Three Mile Island Safety Report

8/16/2019 Three Mile Island Safety Report

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Lanz Christian C. de la Cruz BSEE-3

Engineering Accident:

Three Mile Island Accident

Disaster Type:

Industrial Accident (Nuclear Meltdown)

Details: The Three Mile Island Unit 2 (TM-!" react#r$ near Middlet#%n$ &a.$ partially'elted d#%n #n March !$ )*+*. This %as the '#st seri#us accident in ,.S. c#''ercial

nuclear p#%er plant #perating hist#ry$ alth#ugh its s'all radi#actie releases had n#

detectale health e/ects #n plant %#r0ers #r the pulic. ts a1ter'ath r#ught a#ut

s%eeping changes in#ling e'ergency resp#nse planning$ react#r #perat#r training$

hu'an 1act#rs engineering$ radiati#n pr#tecti#n$ and 'any #ther areas #1 nuclear p#%er

plant #perati#ns. t als# caused the 2C t# tighten and heighten its regulat#ry #ersight.

All #1 these changes signi4cantly enhanced ,.S. react#r sa1ety. A c#'inati#n #1

e5uip'ent 'al1uncti#ns$ design-related pr#le's and %#r0er err#rs led t# TM-!6s partial

'eltd#%n and ery s'all #/-site releases #1 radi#actiity.

Summary of Events

The accident egan a#ut 7 a.'. #n 8ednesday$ March !$ )*+*$ %hen the plant

e9perienced a 1ailure in the sec#ndary$ n#n-nuclear secti#n #1 the plant (#ne #1 t%#

react#rs #n the site". Either a 'echanical #r electrical 1ailure preented the 'ain

1eed%ater pu'ps 1r#' sending %ater t# the stea' generat#rs that re'#e heat 1r#' the

react#r c#re. This caused the plant6s turine-generat#r and then the react#r itsel1 t#

aut#'atically shut d#%n. ''ediately$ the pressure in the pri'ary syste' (the nuclear

p#rti#n #1 the plant" egan t# increase. n #rder t# c#ntr#l that pressure$ the pil#t-

#perated relie1 ale (a ale l#cated at the t#p #1 the pressurizer" #pened. The ale

sh#uld hae cl#sed %hen the pressure 1ell t# pr#per leels$ ut it eca'e stuc0 #pen.nstru'ents in the c#ntr#l r##'$ h#%eer$ indicated t# the plant sta/ that the ale %as

cl#sed. As a result$ the plant sta/ %as una%are that c##ling %ater %as p#uring #ut #1 the

stuc0-#pen ale.

As c##lant #%ed 1r#' the pri'ary syste' thr#ugh the ale$ #ther instru'ents

aailale t# react#r #perat#rs pr#ided inade5uate in1#r'ati#n. There %as n# instru'ent

that sh#%ed h#% 'uch %ater c#ered the c#re. As a result$ plant sta/ assu'ed that as

l#ng as the pressurizer %ater leel %as high$ the c#re %as pr#perly c#ered %ith %ater.

As alar's rang and %arning lights ashed$ the #perat#rs did n#t realize that the plant

%as e9periencing a l#ss-#1-c##lant accident. They t##0 a series #1 acti#ns that 'ade

c#nditi#ns %#rse. The %ater escaping thr#ugh the stuc0 ale reduced pri'ary syste'

pressure s# 'uch that the react#r c##lant pu'ps had t# e turned #/ t# preent

danger#us irati#ns. T# preent the pressurizer 1r#' 4lling up c#'pletely$ the sta/

reduced h#% 'uch e'ergency c##ling %ater %as eing pu'ped in t# the pri'ary

syste'. These acti#ns stared the react#r c#re #1 c##lant$ causing it t# #erheat.

8ith#ut the pr#per %ater #%$ the nuclear 1uel #erheated t# the p#int at %hich the

zirc#niu' cladding (the l#ng 'etal tues that h#ld the nuclear 1uel pellets" ruptured and

the 1uel pellets egan t# 'elt. t %as later 1#und that a#ut hal1 #1 the c#re 'elted


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during the early stages #1 the accident. Alth#ugh TM-! su/ered a seere c#re 'eltd#%n$

the '#st danger#us 0ind #1 nuclear p#%er accident$ c#nse5uences #utside the plant

%ere 'ini'al. ,nli0e the Chern#yl and ;u0ushi'a accidents$ TM-!6s c#ntain'ent

uilding re'ained intact and held al'#st all #1 the accident6s radi#actie 'aterial.

;ederal and state auth#rities %ere initially c#ncerned a#ut the s'all releases #1

radi#actie gases that %ere 'easured #/-site y the late '#rning #1 March ! and een

'#re c#ncerned a#ut the p#tential threat that the react#r p#sed t# the surr#unding

p#pulati#n. They did n#t 0n#% that the c#re had 'elted$ ut they i''ediately t##0 stepst# try t# gain c#ntr#l #1 the react#r and ensure ade5uate c##ling t# the c#re. The 2C6s

regi#nal # a.'. #n March !. By a.'.$

2C ?ead5uarters in 8ashingt#n$ D.C.$ %as alerted and the 2C @perati#ns Center in

Bethesda$ Md.$ %as actiated. The regi#nal #


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Health Eects

The 2C c#nducted detailed studies #1 the accident6s radi#l#gical c#nse5uences$ as did

the Enir#n'ental &r#tecti#n Agency$ the Depart'ent #1 ?ealth$ Educati#n and 8el1are

(n#% ?ealth and ?u'an Serices"$ the Depart'ent #1 Energy$ and the C#''#n%ealth #1

&ennsylania. Seeral independent gr#ups als# c#nducted studies. The appr#9i'ately !

'illi#n pe#ple ar#und TM-! during the accident are esti'ated t# hae receied an

aerage radiati#n d#se #1 #nly a#ut ) 'illire' a#e the usual ac0gr#und d#se. T# put

this int# c#nte9t$ e9p#sure 1r#' a chest -ray is a#ut 'illire' and the area6s naturalradi#actie ac0gr#und d#se is a#ut )-)!> 'illire' per year 1#r the area. The

accident6s 'a9i'u' d#se t# a pers#n at the site #undary %#uld hae een less than

) 'illire' a#e ac0gr#und.

n the '#nths 1#ll#%ing the accident$ alth#ugh 5uesti#ns %ere raised a#ut p#ssile

aderse e/ects 1r#' radiati#n #n hu'an$ ani'al$ and plant li1e in the TM area$ n#ne

c#uld e directly c#rrelated t# the accident. Th#usands #1 enir#n'ental sa'ples #1 air$

%ater$ 'il0$ egetati#n$ s#il$ and 1##dstu/s %ere c#llected y ari#us g#ern'ent

agencies '#nit#ring the area. Fery l#% leels #1 radi#nuclides c#uld e attriuted t#

releases 1r#' the accident. ?#%eer$ c#'prehensie inestigati#ns and assess'ents yseeral %ell respected #rganizati#ns$ such as C#lu'ia ,niersity and the ,niersity #1

&ittsurgh$ hae c#ncluded that in spite #1 seri#us da'age t# the react#r$ the actual

release had negligile e/ects #n the physical health #1 indiiduals #r the enir#n'ent.

Mitigate the accident:

T# 'itigate and preent nuclear accidents$ the nternati#nal At#'ic Energy AgencyGs

nternati#nal 2uclear Sa1ety r#up created the c#ncept #1 de1ence in depth.

Defence in depth

The c#ncept #1 de1ence in depth is 1unda'ental t# the sa1ety #1 nuclear installati#ns.2uclear sa1ety d#es n#t rely #n #ne line #1 de1ence ut is achieed using a range #1

c#'ple'entary 'eans. These 1act#rs start %ith the design and uilding #1 a nuclear

1acility %hich re5uires ch##sing a g##d design and appr#priate site$ use #1 high-5uality

c#nstructi#n 'aterials and testing e1#re #perati#n. They als# c#er the %h#le range #1

#rganisati#nal and ehai#ural issues that are critical t# #perating a nuclear installati#n.

This c#'prehensie appr#ach is su''arised in the Basic Sa1ety &rinciples 1#r nuclear

p#%er plants prepared y the nternati#nal At#'ic Energy AgencyGs nternati#nal 2uclear

Sa1ety r#up (2SA" #1 e9perts:

HAll sa1ety actiities$ %hether #rganizati#nal$ ehai#ural #r e5uip'ent related$ are

suIect t# layers #1 #erlapping pr#isi#ns$ s# that i1 a 1ailure sh#uld #ccur it %#uld ec#'pensated 1#r #r c#rrected %ith#ut causing har' t# indiiduals #r the pulic at large.

This idea #1 'ultiple leels #1 pr#tecti#n is the central 1eature #1 de1ence in depth...J

(2SA"

The 0ey #Iecties #1 de1ence in depth are:

). T# c#'pensate 1#r p#tential hu'an and c#'p#nent 1ailuresK


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!. T# 'aintain the e/ectieness #1 the arriers y aerting da'age t# the plant and

t# the arriers the'selesK and3. T# pr#tect pe#ple$ including %#r0ers in the nuclear industry$ and the enir#n'ent

1r#' har' in the eent that these arriers are n#t 1ully e/ectie.

T# 'eet these #Iecties$ the strategy 1#r de1ence in depth is$ a#e all$ a#ut

preenting accidents. ?#%eer$ i1 preenti#n 1ails$ the strategy li'its an accidentGs

p#tential c#nse5uences as 'uch as p#ssile and preents any escalati#n t# '#re seri#us

c#nditi#ns. This 'eans ensuring a l#% chance #1 1ailures in the syste's used$ c#'ined%ith redundancy in design$ s# that i1 #ne syste' 1ails #ther independent$ dierse lines #1

de1ence ensure an accident d#es n#t result (de1ence in depth".

ive levels of defence in depth

De1ence in depth is generally structured in 4e leels. Sh#uld #ne leel 1ail$ it %ill ec#'pensated 1#r$ #r c#rrected y$ the suse5uent leel:

The #Iectie #1 the 4rst leel #1 pr#tecti#n is the preenti#n #1 an#r'al #perati#n and

syste' 1ailures in the nuclear react#r. 2uclear react#rs are designed t# ensure reliale$

stale and easily 'anageale #perati#n. Thus sa1ety-critical c#'p#nents in a react#r are

ased #n ery high-5uality techn#l#gies.

1 the 4rst leel 1ails$ an#r'al #perati#n is c#ntr#lled #r 1ailures are detected y the

sec#nd leel #1 pr#tecti#n. This leel #1 de1ence-in-depth in#les the rapid detecti#n #1

any deiati#n 1r#' n#r'al #perati#n and %here p#ssile$ its aut#'atic c#rrecti#n y

pr#cess c#ntr#l and pr#tecti#n syste's$ %ith#ut inter1ering %ith n#r'al #perati#n.Sh#uld the sec#nd leel 1ail$ the third leel ensures that sa1ety 1uncti#ns are 1urther

per1#r'ed y actiating speci4c sa1ety syste's and #ther sa1ety 1eatures. 2uclear

react#rs are designed t# %ithstand a set #1 an#r'al #ccurrences and p#tential

accidents. The third de1ence in depth leel is the c#ntr#l #1 these accidents

#ccurrences. This leel #1 de1ence %ill ai' t# aut#'atically place the react#r int# a sa1e

c#nditi#n and c#ntain the radi#actie 'aterials.

Sh#uld the third leel 1ail$ the 1#urth leel li'its accident pr#gressi#n thr#ugh accident

'anage'ent$ s# as t# preent #r 'itigate seere accident c#nditi#ns %ith e9ternal

releases #1 radi#actie 'aterials. All nuclear plants hae seere accident guidelines and

pr#cedures that #perat#rs can i'ple'ent. These are tested and e9ercised #n a regular

asis.

The last #Iectie (41th leel #1 pr#tecti#n" is the 'itigati#n #1 the radi#l#gical

c#nse5uences #1 signi4cant e9ternal releases thr#ugh the i'ple'entati#n #1 an #/-site

e'ergency plan. The e


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The 2SA gr#up #1 internati#nal nuclear sa1ety e9perts issues guidance and adice #n

the %h#le range #1 nuclear sa1ety appr#aches$ p#licies and principles. These are ta0en

up y E2SEGs 'e'ers in nati#nal strategies 1#r ensuring nuclear sa1ety. @ne

i'p#rtant 1uncti#n #1 E2SE is t# enc#urage the applicati#n #1 this guidance acr#ss the

E, and t# act as an E,-leel 1#ru' 1#r e9changes #1 e9perience and est practice in the

4eld.

Documents

Three Mile Island Safety Report