium into tritiated water, w hich is subse-One big advantage of gas as a coolant l 1 cuentia!!) 7ero Routine decontamina-quently solidified and handled as solid is its transparency, which maics it pos-ill; q tion procedures can be expected to pro-waste that can be readily isolated as the sible to inspect man) areas within the 1 Juce small solumes of low level liquid tntium decays. (The half life of tritiam PCRV sisually. The radiation shield-l' l a astes (!cw than 2,000 gallons per year is 12.26 years.) ing inherent in the design of the PCRV ',t with a toul actnity of less than 150 The itTGR has evohed a number of makes it possib!c to carry out many in-c urieu Such small solumes can be features that simplify operation. main-spection and maintenance tasks while 61

C. TEAM.TfMPEnATURE 540 the reactor is rurinmg, w hich reducss the. i iDEGREES FAHRENHEIT) .,egV ,e timt.the reactor must be taken out cf service for such purposes. Essentially' all structural members cf 1,00o the PCRV, such as the vertical tendons and the circumfe'rential cable wrapping, can be inspec,ted visually while the reac-NET PLANT THERMAL o. W 32 tor is operatmg. Selected members are EF FICIENCY (PERCENT) ~ continuously monitored for changes in tension or strain that wou!J indicate a 38 g deterioration in performance. If neces-sary, a,v structural member can be re. 3 external concrete surfaces, placr excep,15e immediately surrounding REACTOR CORE POWER DENSITY . w (WATTS PER CUBIC CENTIMETER) A j q N, p, 100 the ports for the control rods, can be inspected visually while the plant is run-ning. The control-rod ports and the sur-7.1 faces surrounding the site where the control-rod drives penetrate the PCRV can be readily inspected in the course of refueling. MAKEUP COOLING WATER REQUIRED p g g., (WET COOUNG TOWERS WITH FORCED [q v - , *;se 19.900 JK-ORAFT. GALLONS PER MINUTE) Decent refueling experience at Fort St. R Vrain has demonstrated the case of 14.400 handling the llTGR's block type fuct el-R

• IIS 7c'tEs$E ements. About 240,or a sixth,of the fuel 0

YEARS OF PLANT OPERATION clements were ternoved from the core (SHORT TONS OF UiOs) and replaced with fresh fuel; the other 1,240 elements were left in place. The [ PWR URANIUM OF LOW 6.000 refueling crew was exposed to such low w ENRICHMENT ,Cj$ , ONCE-THROUGH levels of radiation that measuring them FUEL CVCLE called for a microrem meter. By extrap. HTGR: URANIUM OF MEDIUM ENRICHVENT 4.510 olating from existing data one can cal-culate that the sum of the integrated man-rem exposure for the entire refuel-ing operation following on the opera-7 PWR LOW-ENRICHMENT URANIUM q 4.100 tion of the reactor at full power will be WITH RECYCLE OF PLUTONIUM W'%RCYCLE less than fne man rem. Federal regula-gg HTGR HICH. ENRICHMENT URANIUM tions currently limit individual workers WITH RECYCLE OF U-233 2280 to five tem over a period of a year. Each IITGR fuel element is a graph-ite block, hexagonal in cross section,14 RADIOACTP.E WASTES. inches wide and 31 inches long. The ,7 M 310

1. ~

block is perforated lengthwise with 72 uOUo coolant channels and 138 blind holes (CUnlES PER YEAR) for fuel. Graphite is an ideal choice as ,34 a moderator and a structural material because its strength actually increases with temperature. In the reference de-I ~ 180 sign the graphite fuel blocks are stacked SOLID in columns of eight. This axially seg. (CUntC METERS PER YEAR) mented arrangement facilitates fabrica-et tion, handling and refueling. The convenient block configuration l has been made possible by the develop-ment of a specially coated fuel particle. 1200 The kernel of each particle is a micro-GASEOUS sphere of uranium oxycarbide (suitably 4 l (CURIES PER YEAR) enriched in uranium 235) about.01 inch 450 in diameter. Around each Lernel thin i layers of carbon, pyrol) tic carbon and l Op0RAllNG CllARACII.RISTICS of the 860-31We llIGR (color) are compared with silicon carbide are applied at high tem-those of a pressurised water reactor of the same generating capacity (grayh The lower fuel perature, yiciding a tightly encased par-l consumption of the llIGH can be attributed in part to higher thermal efHciency and in part to ticle with a total diameter of about.03 the het that for each stem of U 235 consumed in the llIGR about.7 stom of new fuelis cre-inch. A similar form of encapsulation ates the pressurised water reactor creates less than.5 stom of new fuel for each atom con-is used for the thorium particles. The sumed. With a once through fuel c)cle both systems consert a certain fraction of U-238 o' technique ensures the containment of ih-232 atoms into hotopes of plutonium or uranium,some of which are beneficially consumed the fission products. The tiny spheres before the fuel needs replacing. If the spent fuel could be rec 3cled (which was contrary to the are tested in batches of 2,000 for struc-policy of the last Adminhtration),it would be preferable to fuel an IIIGR with a misture of tural integrity when they are exposed highly enriched uranium (about 93 percent U-235) and tho* lum. Some of the thorium would be conierted into fiwionable U 233,which could be recosered and rec 3cled to replace U-235 to a radiation flux that simulates the in. In seine.guent fuel charges. Smaller,olume of radioactise wastes from an IITGR results part. ternal environment of the reactor. The 13 from its higher eRiciency and partly from adsantages of helium oser water as a coolant. particle production process, which is 62

m 4 0c0 , temi2utomatic, and the rigorous test-ing procedure work together to achieve RE a closq (,ontrol of qdality. $$^Ng Although severe and unforeseen serv-N ice conditions in one region of the reac-h ^ PWR BWR tor core might cause the particle coating 3 3.000 - to fail and release fission ptoducts, the y failure would be limited to the area di-g rectly insolved. In most reactors, where u-the cladding of the fuel elements runs $ the entire length of the reactor core, an E operating upset that ruptures a small 8 2.000 section of cladding could release fission 8 i , products from the entire length of the E j fuel rod. The performance of the fuct R clements at Fort St. Vrain has fully met 5 'l design expectations. Indeed, the release f of fission products has been well below 3,'go i the predicted levels. In sum, the fission- [ product barricts in the IITGR fuel el:- y ment hase been demonstrated to have a high degree of reliability. o e i , i l t t t t l l {j The properties of the llTGR make it ponible to exploit a wide variet) 6 1.2 24 60 60 l: of nuclear fuel cycles with it. The cycle MINUTES AFTER INSTANTANEOUS LOSS OF FORCED COOLING { that has been most intensively studied INIIERENT SAITTY OF AN itTGR is show n in graphs that compare the temperature in the and tested is the u anium.thoriun one, core of an IITGR,of a pressurized wster reactor and of a boiling uster reactor fo!!owing a hy. in *hich fully enriched uranium (93 potheticat loss-of-coolant or loss-of-forced-circulation accident. In the water. cooled reactors I percent U 235) serves as the primary the nuclear reaction is halted automatically by the loss of water, which serses as a moderator. hasile material and thoriem (Th.232) in the IITGR the reaction must be stopped by the insertion of control rods that absorb neu. i i scrs es as a " fertile" material. In the reac-trons. At the moment of shutdown deca}lns ihsion products in the fuel release heat at a rate tor the thorium absorbs neutrons and is equhalent to 7 percent of the thermal output of the reactor. The heat release falls to 1 percent in about two hours and to.5 percent in 24 hours. In the water-cooled reactors,in the absence ultimately converte f into the tissile iso-of emergency cooling, the tempe ature of the cladding of the fuel would rise in less than two tope uranium 233 which can be recy, minutn to 3,000 degun F, caus!q the chdding to fait. In thc IITGR the mass et the graphite j cled in subsequeru fuel reloadings. The modnator would abmb the heat nkawd by 6ssion products, so that 3,000 degrees would 5 9 Fort St. Vrain reactor is fueled with ura-not be reached for at least an hour. A temperature high enough to damage the graphite core nium enriched to 93.5 per:ent U-235-tabout 4.000 degrees) would he attained only after at least 10 hours without forced cooting. { i in combination with thorium. The de-sign of the plant allows the use of cither r fully enriched or medium.cnrichment Over the past six years orders for this summer, and has dernonstrated the i-i uranium (about 20 percent U-235). The about 55 nuclear power plants have exceptional safety and reliability that its 1 IITGR fuel-cycle costs, under the cur-t>cen canceled. Only six years ago U.S. designers confidently predict, it is rea-rent restraints on fuel reprocessing and utilities had demonstrated interest in sonable to assume that U.S. utilities will recycling, are essentially equivalent to constructing 10 IITGR plants. Once the look favorably on the HTGR when they o those of other commercial plants. Un-Fort St. Vrain reactor has been brought are again ready to place orders for nu-l less the policy is changed by the Admin. up to full power, which is scheduled for clear power plants. istration snent fuelis to be stored indefii 1 nitely, without the recovery either of the unspent U-235 or of the U-233 or plutonium created during the operation ,A AMB[S EM PLANT OVERALL PLANT of the reactor. ' Ibis fuel c)cle is com-SUPPLY SYSTEM AVAILABILITY CAPACITY FACTOR MAR (PERCENT) aPERCENT) (PEACENT) n only called the stowaway cycle. If an llTGR were operated on a stow-1967 81 7e o way uranium thorium cycle with fully un es u u enriched uranium, it wou,ld consume ,gg, g, ,7 about 20 percent less uramum oser its 97; 95 95 es 40-> car life than a light. water reactor 197 M 87 78 would. If both types of reactor could be 1972 71 n se operated with a full recovery of their 1973 95 N 78 uranium and plutonium, the llTGit would consume about 50 percent less 1974 96 95 70 uranium. The llTGR therefore offers CORE i AVERAGE 85 83 73 the opportunity of saving substantial CORE 2 AVERAGE 89 Sa /4 amounts of uranium with either a slow-f0TAL LIFETIME g g, y ara) policy or a full-recycle one, pro-STATION AVERAGE sided the reactor is designed to accept g fully enriched fuel. ~lhe significance of ggg gA,g,Lggy gg. I1RST llIGR PLANT designed by General Atomic, the Peach Bottom the potential uranium saving can be ap' Atomic Power station No.1,is attested to by the stat;stics shown here. Apart from scheduled pn ciated when one considers that the dow n time or time lost for reasons unrelated to the reactor,the llTGR w as as aitable for suppt). . total fuel cost oser the life of a nuclear ing steam for power generation 88 percent of the time. In ashiesing 74 percent of its rated elec-power plant is roughly equal to the total tric. generating capacity os er its sesen-and a half-year lifetime the Peach Bottom reactor es. 'nitial (ost of the plant. creded the t3pical figure of 66 percent achiesed by light-water reactors operated by utitities t 63 ,}}