1987-01 – NRC – Report on the Accident at the Chernobyl Nuclear Power Station – ML071690245

1987-01-nrc-report-on-the-accident-at-the-chernobyl-nuclear-power-station-ml071690245

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Report on the AMcclint’ at the’
Chernobyl Nuclear PoWer. Station
0UE-1250
(TU.S.) Nuclear Regulatory .Comission
Washington, DC
Jan 87
.7 – 7.
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BIBL00RPHI DAASHEE NIJREG- 125-0
1. TITL. ANO S”TITLE I i
Report on’ th~e Acc’ident at the
Chernobyl Nuclear Power Statior I
I
3 LIAVI OL8%k
………….~……………………….. ______4 -.
January 198
a Dore “,P1UImO I
I AUT”0• IS
Multiple Authors
9 i MONT”
Januar
1.ya”
1987
Department of Energy -Inst., of Nuclea wr–,——– ….—- .—— Electric Power Research Institute V .. .ow M% Oft W-Pasi Environmental Protection Aoency
Federal Emergency Managemet, Agency. . – i—
Nuclear Regulatory Commission ._”_._
_ __•
U. S. Nuclear,, RegulatoryE c ot ssnion d.ed r i ilty A cy WashingtonD. C.ý “20555- ~ ~ ‘i’.
oSWO”P”A”N~T&ARN OTES
A5YRAC-I .,.ae
This report presebts the CoiAM~e .,finfogatias obtained by various organ- izations regarding the accideot (MWd -the comsq8*eces 04: the accident) that occurred ý.t uikt 4 of the-nuclear power station at Cberasbyl in the USSR on April 26. 1986. Each organistation baa indepeodently accepted responsibility for one or more chapters. thre various authors are identified in a footnote to each chapter. Chapter provides a8 overvieW of the rteprt. Very briefly the other chapters cover: desi f. teei l nuCclpetracr2 ,te Uiit 4; Chapter station 3, safety analyses for E3t.1 ; .Chaappttse r the accident scenario; Chapter 5, the role of tbhe operator; Chapter 6, a-a ssesneat of the rad.oactive release, dispersion, an tsanport;-Chaterd 7L,2 e a tiLes. associated with muergency actions; emid-Chte6-ifatiem t-e health and environmental consequences from the accident. ltes8e subject cover the major aspects of the a.ccident that have the pote• •il to’pcOet n;w sjnfe*Mation and less•os for the nuclearlindustry in seomral.et;Z
The task Of evaluatingft”_M ‘4igo~~u ta6 kaaiiw tedte -‘s
pursue according to the relevace ofmthe suJect to thei o ,. To..s findings will be Loased” qrtlb h emiatog~”~ The basic purpose of this report s -to pr•vide -the; afomettif ýo wb.kcn such 1ssfsnments can be ,.ade.
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1.
Chernobyl Accident, Russian Reactor, Severe Accident, Core Melt.,
Radioactive Release, Reactivity Accident, Graphite Fire, & Pressure Tube Reactor
OW044sw e”Aft”D, te•~aim $t*l
Unlimited
UnZcl assi fled
Unclassified
Z0)9 A
-. : ; ” :aII– c u ~
.,,n7-‘Cernbvi uclar
dv t o
a9

Report on,&t Accid-ent C-htehv ~iNucdear~
PowerSS tation
SS
U.S. NUCLEAR
..REGULATORY
,COMMLSION
-‘,Prepared by:
ent ofý Energy
I’.. -Electric Power Research Institute
‘ :Environmental Protection Agency
Federol Emergency Management Agency
Institute of Nuclear Power Operations
Nuclear Regulatory Commission
-ABSTRACT
_This report presents the compilation of informatix-,* obtained by’ various organizations
regarding the accident (and the consequences of the accident) that
occurred at Unit 4 of the nuclear power station at CbernobyiL in the USSR on
April 26, 1986. Each organization Ls independentl7 accepted responsibility
for one or more chapters. -The various authors are identified in a footnote to
each chapter. Chapter 1 provides an overview of the report. Very briefly the
other chapters cover: Chapter 2, the design of the Chernobyl nuclear station
Unit,4; Chapter 3, safety Chapter 5, the role analyses for Unit 4; Chapter 4, the accident scenario; of the operator;Chap-ter6,.an assessment of the radioactive
release, dispersion, sandtruasport;-.Chapter 7, the activities associated with .emergency actions; and Chapter, infoat:ionm on the health and environmental
consequences from the accident ,•,••These subjects cover the major aspects of the
accident that have pthepont, -pew. information and lessons for the
nuclear industry ,in-.general’.
The task of evaluating .the iufomtion i-obtained in these various areas and the
assessment of the potential Aiplications bas been left to each organization to
pursue according to the relevance.of the subject to their organization. Those
findings will be issued separaLely by the cognizant organizations. The basic
purpose of this report is to provide the information upon which such assessments
can be made.
ttI
Pagte
Abstfract …………………………………………………… …. iii
Acknowledgments ……………………………………………….. ix
ýýater T:-;
IO verview …………………………………………………. 1-1
2 Plant Design ……………………. . . . . . 2-
2.1 Reactor, -Fuel,-a nd Fueling z.-achinei i’…. …4. …………… —
2.2 Fluid and Heat Transport ,Systems……………………….. 2-18
2.3 Reactor Physics …………………………………………. 2.24
2.4 Instrumentation ands.Control. ……………………… 2-27
2.5 ElectricalPower System…………………………….. .2-36
2.6 Safety Systems ……………….. ……………………… 2-37
2.7 Reactor Operations…………………………….*.. ….. :2-49
2.8 References ……… ……………………………. 2-51
3 Safety Analysis …………………….. …………………….. 3-1
3.1 Introduction………………………… *.. ……………. 3-1
3.2 Soviet Safety Analysis of the Chernobyl Unit 4 F.,.;actor ……. 3-3
3.3 Independent Safety. Review .. . 3-27
.3.4 References…………………………………………….. 3-53
4 Accident Scenario… ……. ……………. …………………… 4-1
4.1 0,verview… ; –. ;; . … …. . … -,.. . .. . . . . . . . . .
4.2 -Event.x1ed tbi h4eiAc•cdent.. . I …….. 4-2
4. 3 EZvents:Vurift.-sa*d Atr( thel-c~dde. ……………… …….. 49;
4.4 References ………. … . . …………………… 4-12
5 Role of Operating Personnel …….. ……………….. 5-1
5.1 Operator Actions and Plant Activities Before the Accident… 5-2
5.2 Immediate and Short-Tern Operator Actions ………………. 5-3
5.3 Sumary of Key Operational Events and Errors ……………. 5-6
5.4 Operator Actioms Following tha Accident ………………… 5-9
5.5 References …………………………… 5-10
6 Radionuclide Release and Ataospheric Dispersion arid Transport 6-1
6.1 Radionuclide Release …………………………………. 6-1
6.2 Atmospheric Dispersion and Transport ………… …………. 6-8
CO:TENTS (Continued)
Chapter f Page
6.3 Consistency of Soviet Estimates of Rad’.onuclide, Release
With Observed Data From Other Countries …………… …… . ,10
References…………6-12
7 Emergency Preparedness and Response…… …………………… 7-1
7.1 Emergency Plans. ……………………………… :7-1
7.2 Emergency Organization and Facilities ………………….. 7-6
7.3 Alert and Notification System ………………………… .7-7
7.4 Protective Actions Taken…….. ………………………. 7-8
7.5. Radiological Monitoringand Exposure Control,……… ……. 7-10
-76.- ‘.ed ical Treatment. …………….. 7-14
7.7. Soviet .,Guidance _,on.’Acep ble•-i vels. of Public
Radiation Eposure.. 4 .. v :. …………………………. 7-16
7.8 Decontandtio………………………..7-18
7.9 Site :Recovery. ….. . ……………………….
7.10 Relocation-and Xeienr (Off Site) …………………….. ‘7-21
7.11 Public.-EducAtionaadImoxmtion Prog•rams…..:. “. …..- §7-21
7.12 Training. rram………………………………………………… 7-22
7.13 Summary. . .. -. ……………………………. 724
7.14 R7.elf4eRreefrnecnceess .. …… …………………………………….. 772-27
8 Health and Environmental Consequences …………………. ……. 81
8.1 Pathways of hNmaaExposure ……………………………. 8-1
8.2 Health Effects …………………………………. 84
8.3 Radiological Effectsa on the Soviet Union ……………….. 8-6
8. 4 Radiological.Effects on turoFe Outside the Soviet Union ….. 8-11
8.5 Radiological Effects on the Umited Etates ………………. 8-14
88..76 Global Effects on Agricultwre and Food …………………. 8-24. .-.kological•Iffects,•, ,:……….. ……… ………………….. 816
8.8 References. ….. .. -…. *…* 8416
Figure Pg
2.1 Cross-sectional vievofR -000 ………………………….. 2-9
2.2 Fuel channel 2………………………………………………2.3 Zirconiui-to-stainless ‘steel transition Joint. ………………. 210
2.4 Assembly of graphite riags on pressure °ube and graphite block
cooling ………………………………….. …………..-……. 211
2.5 Cross-sectional view of reactor cavity……………………… 2-12
2.6 Cross-sectional view of reactor building elevation, Chernobyl
Units 3 and 4 ………………………….. 2-14
2.7 Layout of main building of Chernobyl Units 3 and 4 ………………… 2-15
2.8 Scbematic drawing of the 36-rod fuel element ………………… 2-17
2.9 Cross-sectional view of the fueling machine …………………. 2-19
2.10 Grab book of refueling machine …………………………….. 2-20
vi
‘A_,iý,COrflNTS. (Continued)
Figure Page
2.11 Normal and .emergency cooling system of the Chernobyl Unit 4
Leactor. …. ………I ……………………….. … ………. … 2-21
2.12 Schematic drawing of control rod cooling system …………….. 2-232
2.13 Gas circuit system ………………………………………. 2-24
2.14 Effect of reactor Operation on the coolant void, fuel
temperature, and moderator temperature reactivity coefficients… 2-27
2.15 Control rod design …………… ……….. i …………… 2-31
-2.16 Schematic drawing of fully withdrawn and fully inserted
control rods……… ………………………….. 2-32
12.17 Functional diagram of a*.control rod irlyc.. 2-35
of-the reactor:_.ergency. +cooling system…… …. 2-38
2.19 Schematic drawing of themsystem for discharging steam from
the main safety -valves inteo’tepreslure suppression pool of
the accident locAllitlastis .,ta , …………………. 2-41
2.20 Systep .o protect the eactor vault from excess pressure ……… 2-43
2.21 Schematic diagram of the accident localization system ……….. 2-45
2.22 Evolution of reactorparsmeters during startup ………………. 2-50
3.1 Nuclear safety regulatory bodies and docume-ts in the-USSR …….. 3-6 I
4.1 Chronology of the accident at the Chernobyl Nuclear Power
Station …………………………………………………. 4-3
4.2 Key reactor parameters for the last five.minutes before the
accident ……………………………………………… 4-6
4.3 Chernobyl data evaluation of power vs. time during core
destruction phase ……………………………………… . 4-. 10
4.4 Photographs of the residues from model fuel pins (SPXN rods)
nfter tests in the +CDC.,(capsule driver core) siz/.Iting power
.excursions fnr mre acuivity laseitio c.id……… …. 4-1
5.1 Schema tic diar O0……………….. 5-2
6.1 Daily radionuclide release In the ataoephfte from the – –
damaged unit ……. 6-3………………….
Table Z +e
2.1 Development of Soviet-graphbltmodarated, -water-cooled
reactors ………… ……………………….. ….. 2-2
2.2 Chernobyl Unit 4 design parameters ……… …………………. 2
2,3 Fuel assembly desigp parsmeters forCharnobyl Unit 4 …………. 2-18
2.4 Calculated reactivity coefficieuts for R …………………. 2-26 I 2.5 Types of :ontrol rods ….. … * ………. . …………………….. 2-29
2.6 Control rod specifications ………………………………… 2-32
4.1 Chronology of tbh accident at the Chernobyl Nuclear Power
Sta o …….. …………………………………………. 4-13
, •. .. •• ll l ~ eo le l le ll ll 1. ,. l ~ ~ l lll.l4 ~
CONTENTS (Co tined)
Table mage
5.1 Operator violations of ýprocedures ………………………… 5-8
6.1 Core inventories and total releases, at he time of the
Chernobyl accident ………………………………………… .6-2
6.2 Daily release of radioactive substances into the atmosphere
from the damaged unit……….. ,;•……………………………..6.
6.3 Radionuclide composition of release from the damaged unit of
Chernobyl Nuclear Power Station ……………………………. 6-6
6.4 Estimates of percent of core inventory released based on
measurements outside the Scviet Union… 6_12
7.1 griultralprouct in-_c’tepermitted: radioactive_
Contamination was-found-to beexceeded………………………… 7-13
•7.2 Levels of 1-131 in milk, Ny 196. ………………………… 7-13
7.3 Criteria for makig erProttaibn of thepopulation.. 7-17
:11 …..
f.
8.1 Radionuclide contributions- .to external dose based on
spectrometric measuraemntse lin southern-Finland on
May 6 and 7, 1986. …… ………………………………….
8.2 Radionuclide deposition in two U.S. areas ……………………
8.3 Maximum radiation levels found in Europe following the
accident, by country …………………………………….
8.4 Haximum individual doses tosgroups in the United States
due to exposures or-,intakes.,•n the first.year after the
accident ………………………………………………
8-2
8-3
8-12
8-15
– 1
The following individuals have :contributed substantially-in the production
of this report: From the U.S,. Department of Energy – S. Rosen, E. Purvis,
D.. -HcPherson, ‘F., -Tooper and their contractrs-,, otably PacifiNoirthwest .
Laboratories (J. McNeece and L. Dodd); from the. Environmental,.,Protection
Agency – S. Myers, D. Janes, J’. Puskin, C. Nelson, and*N. Nelson; from the Electric
Power Research Institute – G. Vine; from the Federal Emergency Hanagement
Agency – .- Sanders and V. Adler; from the Institute of Nuclear Power Generation
– W. Conway and S. Visner, and from the Nuclear Regulatory Commission –
Sheron, C. Allen, F. Congel, and S. Archarya…
the Nuclear ‘Regulatory Commission provided a cordinti ‘function, wih regard
to the production, of ,the repirt.. C. ‘Allen’fromthe IR¢acted “..manager as ther project for coordinating the production oftthe report.-‘The Nuclear Regulatory
Comission also provided substantial editorial (1. -arwell and staff), graphics
(J. Thot-Thombson-u •ai staff)’ :.:typig ý(L. ffcKenzie and word-processing staff),
and printing.(N. Dsgttdand staff) -services supporting the publication of this
report. . .
,Ix
CHAPTER 1
OVERVIEW
in response to the Chernobyl Nuclear Power Station acciden°. in April 1986, a
group comprised of representatives from the Federal Government and the nuclear
power industry met to compile factual data and information relevant to understanding
that accident. Specific organizations, as noted below, prepared descriptions
of the accident. The, individual inputs are herein compiled and
represent, therefore, the views of the responsible organization.
iThe effort drew heavily on th:ze sources during the preparation.ofits report.
The first: source is a report prepa’ed in the Soviet Union (USSR’ 11986); that was
presented to the Internatioral . ic Energy Agency (IAEA) at a meeting held
August 25-29, 1986, in Vienna, Austria (IALA Experts’ Meeting). The second
mzjor source of information came from discussions with Soviet representatives
attending the IAEA Experts’ Meeting in August 1986. The third major source is
a report prepared by the International Nuclear Safety Advisory Group (INSAG,
1986) for the Director General of IAEA (Post-Accident Review Meeting,’
August 30-September 5, 1986).
The focus of this report is limited to the factors bearing directly on the
accident at Chernobyl. It does not extend to all aspects of the design and
operation of the Chernobyl plant. As such, the report includes information
on the relevant areas of plant design, plant safety analysis, the accident
scenario, the role of operating personnel, radioactive releases, emergency
response, and health and environmental consequences..
Chapter 2 was prepared by the U.S. Department of Energy (DOE). It describes
the unique design of the Soviet high-power, graphite-moderated boiling-watercooled
reactor at the Chernobyl Nuclear Power Station. This uniquely Soviet
design evolved “rom early demonstration and plutonium production reactors.
General characteristics of the RM1 and its predecessors include the use of
graphite as a neutron moderator and light wate-r as the coolant. Pressure
tubes, contained in vertical channels in the graphite, either contain lowenriched
uranium oxide fuel or are used as locations for control rods and
instrumentation.
The use of boiling wser as a coolant ia a pressure-tube, graphite-moderated
reactor distinguishes the RBIK desiar, from any other reactor design. Other
distinguishing features of the RBHI design include:
• on-line refueling
* single uranium enrichment level
* separation of core cooling into independen. halves
* use of computerized control systems
• separate flow control for eac’ pressure tube
* positive void reactivity coefficients under most operating conditions
slow scram system
1-1
steam suppression ssystet .
programmed power .setbacks (rather than scrams) for various abnormal
clcoj•x aic to ooiolnas nt–.f'”u•*e+i+.•r at’•i o.: -.i.•”.-.
accidenL localization systems
%.hapter 3,-prepaied by the Blertric Power Research Institute (EPRI), is directed
at a safety ana•lysis .of…Chernobyl- _Unit4 one of 14 operating. RBMK-.1000 reactorplants.
Significant differences exist in RBMK-1000 designs, as they h:ve
evolved from the early Leningrad design (first-generat4in RBtK, eight tctal
units) to the more 2odern Smolensk design (second-generation RHBK, six total
units, including Chernobyl Units 3 and:4). ‘-This evolution of the RBHK design
is often difficult to-discern in Soviet literature, and details of the plantspecific
differences among the 14 plants are not available. However, descrip-
.. tive.material of second-generation RBK-lO00 reactors is more: complete:
especiaAlyass a .result -of information in-the Soviet :report… on .the-, act.ident,
(US,18),The *Afety analy*sis, in this- chapter ýsometimoes .%present 0scm
* ri…, enri aalsi fý _second-generation- PSNK-460 r’easc’tors.–here -known
differences exist betveen first- .and s&cond-generation reactors, a brief dis
cassion is included of teeff+ctsof thosedifferences o.2 the RNK safety
analysis, but ean. a”nlysis-oft,,e olde+:-d esin is not included in this report.
Since many of the- design feitures’unique to the second generation do not appear
to Lave been backfitted into .the,-first generation, the reader is:cautioned
against assuming that•safety capabilities discussed here apply to the eight.
older RBmK-1000 reactors.
Chapter 4 was prepared .by :the r.S..Nuclear Regulatory Commission (NRC). It
presents the. events leading to the accident at Chernobyl Unit 4 on April 26,
1956. The events are detailel-in narrative form and are summarized in
Table 4.1. The.accident-.chronology.includes relevant information on several
aspects of tae plant design characteristics and operation and includes the
operator and procedural errorsethat contributed to the accident. These factors
were important in the.sequence of-events that. ultimately resulted in an uncontroll(
d power excursion that destroyed the reactor and breached the integrity
of the reactor buildine. -he-fociuns -t he chapter is on the response of the
syslte to the ai’rJus mats. zts Upotln used in reconstructing the sequence
of events was 9 Of mry reports cn the Chernobyl accident
prepsreA by the WI 3`ttitta OR the U1tilization of Atomic Energy (USSR,
1986) and the Intermatio”mLl,_1earSafety Advisory Group (INSAG, 1986).
Chapter 5, prepared by .t.be_.titute for Nuclear Power Operations (INPO), explores
the role of operatitS.personnel at Chernobyl Unit 4. During the performance
of a turbineVgnerator test eo April 26, 1986, Chernobyl ‘iit 4
experienced a core-damagin&gaccident._- A severe excursion was accompanied by a
pressure surge and fire that..destroyed the reactor and breached the surrounding
building. The test procedures had not bean adequately reviewed from a safety
stanepoint. Nanagenrat control of the performance of the test was not maintained;
thebtest.procedure was not followed;-safety systems were bypassed; and
control rods were misoperated. Operators lost control of the reactor during
the performance of the test. Chapter 5 focuses on the operator actions during
the event and on the breakdowns to management/administrst.ve controls.
I:
[
.4
~-C-,
Chapter 6 wps prepared by the U.S. Nuclear Regulatory Commission (NC). It has
as Its firet topic the magnitudes and timing characteristics of release of radlonuclides
iron the Chernobyl Unit 4 plant. Its second topic is the atmospheric
1-2
. dispersion and transport, of th r-released radionucl ides-.reult.inginenviron
mental contaminatin within nd- Outside- of the Soviet geographic bundary,
-Radionuclide release -ana.aitmospheric -dispersion adtriansport fro”m’• C•eribl as
described in Chapter tare derived from the i&formation contained primarily :in:
the two reports cited.(INSAG -1986; SSR, 1986). –T-he last section:of Charter 6_
offers a short discussion on ctousistency of the estimates of the radionuclide
release providedin- the Soviet-, xr t-,with.the observeddats from-:-
side the Soviet boundary. osvd. forin o.t_
Chapter 7, prepared by the Federal Emergency Management Agency (FEHA), documents
the av.ilable offuite- and 0nsite emergency plans and preparednessmeasures
that were in place for the Chercobyl-nuclear facility. also0 Ite scribes
the Soviet response to the accident, and relates it, where feasible, to the
-preaccdent-emergency planning and preparedness activities. Where: known,
.eme~rgency .response .orga’iizations re identified and their.. .r oles,a re’ described.
._The a~lert and. notif icatilon _4yste sd by theSvesi aaned The po
ýýtective actions-take byl thAve r ls ecied, incuing’evacUation,-
sheltering, use of radioprotective drugs., and medical arrangements.. -PYinally,
Soviet information -pertinent •todecontmntion, relocation, .and re-entry is
documented.
Chapter 8 was prepared: bytheEnvir’omntal Protection Agency `(EPA). It.examines
the radiological, health and environmental consequence” associated with the
Chernobyl accident. “adiation doses and their reported or calculated health .7.1 effects are discussed for populations at the site, within 30 km (18.6 mi) of
the site, in the balance of the European Soviet Union, in other European countries,
ano in the United States. Because of limitations in the exposure data, however, most of these estimates must be regirded as tentative.
Data for the Soviet Union were -drawn chiefly from the Soviet report to the IA-.
(USSR, 1986). Estimates for other. European countries were based largely on
information reported by the World -Health Organization (WHO, 1986a and 1986b)
and individual European governmental agencies. For the United States, measuremerts
made by or reported to EPA were ..employed.
References
INSAG, 1986 International Nuclear Safety Advisory Group, “Summary Report on
:the Post-Accident •Review. Meeting on the Cherrobyl Accident,”
August 30-September 5,. 1956, GLC(SPL.I)/3, IAEA, Vienna,
September 24, 1986.
USSR, 1986 USSR State-Committee on the Utilization of Atomic Energy, “The
Accident at tte Chernobyl .Nuclear Power Plant and Its Consequences,”
Information compiled for the lAEA Experts’ Meeting,
August 25-29, 1286, Vienna;’ 1986.
WHO, 1986a World Health Organizetionj Regional Office for Europe, “Summary
Review of Measurement Results Relevant for Dose Assessment,”
Update Revision No. 7, Copenhagen, June 12, 1986.
1-3
WHO, 1986b World .H~ealth.O rganizatin 1eOifofi cE frErpe Smr
Report of Workin.g Groupo !”6iAssessment of Radiati6n- Dose Cmi’t-.
mentei E7u rope D9,.; ote ahern, byA ccident, Bilth.”ven,
June:!ý 25-2, 1986, Copenhagen, Septemiber. 8, 1986.
1 5
SCHIAP:E’ 2R
-‘?LPANT DESIGN
The Soviet high-power, -esuei-eitbo r (Soviet designation: • )BIiKs ) a
graphite-moderated, ýboiling-water-cooled ..reactor. -,This unique design, which
has been constructed only:in’ the ,tSoviet Union, evolved from early demonstration
and plutonium production reactors General characteristics of the RBIK and its
predecessors include the use of’ granphite as a ne•-. rir uioderator and light water
as the coolant. Pressure tubes, contained in vertical channels in the graphite,
either contain low-.enriched uranium oxide fuel or are used-as locations for
control rods ani iastkrentation.
•The.: use.! of boili$ngwater• •as a coolant i•n iapressurerttube- giraphit&m.derated
*”reactor distinguishes i~the design from any other reactor design. Other distinguishing
featiures-.ofthef ý R deajwg include
* on-line refuel.ing.
* single uranium enrich tlevel
• separation Of corecoling into in endent halves
* use of computeri-ed control ..systems
separate flow control-for each pressure tube
positive void reactivity coefficients under most operating conditions
* slow scram system
* steam suppression. system
* programied power setbacks,(rather thaný,acrams) for various abnormal
conditions
low coolant-to-fuel ratio
accident lccalizatioa .syste”s
These features are described An detail-1ater in this chapter.
The Soviet ,nuclear;;og m arch ‘sa,dd eelc ment .onse0eral
types of reactors 1Wd thecostruction4ad• operaition of
various prototypes.i tihde- ;l96Oa, -t-he Soviets decided to develop two types
uf power reactors: thbe VVXl.:(pressurized-water reactors) and the IBlKa
(boilins-water reactors).
The evolution of the general design parameters related to Soviet graphitemoderated,
water-cooled -reactors s-ýpresented in Table 2.1 (SMenov, 1983;
Rlimov, 1975). The units at thetiberim Atomic Power Station were built as
dual-purpose reactors .:(J•iv, 1975).to produce both plutonium and electricity.
The Beloyarsk reactors are demonstration plants and are unique because they
superheat the steam in the reactor-. core.__,
S. Rosen, 1. Purvis, D. McPherson, and F. Tooper of the U.S. Department of
Energy (DOE) and DOE contractors, notably Pacific Northwest Laborstorief
(J. ;Neecre and L. Dodd) cqpiled this chapter.
2-1
Table 2. 1 Development of Soviet graphite-moderated, wuter-cowoled reactors
Item
Year of operation
•lectrical capacity (mle)
Thermal capacity (“WtO
Nmber of fuel channels
(equilibrium loading)
Ymber of stem superheat
chaunels
, S(ateta.m) prelsure at tumbise
Stem teortUre (0C)
Total uranium loading
(tonne)
Average’ enrichment (%)
Burnup (“WARg)
Specific power (kl/kg)
Fuel cladding material
Obainsk
1954
5
3.0
Ii.
54.6
Stainle~ss
s’t•.e
SAPS*
1958
>100
Peloyarsk-l
1964
100
286
0
998
268
87
500
Beloyarsk-2
1967
200
‘530
998
.266
87
560
48
3.0
14’.6
16.7 •
Stainlesse
steel
Chernobyl-4
1983
1000
3140
1661
0.i”..
BMKs
Ignalina-1
1984
1500
0
4.3
Aluminum
67
1.8
4.0
11.3
Stainless
steel
65
280
189
2.0
22.3
25.4
Zirconium
1% niobium
65,
280″
19
2.0.
21.6
Zirconium
1% niobium
*Siberian Atomic Power
generators.
Station – SZx identical units using double coolait circuits with steam
I
TAhtec jifci rsPto wReBr HKSt awtaiso na lO•” O.O–tHWhCeh erplnaenbty.lb rUoungijt ht4 roena. clitoner – iiin .c1 o97n3s idaetr,e tdh e,a Lseeci•ognrd-ad
generation plant because, etdhees ign includes a number of safety features- not
present in Leningra•dU nit. –
At the time of the accident,:-•1 RBMK- 000- ractors were In operation adi.d. ition
to a 1500-NWe REII. plantoperatingat. Ignalins (Table 2.1). The M ” 1500
design differs little tra•uM t-e1 000-design. The, cores are, :essentially
identical. ‘,ýP]ahs:e:esLx ias -t: to !butilXd eeven larger plants vith electrical capacities
as large as 2400 lIe.
The Soviets had seve reasons -for pursuing the RBWK design. Theýe reasons
included .(Semenov ‘1983)
an extensive engineering experience base with graphite-moderated, boiling- X
water-.cooled-reactors .
* ,existing, madufatua g lants’ coud’.fabricate -major.ccI o nets
the reactor sizeoii liktedibi c•o nsiderations related to fabrication,
transportati, or.insa•tion, of. co• nents
a serious loss-of-coolant accident larger than that considered as design
basis thought tobe .virtully.ibpossible because of the use of numerous
pressure tubes .rather than a single pressure vessel
• very efficient fuel use
• use of online refueling could achieve a very high plant capacity factor
The Soviets considered-the MW to ýbe their “national” reactor and showed con.
siderable pride in thedevelopment of the design. A number of design issues
were identified by the Soviets and. addressed in newer designs. Economies of
scale, control, and safety vre ,three such issues:
• Economies of cae..• ,he .economica were -recognized to improve substantially
by going to -ger desips. Asae t, one 1500-1BWe RBM iswcurrently
operating aa-.ye-mg 4W in construction.-“”,Plans -exist for ”
plants as large as -2400 MIe.
Control: The 83IS-1000 -was recognized to have stability problems and was
difficult to-control, particularly at low power levels. The approach to
resolving these problems was to place increased rel.iance on automatic control
systeas and adopt a-slightly higher fuel enrichment and slightly
lower graphite moderator density in order to decrease the positive void
coefficient..
Safety: The Soviets. re-evaluated the safety systems of their reactors.
– As a result, later -3J -desigpns, incliding Chernobyl Unit 4, incorporated
improvements in emergency core cooling systems and steam suppression pools.
A summary of the key design p4rameters of the Chernobyl Unit 4 reactor is liven
in Ta,’1r 7.2 (USSR, 1986).
2-3
Table. 22 hernobyl — 7t design parameters
I tern -D ecript Ion
General Design Characteristics
Reactor type ‘ Vertical pressure tube, boiling water,
moderated
Refueling .. On-line
Design power generation. .W 3200
Total reactor coolant flowrate 37,600 tonnes/hr (23,026 lbm/sec)
Core Description
Core- dimensions (active .”zone).
Height 1 0 A (23. 0 ft)
Diameter .- 11.8. “(38.7 ft)
Volume 7ý5•0O: 4 (20,655 ft3)
Total number of fuel channels 1661
Lattice spacing 25 cm z 25 cm (9.8 in. x 9.8 in.)
Moderator material Graphite
Maximum allowable measured -7500C (1382°V)
temperature
Material density 2./6cii•-s (103 lb/ft3)
Reflector.ý dOmentonai -.
Top and bottom .84 a (1 -,64f t)
Sides 0-OA.8 8 (2.89 ft)
Graphite core weight 1700 tonnes (3.74 x 106 lb)
“-6s
J-a
Q4
g-A
Fuel Description
Design
Uranium aterial
Cladding material
Enrichment
-Two 18-rod elements connected in series
U 2
Zr-li Wb
2.0 vt% V-235
2-4
Table 2.21 (Continued)
DeesItcermip tion
Fuel Description (Conti.ý.d-)
Fuel A8 ssembly” eSieolnt ent -‘,6.9 * (22.61 ft0
Maximum cladding temperature 3230C (613 0 F).
Maximum fuel. temperature -2100*C (3812*F)
Total uranium weight 140 tonnes -(418,500 lb.)
-`-Maximm fuel exposure 2. iDk
Wate , R ecirculartion System,
System material Abstenitic stainless steel
Independent flow loops 2
Steam drums -. , total, 2.per loop
Pumps 8 total, 6 normally operating
Pump dynamic head 1.96 HPa (284 psi)
Net positive suction head – .6 lia (87 psi)
Main pump suction anddischarse -90 co (35.4 in.)
header diameters
Main pump capacity 5500 to 12,000.1 3 /hr
(24,200to 52,100 Via)
Dirensions of indivi&dsua-l pres sure 5.7 z 0.35 cm (2.2 x 0.14 in.)
tube inlet piping (010:z vall)
Dimensions of individual pressure 7.6 x 0.4 cm (3.0 x 0.16 in.)
tube outlet piping (OD z wall)
Fuel Channel
Number . 1661
Pressure tube diameter (0D) 1.8 ecm (3.46 in.)
Pressure tube wall thickness 0.4 cm (0.158 in.)
Materidl Zr-2.5% Kb
Connection Diffusion welded Zr to stainless steel
joint in core sone
T,4’~
* .- AR
M,
* ~ 4 ‘g
2-5
-1T-ah annel2le. (Continued
• I em-,.,.,• ,.,:.,•.-,_.•;:• ….. ,• …. D]escription.. .
Fuel Channels (Continued)
Individual channeljflov – Manually-#adnjtursotel d regulatng”valve,
Inlet temperature -270°C?(518°F)
Ou-;ýet temperature (avg. 28140C f(5430F3
Operating pressure .- 6.8 HPa (986 psig)
-Quality , – . 4. ,(average steam), 20. mxmm
Average tube power– 1890 kWt
Axial peak/avg.. powerratio1 40
Radial peak/avg. power -ratio .48
Steam Secondary System,
Steam collector yPdsmyssr tem steam drum separators
Number of collectors 4 total, 2 per loop
Collector (ID x lengt.),. .. 2.6 30.984 m (8.5 x 101.7 ft)
Steam flow rate (total) _5800 MT/hr (3552 lbe/sec)
Power generation 1000 Ee (two 500-EWe turbine
g eritors)
Beat rejection. ,wit o atsrý eservotr :(condenser)
generators
. .
Feedwater inlet temperatmre toi_-steas ‘•1-656C A3290F)
separators •”
Control Shutdown and .$fety q hutdown
syste’
-Type
3
4
eets *Acssed is alumintm,
Number of control shutdown assesblite
Neutron absorption materiel
Control rid spacing
ýIoweroid• and retrieved from ab~ove Dy a
belt .6able and motorized drum
211
34 C
500 m x 500 m (19.7 in. x 19.7 in.)
2-6
STable 2.2, (Continued)
Item Description
0ontrol Shutdown` an4Sfety- Shutdown
S- s em (Continued) .,-
Control rod tiravel, 6.425maf (20.5
rod-4.5m
ro-0Om
4..
-~
‘~-
55 4.-
* 452 -~ S -s>-‘ 55.S~
4
(14.8 ft) and axial control
(23f)
L0011U• 0etnoa 5_ernarate.e
do~wnvarf
Contrrod u~ltrertimm time 20seicond,
9O2t reactivity. Insertion timle , 0secod
Owe Epre ssure Control. &ate
Type Partial 4sti
ster-cooling syistem with
low ‘in iAndividual chnnlso
a Ahr (15Yt ~ tlr
Z
san suppfression of releases
Enclosure
Function
Design press
Operationandthe
reactrs cavity, ilet.pipin
-Reactor core inlet and piping system
-C-ten steamtr from piping break or
steam separator relief valves
ure rUclosure areasdesigned for either
0.-4S MPa (65 psig) or 0.18 HPa
(26ipsig) beko. ta
…….. •:..•. …•,•.,••; • ter- from pip• resko~tn••….. ….
740 epastor relief ‘-vale irectdo
– – ,t&6dinwg ater in bubbler pond below
” .a•Csctor. Water spray above bubbler
Pond helps condensation process.
2.1 Reactor, fuel., a uua chine
2.1.1 Iighlights
Chernobyl Unit 4 is-!& 1000-,e, vertical pressure tube, boilini-water reactor
that uses online refueling. Tbe core and reflector are in a cylindrical
graphite stack witb a diameter of 13.56 m and a height of 8 a. The reactor is,
penetrated by about 2000 channels that provide locations for fuel, control rods,
and instrumentation. The fuel is 2% enriched uranium oxide clad with zirconium
containing 17 niobium (Zr-lI b). Fuel elements are constructed in 18-element
clusters connected to a ceatral support tube. There are two subassembly
clusters approximately 3.5 w (11.5 it) long in each fueled pressure tube. The
2-7
fueling machine is. a massive piece of e u “ipmentt hat operates over the reactor
operating• ‘floor and’ is’Ides-igned tfolad ful while the reactor is at full poer.- –
2.1-.2 Reactor (Dollethal 1980b usS 1986)
Chernobyl Unit 4 is ‘aI’1000-We, vverticl•. pressure-tube, boiling-water reactor
that uses online reiueling. -The plant contains two independent primary.,, recir- culation coolnt loops-tr•t{ . ere separae h&lves of the reactoar. Figure 2.1
shows a schematic cross-section of the Leningrad first-generation RBIMK-1000,
which is representative: f -Chernobyl Unit 4. Each loop has four primary
recirculation pumps (with three -functioning under normal operating conditions)
and two steam separators..
The primary coolant from these pumps discharges to a common header to.-which:. 22 group distributi1on`,ihe aders are'” c”onnected., Supply lines for individuAl.ýprei6sure -tubes originate at onaeneheduply line. containmsaanu•a llyoperat
flow-regulatings” valve andilov melter. The ‘coo-lant is..dirce upte16 ue!’
channhels pa st -the “fuelasmle (see FIigure’ 2.2). T he JinlIe’t water reaches the saturation temperatureit-a-bout one-third-of the-length of the fuel.element. Nucleate boiling occurs– ove zrte idif -the fuel length.
The pressure tubes in the ýcore sare made of z=irconium containing 2.5% niobium.
The Zr-2.5% Nb is diffusion -weldedto.stainless steel piping by heating it -to
600°C under a vacum ý(see Figure 2.3) .-The joints are constructed- separately
and joined to the tube- 8ass8 ly before installation. The top and bottom transition
joints are located immediately above and below the graphite reflector.
A permissible rate of heating and cooling of 10 to 15°C per hour has been
established on the basis of thermal and strength tests.
.Chernobyl Unit 4 has 211 cont.rol dishutdown rods. The rods are functionslly ” divided into manual control rads,”automatic control rods, emergency power reduc- tion or scram rods sho~ bsorbi g rods, and compensating rods.
The 1700-tonne graphite moderator-is stacked in the shape of a vertical cylinder 11.8 m (38.7 ft). in diameter and 77″ (23 ft) high. -Each column is composed of 25 cm z 25 tm (9.inz9. laa.) apbitebloc Teuiblcks are60
(23.*6 in)high, -anid b,iki 4bU1edo sat. Latalled An the-SO-cu (19.7-in. top -and- bottom reflectors a toa rai 1foter skheightof800 i(26 -2 The outer side reflector a ft). ” 088 (.9 1t) .t1h. ick, making a total stack diameter of 13.6 m (44.5 ft). The :aide reflector graphite columns are pinneo with cooled steel tubes to enhance rigidity and provide reflector cooling. The -moderator and reflector -columns are-capped• n both top and bottom with a thermal shield. The top caps are steel-blocks 250 ‘ (9.84 in.) thick and the bottom caps are also steel but 200 ‘-m (7-87 4a.) thick.
A gas mixture, nominally 80% helium and 201 nitrogen, is fed into a chamber below the reactor where it is distributed across the bottom face of the reactor. The gas mixture flows between the graphite columns, providing a heat-conducting medium for transmitting the graphite heat to the coolant channels. The space between the tubes in the channels is fitted with graphite rings, which are fitted alternately to the tube and graphite chanoel opening (see Figure 2.4). During reactor startup operations a pure nitrogen cover it used. The graphite temperature can reach 7500C (13820F) under these conditions. The gas mixture is monitored for moisture to detect leaka&e from the tubes.
2-8
I
Figare, 2.1 Cross-Aectional iie’w of RIMAtA
~ 7~p11
I
* 4h
~’1
C4
ap
lN
I –
P:
V
2-10
I
Centerline
)662*Fl
)I f6OSIF)
,o(590*F)
284*C
1543*Fl
‘Pressute Tube
0 4 6Sm n0. )
cm (3 46 re
n13 68efin
V… … …… .
• i~• .•
Figure 2.4 Assembly of graphite
rings on pressure tube and
graphite block cooling
2.1.2.1 Reactor Core, Reactor Cavity and Vessel (Dollezhal, 1980a, b;
Dubrovsky, 1981; Dollezbal, 1q77; .USSR-, 1986)
A-cross-section of the reactor ccre,
The reactor ic located in a cavity 2K
(7! ft x 71 ft x 84 ft). The reactoc
cylindrical vessel forr.ed by a 14.:-,:.
steel shell. This shell is bou”dcl
biological shields. The shell, Lop’,
shields, forms the closed reactor si,
:vy.-nd vessel is shown in Figure 2.5.
x 21.6 m long x 25.5 a deep
ILe core is located in a sealed
(47.6-ft) x 9.75-m high (32-ft)
and bottom by upper and lower
the top and bottom biological
The 16-mr (0.63-in.) thick reactor v(. servee sairly as a gas barrier and
structural restraint for the graphite. reactor vessel contains the circulating
helium-nitrogeu atmosphere for L’. graphite moderator at a pressure of
about 0.0015 KPa (0.22 ps•g). The spat outside the reactor vessel is filled
with nitrogen at a pressure of’0.0017 MI’a (0.25 psig), which is greater than
the oressure in tCe reactor vessel.
‘e
U
Wtided
Tube Ducts
UBP i.opleorgical .. … < :, ':. .. Rollersf Graphite Reactor Vessel Nitrogen Annular Wiwe Tank . -Lower J Shwid -Sourp port ~8l1 t) in dia """ ided to a Irical tube grate. The er1 to ical sbioedrive -. 79 7 Pre. su. Boun.ar,.!. Figue 2.5iCt~as~ct!fioi_*tl i.,<.f -reactor cavity 2.1.2.2 Upper and Lover.Shield vand eactor Suppott (Dubrovsky, HS Dollezhal, 1977; Dollehal, l:980b• USSR, 1986) The upper biological shield is a.cylindrical shell about 17 a (56 1 meter and 3 a (10 it) thick. -It consists of two circular plates ie cylindrical outer shell. :Additional strength Is provided by vertic ing ribF. 0peninsP for Lhe pressure tubes consist of welded cylind ducts. The space between the ducts is filled with serpentine sggre entire assembly, whichiweijhi '1000 tonii(2.24O05 lb), retts onto accommodate thermal expansion. Xs addition to providing for bioloi ins, it also supports the weight of the fuel channels, control rod channels, the upper reactor outlet piping, and, tioe removable fl.vr covering. The lower biolotiral shield is 14.5 m (48 it) to dism'ter sod 2 m (6.5 ft) thirk. It is similar tn construction to the upprr binollfcal thield. This 2-12 shield- transmits' theis.d'; the, graphite Anil" lower pipin$- toý the main reacto'r su~pport immediately,, under it. The main reactor support 4s made ot two steel platsi stiffening ri o.3 " Theflorse~s S •0•h•s,81dto6g~b ''l~d plate wi sthe f enriegr. 's- 5.3 ' (17 ft) high placedperpendicular to each other (cruciform, shape). This sWupport transduits the, weight of the lover shield and threi eol r to thelding foundation. 2.1.2 3 Uipper Flo Sa (urovaky,18;Dleza,18 USR 1986) The floor of the reactor haila-cotrteofremovable eCti'ons tfr. e allow, access to the fuelnchanes;t io-!r6--m-iit .iieoiedansd, controdsl r drives. The floor set..ves as she aAnbdo i(o logiinl.aJ barrierk. 1The re.- movable sections are made of steel, structnres filled with iron-bariumt-serpfentine concrete and rest onpthe -et% s -nel du biologicaldsh ield. r' is extracted from th 6ý reacto§ th5q~n hgp ntefoo opoiefrc ing inle theh firoe r,. t. prvd 'end to preventsthTpossbnterintiv ste building;iym nein h eco 2.1.2.4 Sidet io icat d--198; SolleS9h al, 90,b USSR 1986) 'double-walled vess(eDl , 66 m( )nside d4iaimeter (l ) -zh 19.0, (62ik t outside diameter (OD) su obste reactor' edvessel inside the reactor'cavity. The vessel consists of-16 wa ter-fied compartments and prov des shielding in the lateral direction. I-c e V,e ssel Wlls ,are 30m (02 in.) theTichek . space between the water-filled-shield and the walls of the reactor cavitytis fill8d with sand. The space between the water-filled shield and the reactor vessel is filled with nitrogen. 2.1.2.5 Reactor Cavt li-s (brovaky, 191 USSR 198) The reactor cavity walls are msde offte force concrete 2 a (6.5 ft) thick. 2.1.3 Reactor Nall .(Dubrovid 11 'hielifa- 1981; Dollezhal,.. .198c,: eý.; Usike 1984; USSR-,,18)>K~;i
‘A cross-section of b .ild 8pet fuel d4toL sh esh oonl ns Figure 2.6. A
plan view of-Units 3 and 4 asonA iue2.7.
26 hall (the the reAlddtrnega ctor -caoveear, bofo vth e reactor) is a
lUrge open workspace containing the refueling machine and an upper, higbh-ay
area with a 50-tonne-capacity overead travelint crane. The refuelin& machine.
which weighs about 350 -tounmesq,1,_m Fo1na e on a traveling bridge. The inside
dimensions of the reactor -ball ýare about 24 a -wtde x 80 a lons a 35 a high
(79 ft x 262 ft- z 125 ft). -Th1e lever bay As- constricted of reinforced concrete
&and has, walls about 1.3 a (5 ft) thick. T1he massive walls and columns support
the fueling machine and provide shielding- -for the ate&* separators- located
adjacent to the reactor hall. A–s pent fuel storage pool, 1,9 located in each
reactor ball. The bigh-bay portion of the reactor hall is of steel frame
construction using precaat concrete panel sheathing for the walls. Tbe reactor
hall roof, atop the high bay, is supported by steel trusses about 6 m (20 ft)
deep. The mass of a preassembled roof block is 50 tonnes. The reactor has
four roof block&, and each block is 20 a x 24 • x 6 a (66 ft x 79 ft x 20 ft).
2-13
as
tg-vmfFmuw 2. 12’20t ins auln aw. 3 l metaw wUm-S3mWsuu-wst6n.WICn4m wO-Adma o~ 1 ~ ‘west. S. 0.u~ 5 60 104 -mi-edti-m-lfige tane: 10 -Main citculatng-YMn II Elgetrc temok in cwlculoftlpump.; 12, OniinSepaf sta. 3W. *at e.sp omulswd 8si9wedts=s:qwija 14 m-hnim IS5 tfen SMK1tO00OMec-s, 6S-. AcII cottdmi~nmet avsO9. 17- Sut1s pnD.A 0%”e ýs* Mgw eir Coeilali i6 1ws w 2 om;2beard w.h~o oalns 2Eaas ~mato latlcaens 3 Pau
Figure 2.6: Ckroe-sectional view of
,,Chernobyl Units 3’and 4.
ieaftorý buildingelevation,
” .4
2~
– ~ I ~4WA Ii ,
51 1 .~1wA
hit taxWis
Figure 2.7 Layout fi nbil OfCherobyl Units 3 and 4
.So•~c •~Dubrovsky, 11981, p. 95.
21.4 -Reactor- Building and Turbine Generator aill (Dubrovsky, 1981; Konviz,
1981; USSR, 1986)
rk~e• overal-l-dimensi~ons”-of be-ctoruild~~tins, not including the turbine
generator hall and conneLting mounting fframe, are about 72 m wvde x 160 m long
x 50 a high (236 ft x 525 -ft., ••164 ft) (see. Figure 2.6). The distance fromground
elevation to the top oftei ghb ay-is 71 a (233 ft). The reactors are
Separated by a wall and shared ventilation .systems. A ventilation stack is
mounted between the- two units drectly above the ý-enera1 –ventilation equipment.
Mke control rooms of’ýC& 1ro~ 3nt r [email protected] 41d e
Large room.
rhe ‘reactor building is enelly -constracted. of veintorced co:•crete, most of
ihich is precast, but thick walls o10aer: 70 cm (2.3 ft)] are bi t by the
3recast cast in situ” -metbod usiagprefabricated reinforred forr. panels.
Aore than 200,000 m2 (2 million ft’) of building surface on each power unit
As a special protective coveritg stated• to be polyethylene, presumably for
!ase of surface decontamination. *
turbine generator hall, about Wec wide x 400 a long x 30 a high (167 ft x
312 ft x 98 ft), adjoins the reactor building. The saace between the turbine
Square brackets denote information believed to be ty.je but not found in Soviet
2-15
generator hall and’the reactor buatiding is oiccupied . an intermedie bul ing.
Theuperflor floor. are ae ccpied-b y d&-arator and f pipe aisleý, and- ihe lower occupie by a ‘,entral control. board, unit control ba-ds h .. switchgear, stor age an f.sth elveel.e,c t ricale +u.ii.smeent –
21.5 Fuel Assemblyo esign (Dollezhal’, UWS9R81 ; 96
The fuel assembly onits of, two circular.lb-rod clusters, connected by at cen- +. l r r o d . • E a ch ,4 “: -i-ý+” ” • • , .. .. .dt •f+- . + – :••. . . – . . . . – . . . . . .: .. ..+. l r fEt ) c n adConsists ring of 6 rods and of an inner. an-outer rino~f12 rods,held by: stainless steel spacer grids and 2 end plates. Th ulrd r opsed ofcldigtbs(rl ) containing sintered aium ozd pellets. ‘The central rod is made of Zr-2.5•, . Nb. A schematic dawn oth asebysshowninFgr2..Dtlso the design are given in Tablea, 2.3……..
21.6 Fueling
.achine
(Dollethal, c, Sb, 1986)
The refueling aystem-includes.. a-W @’tlune cran t at spans .the re ctor area; a
carriage tht opeaes along the crane;-ils; and the refueling mchine, which Is held by the carriaie-.-V is by~ th~ ca~ri ag ~ h(Felg 1 r i-•.•••….::..- :-. _i c (770,0_0 . Tbe ) h hole assembly weighs about 35ý0 tonne fuel channels and positioned over any of the 1661 over,: th . t g aa. T .n .machineisdsned to refuel five fuel channels: dui .a .24-oi o l at l … re…f. ulin is,ý&….a… o-ed’ atprmgi~- The refueli d-l -. .. system is designed-toefuel -lte ast period while 10 channels every 24-hour the reactor iabtdown. Aefueling at full powrprisrpae gseenner atioonff dd e.feetf ive fufuele limnelg, m t se amnado-n dnral rruehf•uwetoliuntrg Pnermits relae ..n n Ti. without interrupting power m n .caUbe used to move -irradiated fuel assem- blies from storage to the rasctor or from ome reactor position to another.
Wh ile centered over a fuel channelth’ e refueling tha Cotan a qelýkc ……. 6q&mma•aucch hiinnee . ll owers aa ccyylilndienr der
tha caostaeias , wichfit vr-the. outside of the fuel channel nozzle.
TThh e ccyyliinndeerr , whic :L*,+.osrt ‘ +i whc ht i par. of te preessuVe vessel, can on-board ve- is filled with water from — ank-. h st- – is , .Pressuriraet dw, hich cap isaready for remval. A grbab time the nozzle hook,o loated inside the pressurized cylinder
grab hook are rmntely-ci•eed ao4 +h-em la,-+ – nova ug Ozten actuating of thesios : device, ” lotIM-Ahe outside of the lug is t h e n r o t at e d . T hik” + . . .+ – P , I ” then otatdT.i s rtatin ineals the nMOzzl -plug gasket and b l g. e tt he:m e :p. lu in place. The releases the pressurized refuelng pressure in the Internal, low;.. prf~ hi •.e.h ns cytol ader i9 hh ilbee r tthan the pressure tn the iN, the shieldt hpuls; , – ‘ t ozzle Plus frCi being ejected. The nozzle
pl~a,s hteeld plu~ th suPeaO”10 r~od and the fuel assembly are lifted into the Pressurized cylinder of.,the refuelig machine and reandwtia cartridge bolder. The cartrid.geis rotated tpemtisronfa gauge (used to check the f”el ch”-i . er. The fresh fuel assembly, with attached nozzle and shield plug, 12 tm lowered Into the fuel channel.
)uring-.this entire refueling operation wster is pumped at a crntr-lied rate rro. the pre1surizd cylinder inO the flchannel to cool the discharged fuel tlenrnts. After the fresh fuel is in place., the nozzle plus locking device is ‘Sal engaged, sealing the plus gasket. The refueling machine seals are then Irpressurixed and the cylinder is retracted. A biological shield plug is moved
2-16
‘4
-J-6
ote- that the fuel le*Sth i,e ci.+Ib asembIy- .- 3.43a (11.2 wth aa- t2),0 -rm
(0.79-in.) Sap between the subassemblies. T•be upper and lover assemblies have
their rod plenums at the upper and lower ends, respectively.
Figure 2.8 Schematic dravi*g of tbe 36-rod fuel element (18 rods ica ech
of two subassemblles)
Source: Dollezhal, 1981.
.2-17
Table 2.’3: Fuel ii’se.b•y• design pa.am ekt iit” fo,r. Ch enin Init 4 – ,.”•
Parameter . Value
Subassembl ies per assembly 2
Number of ro-ds-:pe–r 46 asikblo~~.~-
Assembly out.er diiamete’r 9 mm (3.1 in.)
Length of assebly fe reion 6.9 a*t ) (23.0
Length of active, fue per rod 3’ 43 . (11.25 ft)
Plenum length 17 5 cm (6.9 in.)
Cladding tube outer diimeter 13.6 – (0.5 in.)
Cladding radial vall.thickness 0.9 -m (0.035 in.)
Cladding material
Fuel material ‘0
Fuel enrichment – 2 0 wt 7. U-r—3253-‘
.Fuel pellet.diamete’11.5 – (0.45 in.)-
Fuel pellet length -`.15. 0 (0.59 in.)
Minimum pelle 46e8sit -&104/,cc (0f.37.6 lb/in.)
Pellet end Ds-hed
Fuel cladding gap –0. 18 to 0.38 m-
(0. 007 to 0.015 in.)
Fill gas compositi’on”. Be
Fill gas pressure 0.1 P&P (14.7 psi)
Water-to-fuel volume .ratito 1.23
-V.– ~
9-V<* ,$ IA,' .9 9A9~ * 7. into, position belov the .refuting -machine, and the discharged fuel, element. is transported to the spent fue•l -.storage pool. -2 fluid and deat lTrawort. Sysltes '.2.1 Highlights - - Three principal f udn'saw .- aerytm are usedinteCroylUt4 reactor: (1) Vthep i 7 i g ytem, ehhcoolsthe core- and-produce .. -power; (2) the. rod cooling system, wwohnictlh provides cooling to the control rods and the reflectors; ,a (3) the .reactor gas circuit, which enhances heat transfer from the :graphite.moderator. -Ito the preasnre tubes. 2.2.2 Primary Cooling. System (Sedov, 1979; Novosel'skii, 1984; Dubrovsky, 1981; Dollezhal, 1951;-loromn, 1980; Kulikov, 1984; tVSR, 1986) 'The Chernobyl Unit & reactor contains two-1ndependent primary coolant loops, each of which cools half of the reactor. .-A schematic drawing of the cpoling system. is shown in Figure. 2.11.. Ech loop._ .as four _primary coolantpump s, three of which are normally i tn-t the fourth acts as a backup. Each pump has a capacity of 5500 Lo 12,000 us/hr (about 24,200 to 52,800 gm) and a dynamic head of 1.96 MPs (284 psL). -The discharge line from each pump also has a check valve, to prevent backflow should the pump fail, and a flow-regulating valve. The pup.ps are fitted with heavy flywheels to provide a 120-second rundown time in cant of a loss of electrical power to the pump, and to provide interim cooling until nA'tural circulation can be established IFtural circulation is expectrd to be established 30 to 35 seconds after &in pumps are deenersized. 77 LZGEND: 2-Cartridge; -2fSupport *Itoipm t; 3ý-Upper Pressure ,4-Grab Vessel Seonion; Drive; 5-Grab Actuating Chains; 6-Framevork; ?-Chain Winding Necbanimo; S-Cartridge Rotation Drive; 9-1,dd. e-rssure Vessel Section; 10-Shutoff Device;. li-Planual ?ube Location Device; :12-2elevision Tube Location Device; 13-lovable Lower Shielding; 14-Lower Pressure Vessel Section; 35-Special Book; 16-Se.lng• Drive;. 17-Shieldi..; 18-Cram-; 19-Carria.e. Figure 2.9 Crouu-soctional view of the furlifig "Cahinie 2-19 .... .. .. , ,R e.. '•it•t:•Zt. . •" d, .' .. , RM 2ach of these Fall~~ permit natural- _cirutio hugte stalled pumps. -Plilions GooaR,a C* .,.•........................•..•.•......,.•., .... .. ,.!:. ~Jews ,ueling machine. toth eW.. ý,Twom46mWl y ope ft and tbe outlet of the pump after shutdown 5f the four in- :4 zeato 3T2he.5 -ccouo lant from the 'P s flows toA cmon.'header and then co twenty-two (12.8-in.) diaemeter datrai' or hders on each half of the reactor. The individual supply pipes of 5.7-m (2.in.) diameter, and 0.35-cm (0.14-in.) wall thickness to- the presWre tubes are connected to these dis- tributor headers. Lack supply pipe contains a manually operated flow- regulating valve and £fi1• meter. .. Pressure tube coolant flow, and quality, thereby steam is set by adjusting these flow-control valves on the basis of calcu- lated channel power, calculated power distribution, and measured inlet temper- ature. The coolant is directed frm the supply pipes up through the fuel channels. The full core coolant flow at 200% power is 37,600 tonnes per hour. The inlet water, initially at 2700C (51307), is Leated to the average saturstion temperature, 2864C (S43el). 2-20 trator '~2. ", W* CbW'44. Figure 2.-11. Normal and emergency cooling systems of the Cthernobyl -Unit 4..reactor At approximately 2.3-a(755 i.tc).ito-the active core, bulk nucleate boiling' -ýoccurs, and this. pces..continuaes alongthe remainder of the ch*nnel. The average exit steam qnulityot the core is 14.5%, and the maximum exit steam quality Is 20.1%. ~~ '.Tchaer rsieteda mby- va:ptiapre-s 9*W~Aftuz~sfee rsue ue r ~dvdal .... , d ter and-0.4-cu (0.16-u.) wall thickess to four trontd.--,se arators, 2.6 m (8.53 ft) in internal diameter and 31.0 -mi. (10.1. f)A" A& ength. Two separators serve each loop. Steam exits from the tp-:.f ea.chseprator into two 426-rn (16.77-in.) diameter steam headers. BDeteean .theseparator.*outleta and the main turbine or steam dump inlets, these two h*eaders7jijon U .fom a single 630-m (24.8-in.) dimetar header, which passe . 1thf rm e tor building into the turbine gallery. There are four 630-m (24.8-ih.)••headers. T-:hese headers are cross-connected to headers that can f :eedeitrh steam duo or one or both of the 500-eWe turbine generator sets. . The pipe section locatsd :before the-turbine main steam valves contait- various steam discharge devices: eight mim safety valves with a throughput of 725 tonnes (1.5 million Ibm)-of stem per hour, four tutbine condenser fast-acting steam dumv stations with a cavacitv of 725 tonnes (1.5 million lb.) of steam per hour (two per turbine plant), and six service-load fast-acting steam dump stations. 2-21 Steam. at 6. 46 Mls(97pia,20C(3F) n 0i61.11 or ois relative humsidity Sfed: from. the; iin sea.,e'.-aer into the firs.t. ta ofhe four-,s tg•.. higk. pressure tubine. :bSom 1ighIe+ •] essm , :fi, bled•Io- ff Vstjream of te turbine inliet' v'alvet, as well: ~asm f r66m inar-stage #9"i t~hg-pisr turine,- and sent to the heating-side of the reheater/sueraters.,g the jJ et pumps for te ' main condenser air ejectors, a he m'ainn ndt u.rbiee- u.if. a, -tem. After exiting the high-pr~essure turbine, the stea*ass hog oeo h e . . g e s t • d h. o f t e•oe two separator/reheaters and.ia dried and sup`4.oer•h d to 0..4V0OW (58s!ia ).and 2630C (4730F) b+•i tes•i8i f... th f r:: 26(0 7 0F eore entern one ofteor 4-staige low-pressure- tunrbiui. Inter-stage steam is ed fro6 a*rtiaop u in the o turbines.t service condensate .reheaiid:•itersaduiiay the oads. :.:-•.d:.;.;...-.+ :'.rl+i ": " After leaving the low1-pressure turbine, the steam en.t ers one of the four sections of the main conde'nsr where it ondensesa. 04 Ea (5.8 psia),-From the: condensers, the watr s'umpdoac .t o -- _-manztamsear-os(;in-fu ýelectric bigh-pres'sure -feeps a dsi po isher(for pu ificto and water them"iistrIro,' _nd*• '-rwaitthoar attached explosive gas recombiner The feediater entest sfparntors, at 6.964 HPa, (1010 paia) a"nd.6• 56C .(-3290F).-.Iti's4 mixed- with 2oC (U. 3F) .. saturated water to-povdreciltion water 270oC (518).). Twelve downcomer- pip Area-itta-ched to"t-hebottom of :cac seam seprator. .. These .pipes connect .wit~h