ML19224C148

Revised Unexecuted Draft of Notice of Incident on 790328

ML19224C148
Person / Time
Site:	Crane
Issue date:	03/28/1979
From:	Chilk S NRC OFFICE OF THE SECRETARY (SECY)
To:
References
NUDOCS 7906290176
Download: ML19224C148 (13)

Text

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AattDRMAL OCCURRENCE EVENT 7 _

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NUCLEAR -ACYiertif-AT THREE MILE ISLAND

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.Section 208 of the Energy Reorgant ration Act of 1974,.as amended,

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. requires the NRC to disseminate inforTr.ation on abnomal c.ccurrences i

'I

,1 (i.e., unscheduled incidents or events which the Commissf on detemines are significant from the standpoint of public' health r.2d safety).

The.

i following incident was detemined to be an abnorTnal occurrence using the criteria. published in the FEDERAL REGISTER on February 24, 1977 (42 FR 10950).

Paragraph 3(a) of the General Statement of Policy notes that an event will be consiiered an abn,ormal occurrence if it involves a major reduction in the degree of protection of the public health or safety. The following description.of the event also briefly lists the rer;edial actions taken to date.

The information presented be' low should be considered prelimjnary

.since the sequence.of events and the c.auses remain under extensive

. investigation.

The total extent of corrective ar.tions is " dependent on the ongoing investigatP is.

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.. ' Three Mile Ir.laryd Unit 2 is a pressurized water nuclear power plant I

located in Dauphin Count.y. ' Pennsylvania, about 10 miles southeast of..._

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.Harrisburg.. ~The plant was des tgned by. the Babcock A WCcox Company (B.*N).

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Nature and Probable Consequences - At about 4:00.A.M. on March 28, 1979, a series of even'ts, initiated by a malfunction in the acon 4*y htd4)aiff Ot7d

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3deffdh % System, resuited in apparent ; extensive core damag. sisg)ifica eUI YW J gy C

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....-t radioactive contamination the containment vessel 1 an iseveral p nned

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and unplarned releases of radioactivity to the environment.

Since low sured off the plant site the G vernor of levi:% of radiation werefG th0Tp>eC)IC Wlihll1 U.hVCYm r-rttCI11I11tlI YO(JIV Yhh.*.

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r phn t d.c c.;castc; e alvo requbsted others within a ten mile radius to remain indoors as much as possible.

These requests were in effect for several days.

Three employees of the 1 see rgcei ed OCot*

I41701 tZ OMO radiation exposures slightly le works of the NR fter4y 1 mit of in exce i

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on sn 3 remsf he a erage do,se to the public a 50 mile radius of the d b he ObCdf /

Iwwas recewedn,h 177Jf/77 plan was pbout '.5 mn.r..cO[h ono the.

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gg J 1agram of -the TMI-2 reactor plant. There are two: loops in-the: primary coolant system, -Water-is pumped-by-the' primary coolant' pumps (2 in each loop) through the core where it picks up heat emitted by the fuel rods.

The water passes through the prima'ry side of the steam generators (1 in each loop) and flows back to the primary coolant pumps. h*ressure in the# primary sy tem is con P

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M-the-sec:ad a,.7,j: tem, feedwater pumps supply water to the secondary side of the steam generators.

The heat f om the primary Mb d throo hthesenm tenemTor[vbes10 a E=4 rcqg,sf up by-the pecondary water, led MI' p _< p re and since the latter is at pp water ie BOWS.

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a 4ew-pressure, the water flashes to steam.

, 'CE N turbine (which turns the electrical generator) and on to a condenser g g$ -

0ll renlullili?C C Su G in whichpthe steam cc r.denses to watcr. --Th45%m-tcr rcta. as -tc the gg 4ccdaateMwps--viu the ccadcasste purps cad cic nap s,7 ster.

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• W In the g-steam can bypass the turbine and 90 event that 4he-normal feedwater -s@j.d.~i. is not available, the system o

is designed with 3 auxiliary feedwater pumps ta N..p-feedwater to prr the steam generators.

Preliminary information indicates that at about 4:00 A.M., there was a loss of a condensate pump in the feedwater return system, apparently due to moisture in the control air of a valve.

This reduced suction pressure to the feedwa2r pumps which caused them to trip off and a subsequent turbine trip.

Two auxiliary feedwater pumps started, but no flow was injected since the discharge valves were h'e io ion o NRC requi remen ;s ). ih lo

.of th heat sink (bosed(adeNliou) fb Mle secep0ary 6the 8tne deanl Gen &TTIdrs) eduj caused the primary coolant temperature abd pressure to rise. whidh automatically shut down the reactor (control rods dropping into the cor3) and the pressuri er relief valve to oplnfome FeMrcr ecc ohtdW ter hnd stea valveIb directe' um k

w c vented nqued tonk located within the containment.

As the pressure in the reactor coolant system decreased, the did noT pressurizer relief valve should have closed, but diJ..';; within 2 kis f20htV bt4f CLLk q/LS Y &

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mi$utes, the pressure had dropped to 1600 psi (normal operating g

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tigh Pressure I..,'ection "O,

This injected relatively cool borated water 1.

o *..a pr.imary c ys tem.

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designed with sensors 'to give an indication of the coolant leve' in u.du..,n.x csef a.~ W

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2, the secondary side of the steam generators dry and the shock of the cold water input caused one or more was tubes to fail, resulting in a primary-secondary leak..

The pressuri2ar level came back on scale aC1' ^-

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-Mte bout an hour af ter the incident began, the system -

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parameters stab lized in a saturated condition at about MM psig and

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. h... degrees F., Between 1.and 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> into the incident the operators

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turmed off the four reactor coolant pumps which circulate the reactor coolant through the reactor.

The reactor core began a heatup transient, reaching terrperatures beyond the range of the instrumentation.

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Cooling of the reactor was attermted by " feed and bleed", that is black vakt. dodnS~ ream. a pumping with HRL system ano.;ontrolling pressure with the-ppressurizer 16

.thuu p-val ve. St rice th valv was frequently open, thousands TTl) of gallons of water were pum;;ed into the containtren tp and transferred I

to the auxiliary building "' *' - -

-- until the containment I

meadeifi vegan.ually isolated,ChrG:lWdfd

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. Extensive fuel damage occurred durin.g -these periods. releasing fission d.

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si te wMidn-a <ev k 28,1979) -/r OlM ON[ 07df 3

y om -e" being noti fled on March

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large group of personnel wg dispatched on March 30, 1979, c

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i eventually reaching a contingent over 17.

Several fed ral and (t' 10 b a}tQY YG\\lb&lk Ob itilhCL f$g QIld jw s tate agencies became involved in an f ronnental moni tori g The

! Governor of Pennsylvanta 44vu ed }.hc=htC+bcw.

recon 3n1rn e t o e.

.,g most suscep ib to radiation gg0 (p,ynont wun=:n and pre-school children) within a five mil radius to M

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evacuate, and oth'ers to runin indoors.

This eenice a rz ei..ded-O (c::,'

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.several days later when radiation levels returned to essentially natural background levels.

Environrnental neasurements continue to

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.E guse or Causes - The details of the incidc:st ecntinue to be extensively investigated.

However, based on the partial investigation ~s to date, the apparent causes were a combination of-p.ene-ne! e f OD$. )

design deficiencies. ao4-compnnent failures,f Spcc _) c(+m:Y%0017f 2.YTOf*L a

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The containment not isolating when the em,ergency core F_ t

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cooling system initiated.

It is designed to isolate

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actively investigate the incident to fully understand the incident

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and to take appropriate' corrective action::.

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ch'anges necessary both at this plant and the other plants designed h'

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by,B&W.

Changes may be necessary in operator training procedures,: and

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equipment design.

The licensee is also investigating procedures for.

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cleanup of radioactive contamination within the plant, renoval of.

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NRC - The NRC's incident; response centa d in Bethesda, Maryland-wes-- LOf76- %..._...

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activated. '.:The NRC dispatched a team of experts to the site to

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.-:t Fk. [f 7" inves tigate. the event and to. follow the licensee's folicmup actions.

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The President. appointed the Director of !!aC's Office of Nuclear

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{eactor Regulation as his pehonal r;epres entative at the site; the N latter coordinated all NRC activities at the site and was thei

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An extensive investigation of the incident is being conducted by g

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Meetings have been held with all of ' le r eactor vendors to f

discuss the event and the actions requirer to prevent recurrence of such an incident.

For some Westinghouse designed plants, this involves l'

operato'r initiation of the emergency core cooking system based solely'.

upon low-pressure signals from the. pressurizer.

r:M NRC inspectors were sent to all sites with B&W designed o

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- A ;;eries of NRC In:;pection and Enforcermnt Bulletins were sent-to

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probable causes.

Actions required by.the 1 icens.ecs were desc'ribed,

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--and/or ECCS initiacion, and proper determination of coolant levels S(f' F-. in the sys tem. The NRC is meeting with ipower reactor licensees to

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.qg.m._n1. ~ based ~on licensee responses, vendor s tudies, and the on-going 'NRC W: k .l;-* 3.T.Ri.~'.*h investigations. The NRC's Office of International Programs has kept applicable foreign countries informed of the incident and. followup actions. - i For the Nuclear Regulatory Comission Ii Samuel J. Chilk ~ Secretary of the Conmission Dated at k'ashington, D. C. this day of

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