ML20235D705

Paper Entitled, Causes & Consequences of Chernobyl Nuclear Accident & Implications for Regulation of Us Nuclear Power Plants

ML20235D705
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Issue date:	07/09/1986
From:	Harold Denton Office of Nuclear Reactor Regulation
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Pnnied m C,rco Bw.r. M ngu regrvey Pergamon Jov nah Lui e

e THE CAUSES AND CONSEQUENCES OF THE CHERNOBYL NUCLEAR ACCIDENT AND IMPLICATIONS FOR THE REGULATION OF U.S. NUCLEAR POWER PLANTSt i

H R. Drvros i

Director.OMce of Nuckar Reactor Regulation U.S Nuclear Regulatory Comtrussaon.

Wastungton DC 20555. U.S.A.

(Recrud t March 1981)

Ahcract-As in the case of the TM1 accident, pubitc concern around the morie e,er nuclear safety has been arousee by the Chernoby) nuclear accteert.

accause of its severity and enorm0Vs impact on publiC opinion, it is important te stuey the accidert and its impitcations carefully and provide accurate information to the public. Since this was the first nuclear accideet with j

large off site releases of radionuclides, valuable insights are to be gained

1 especially, for exagele, froe Soviet actions to tertinate the accident and mitigate its consequences, emergency preparedness and evacuation measures, i

medical treatment, protection against contesinated food and mater suppites, i

and a variety of post accideet recovery measuns. With the perspective of a 1

. year since the accident and a recent visit by the author to chernoby1 with a i

ti.$.- nuclear sarety delegation, this paper reviews a number of new studies to erav conclusions about the causes of the Chernoby1 accident, its health sne environmental consequences and some of the impiteetions for regulation of the safety of U.S. nuclear power plants.

1. Cat:sts oF THE CHEbOaVL Nt)CIAA ACCIDENT not readily allayed even with the availabihty of a:re "I

""* " "I Until the tragic nuclear accident of the Unit 4 reactor ede y hat eme@ b ht few mones at Chernobylin the Soviet Ukraine beginning on April 261956, there were well over 3000 yrs of commercial w ng e accida Momver, operatw mn l

P ayed a signi6 cant role in both the TMI and Cher.

nuclear power plant operations without signi6 cant "S*' **" "'** "I "Y

loss of life to the public due to a nuclear accident

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' " ##5 (Kemeny,1979). Even after the Chernobyl accident.

views were expressed as to the irrelevancy of the Soviet c urse, sin e tha was the first nuclear accident with large fr site releases f radionuchdes, there is an i

accident to the outlook for a similar worst case'acci.

dent happening to reactors operating in the Western "EE*" E

". " 8* " 8 ** "" * *'N World The design of the RBMK graphite-modersted,

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pressure tube reactor units at Chernobylis simply too different from the more prevalent type of reactor The latter meludes emergency preparedness and

"""" " "****' m8d C8I tf*8tment. Protection designs in the West to draw meaningful inferences from this accident regarding their safety along with against contaminated food and water supplies and a the presumptions that safety regulation in the USSR 18 Sd@dit8 at mcmen measm.

nt Providing an overview of the causes might not be so stringent as in other nations.

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While not discounting the possible correctness of 88 8 CN89UCDCe5 8 8e pc Paper wW also these views, government omeialsin the U.S. and other affected countries felt it prudent to withhold omeial include methodological issues in assessing the health judgments on what safety lessons,if any, are to be o naequen es f the accident and provide a pre.

learned from the Chernobyl accident until adequate

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"'I"plications of the Chernobyl nt w mgu au. no nuckar power factualinformation and analyses could be generated.

As in the case of the TMI accident, public concern i

around the world over nuclear safety had been aroused by the Chernobyl tragedy. Such anxieties are Chronology of et'ents in the a:cident scenario t An invited paper as a follow up to the International NRC's Severe Accident Policy Statement defmes a Energy Seminar on "Chernobyl: The Imphcauons for ' " sever nuclear accident" as an accident in which sub-Nuclea' Power and the Intemational Nuclear Regitne",

stantial damage is done to the reactor core whether sponsom! by the International Energy Program of The or not there are serious offsite consequences (NRC, op ins Foreign Pokey lastitute, Washington, DC, n

g g g, g Dr Miller B. Spangler, Special Asmstant for Pohey Devel. dent unless a number of equipment or human failures opment asmssed in the preparation of this paper secur in sequence of concurrently. Each unique com.

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296 H. R. DEmm binadon of failures that theoretically could yield a diversity and redundancy of various components and severe accident is called a scenarie. Computer models suo-systems. In addition to containment, defense in and quantitative risk assessment methods are used in depth is also achieved by maintaining the integrity of the U.S. and several other countries to compute dw se"eral other barners between the radioactive on site and off site consequences of each sccwio and rnverials in the LWR reactor core and the human the probability ofits oc.;urrence, albeit with a broad environment: the metal cladding of the reactor fuel l

l range of uncertainty. If the severe antent scenarm rods; the water in the reactor coolant system ; and a i

goes beyond large-scale core melt and breach of con-high-strength reactor vessel that provides the reactor tainment, then it also must include weather and radio-coolant pressure boundary.De RBMK design of the nuclide dispersion anct deposition modelling as well Chernobyl-4 reactor unit contains some, but scarcely as assumptions regardmg time of day, momentary al'., of the above LWR design features providing population distribudon, m.isucy sheltenng or defense in depth capability to limit the risk of certain evacuation measures, medical treatment and other severe accident sanarios. Notably absent in the factors to complete the basis for computing conse-RBMK design is a reactor vessel and a containment quences. Accordingly, there are literally hundreds of with adequate strength for overpressure at the top of I

theoretical severe accident scenarios that are in the the reactor for the type of accident that occurred at l

realm of possibility, although some are of such very Chernobyl.

l low probability as to provide a negligible contribudon ne following is a brief chronology of the more

'I to the total (or overall) risk of the fuller spectrum of salient events in the unique accid nt scenario that took -

accident scenarios.

place during the 10-day period between April 26 and Posidve and timely operator actions can sometimes May (1986 (USSR 1986 ; INSAG 1986 ; NRC 1987a).

terminate a sequence of accident precursor events, Of necessity, some of the more technical and complex thus preventing a severe nuclear accident. In most aspects of the scenario are omitted. The accident took cases, passive and automated engineered safety fea-place during a safety-related test being carried out on tures are relied upon to assist in the defense-in-depth a turbogenerator at the time of a scheduled reactor capability of accident prevention or consequence miti-abutdown. This was meant to test the ability of a gation, given that one or more failures have already turbogenerator, during statior blackout, to supply occurred. Redundancy and diversity of engineered electrical energy for a short period until the standby safety features are employed to reduce the probability diesel generators could supply emergency power to that a chain of failures will produce a severe nuclear awrt a severe accident.

accident. Among such functional safety features included in the Light Water Reactors (LWRs) preva-GFrom 0100 to 13:05 on April 25, reactor power lent in the U.S. and many other countries are (Okrent, of Unit 4 was reduced from 3200 MWt to 1600 1981):

MWt in accordance with the start of the test procedure; turbine generator No. 7 was then (1) reactor tnp or scram cystem that rapidly inserts mn

& m 8erdee as P aned l

reactor control rods to stop the fission process e At 14:00, the emergency core cooling system and terminate core power generation, (ECCS) was disconnected to prevent inadvertent (2) emergency core cooling system that cools the l

actua n during the test (the ECCS is designed to core, thereby keeping the release of radioactivity ensure the core remains cooled during postulated from the fuel into the containment building at bss of-coolant accidents). At this time, the test low levels was delayed at the request of the load dispatcher, (3) post accident radioactivity removal systems to a

reactor plant was Mt in mWm for an remove radioactivity from the containment addition 9 hr.

atmosphere e After the load demand was lifted at 23:10, power (4) post accident heat removal systems to remove reduction was resumed in preparation for the test decay heat from within the containment build-ing, thereby preventing overpressurization of (test specifications required the experiment to be performed at a reactor power level between 700 l

the containment building, (5) containment integrity systems to prevent radio-and 1000 MW ). However, despite operator ef ris, reactor power subsequently dropped activity within the containment building from w 0 Wt, a level far too low for staW escaping into the environment.

reactor operation prescribed in the test pro.

The systems reliability of the above ESFs,except poss-

, cedures.

ibly containment integrity,is greatly enhanced by the

-eThe' operators were able to stabilize reactor

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Impheauons of the Chernobyl Nuglear Accident m

power at 200 MWt by 01:00 on April 26.

to coast down. At this point an uncontrolled However, as a result of xenon build up in the power excursion began. Shortly after the start of fuel, which is a natural occurrence that intro-this power increase, the unit shift manager gave

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duces large amounts of negative reactivity during the order to scrarn the reactor using the highest i

prolonged low power operation after high power level of emergency shutdown function available.

l operadon, the operators had to manually with.

This would aUo* insertion of all control and l

draw the control rods beyond safe operadng shutdown rods into the core. After the scram j

limits to increase power, was initiated a number of severe shocks were J

GDespite the inability to meet established test reportedly felt in the control room and the oper.

power condidons, the decision wu made to pro-ator observed that the control rods had failed to ceed with the test. At 01:03 and 01:07, two fully insert. ne controt rod drives were then de.

standby main circulating pumps were started and energi ed in the hope that the rods would fall a

joined with six pumps already running ; the water into the core under their own weight, which they

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flow in the reactor core was then excessive, viol-might not have done.

1 adng manmum flow limits. De increased water ein only 4 see after the uncontrolled power excur-l flow through the core caused a reductionin steam sion began, the power level of the reactor reached i

generation and a drop in steam pressure and 100 times (according to Soviet estimates) the 3200 liquid levelin the steam drum separators.

MWt design capacity of the reactor. According e At 01:19, to prevenI an automatic shutdown of to the INSAG analysis (INSAG,1986), with such the reactor under these varying level and pressure an extreme surge of energy addition to the fuel j

conditions, the opemtors blocked the reactor (thus overheating it), the hot fuel and other frag-j protection (scram system) signals related to the ments would have interacted with the sur.

I pressure and liquid level in the steam drum sep.

rounding water. He subsequent steam pro-

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arators. The feedwater flow to the steam drurn duction resulted in a runaway pressure increase.

separators was then increased (but excessively)

%e overpr:ssure and the heat production rup-j to restore the depressed water level, thus lowering tured a number of fuelchannels. During this first the core inlet temperature and further reducing explosion, fragmented material was ejected and steam production. Particularly at low power the roof of the teactor hall was blown open. The levels, a reduction in core voids (reduced steam reactor space, which is designed for the assumed generation) produces a negative reactivity inser-rupture of only one fuel channel, overpressurized tion in plants of RBMK 1000 design causing a and the upper plate with a weight of about 1000 reduction in reactivity. Within 30 sec, the auto-tonnes was lifted abruptly off the top of the reac-l matic control rods had fully withdrawn from the tcr. At this moment, all 1661 fuel channels were core to compensate for the reduction in reactivity, ruptured, tle control rods lifted, and the hori-The operators then assisted the automatic control zontal pipes sheared off. A second explosion may rod system by withdrawing the manual control have happened about 2-3 sec after the first rods but ow%usated for the reactivity explosion. But this issue is not yet clear and may reduction causing the automatic rods to move never be fully understood. About 25% of the back into the core.

graphite blocks and material from the fuel chan-0 At 01:22, the decision was made to proceed with nels were ejected. De inventory of the system the test. ne reactor protection signals associated was blown into the reactor core, the reactor hall with the turbine stop valves on both turbines and the space below the core. The water con-were blocked (in violation of test procedures) to taining shielding tanks broke.

prevent the automatic shutdown of the reactor G All of the key events and activities following this when these valves were closed. A computer prin-moment (01:24) are described in Part 11 that deals tout showed that the available excess reactivity with accident management and other measures to margin had dropped to a level requiring immedi-limit or reduce the consequences of the accident.

ate shutdown of the reactor, a requirement that was ignored to permit test completion. By this time the majority of the control rods were prob. Root causes of the accident: pleit desen, safety ably rendered ineffective for power control.

objectives and procedures, and operator actions and e At 01:23, the stop valves of turbine generalor No.

stritudes g were closed to begin the test and the four main The RBMK 1000 reactor design utilimd in each of circulating pumps on the generator busbar began the four units at Chernobyl produces 3200 megawatts l

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.g 298 H. R. DmToN of thermal power (MWi), yielding 1000 MWt of elec. a loss of coolant accident or LOCA, a technique trical power (MWe). The RBM K design uses graphite which it is believed the Soviets might not have as a neutron moderator and light water as the coolant. sufficiently emphasized. Moreover, appropriate atten.

Pressure tubes, contained in vertical channels in the. tion to man machine interfaces in safety analysis can graphite, either contain low etriched uranium oxide lead to designs (includmg contro! room displays) that fuel or are used as locations for control rods and make certain human errors less likely or less preju-instrumentation. It is also distingmahM by eatensive dicial to the performance of safety functions, or pro-use of computerized control systems, but a slow scram, vide greater margins of time to recover from operator system, its reactor safety systems provide for emerg-error, ency core cooling, main coolant loop over-In the case of Chernobyl Unit 4, the plant design pressu-ization proacetion, reactor space owrpressure plamd a beavy dependence on adberence to admin-protection, midgadon of radioactive releases, steam. intenal controls and procedures for safe operation.

pressure suppression, and hydrogen gas removal The following major operational events or errors and

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(NRC,1987a).

administrative or snanagement control breakdowns q

ne Soviets regard the RBMK as their " national" contributed ' importantly to the accident (NRC, j

design and thefollowing advantages were influential 1987a):

in its design:

e Engineers already had extensive experience with UI ".rall management c ntr 1 ( the test and clearly establis% plant operations were not ns mkgr**

graphite-moderated, boiling water cooled reac.

hed. The test was directed by eMajor components could be fabricated at caist-an engineer with expertise in the turbine gener-ator/ electncal area and not in nuclear safety, e e mod a gn t that reactor size was (2) ec w p mt & an @uau safety m SnepW h h was a poss%y not limited by considerations related to fabri-cation, transportation or installation of com.

at the dent nugM haw been b seven if j

the ECCS had not been blocked. Also, necess-Pomts.

e A serious loss-of coolant accident larger than ary safety precautions and instructions in the that considered as design basis was thought to be procedure were evidently not adequate, virtually impossible because of the une of numer-(3) the operators may have felt an undue sense of ous pressure tubes rather than a single pressure urgency to complete the test since the test would have been delayed for a year had it not been e Fuel use was very efficient. -

performed, e A very high plant capacity factor could be octa-(4) the power reduction for the test wasinterrupted seved with the use of online refueling.

for 9 br at the load dispatcher's request. This delay changed the initial core conditions from in view of the many safety features in the RBMK that contemplated in the test procedures and design, it is not surprising that the Sovict's report contributed to an unstable safety regime, at the Post Accident Review Meeting in Vienna on (5) the operators did not follow the test procedure.

August 2b29 emphmmt operator errors during the GThe test was started at a low power level that test as the primary cause of the Chernobyl accident violated both the test procedure and station (USS R,1986). The Soviets felt the operators lacked a operating instructions. At 6% power instead proper vigilance toward safety, in part because the of 22 to 31% speci6ed in the test procedure, previous excellence of performance by the operators little steam was being generated, so the eight of Unit 4 created an attitude whereby plant personnel circulation pumps produced a flow rete felt that close adherence to procedures was unnecess.

above allowable limits. With the high flow ary. However, our own experience and analysis of the rate and low power level, the water inlet tem.

J human factors where errors could contribute to the perature to the core was very close to satu.

l risk of severe accidents reveals the important of oper-ration. Under these conditios.s, an increase stor trairdng, particularly for those accident scenarios in power caused a much greater increase in exceeding 'the spectrum of design basis accidents.

steam voids and reactivity than normal.

Especially valuable is the use of simulators to test GThe reactor scram signal for she trip of the operator response to the preliminary stages of various second turbine generator was blocked, which realistic severe accident scenarios as well as making violated safety procedures and was not called appropriate accident management decisions following for by the test procedure.

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Impbcadons of the Chernobyi Nuclear Accident 299 eThe operators failed to maintain in place the on failure of the largest ppe in the com-minimum " equivalent" of 30 control rods

partment, required as excess reactivity margin.

(6) Other safety systems were also defeated, (5) the RBMK design included compartments to cope with pipe break failures. However, this eBlocking the steam separator pressure and safety feature was of no value in the accident water level scrams allowed reactor operation that actually occurred.

despite unstable condidons.

OControl rods were withdrami well beyond He combination of limited capability to accom-safety distance limits speci6ed by plant pro-modate thermal transients, a slow acting control rod cedures. This error rendered the emergency system, the limited thermal margin provided to the protective (scram) system ineffective.

fuel, the effect of flux and power peakmg on the fuel, (7) The plant operators and stadon management the lack of adequate containment, the capability for did not demonstrate an adequate under-common cause failures in eacess of the design basis standing of the safsty imphcations of their and the lack of design characteristics to accommodate sedons. Their wilbogness to conduct the test beyond design basis events are RBMK type reactor at a very low power level, with abnormal and safety characterisdcs that would not be aa:eptable in the U.S.

unauthorized control rod con 6guration and it should be noted that other units of RBMK design core condidons, and with safety features are being substantially modi 3ed to improve their bypassed indicates an insufficient under*

standing of the reactor and its behavior under aafety characteristics. In March 1987, I visited the these conditions-control room for Units 1 and 2 at Chernobyl (whose operation has now been resumed) and found the fol.

There are a number of design characteristics of lowing safety innprovements inn esecu RBMK type reactors that may have contributed to the Unit 4 accident or cancerbated its severity (NRC, one control rod position set points have been 1987a):

reset and physical stops have been added to pre-vent their withdrawal beyond 1.2 m of the top of (1) the RBMK-type reactors have a limited capa-the core bility to accommodate the structural (stress and ein order to limit the influence of the positive void strain) effects of thermal transients' (or reactivity) coef5cient and to facilitate a more (2) the RBMK-type reactors have slow acting con-rapid reacdvity inscruorsmder off normal oper-trol rod systems. It takes about 20 see for a ating conditions, a minimum integrated worth control rod to become fully effective (versus the value of 70-80 control rods in the reactor at any 4 see of the rapid power surge m the accident),

one time has now been established.

(3) the RBM K-type reactors operate close to a con-eThe by-passing of vital safety features by oper.

didon that is beyond departure from nucleate ator action is now access controlled with the lock-boiling, and at which there is a limited margin up by reind in & possession of & plant until the onset of a heat transfer crisis, fue' manan center lin: meldog and fuel hilure, OOdy a fm of W plannd higher-enrichd (W (4) RBMK type reactors use local area com-assemblies (to reduce the void coefficient) have, partmentalizadon to accommodate the effects as yet, been added to Ornts 1 and 2.

of breaks of the primary coolant pressure e14one of & plannd rapid-acting contrd rods boundary. This concept relies on the pressure hoe pt W istand.

containing capability of each room, cell, or 4The sarcophagus (see below) that entombs the vault to contain rnaterial released in the event defunct Unit 4 has been constructed as planned of an accident. The " compartments" are not and real time monitoring of the low radiation 1

designed to accommodate more than one pri-levels of filtered / vented gas is displayed in the mary coolant pressure boundary breach based plant manager's office.

it. SoVII.T ACT10NS TO TEatMINATE THE ACODENT t his explosion is not to be confused with the type and AND MrTICATE ITS CONSEQUENCES force levets of atomic benb explosions. An atomic bomb type of explosion is simply not possible in a severe accident Termmaring the occident and contaawy the release of with a commercial nuclear power plant, his aho appbes to rodsonuchdes to the ofsire environment the type of fuel and fusioning proms: of the Queinobyl plant At 01:24 on April 26 when the steam " explosion"t design.

irrevocably destroyed the reactor and its operability,

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4 300 H. R. DmTos about 30 fires broke out on the surrounding structures the internal beat withm the core space by from the bot ejecta of the accident. The most worri-absorbing the energy of the burning graphite, some of these was on the roof of the turbme build.ng (3) clay and sand (1800 tonnes) to introduce an which was commonly shared between Units 3 and 4.

inunediate filtration for radionuclides being A t 02:54 (90 min after the explosion). fire 6gh ting units released and to quench the fire, arrived on the scene from the towns of Pripyat (3 miles (4) about 2400 tonnes oilead to absorb heat by distant) and Chernobyl(11 miles distant). The beroic melting and to provide a liquid layer that would efforts of the fire 6ghters, who reaived burns and in time solidify to seal and shield tbc top of the dangerous levels of radiation some of which proved core fault (INSAG,1986).

fatal, brought the 6rst in the turbine buikiing under control by 03:34. All fires, other than those in the The course of the radionuclides releases and the reactor core, were extinguished by 05:00 and Unit 3 sucass of measures to halt them is shown in Fig.1.

was shut down. However,it was not until the morning The release of radionuclides from Chernobyl did not of April 27 before Units 1 and 2 (physicauy separated occur as a single acute event. Rather, only about 25%

from the other units) were shut down, of the release took place during the 6rst day of the According to the INSAG analysis (1986), the acci-accident; the rest of the release occurred as a pro-dent management actions taken at Cbernobyl were tracted process over the following nine days ending generaUy quite successful. The 6rst attempt to supply on May 6. Throughout this period, and particularly water to the core from emergency auxiliary feed on the 6rst day, the release was accompanied by large pumps to quench the core debris was apparently amounts of energy which elevated the radionuclides unsuccessful and quickly abandonat The subsequent plume to great heights. The height of the plume on steps, namely, dumping ma terials into the reactor weu the 6tst day foUowing the explosion reached about (boron, carbide, dolomite, sand and clay, and lead), 1200 m (3900 ft) and a beight of 200-400 m during supplying cold nitrogen to bring down the tem-the following nine days.

perature in the core space and to reduce the oxygen FoUowing the initial burst of release energy in the concentration, and construction of a flat beat exch. first few bours after the accident, the release raus anger beneath the foundations of the reactor buildmg, sharply declined and continued a more gradual decline stabilized the situation at an early stage (about nine of the cooling period through May 1. This cooling days after the initiating power surge) of the accident, was abetted by the aerial drop of the materials noted

)

The uniqueness of the worst case type of nuclear above which continued in heavy force during the per.

accident that took place at Chernobyl meant that iod April 28 through May 2 and at reduced levels practically all measures to achieve a short te rn sta-for some days thereafter. A beat up period continued bihzation of the accident and longer tenn post accident from Msy 2-5.

recovery measures, including reactor entombment, This was principaUy due to the beat a:ising from are of a pioneering, experimental character Par-residual decay of radionuclides in the reactor core ticularly imaginative and highly sucassful was the debris. The Soviet experts estimated this raised the fuel prompt commandeering of military helicopters to temperature to above 2000*C. Also,it is hypothesized dump (beginning April 28) a variety of materials, that carbidization of uranium dioxide made it' easier tota!!ing 5000 tons, through the open roof of the Unit for volitalized Assion products to escape.

4 reactor building in order to terminate the atmo-Starting on May 6, a sudden decrease in the release spheric release of radionuclides being distributed over rate of about 1% of the initial rate occurred and it western U.S.S.R. and many other European nations continued to decrease thereafter. Soviet experts attri-due to the changing pattern of winds. It was necessary bute this to special measures taken, especiaUy the to fly the helicopters at sufhciently low levels that introduction of cold nitrogen on May 4 and 5 into the the pilots were exposed to undesirable high levels of reactor vault, preventing further oxidation reaction of radiation. The amounts of materials dropped on the the fractured graphite, and the formation of more reactor core in this manner and their accident recovery refactory compounds of Assion products as a result functions are as follows :

of their interaction with the material deposited. It is believed that the effectiveness of the cold nitrogen (1) forty tonnes of boron carbide to ensure against injections was increased due to the liquefaction of the recriticality of the remaining reactor fuel, core debris resulting from the excessive temperatures (2) about 800 tonnes of dolomite to generate car-of 6ssion product decay heat that relocated the molten bon dioxide that could provide " gas blan-mass into the lower pipe runs where it solidi 6ed.

keting" and could also contribute to dissipating Although radioactive releases to the off site

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t Dere efter stort of oceedent Fig.1. Daily releases of radioacdvity from the Chernobyl Nuclear Plant following the accid monang of April 26,1986.

environment fell to 10000 Ci per day by the fourteenth day and later to only 2 Ci per day, it was deemed entombed plant is ventilated by the ink.ction of air necessary to entomb the reactor to prevent significant with the outlet shaft provided with fdters to ma{

i hea!Lh effects from cumulative small doses over an low radioactivity releases commensurate with tho I

extended period of several hundreds of years. This of a normally operating nuclear plant.

f required a ma}or technical innovation. Design goals Emrpeney preparedness asdevacuation measuresl wert established to achieve a radiation kvel not ex.

ceeding 5 mithrems.hr-' at the roof and I millitem, According to the INSAG report (supra), an overall hr-' at the walls of the sarcophagus as well as conclusion to be' drawn from the emergency response protection'against natural events such as tornadoes, is that although it had to be initiated at the l j

earthquakes, and extreme temperatures at an annual nevel, the actual management of the total emerge ci situation and response required a rapid acceleration probability of once in 10000 yr or greater (INSAG, of resource commitment. Owing to t 1986). Criteria releated to construction techniques included: minimization of construction time; mini-accdent, such resources, and the authority for their mization of radiation doses to construction worLers ; commitment, could not be expected to exist at and the use of the simplest, most reliable, and well nocal kvet it must be recognued that for any accid established means of construction.

of this severity, irrespective of the location or country The massive entombment structure was completed of occurrena, there would need to be a maj by November 15 and the construction was carried out mitment of manpower and equipment resources in 3

order to regain control of the situation and to reduce

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without any human presence on the plant site (NEl, the consequences for the pop 1987). The work was done by robotics with television ment.

cameras mounted on the construction cranes so that I

operators could direct their movem:nts by remote Because of the unusual energy of the initial control. The heavy walls of the stacture utilized explosion and the additional heat of the many fires.

410,000 m' of concrete and 7000 tonnes of reinforce-the radionuclides re==ad from the accident were ment bars. They were constructed in 12 m steps to an thrust to a higher level than would be expected f

overall height of 60 m (200 ft). Sensors have been most of the theoretical U.S. severe accident scenarios.

placed next to the damaged reactor as well as on A result is that the radionuclides were dispersed to the roof to monitor the condition of the radioactive more distant locations with consequent reduad early material and the escape of radioactivity. Tbc depositions within ten miles of the plant than might have been expected. However, local plant officials 1

1 302 H. R. DcmoN initially underestimated (or underreported) the sever-soon as possible. On the morning of 26 April. people ity of the immediate threat of the accident. According were instructed to remain indoors with vcindows and 1

to Ramberg (IN7):

doors shut. Schools and kindergartens were closed l

"Notwithstandmg the silence of Soviet officials at The collection of meteorological and radiological j

the time, policymakers in Kiev and Moscow were a nit ring data was organized and aerial radiolopeal j

informed within bours. Major General Gennadi m nit ring began. The military helicopters used were Berdov, the Ukrinian depury minister ofinternal equipped with air samplers and radiation detection affairs, initially took command of efforts to control instruments and the crews were provided with per-the situation 90 min into the accident, scaling off a nal dosimeters and respiratory protection.

the immediate area around the complex with local As described by INSAG (1986), late in the night of mibtia. A team of doctors and technidans from 6 ApM, radne levels m Wat staned nskg.

l Moscow reached the Chernobyl environs at 8:00 reaching a value of the order of 10 mSv h-, on 27 a.m. on April 26. But it was not until a senior April.1 It soon became apparent that the lower inter.

<ielegation of government and party members at a kvel for evacuation (250 mSv whole body arrived at the site that evening that policy-makets dose)could be exceeded and eventually even the upper at the highest level understood the seriousness of interventi n level (750 mSv whole body dose) if the d e dius h.,

p pulati n remained in their homes and no other countermeasures were taken. Ad hoc evacuation There is limited information on the specine nature plans, taking into account tbc actual situation, had to of advance radiological emergency planning for the be devised. The evacuation of Pripyat (45,000 persons)

Chernobyl power station, altbough a Soviet paper started on the morning of 27 April after safe evacu.

presented at an IAEA workshop in 1980 describes ation routes had been estabbsbed for the 1100 buses l

a general planning framework that includes a plant on the basis of the first results of radiological moni-locazion strategy, accident class 6 cations, public toring, and all the necessary transportation means, safety measures, and an accident management organ-equipment and escorting personnel were gathered and I

iration structure for nuclear power plants (Bekrestnov relocation centers had been de6ned, manned and and Kozlov,1980). At the top of the management equipped, organization is a " coordination center" involving Of the on-site personnel, abc,ut 300 had to be bospi-both government authorities and plant personnel, div-talized for radiation injuries and burns. Specialized ided into 6ve sections and attending to one of the treatment and care were given during the 6rst few following problem areas :

weeks. No member of the public from the off-site area e Constant surveillance of the operating conditions had to be hospitalized for radiation injuries, although of the power plant.

many attended bospitals for other reasons. Necessary e adiatim cetrol provisions had to be made for the decontamination e Dosimetric inspection of the territory around the of the people's skin and for the exchanging of clothing in b ee folhig days me e pre plant and the environmental protect >on zone.

eProtection of the population and provisional tective actions had to be gradually applied to the other nacuad n,if necmam population (90,000)in an area of radius 30 km (or 18 miles) around the plant. In addition, sorne GMedical aid for tpe population and plant per-19,000 cattle had to be evacuated from the area in sonnel, m, eludmg nodine prophylaxis.

hundreds of trucks since many farmers refused to However, the Soviet delegation at the IAEA meet-leave unless such provisions were made. However. the ing in Vienna in August conceded that existing emerg-total number oflivestock evacuated eventually grew ency response plans had only limited value to the to 50,000 from the Ukraine and 36,000 from Byelo-l response teams arriving in Chenobyl and substantial russia (Shabad,1986).

adhoc planning of evacuation and other emergency According to Soviet news accounts assembled by actions was required. One of the initial decisions was Shabad (1986), when the Pripyat residents got the that a precautionary evacuation of the town ofPripyat order to evacuate, a delegation went to City Hall to l

(2-4 miles from the plant) should be carned out as inquire about the need for the emergency measure and was persuaded by General Berdov, the Ukranian i

police official, that it was nemssary. The buses, for-l

,1One nViliSeivert (rnSv) is equal to 100 millirems which is roughly equivalent to the natural background radiation minE a caravan 10 km long, moved to the entrances remived annually from cosmic and terrestnal sources in the of spanment buildings according to a prearranged U.S. and most other pista around the world.

plan. Residents thought the move was for only a short

l Imphcations of the Chernobyl Nuclear Acxsdent 303 time, and travelied light as they climbed into the buses. dose limit of 5 rem. for an individualin the first year The pohce searched all apartments to make sure every-was established ONSAG,1986).

one was gone. Of the total Pripyat population, atr>ut According to Shabad (1986), programs to rehabili-10,000 children, including 7000 school children and tate contaminated land for agricultural purposes I

3000 children of preschool age were apparently taken should diNerentiate between areas close to the nuclear directly to summer camps in the Ukraine and in other power station, where radioacdvity is higher, and more Soviet republics, while 25,000 adults were evacuated distant land. The more highly contaminated area is 4

in about 3 hr to nearby rural areas in Kiev Oblast, unlikely to yield usable crops in the fomecable future, I

l mainly to Polesskoye Rayon, to the west. When the and should simply be treated with calcium compounds Pripyal evacuees arrived during the night of April 27-that would fix them in the soil and prevent migration j

28, the population of Polesskoye Rayon, which was and dtssemmation. Other areas might be sown with 35,000, virtually doubled, in tbc confusion many fam-crops such as lupines that absorb radionuclides. These ilies became separated,and it took weeks to sort mat. crops would then be harvested and buried. Some of ters out. When it was learned that the evacuation of the leu valuable land might be left idle altogether to Pripyat would be for a long period, residents were revert to natural vegetation. In general, it would be permitted to return for brief, supervised visits to pick advisable to modify the type of farming in any area up essential household items, family documents and expowl to radiatien hazard with a view to planting other needed articles that had been left behind in the crops 2.a an more immune to radionuchdes. For rush. The evacuation of the remaining 90,000 from exan? c, rye tends to absorb strontium to a lesser the 30 km zone took several days and was somewhat extent than wheat. Industrial crops are particularly I

more difficult since it involved 71 villages and large suitable in areas with radiation polluuon since they j

numbers oflivestock. Soviet otheials who supervised an subjected to processing after harvesting. Potatoes, the tvacuation reported that generally the behaviour instead of being consumed as food, might be used of the evacuees was exemplary and without panic to make starch since radionuclides tend to become (NRC,1987a).

elaninated in the starch-making process. Another l

industrial crop that might be cultivated in the con.

Praircting againsi contammatedfood and meter sup-taminated zone is flax. As it happens, rye, potatoes

1. y#

and flax are the customary crops m the sandy soils Other emergency measures included the short and of the Chernobyl area. Much experimentation will doubtlessly be needed to demonstrate what measures long term protection of ta' e population against radi*

ologically contaminated food and water supplies, will prove to be the most economical and safety effec.

j Consumption of milk containing more than one ten-tive in restoring these agriculturallands to productive use over subsequent decades.

millionth Ci/l of the radioactive isotope '8'I was There is also concern over contamination of the banned. Also, standards for permissible levels of con-groundwater and surface water in the area of the tamination in other food products were issued in es rly Chernobyl power station which also serve the Kiev Msy. Special measures were taken to prevent or region. These water supplies are being monitored and minimize radiation exposure via the ingestion remedial work has been done. In the early stages of pathway. Decontamination activities were extensive the accident, well water was readsed for emergency in the 30 km zone and other measures have extended use by the residents of Kiev as a preventive measure, beyond that zone, particularly to the city of Kiev (80 'the public water supply has been used subsequently, I

miles to the south). Another account, given at the but with. constant sampling to assure that any con-Vienna meeting, indicates that the primary con-tamination falls within protective action guidelmes. A tamination of evacuated dairy cows was surface con-unique aspect of the Soviet emergency response was tamination and most animals were washed down the seeding of clouds with silver iodide by aircraft to (NRC,1987a). Those animals which had not ban break them up and prevent rainfa!!in the region for j

i washed down or were injured during evacuation were a number of weeks aner the accident--an action that slaughtered. In addition, intervention levels for 88'l reduced deposition of airborne radionuclides in die in milk,75% of which is exported from the area, area.

as well as leafy vegetables, were established with the The Soviets reported that, in June, construction object of limiting the dose to a child's thyroid to r

o a series of bydraulic engineering structures was 30 rem. per year. Other, unidentified standards were initiated in order to protect the groundwater and sur-1 selected for '8'l in meat, poultry, eggs, and bernes face water in the Chernobyl area from contamination later, still more foods were included and an overall (USSR,1986). Among such measures was the (now I

i l

,7 A,

t t

4

_s'

]

n i

,w i

\\

H. R. Dorrow 304 j k i

completed) strengthening of the dam for the cooling at the zone boundaries to reduce'the spread of con-b water channel at the Chernobyl site and the building tamination.

In early July seven villagesin Bragin Rayormithin I

of a hold up reservoir for rainwater along the whole.the 30 km zone had been decontaminated and cou periphery of the 2 km channel (NN,1987). Another protective measure was described by Yevgeny Veli-be remetued. Bragin,' a town of over 6000 population j

~

i khov, Vice President of the Sovec Academy of just outside the 30 km zone had over 1000 homes and Sciences, at a bearing on January 20,1987 of the U.S.

other stru::tures washed down to remove radioactive Senate labor and Human Resourtes Committee traces. Some of the moasy older structures and fences (Wamsted,1987). This involved the cacavation and - that could not be easily decontaminated were dis-construction of a 15 m deep cosaete wall into the mantled. Tbc rehabilitation effort also involved the ground at the Chernobyl4 unit ir, oeder to prevent decontamination of thousands of trees, the uprooting -

q contaminated groundwater and rainwater from leak - of shr.sbs, and removal of a 5-10 cm layer of topsoil.

1 ing into the Pripyat River that empties into the Kiev The Byelorussian environmental protection chief, I

Reservoir. Also, a seassive concrete alab has been. Viktor Kozlov, said peat soi!r retained more ra o-j di constructed beneath the Chernobyl4 unit to protect ' activity and were to be decontaminated by being j

against contaminated groundwater. Miners were plowed under, as well as the use of irrigation and '

- 1 l

brought from various regions of the U.S.S.R. to esca-timing (Shabad,1986). To prepare for the runoff of vate a tunnel 136 m long in order that this concrete enowmelt water in the spring of 1987, steps were taken j

banier could be constructed at the base of the reactor to bury radioactive garbage and to remove cow l

l manure from 6 elds since this organic material tends l

i (NEl,1986).

to retain radioactivity,la the Ukraine and the Gomel Other post-accidmt recocery measures Oblast of Byelorussia emergency housing programs l

l Bernuse of espected power shortages in the Soviet got under way with plans calling for the construction l

Union in the winter and to reduce health effects of of entire new settlements, accommodaung at least 50

]

tbc accident, site decontamination was expedited.The households each. A total of 4000 new homes were site, the turbine building roof und the sides of nearby targeted to be ready in October,in time fe,r the winter.

l

]

roads were spray &mith rapid polymenzng sol.

wticas f.o congeal upper layers of the soil to prevent resuspension of radioacuve dust ie.to the atmosphere.

m.amam N mEs u m m m u m According to Velikhov (Wamsted,1987), about 20 cm estpcu or ut ectomt -

I (8 in.) of topsoil was removed from thousands of Jtadiation sickness and pronqpt fatalities: the role of, square meters of surrounGr4g land and placed in nacks/ trearnient newly constructed metal r.roctures within the Cher, nobyl site. Other measures included removel of debris A review of the health and environmental conse.

' and contaminated equipment from the site and isying, quences of the Chernobyl accident is p er.ented in where necessary, concrete slabs or Allingin with clean Chap.8 of NUREG 1250(NRC,1987a). At Idgh doses soil over bot spots of radaonctivity.

. ofionizing radiation, many cells will be killed or func.

l These decontamination efforts permitted the restart tionally compromised resulting in possible severe dam-of the Chernobyl i unit on October 1 and Unit 2 on age to the individual. The effects of such damage November 6. Unit 3 is expected.to restart by June appear rapidly and, at very high doses, may include L

1987 and the start of construction of Units 5 and death. After total body exposures of different mag-6 will then begin. According to fNSAG {l986), the' nitudea, the foNowing effects are possible or expected:

l contaminated area within a 30 km radius was divided. at gristet than 50 rods (or rems), radiation sickness into three zones : a special zone (some 4-5 km around such as nausea, vomiting. and weakness may occur the plant), where no re er>try of the general poptstr. tion with 100% incidence expected at about 200 rads t at idcieseeable in the near future and where ro activity greater than 150 rads,in addition to radiation sickness, i

besides that required at the installation iM be per-start of. bematopoieuc syndrome with blood and mited; a 5-10 km zone, where partial re entry and - immune system problems and some deaths within 60

[

s;wia! activities may be abwed after some tira:; and days; et 300-500 reds, death in 50% of those exposed s

s.10-30 Sn zone, where the population may eventu-within 60 days; and at over 700 rads, nearly 100%

ally be allowed in and agricultural activities may be soortality is expected.

resumed, but which will be subject to a strict program Sorne organs are at partseular risk. For example, a of radiological surveillance. Access and egress cort 15 rad dose to the testes can temporarily reduce fer-i trols for personnel and vehicles have been estabbhed tility; at higher exposures, the severity and duration l

i u

(,

___mm_'__.__

_m

l I,

lenpbcations of the Chernobyl Nuclear Accident 305 of reduced fernbty is increased un61 at 300 700 rads, dose estimates are reasonably axurate, the above data permanent sterility may result. In the ovary, a dose of suggest a me&aa lethat dose above 400 rads.

20(M50 rads may cause sterility. A 200 rad dose to the ne Soviet wntten report and presentaUons in lens of the eye may cause cataracts ; for the skin, a dose Vienna incGeated extensive and reladvely prompt me6-of 250 rads may cause erythema,700 rads-loss of hair, cal treatment measures shortly after the Chernobyl more than 2000 rads-severe dermatitis or radiation at began (USSR,1966) he me6 cal and health

" burns" The thyroid presents a special case because it section serving the pitot was informed of the me t at about 02 00 on April 26. Rese medical conantrates radioiodines which have been inhaled or n

ingested. He dose from these radionucbdes in the thy. penonnel assisted the 6rst 29 vetuns within the first roid can greatly augment the thyroid dose received 30-40 min, =Mmr them immeaately to the hospital from external irra&adon and from other internal emit-As an indicator of the speed and extent of the emerg-ters. Total doses of 200 rads may cause impaired func-cocy mksi response, the Soviets reported that ey tion, but loss of funcdon is morelikely for doses g eater 06:00 on April 26,106 people had been hospitalized l

than 3000 rads. Complete destruction of the thyroid and an additional 24 were admitted during the day.

I requires doses of 100,000 rads or more.

After initial diagnosis in local or regional hospitals,129 Energy deposited in a cell by ionizing radiadon may padents suNering acute radiation sickness were sent to not immediately aNect vital cell functions but may dam.

's -4=1M bospitalin Moscow and 72 patients were age the celfs genetic material, leading to an adverse sent to chrucal institutes in Kiev. Teams of specialists eNect expressed at some later time. These eNects are arrived within 12 hr, consistmg of health physicists, often referred to as statisdcal or stochastic efects. A radiology therapists, laboratory assistants and bern-l stochastic efect is one for which the probability of atologists. Within 24 hr, these speaalists exammed 350 l

occurrence in a person is proportional to the radiation persons and pedormed about 1000 blood dose received, but tbc seventy is not. Induction of analyses, cancer and genede effects are the two types of stochastic Ultimately,203 persons were treated for acute radi-effects associated with radiat on exposure causing the ation syndrome resulting from ramma-and beta-ray greatest societal concern. Cataracts, operable thyroid exposure; none of these venms were members of the (non cancerous) nodules, temporary or permanent general public. Be6a-ray exposure resulted in severe sterihty and certain damages to the fetuses (ter-skin burns in 48 vicums Dr Robert Gale, a U.S.

stag ne6c effects) d.. ring the early months of preg-physman, assisted Soviet doctors in giving bone mar-nancy are also stochas6c effects of signi6 cant concern. row transplants to 13 of those who reccind sub-Esdmating stochas6c erects, parucularly at low doses stantial radiadon exposures, but 12 of these did not of radiadon,is scientifically controversial since direct survive (INSAG,1986). Bone marrow transplantation observations of these effects at doses under 50 rads or has only been moderately e6cetive according so Dr rems cannot be made. Estimates of these kinds from Angelina Gus'kova, one of the Soviet representanves the Cherr.obyl accident and the related issues will be at the Vienna meeung, and would not be expected to discussed in the following sec6on.

play a signi6 cant role in any future major accident.

After the Chernobyl accident, acute radiation effects Many of the deaths were hastened by burns resulting were diagnosed in 203 individuals, all of whom were from beta exfosure. Of the 203 bospitahmi victims, either working at the reactor or were brought in to 35 eacceded doses of 400 rems (up to a maximum of deal with the -r y. Twenty nine penons were 1200 to 1600 rems). Ahogether,1240 doctors,920 c

reported to have shown some aceute effects within the nurses and several thousand supoorting assistants first 30-40 min after the accident, and within the first were mobilized to provide medical care servi:es to 36 hr, acute radiation sickness was diagnosed in these these victims and others among the 135,000 evacuees.

203 individuals Estimates of radiation doses received Each evacuee was medically examined and blood tests were based on chnical criteria, not on dosimetric data. were carried out long term programs are being Of 22 persons esumated to have received more than established for biological monitoring of exposed wor-600 rads,21 died in 4-50 days; one died later. Of 23 ken and the general population of evacuees estimated to have received 400400 rads,7 have died.

All $3 persons estimated to have received 20M00 rads Uncerramties in assessing delayedcancerfamfities and all 105 estimated io have received 80-200 rads have in view of the many sources of uncertainty in pre-survived. At this time,29 persons have died as a result paring estimates of delayed cancer fatalities from the of ra&adon exposures;in addition lone penon died of radioactive releases from the Chernobyl accident,it is severe burns and another was killed when part of the scarecely surprising to 6nd a wide rarige of estimates reactor building collapsed. Assummg that the Soviet of tiese long-term fatalities. The Soviets provided

as H

306 H. R. Do(Ton estimates of these fatalities (within their own ter-fatal canars in the population attributable to the ritories) at the August meeting in Vienna staying external radiation exposure. It would, however, be within the range of dose msponse rates for delayed very difficult to detect this excess since, according to l

cancer fatabdes commonly accepted by western the Soviet report, in the course of normal events a bou t l

nations (USSR,1986). It is generally agned by the 12% of the evacuees (about 16,000) would normally experts that the greater the radiation dose received by die of cancers from other causes. In addidon to these an individual, the greater the probabibty of a fatal fatalities from external radiation would be those cancer being induced during his or her remming life resuhing from inhalation or ingestion of radio-span.

nuclides.

All of the 203 individuals who developed acute radi-Although inhabitants of the 30 km zone were given ation sickness were estimated to have received in potassium iodide (KI) to mimmm uptake of radioiod-excess of 100 rems of radiation dose and 29 of these ines, the population received appreciable doses to the have since died. Accordingly, each of the 174 survivors thyroid through inhaladon and ingestion of the of this group have incurred a demonstrably higher radioiodines "'I and '"1. The uptake of "'I in the risk of cancer fatality. Since camer is pnmarily a 30 km zone and elsewhere along the path of the radio-d;sease of the elderly, there may be a lapse of 20 50 active cloud was monitored extensively. Doses to the yr before the incidence of cancer from tbc Cbernobyl 100,000 children who were monitored are of special radiation. A notable exception is leukemia, a relatively concern, primarily because their smaller thyroid rare form of cancer, which may emerge within s period glands receive higher doses for a given intake and of 2-12 years according to the experiena data of the because of their high consumption of milk, a food in A-bomb survivors at Nardi and Hirodumn. Less which "'I fallout is likely to become concentrated. It demonstrable is what increase in can=r fatality rates was estimated that most doses to the thyroid from might be experienced by the 45,000 residents of Pri-inhaled or ingested radioiodine were less than 30 rems, pyat and the 90,000 otber evacuees from the 30 km altbough a few children may have reaived doses as zone surrounding the Chernobyl plant.

high as 250 rems. Children receiving more than 30 l

The Soviet report (USSR,1986) states that doses rems to the thyroid were put under continuing medical

{

for the vast majority of the population did not exceed duervadon, but the risk of hypothyroidism appears

{

25 rems, although some people in the most con-to be negligible, below about a 1000 rad thyroid dose taminated areas may ha ve received 30- 40 rems. How-from "'I (NRC,1987a). If the average dose to the ever, the Sonet report also indicates that some inhabi-gland were about 30 rems, the collective thyroid dose tants who remained in the area for 7 days or more would be about 4 million person-rems. If one adopts before being evacuated would have received at least this collective dose and the thyroid risk coefficients 64-80 rems from external radiation alone. Moreover, presented in recent NRC reports (Gilbert,1985; the average dose for inhabitants of the zone 3-7 km Maxon,1985), then about 100 excess thyroid cancers around the plant is estimated to be 54 rems. That are estimated for this population,10 of them likely to no acute radiation sickness symptoms were observed be fatal.

despite doses in excess of 50 rems might be explained The Soviets also estimated the collective radiation by the fact that doses were protracted over a period impact on the European part of the U.S.S.R. which of days. On the other hand, the tabulated values are received the bulk of the radiation dosage. About 75 once referred to as "maximwn estimates", and this million persons exposed to varying amounts of radi-may help to explain some apparent inconsistencies-- ation are found in four of the Soviets:The Ukranian i.e. 30-40 rems may be intended as a more realistic SSR, the Byelorussian SSR, the Moldavian SSR and estimate of the maximum dose received off site. The the Russian SFSR. Estimates of the external dos report indicates that the dow estimates for the were provided in the Soviet report for various regions evacuees are preliminary and that more accurate esti-of the European part of the Soviet Union, both urban mates will be forthcoming.

and rural dwellers. Doses tended to be higher for The maximum collective extcrnal dose delivered to people in rural areas ba:ause they spend more time the 135,000 evacuees by direct radiation from the outdoors and eat more locally produced food. The effluent cloud and by radionuclides depo;ited on the individual doses for the year 1986 ranged from 3 ground was estimated by the Soviets to be 1,6 million mrems to about I rem. The collective dose to all 75 person rems, or an average of about 12 rems per million people over the next 50 yr was estimated to be person. On the basis of that collective dose estimate 29 million person-rems, about 30% of which would and assuming a cancer fatality rate of about 2 per be received in 1986.

10,000 rems, one would calculate about 320 excess The Soviets also estima.ed exposure through the

s Irnplications of the Chernobyl Nuclear Acadent 307 food pathway. For food produced in 1986. there will short distance away. The effect on the food pathway be contaminadon from a vanety of radionucbdes, due to deposidon of "'Ce with a 30 year half-hfe especially "'I. '"Ru, '"Ce, "'Cs, and "'Cs The decay rate is especially important to the assessment of highesi doses from "'Cs and "'Cs were beheved long term ingesdon doses from agricultural products.

to be in the Ukranian and Byelorussian regions of in the short term, deposition of "'I with an eight day Poles'ye where an esumated 100,000 Ci of "'Cs was half-hfe is important to computadons of ingesdon deposited. A critical consideration h that the soit doses.

characterisucs are such that radiadon uptake by Better data of the above kinds than presently exists plant; is expected to be 10 or 100 times tnore than as well as refinements in computer tnodehng are what it would be in other soil types. The collective needed to improve the quality of health effects esti-dose delivered through the food pathway to the popu-mates from the Chernobyl radionuclides releases. As lation of the Poles'ye region for a period of 70 yr after a tentative approsimadon, the average individ tal in the accident was estimated to be 210 million person-Europe (outside the Soviet Union and those countries rems. Experts at the IAEA meeting in Vienna ques. reaiving very httle of the fall-out, namely, Spain, tiened this 6gure because previous experience in esd. Portugal, Ireland, England, Denmark and most of mating colleedve doses from release of cesium to the France)is estimated to receive a 60-mrem dose from atmosphere (e.g..from ouclear weapons tests) suggests the accident, this dose being spread over a period of that the dose via food consumption is roughly equal years (NRC,1987a). For comparison. the average to that from external exposure. Furthermore, pre. individual will receive about 100 mrem each year from hminary whole-body scanning measurements suggest background radiation. Using this estimated average that cesium transfer through the' food chain may be dose and a total population of about 350 million only about 10% of what was predicted for the region. people in that part of Europe being considered, a col-According to tbc U.S. attendees of the meeting, there lective dose of 20 million person rems is calculated.

was general agreement among both Soviet and West-Based again on a cancer fatality rate of two deaths ern experts that the estimated collective dose given in per 10,000 rems, about 4000 excess cancer deaths out-the Soviet report tas probably too high, perhaps by side the Soviet Union may be calculated to result a factor of ten (NRC.1987a).The estimated effect of from the accident. These deaths would be completely the Chernobyl accident on the exposed population of masked by the 70 mi!! ion or so cancer deaths from 75 million is quite substantial. Even if the Soviet report other causes predicted in the population over the next overestimates the dose via the food pathway by an 70 years. Because of the very small doses of radio-order of magnitude, one estimates a total collective nuclides reaching the United States (primarily "'I dose of about 50 mi!! ion person-rems. Assumieg a in milk), only about two excess thyroid cancers are cancer fatality rate of 2 per 10,000 rems, then about projected having a low probability of fatality (NRC, 10,000 fatal cancers (plus a comparable number of 1987a).

nonfatal cancers) would be projected over the next 70 In the first month or so following the Chernobyl yr.

accident, data on radionuclides releases and deposition Beginning with the initial detection of radiation patterns was so sparse and pootiy organized that few from the Chernobyl release at the Forsmark nuclear experts would hazard s guess as to the likely bealth power station in Sweden on April 28, radioactivity effects of the accident. Thomas Maugh, a science was monitored in air, on the ground and in food writer for the Los Angeles Times, reported in less than throughout Europe. The quality and completeness of a month after the accident the estimates of several these data vary greatly by country. A summary of this scientists suggesting that as many as 5000 to 40,000 data is presented in the June 12 report of the World cancer deaths could ultimately result from the acci-Health Organization (1986). In addition, more than dent (Maugh,1986).The highest of these was by John ten European nations have produced reports on the Gorman, professor emeritus of medical physics at the national effects of the Chernobyl accident, the most University of California, Berkeley. He estimated detailed of which are by Italy, Finland, and Swden. about 23,000 cancer deaths in the U.S.S.R. and 16,500 The assessment of short and long-term collective deaths in Scandinavia and the rest of Europe. The external doses requires a population-weighted sum conservative estimate of $128 excess cancer deaths in of doses from ground deposited radionuclides over the U.S.S.R. and Europe were prepared by physicists geographical areas that is sufficiently fme-grained to Frank von Hippel, of Princeton University and reflect the significant variaCons in deposidons result. Thomas Cochran of the Natural Resources Defense ing from wind and rainfall patterns. Rain can cause Council, who cautioned that their estimates could be large increases in deposition versus dry areas only a low by a factor of ten.

4 J

l 308-H. R. Dorrow 1

As reported by Maugh, the gaps between the two result of Soviet data supplied at the Vienna meeting sets of fatality estimates result from marked differ. - of the IAEA and further stressed that:

ences in methodology. Von Hippel's and Cochran's estimates were based on computer simuladons of radi-

Large uncertaint.es will remain, however, if only ation releases conducted at tbc L.awrena Livermore because of the contmumg uncertamty m cancer National!.aboratory and the use of the same fatality dose-eNect coemeients. Our knowledge of these rate of 2 excess deaths per 10,000 person-rems as used c emeients, especiaHy the iodine 131 thyroid dose-above in the Soviet estimates as derived from the.-

eNoct c e5cients, could be considerably improved BEIR 111 report of the U.S. Nadonal Academy of by a proper epidemiological follow up of those Sciences (1980). By contrast, Gofman's approach was BrouPs near Chernobyl who received the highest based on measured radiation levels in selected cities.

exposures, most sfrected by the Chernobyl accident, but also by Professor Richard Wilson, Professor of Physics at his own estimates of dose-response that are about 17 Harvard University, also commented on the uncer.

times higher than the fatality rates per unit dose of tainty surrounding cancer dose effect coe5cients :

the BEIR Ill report. Such estimates an highly specu.

lative in the low dose range expenenced by most per.

"The individual doses and the dose rates resulting sons exposed to radiation from the Chernobyl acci.

from the Chernobyl plant emissions are so small dent. The more extreme estimates of fatalities from that the cancer risks are uncertain Most estimates low doses have been seriously questioned in a recent of risk use a linear dose-response relationship of l

paper by Webster (1987).

one cancer (fatality) per 5000 to 10,000 person.

A more recent and detailed analysis and fatality mms, but animal data suggest that the linear estimates prepared by Von Hippel and Cochran are relationship overstates the risk when doses are given found in the August / September 1986 issue of the Bull.

at a low rate.... We can characterue the effects erin of the A romic Sciences (Von Hippel and Cochran, more acct.rately by comparing them with the health 1986). It is notesvorthy that this carefully reasoned risks from burnmg fossil fuel, using similar cal-report did not provide any bottom line number for culations and assuming a similar dose-response cancer fatalities. Ratber, the following conclusion was relationship at low doses although the biological reached for the expected fatalities for the exposM endpoints an different. Such calculations suggest population of Europe, including European U.S.S.R:

that the health efects in Europe of toxic pollutants caused by Soviet fuel burning each year are as bad "It is the addition of such small extra risks over as the total health effects caused by the isolated many millions of indidduals that results in our accident at Chernobyl."

estimate of thousands to tens of thousands of extra cancer deaths... As a result of all the compounding in this forum article, Dr Robert Gale presents the foDowing calculations of excess cancers and cancer uncertainties m the factors mvolved, our estimates of the long-term health consequences of the Cher. deaths using Soviet projecdons and then provides a nobyl accident are uncertain even as to order of commentary regarding their likely ovenstimation (pgg,g9g7) magnitude."

~

"For the 135,000 people in the evacuation zone,1000 One of the lowest estimates for cancer fatalities excess cancers and 500 excess cancer deaths; for expected to result from the Charnobyl acx:ident -

the other 75 million people in the European Soviet resulted from' an analysis of the Commission of the Union,5000 to 50,000 excess cancers and 2500 to European communities that put the number at 1000 25,000 excesss cancer deaths; for the other $ billion excess cancer deaths over the next 70 yr, compared people worldwide,2500 to 100,000 excess cancers, with a projected 60 million cancer deaths from other and 1250 to 50,000 excess cancer deaths The esti.

causes over the same period (CEC,1986).

mated worldwide total would be 8000 to 150,000 in a Winter 1987 publication by the National Acad-excess cancers and 4000 to 75,000 excess cancer emy of Sciences, National Academy of Engineering deaths. These ranges are approximate.

and the Institute ot' Medicine', forum articles by Rich-

" These data are controversial. In my opinion the ard Wilson, Robert Gale and Fr.nk von Hippel con-number of excess smacers is hkely to be over-tinued the dialogue on the cancer fatality effects from estimated by this approach for the reasons 1 Chenobyl (NAS,1987). Vcm Hippel noted that cal-described. Even the lower estimates may be too high culations he and Cochran made in their August article and the actual number of cases may be considerably (1986) would have been "somewhat different" as a lower, perhaps by a factor of 10. These excess can.

l 1

Iropbcauons of the Chernoby! Lclear Accident 309 cers would represent a less than one percent through the contaminated food pathw'ay is high bv increase from normal levels in the European Soviet a factor of 10, the esdmated average individual population. Nevertheless, each person with an dose from external and internal pathways would unnecessary cancer is important to us and to the be about 0.67 rad, roughly equivalent to the dose l

Soviets."

received from brdground radiation over a penod j

k 6 & W M ham W dal M a f 7 yr. Based again on a risk factor of 2 x 10-*/ rad, of the projected cancer fatahties from the Chernobyl tMs da M pve an esdmated Wme risk d accident relates to individuals who will have received 1

,w is only a ut OR. M (M stated j

reladvely minor incremental doses of radiadon above normal background levels,it was surprising that none A third exampk is the Forum arncle by Richard Wil-of the cited references gave explicit attention to the son WAs,1987):

de mmimu nature of these risks for snany exposed individuals. The use of a de minimu standard ofindi-Wy for the group exposed to the highest amounts vidual risk for regulatory decisions is dra wing increas-dradiadon, the 24,000peopk hving between 3 and ing attention from national and internadonal scien-15 km from Chernobyl (excluding those living in I

ti6c bodies such as the (U.S.) Nadonal Council on Pripyath were the exposures at a level--45 rems l

l Radiological Protection and Measurements, the a verage-st which Luman data show adverse health (U.K.) Nadonal RadiologiaJ Protection Board, the efects. These people will have about a 3% increase International Commission on Radiological Pro-in cancer incidence. This is likely to be compensated tection and the International Atomic Energy Agency, for by the increased health care that they will as well as a number of U.S. Federal agencici and the receive. For the 2 million people living in Byelo-j U.S. Courts (Spangler,1987a,b). Among the sug-russia (downwmd from Chernobyl), the Soviet esti-gested applicadons of de runimu risk concepts are:

mate for increased lifetime dose is 0.7 rem. This is the setting of regula tory priorities ; as a "8oor" for as considerably less than the diNerence in the lifetime l

low as reasonably achievable (ALARA) con-external dose a person receives on moving from siderations ; as a cut-osievel for collective dose assess-New York to Denver. It is also less than the differ-ments; for setdog outer bounds of geographical

• DC' ID d'e dose a person rireives from inhaled i

zones ; as a door for de6nitions oflow-leve! waste ; as radon if he or she moves from an average New a presumption of triviality in legal proceedings; to England house to an average Pennsylvania house.

I foster administrative and regulatory effidency ; and to Sire few people, if any, worry about these differ-provide perspective for public understanding, includ-ens in natural background radiation,it would be ing policy judgmenu (Dads,1984).

inconsistent for the 2 million people in Byelorussia Although not explicitly mendoning de minimu risk to worry about their exposure from Chernobyl and concepts, several of the aforementioned references did even more inconsistent for less-exposed West Euro-provide commentaries of the small nature of the esti-peans to worry.

mated it.crements to individual cancer risk resulting from the Chernobyl accident, some fraction of which During a visit to Chernobylin February 1987, Wil-might justifiably be regarded as de minimu risk. For son Icarned from Professor Pavlowski of the Institute example, von Hippel and Cochran noted that "The of Biophysics that the estimated average dose to the associated individual risks are very small for all but persons living between 3 and 15 km from the plant those populations within a few tens of kilometers of had been revised downward to 24 rems per person, or the accident. However, these small risks, added up about half the original estimate (Wilson,1987).

over bundreds of millions ofindividuals, could total thousands to tens of thousands of cancer deaths and tv, A ratuMINaaY VIEW OF SOME IMPUCAMONS generally less fatal thyroid tumors".

OF M CHEltNORYL ACCIDEM POa M ILECULADON A second explanation of this general kind was pro-0F UA NUC11Aa rowta r:#rrsi l

vided by J. Puskin of the U.S. Environmental Pro-Implicatiorssfor graphite-moderated reactors l

tection Agency, who was the author of the " Health 3g g g jg g

7 and Environmental Consequences chapter of NUREG 1250(NRC,1987a) and safety concepts of the RLMK graphite-moder-ggg "The risk to an a verage individ ualin the population owing to the accident is relatively small. Assuming t & prehminary wems in Pan he not W ncted that the original Soviet estimate of dose received upon by the Danmussion. A draft report for public comment could be forthcoming in the next sewrml months.

.o; i

310 H.R.Donw the Light Water Reactor (LWR) prevalent in the U.S.

required for LWRs. A study of the potentials for have been discussed in Part 1. De Fort St Vrain High

's Chernobyl-type fire and explosions derived from Temperature Gas Cooled Reactor (HTGR) in Weid ~ hydrogen and carbon monoxide " water gas"in Fort County, Colorado and the Department of Energy's St Vrain was initiated immediately with the news of (DOE) N Reactor at the Hanford Reservation in the Chernobyl event. While the study is not yet com-Washington State are the only operating power reac-plete, the 6ndings are expected to conclude that the tors moderated by graphite in the United States. As use of a helium coolant, the overall negative reacthity the N Reactor is not beensed by the NRC and is under coef5cient, completely diverse alternate shutdown and the authority of DOE, the Chernobylimplications for cooling systems and the protection ofered by the it are being assessed separately by that agerey and PCRV against reactor Bres,. internal postulated others.The HTGR type reactor has been under devel-explosions and 6ssion product release to the environs opment in the U.S. and West Germany since the late remove Fort St Vrain from any vulnerability to 1950's. The curren't HTGR development efforts in characteristics of the Chernobyl design.

the.U.S. are concentrating on the Modular HTGR (MHTGR) concept which uses available HTGR tech-nology in combination with saberent and passive Adnsustratior controls over the aqfe operations cf

~

safety features. The MHTGR concept is being pro. madrar power plants: dealing with human error and posed by DOE in conformance with the Commission's accident management recently published " Statement of Policy for the Regu-Administrative controls over plant operations lation of Advanad Nuclear Power Plants" (51 Fr include NRC rules and regulations, facility license 24643). nus, assessment of the Chernobyl impli-conditions and Technical Speci6 cations (TS) and cations and candidate issues has value both to Fort plant procedures. The overall administrative control St Vrain and the MHTGR.

framework requires that safety-related activities at Among the candidate issues exammed by the U.S.

nuclear power plants be conducted in accordance with Nuclear Regulatory Cornmmion are those involving - approved written procedures.nese activities include, operations, design, containment, emnergency planning for example, operations, tests, mspections, cali-and severe sa:ident phenomena (USNRC,1987 ).

brations, maintenance, experiments, modifications.

The only commonality of the 330 MWe Fort St Vrain safety review and approval functions and audits. The reactor and the MHTGR with the Chernobyl design safety design basis of the plant is based upon assumed is the use of a graphite moderator and gravity driwn initial conditions' for transients and emergencies.

control rods. Fort St Vrain uses a helium coolant These initial conditions (e.g. temperatures, pressures, which is pressurized to 700 p.s.i. (4.8 MBa) and which control rod positions and equipment availability)

Sows downward through halfinch diameter holes in astablish a " safe operating envelope". ENective a fully ceramia (graphite) core. The reactor core and ' administrative controls are necessary to ensure that the entire primary coolant system, including steam sanctor operations are conducted within.this safe generators and belium circulators, are enclosed in a operating envelope. Clearly, for administrative con-j prestressed concrete reactor vessel (PCRV) which, trols to be efective, they must be technically accurate through use ofinner and outer penetration seah and and complete, they must-be understood by those in conjunction with a filtered and vented connnement responsible for implementing speci6c procedures, and building, satssnes the NRC's Geners! Design Criteria snanagement must ensure that they are enforced. A for reactor containment. The MHTGR will haw a key inding from the Chernobyl accident is that such steel pressure vessel rather than a PCRV, administrative controls in place at Chernobyl were.

In the issue areas of operations, design, contain-act efective in maintaining conditions within the-ment, emergency planning, and severe accident - safe operating envelope established by the RBMK phenomena, the assessments performed by the NRC ~ designers.

found that the implications have generated no new The administrative controls over plant operations licensing concerns for HTGRs and that the overall in the U.S. were reviewed to determine if adequate conclusions and the speci6c area conclusions are the controls are in place to maintain plant conditions same as for LWRs.. Indeed, following the TMI 2 within the safe operating anvelope..This review accident, emergency planning needs for Fort St Vrain included an assessment of procedural adequacy and were reviewed and it was concluded that a 5-mile compliance, approval of testa, bypassing of safety sys-radius for an emergency planning zone (EPZ) would tems, availability of engineered safety features, oper-i be sufhcient in comparison with the 10-mile radius stor attitudes toward safety, management systems and accident management. The staK con 6rmed that some

e, Impbcations of the Chernobyl Nuclear Accident 311 ongoing activities with a nexus to the Chernobyl acci-operadng envelope. Industry action to improve the dent should continue. In addition, a few neu issues review process reqmred by the NRC has been under-requiring staff attention were identined.

taken ; however, more needs to be done to focus the Emergency Operating Procedures (EOPs) are responsibility for safety. All plant personnel have a intended to ensure safe shutdown and to midgate the safety responsibihty, but this responsibility is coupled cHects of accidents and transients. Facility EOPs are with other functions. He sta# bebeves that the ben.

designed for coping with accidents and transients e6ts of a high level on-site nuclear safety manager, which initiate from within the safe operating envelope. with no other responsibibdes or duties, should be The ability of operators to successfully implement examined.

EOPs depends upon plant safety parameters initially it should be stressed that the sigm6cance oflessons being within the safe operatieg envelope. As a result of to be learned from the Chernobyl nuclear accident the TMI accident, NRC required that new symptom-would have been very :nuch greater,ifit were not for based EOPs be developed These new procedures have the lessons we (and many other nanons using nuclear not been implemented ' j all facibties, and NRC plan ts similar in design to ours) ha ve learned resulting o

audits have identified de6ciencies in implementation from the nuclear accident at nroe Mile Island and at several facibties. Thus, signi6 cant esort by liwnsees subsequent insights and learning expenence from the is needed to compete implementadon of new EOPs.

evaluation of plant operating expenence data and Operator training needs to stress fundamentals of research programs. Institutional arrangements with reactor safety, how the plant should function, and the foreign nations have magni 6ed the shared bene 6ts of underlyin'g danger if plant conditions move outside these kinds oflearning (NRC,1985al.

the safe operating envelope. With adequate training and knowledge, personnel would be less likely to suc-cumb to pressures to speed up, take shortcuts, or' Design implicationsfor accident prewstbn and con-defeat safety functions knowing the possible conse-84mmt Performance quences. Operating experience and the Chernobyl The nuclear design of U.S. reactors, notably the event indicate more training is needed in the areas of absence of positive void coef5cients and control rods maintenance of safety parameters and plant con-that are fast acting and oNer substantial shutdown didons within the safe operating envelope, EOPS and margins, provides assurance against a Chernobyl-type accident management.

superprompt crincal power cacursion. Nevertheless, The Chernobyl accident has emphasized the need the possible need for con 6rmatory reviews of the for conungency planning (assuming core damage has acceptability of risks from other low-probability reac-occurred) to ensure that appropriate controls, training tivity event sequences was asser. sed, including acci-and planrdng have prepared the plant staff to manage dont scenarios that could occur at low-power and plant assessment activities, resportse actions and shutdown conditions that may not be bounded by emergency actions. Signi6 cant effort to prepare for analyses for full power. Safety nament also was events involving degraded core cooling and to made of multiple-unit site impbca tions including con-upgrade emergency planning has been accomplished. sideration of c6ects of shared shutdown-related sys-However, more work needs to be done in training and tems and of radioactive release effects on operator promdure development for coping with severe core safety at the other units. Moreover, consideradon of damage and for effective management of containment. fires focused on the adequacy of protection provisions Management attendon and diligence is required to for fires with radiation present.

ensure that plant operations, testing and maintenance Although the design of U.S. nuclear reactors pro-are conducted within the safe operating envelope. vides assurance against a Chernobyl-type super-Management must focus on assuring that all of the prompt critical power escursion,it was concluded that administrative control systems are effective and thejudgements which determined the identi6 cation of enforced. Audits, internal inspections and review of possible accident sequences analyzed in safety analysis operating data and events must be performed to reports and underlying design approvals should be obtain feedback on the quabty of safety activides. reviewed for reconfirmation of their validity with the Control over reviews of changes, tests and procedures more sophisticated analytical tools now available.

must be conducted by qualified and knowledgeable This could be accomphsbed either by the NRC or by individuals. Experience has shown that the quality of bcensees with NRC groundrules and review some of these reviews has not been consistent and, in One of the unique aspects of the Chernobyl amident some instances, design changes have been made and was that it occurred at a relatively low power (< 7%).

testing conducted that plam the plant outside the safe While low powr operation is generally considered

I l

4 312 H R.Do m safer than high power operadon for LWRs, this is way for some time at the NRC (Pratt and Bari,1981 ;

not true for the RBMK. The aspect of low power NRC,1983,1985c) The Severe Accident Policy State-operation considered in the NRC review is whether ment issued in July 1985, stated that the Commission the design basis events are presently being evaluated will strike a balance between accident prevention and at their most limiting power level or whether more consequence midgation encompassing actions that attention should be given to these events at low power. improve understanding of containment building fail, it was concluded that a systematic evaluadon of acci. ure characteristics and design features or emergency dent initiators at low power should be camed out, actions that decrease the likelibood of containment especially in view of the fact that existing Probabilisuc building failures (NRC,1985a).

Risk Assessments have paid very litde attention to The Policy went on to state that although not low power conditions or testing in evaluating severe speci6cally designed to accommodate all of the bostile accident risk.

environments resulting from the complete spectrum l

The radioactive gas and smoke release at Cherno-of severe accidents, containments can retain a large byl, Unit 4 spread to the other three operating units fraction of the radiologicalinventory from a portion l

at the site. De airborne radioactivity was transported of the spectrwn. For example, large, dry containments to the other units by a common ventilation system as may be suf5cient!y capable of mitigating the conse-well as general atmospheric disper:; ion paths. This quences of a wide spectrum of core-melt accidents; raises the basic question of how accidents at one unit bence, further requirements may be unnecessary or, at of a muldple unit site afect the remaining units and most, upgrading current requirements to gain limited further questions of how these efects may be com-improvements of their existing capability may be pounded when structures, systems and components neuary. The Commiuion expects that these matters l

j are shared between units. The NRC review concluded will continue to be subjects for study; for example that the Chernobyl experii e should be taken into in the NRC research program and in further plant.

account in the current assessment of the adequacy of speci6c studies such as the Zion and Indian Point l

protection of control rooms of other nuclear power probabilictic risk suruments (Pratt and Bari,1981; l

unitt, on a muld-unit site in the event of an accident NRC,1983 ; Mishima et al,1984). Integrated systems at one of the units. This should be done on the basis of analysis will be used to explore whether other con-recently developed descriptions of radioacdve release tainment types exhibit a functional containment capa-source terms (NRC,1985b,1987b). New plants bility equivalent to that of large, dry containments.

should not share systems forming part of the sbut. Although containment strength is an important fea-down capability.

ture to be considered in such an analysis, credits Fire 6ghting capability, involving about 30 6res due should also be given to the inherent energy and radio-to the Chernoby: accident, was crophncmi by the nuclide absorption capabihdes of the various designs Soviets among the lessons to be learned from their as well as other design features that limit or control accident. The Soviets stressed the need for special combustible gases.

equipment to lift 6 e6ghting equipment to roofs. Also Further research and plant speci6c studies should of concern was the need for protective dothing for improve our understanding of the containment load-6re6ghters when 6ghting 6res in radioactive environ-ing and failure characteristics for the various classes ments. However, the NRC review of our own regu-of facilities. Tbe analyses should be as realistic as ladons, equipment, and procedures to combat 6res possible and should include, where appropriate, revealed that actions already taken to upgrade 6te dynanue and stade loadings from combustion of protection plus those in progress are judged adequate, hydrogen and other combustibles, static pressure and except possibly provisions for 6te6ghting with radi-temperature loadings from steam and non-con-ation present. It was recommended that current pro-densibles, basemat penetration by core-melt matenals visions be reviewed for this particular safety issue.

and effects of aerosols on engineered safety features.

The Chernobyl accident brought new attention to A clari6 cation of containment performance expec.

containments and performance of containments tations will be made including a decision on whether under severe accident conditions. Such challenges to establish new performance criteria for containment include phenomena such as increased pressures from systems and,if so, what these should be. Accordingly, an uncontrolled hydrogen combustion or release of based on the existing research and ongoing con-targe quantities of non condensible gases from core-tainment evaluation programs, new programs or concrete interactions. Research programs and regu-initiatives are not needed as a result of the Chernobyl latory initiatives to address the issue of containment accident that failed a containment of drastically performance during severe accidents have been under different design.

l

l 4

,=

impbcauons of the Chernoby! Nuclear Accident 313 Implications for emergency planning and improved evacuation routes nlso influenced the timing of evaru.

understand ng ofsevert accident phenomena ation. Ingestion pathway protective rnessures were There are three problems in drawing a nexus taken in the U.S.S.R. both within the 30 km zone between the Soviet response lo the Chernobyl accident and well beyond. Similar measures were also taken -

and emergency p>anning implications for U.S. plants : in several Soviet Bloc countries, in Scandinavia and Western Europe.

(1) after the TMI accident, large resources were Regarding EPZ sizr., a major NRC research effort committed to improved emergency planning began about 1981 to obtain a better understanding and response capabilides at each U.S. nuclear of fission product transport and release ut' der severe plant whereas at time of the Chernobyl acci. accident conditions (NRC,19856) The latest of these dent the Soviets apparently had inadequate studies (USNRC,1987b) will be used to identify, plans to cope with the emergency problems analyze and put into perspective the actions taken specific to the Chernobyl accident scenario, during the Chernobyl accident; i.e bow the Cher-(However,it is believed that the Soviets possess mobyl soura term and ernerFeney actions relate to l

extensive emergency preparedness plans for U.S. source tean and emergency actions. These results nuclear weapon attack in the context of civil will have a substantialimpact on decisions concerning defense protocols that could also provide sub the adequacy of U.S. EPZ size,among other things. A stantial guidance for severe accidents at nuclear Preliminary conclusion is that the Chernobyl accident power plants, especially regarding lines of a uth, and the Soviet response does not reveal any apparent crity for decision making and communi. de6ciency regarding U.S.. plans and preparedness cations),

induding the 10 mile plume exposure pathway EPZ (2) the specifics of the Chernobyl release are unique si2e and the 50 mile ingestion exposure pathway EPZ j

to the RBMK design whereas the amounts of size. These zones provide an adequate basis to plan radioactive material released from U.S. plants and carry out the full range of protective actions for would, for most accident sequences, be con. the populations within these zones, as well as beyond siderably less. U.S. plants have substantial con. them,if the need should arise. Notwithstanding tN.,

tainments and severe accidents would generally the basis for the emergency planning zones needs to progress more slowly than at Chernobyl with be reexamined in the light of new information gleaned much longer warning times before any con. from source term research (NRC,1985b; 1987b).

tainment breach fer all but a few low-prob.

Emergency response planning also involves medical ability scenarios involving large scale core melt, treatment issues such as the adequacy of(l) the Fed-i (3) the Soviets had to assemble 4000 buses and eral policy on potassium iodide (K!) prophylaxis ; and trucks for the Chernobyl evacuation, whereas (2) medical services in reasonable proximity to U.S.

in the U.S. most of the public has access to nuclear power plants. The Soviets credited the use of private automobile transportation to be sup. K1 by the Pripyat population with the permissible plemented for emergency evacuation by bus iodine content (less than 30 rad) found in 97% of the and other transportation that is preplanned.

206 evacuees tested at one relocation center. They said there were no serious adverse reactions from the use Regarding cost effectin measures for off site of KI. TheFederal policy statement acknowledges the decontamination, long-term relocation, and res-effectiveness of K1 in certain circumstances ; however, toration of agricultural and other resource use, it it concludes that the preponderance of information would appear that there is much to be learned of edicates that a nationwide requirement for the pre.

value from the pioneering Soviet experience in these distribution or stockpiling for use by the general puclic matters-both their successes and less effective inno-would not be cost beneficial. Further, the staff believes vations.

that the present arrangements and future plans for One issue being reviewed by the NRC is the medical services around U.S. Sommercial nuclear adequacy of the size of the emergency planning zones power plants are adequate.

1 (EPZs) around U.S. commercial nuclear power plants.

Tbc NRC also reviewed the ingestion pathway The Soviets evacuated 135,000 persons from a zone issues from the Chernobyl accident involving the of 30 km (18 miles) radius of the Chernobyl plant. adequacy of(1) U.S. standards for the ingestion of The 45,000 residents of Pripyat (3 miles) were initially radioactive materials through food and water (and the sheltered as a protective measure and then evacuated mechanisms for adapting those standards to changing the following day due to increased radiation doses. conditions); and (2) the U.S. plans and preparedness legistics and contamination control problems along for taking measures to protect the public from the I

o

,a 314 H. R. Drvro,

ingestion of hazardous levels of radioactive materias ena, computer modelling of this phenomena and fur-in food and water. The Food and Drug Admin-ther advances in Probabilisde Risk Assessment will istration has pubbsbed aedon levels (47 FR 47073) to also r:ontribute to a reduedon in uncertainty that will provide state and local agencies recommendations for serve to improve the quality of emergency response taking protecove action in the event that radiadon and preparedness planning for severe nuclear accident causes contaminat on of human food and animal scenarios, especially those that are the dominant con-feeds. These can be used to determine whether levels tributors to the overall level of risk.

of radiation encountered in food after a radiological incident warrant protecdve aedon and to suggest appropriate aedon that may be taken if action is war-ranted. The state and local governments have pri-RINNS mary responsibility for taking proteedve actions to Bekrestnov N. V. and Kozlov V. Ph. (1980) Aspects of l

protect the public from the ingestion of contaminated Accident Managemens at Nuclear power Plants en the

(

foodstuffs. The Protective Aedon Guides (PAGs) for USSR, presented at International Workshop on Planning for Rare Evenu: Nuclear Accident Preparedness and foodstuffs and animal feed would apply during and after an accident, although they may be modi 6ed by CEC CAcm4/ Nuclear rowr Plant Acadent the federal government or by state and local govern-and tu Caueguences in the framework of the European ments. The federal mechanism for providing rec-Cannamity COM (86) 607 Final. Commkon or the Euro-commendations to state and local governments is the pean Communities, Brussels.

Dans Mt W) The De Muuinu Aegidatory Cus4f Conupu Federal Emergency Response Plan (FEMA,1980; Testimony before the Advisory Committee on Reactor NRC.1980). The adequacy of the federal guidance Safeguards. U.S Nuebt Regulatory Commission.

l cannot be tested against the Chernobyl accident FEMA (1980) National Radiological Emergency Pre-because tbc speciScs of the Chernobyl selease are paredneasfAesporue plan for Commercial Nuclear roser unique to the RBMK design. However, the adequacy Plans Acadenu (Master Plan). Federa! Emergency Man-asement Agency, pubbshed in 45 FR 84910.

of the Federal guidance will be reviewed through Gilbert E. (1985) Report NUREG/CR 4214. U.S. Nucicar evaluations provided by U.S. source term research Regulatory Commission.

(supra). To date it appears that the existing federal INSAG (1986) Summary Report an tAe rost Accident Aenew guidance will provide adequate protecdon for mem.

1. eetsag on iAt CArmobyl Accident, International Nuclear Safety Advisory Group, IAEA, %cnna.

bers of the general public from contammated food.

Decontaminau.on techniques employed by the Sova..

Kenieny (l979) A port of the president's Commusion on the Accident at Three MJe Island.

ets, including those for personnel, appear to be similar Maugh T. H. II (1986)I.os Angeles Times (May 22).

to those used by the United States in support of the Maxon H. (1985) Report NUREG/CR-4214. U.S. Nuclear r.uclear weapons tesung program, the TMI-2 Regulatory Commsion.

shima L et 4 (1% Report WREG/CR 3787. US.

accident, and interdiction related to chemical spills.

Nuclear Regulatory Comnussion.

Desert areas and coral atolls have been decon-NAS (1980) The Efecu on populatioru of Erposure to low taminated, but there is little U.S. crperience in the laels oflanizing Aadiation: 1980 (SEIA III). National large scale decontaminadon of forests and orchards Academy of Sciences. National AraArmy Press, Wash-or croplands with the purpose of restoring viability N ( 8 larues in Science and TeeAnology 3, (2)6.

and productivity to the land as now being pioneered NEl (1986) Nuclear Enginecrmg Inamational 31,4.

by the Soviets. However, the effectiveness of Soviet NEl (1987) Nuclear Engmeering International 32,2.

decontamination and relocation efforts will also have NN (1987) Nuclear News 30,63.

to be esamined as the data become available.The U.S.

NRC (1980) Report NUREG 0654. U.S. Nuclear Regu-latory Commnmon.

capabihties will have to be cumined within par-NRC (1983) Report NUREG 0900. U.S. Nuclear Regu-ameters provided by U.S. source term research. Past latory Commission.

and current research results indicate that at least tem.

NRC (19854) Report NUREG 1070. U.S. Nuclear Regu-porary relocation may be necessary for populations at Latory Commission.

NRC (1925b) Report NUREG 0956, Draft report forCorn-distances that will vary with tbc source terms, weather ment. U.S. Nuclear Regulatory Comminion.

states, and other conditions that are unique to each NRC (1985c) Report NUREG 1079. U.S. Nuclear Regu-of a large spectrum of severe accident scenarios.

notory Commission.

Improved understanding of severe accident NRC (1987a) Report NUREG 1250. Report of an Inter.

phenomena, especially radionuclides dispersion mod-agency Task Force. U.S. Nudear Regulatory Com.

nussion.

elling will result from ongoing data monitoring and NRC (1987b) Report NUREG-ll50. Dran Report for Com-analysis in the U.S.S.R. and elsewhere in Europe.

ment. U.S. Nuclear Regulatory Commission.

Reseach on other aspects of severe accident phenom-Okrent D. (1981) Nuclear Araetor Sqfety: on rat Nusory of

o

.s 1

I l

implications of the Chemobyl Nuclear Aa:ident 315 1

the Regulatory Proceu The University otWnsconsin Press, Power Plant and its Coruequences. Informatwe compiled Madison for the IAEA Erperts'Mettma. U.S.S.R. State Comauttee Pratt W. T. and Bari R. A. (1981) Report NUREG/CR.2228.

on the Utihzadon of Atomic Energy, Vienna.

i U.S. Nuclear Regulatory Commission.

Von Hippel F. and Cochran T B. (1986) Bulletin of the J

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U.S.S R. (1986) The Acendent at the Chernobyl Nucitar Wuson R. (1987) Pmonal communicadon.

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