ML20214U349
| ML20214U349 | |
| Person / Time | |
|---|---|
| Issue date: | 06/04/1987 |
| From: | Grimsley D NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| To: | Sholly S MHB TECHNICAL ASSOCIATES |
| References | |
| FOIA-86-763 NUDOCS 8706110151 | |
| Download: ML20214U349 (5) | |
Text
U.S. NUCLE AR REGULATORY COMMISSION Nac *o A newtst Nweta se g.#"%
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INFORMATION ACT (FOlA) REQUEST JUN - 4 1987 ee.,
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.ER,ss o,
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KEOVESTER Steven C.'Shollev PART l.-RECORDS RELEASED OR NOT LOCATED (See checked bonesi s
No agency records subsect to the request have been located.
No additenal agency records subrect to the request have been located.
Agency records subject to the request that are identifed n Appendin 9
are already avadtbie for public inspecten and coppng in the NRC Public Document Room, yy 1717 H Street, N.W., Washmgton, DC.
Agency records subject to the request that are identifeed in Appendix R
are being made assilable for public especten and copyi*g in the NRC Public Document yy f.oom,1717 H Street, N.W., Washmgten. DC, in a folder under the FOIA number and requester name.
The nonproprietary versen of the proposaus) that you agreed to accept m a tekohone convemten with a rnember of my staff is now being made avaiable for public inspecten and coying at the NPC Public Document Room.1717 H Street, N W, Washington, DC. in a folder under the FOIA number and requester name.
Enclosed is information on how you may obtain access to and she charges for copying records placed in the NRC Public Document Room,1717 H Street, N.W., Washmgton, DC.
Agency records subject to the request are enclosed. Any applicable charge for copies of the records provided and payment procedures are noted in the comments section.
Records sub ect to the request have been referred to another Federal agencyties) for review and direct response to you.
t In view of NRC's response to the request. no further acton is being taken on appeal letter dated PART II.A-INFORMATION WITHHELD FROM PUBLIC DISCLOSURE Certain informaton in the requested records is being withheld from public disclosure pursuant to the FOIA exemptons described in and for the reasons stated in Part II, sec-t:ons B. C, and D. Any releawd portions of the occuments for which only paft of the record is being withhe6d are bemg made evadable for public irspection and Copying in M
the NRC Public Document Room,1717 H Street, N.W., Washington, DC, in a folder under the FOIA number and requester name.
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CEEDOg4 OF INFORMATION ACT RESPONSE FOIA NUVBEa Sr F01A-86-763 oATE:
PALT 110- APPLICABLE FOIA EXEMPTIONS
.a-fecords subject to the request that are dracribed in the enclosed Appendices C
are being withheld in their entirety or in part under FOIA Exemptions and for the reasons set forttt below pursuant to 5 UAC. 552(b) and 10 CFR 9.5(a) of NRC Regulations.
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- 1. The wthheld informaten a property classded pursuant to Esecutme Order 12*E;EhtYpTION 11 3
0 T% wthheld 68ermaton relates solely to the intemal personnel ruks and procedures c/ NRC. IEXEMPTION 2)
-y 3 The ethheld informaton a specificaaty esempted from public disclosure by stattte indicated- (EXEMPTION 31 Section 141145 of the Atome Energy Act which wohibits the esclosure of Restncted Data'or Formerty Restncted Data (42 U.S.C. 2161-2165).
t Secten 147 of the Atomic Er ergy Act which prohitn s the dsclosure of Wdessited Sa'eguards information 142 U S C. 2167).
- 4. The withheld Wortnation is a trade secret or commercial o financial irsformation int is teng withheld for the reasonis) Indicated. (EXEMPTION 4)
The informawn is cons.dered to be confidential buseress tpiopnetare irdormaten.
J The informaten is considered to be proprietary information pursuant to 10 CFR 2.790+(1).
The informaton was submrtted and receeved in conf dence from a foregn source pursuant to 10 CFR 2.790td:(2t l
- 5. The withbek1information consists of intersoency'or intraagency records that are not ava.iable through discovery durms htigatiort Doclosure of predecsional informaten would ter a to inhibit the open and frank sachange of ideas essential to the deliberative process. Where records are ethheld in their ennrety, the facts are inextricably g
intertwmed mth the deceanal informa4n. There also are no reasona segregable factual portens because the release of the facts would permit an indirect ingvwy ento predeceonal procas of the agency. IEXEMPTION i Y
6, The wthheld information a esempted from pubhc disclosure because its dadosure would result in a clearfy unwarranted invason of personal privacy. (EXEMPTION 6)
- 7. The nthheld Hformation conssts of bvestgatory, records cornpded for law enforcement purposes and is bemg withheld for the reason (s) indicated. (EXEMPTION 7) s D eraos.no mtNad mterfere mth on enforcement proceedmg because it could reveal the scope, direction, and focus of enforcement efforts. and thus could possibey allow them f7 take acton to shyJ potenbal wrongdomg or a violation of NRC requvements from investgators. (EXEMPTION 7 tall Q.}
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Wclosure would constitute an upwarranted invason ci persor al pnvacy (EXEMPTION 7tC))
The informaton consets of names of individuals and other informatson the disclosure of which would reveal ident4 Des of confidential sources. (EXEMPTION 7(D))
PART ll.C-DENYING OFFICIALS Pursuant to 10 CFR 9 9 and/or 9.15 of the U.S. Nuclear Regulatory Commisson regulatons, it has twen determmed that the mformaton ethheld e exempt from producten or disclosure, and that its producten or dsclosure is contrary to the pubhc interest. The persons responsible for the deneal are those officaals identded below as den @g officials and the Director.
Divoon of Rules and Records. Office of Adrmnstration. for any denials that may be appealed to the Ennutive Director for Operatens (toot DENYING OFFICIAL TITLErOFFICE RECORDS DENIED APPELLATE OFFICIAL Eric S. Beckjord Director, Office Of
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C1 C2' C3' C4' C5 Nuclear Ronnlatnr,v Daca=rc_A X
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~.m-f PART li D-APPEAL RIGHTS The denial by each denying official identM in Part II.C may be appealed to the Appellate Official identified in that section. Any such appeal must be in writing and must be made within 30 days of receipt of this response. Appeals must be addressed as appropriate to the Executive Director for Operations or to the Secretary of the Commission, U.S. NucWr Regulatory Commission, Washington, DC 20555, and should clearty state on the envelope and in the letter that it is an " Appeal from an Initial FOIA Decision."
s ac Fom aos tren 21 U.S. NUCLEAR REGULATORY COMMISSION
- asi FOIA RESPONSE CONTINUATION
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Re: F01A-85-763 APPENDIX B RECORDS MAINTAINED IN THE PDR UNDER THE AB0VE REQUEST NUMBERS CATEGORY B 1.
9/26/86 Article: "The lessons of Chernobyl" by Eliot Marshall from SCIENCE (pp 1375-1376)
(2 pages) 2.
10/6/86 Article:
"Chernobyl Stokes Controversy" by Byron Spice from Albuquerque Journal (2pages) 3.
10/24/86 Paper: by Marshall Berman, Sandia National Laboratories,
Title:
A Discussion of Steam Explosions and Comments on Related Papers 4, 6, 7, 8, 9, 10, 21, 26, etc. (4 pages)
Re:'F0IA-86-763 APPENDIX C RECORDS TOTALLY hlTHHELD CATEGORY B 1.
9/17/86 Memo for Multiple Addressees from Denton, subject:
Chernobyl Implications Assessment: Request for Initial Contributions.
(2 pages) w/ enclosures 9/10/86 Working Draft, Chernobyl Implications Assessment (14 pages)
Appendix A - Chronology of the Accident (8 pages)
Exemption-(5) l 2.-
9/24/86 Insert text to Meyer from. Wright.
(2pages)
Exemption (5) i 3.
9/25/86 Memo to Ross from Kelber, subject: Chernobyl Implications Assessment. (3 pages)
Exemption (5) 4 Implications Assessment.
(6 pages) Exemption (5)yl The Chernob 4.
10/6/86 Memo to Denton from Beckjord, subject:
5.
10/9/86 Memo for Hopenfeld from Meyer, subject: Comments On Chernobyl Implications Draft Report. (2 pages) Exemption (5).
1 NOTE:
These records relate to a draft report, NUREG-1251, which NRC
. expects to publish during the su.nmer of 1987, i
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t ke: F01A-86-763 APPENDIX D RECORDS MAINTAINED AMONG PDR FILES CATEGORY A i
NUREG-1250, Report on the Accident at the.Chernobyl Nuclear Power Station.
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ggE TECHNICAL CONSULTANTS ON ENERGY &
TECHNICAL ASSOCIATES Dale G. B:idenbaugh 1723 Hamaton Avenue-Suite K Richard B. Hubbard San Jose, Cahfornia 95125 Gregory C. Minor Phone:(408) 266-2716
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20 October 1986 EREEDOM OF INFORMATON Mr. Donnie H.
Grimsley, Director ACT REQUEST Division of Rules and Records Office of Administration U.S. Nuclear Regulatory Commission Washington, D.C.
20555 RE:
FOIA Request Concerning Steam Explosions
Dear Mr. Grimsley:
Pursuant to the Freedom of Information Act, please make available at the Commission's Washington, D.C.,
Public Document Room records in the following categories:
A.
The so-called "U.S.
Factual Report on Chernobyl";
B.
Documents related to the occurrence of a steam explosion during the Chernobyl
- accident, including, but not limited to, calculations of the magnitude of the steam explosion (including both thermal and kinetic energy release), discussions of the state of the core at the time of the steam explosion (i.e.,
whether molten, vaporized, or solid), the pressure in the reactor at the time of the steam explosion, and the existence and nature of any alternative hypotheses to explain the event if any NRC or NRC contractor personnel believe that it was not a steam explosion.
C.
All records of NRC-sponsored severe accident code similations of the Chernobyl accident (i.e.,
I SCDAP/RELAP, MARCH, STCP, TRAC, etc.).
If there are any questions concerning this request, please contact me by telephone at (408) 266-2716.
Thank you for your attention to this FOIA request.
Sincerely, C.
Steven C. Shol Associate Consultant
mmw pua m ermunta 7
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/O t' L The Lessons of Chernobyl
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l Q,) V U.S. ofcials say they harc learned little new, but the accident is raisiry old questions about the danger ofsteam crplosions and the strcigth ofcontainments Tseemed confident at a recent meeting HE Nuclear Regu!atory Commission Speis gase four examples. One is the type accident could not happen in the Unit-assumption that it is safer to run reactors at ed Scares it rests on several assumpnon-that the Chernobyl accident will add low power than at high power. Chemobyl about the differences between Smiet and httle to the agencv's expertise on reactor w as running at less than one tenth power American reaaors One is wideh auerted safety. Staff scientists said ther could see no w hen it ran amok. Another is the adequacy that U.S. reactors are not nilnerable to the immediate lessons for U.S. nuclear plants.
of U S. rneuures to prevent a scenano kind of pow er surge that triggered '.he Cher.
The blast thu ripped Chemobyl apart w as nob 1 disaster.
3 triggered bv a runawav fission reaction and U.S commercial reaaors are desced to powered by steam. The NRC seems to put '.
lose power when the core loses w ater it is most of the stress on the first half of the concenable that a U.S. reactor full of coob problem. It has focused on the diferences could have a power surge if sescra!
ant Serw een U.S. and Sosiet methods of fission control rods were ejected from the core control, not on the common hazard of steam instantaneously. But because the scenano a explosions.
implausible, it has been httle studied In On retuming from the Intemational $
addition, it might be possible to mcrease Atomic Energy Agency conference in Vien-power in a ncrmally running reactor bv na. NRC stafers told the fh e commissioners pumping a large slug of supercooled water that they gained a solid understanding of into the core. Again, it is hard to imagine how the accident came about. They had a how this could happen.
less precise picture of the physical event However, the design of the liquid rnera!
itself. De Soviets w cre frank and open, thev fast breeder reaaor-whose construction reported, although not able to ansuer all fi.,
was planned at Chnch Rher, Tennessee and questions about the bla:t. However, NRC
.g has been postponed indefinitely-does hase e
officials found the record clear enough to K
a positise void coefficient. This reaaor feel that there wetc few technical surpnses.
- F p) could gain power with a loss of cool 3
Studying this accident, one expert said. is Chemobyl did.
bke returning to " ancient history." It bnngs
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%1itary reaaors fa!! into another catego-up problems in neutron physics that Amen-W M*
cans eliminated from their designs decades ry, one that for reasons of national secunn-has been less examined. Thev operate out-ago. Experiments on a senes of test reactors h-side the NRC's jurisdict.on and are said to at the Idtho nuclear engineenng lab con-Blowing off steam. This expmment, hase strange power dynamics and ucaker unced U.S researchers in the 1960's that run by Kenurth it'olda: er les Alamos, containment buildings The Department of thev fully understood the hazards of run-8l!")rrar<s Ins.: powerful wkansc ld.ut can br Energy has commissioned an 18.montn awav power accidents
'72damt when rain mms with hot molu" studv of their safety bv a panel at the Narold Denton, head of reactor regula-marmal A simdar mixture at Neruo's El gy;onal Academt of Sciences tion at the NRC, told the commission on 3 Other assumptions about the supenonn j
September that the staff needs time for the
,,,,f,,, gg of U.S. reactors are not so widely accepted
,, j,,,,,,,,y,,4,,,cd at C/smioM For example, esen before Chemobyl. cntics Soviet information to
- seep in." With Cher-
,ng7,g gf,3,77 of the NRC said the ageng had understated nobyl as a guide, the staff will "go back and
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look at things" in U.S. plants that once known as " anticipated transient without the threat of explosion caused by rrdten seemed troublesome and might need review. scram" or the failure to insert control rods in fuel mising with watcr or concrete. Cnte "But I don't see any areas in which w e need a crisis. Chemobtrs rods had been hhber-also think the NRC has userstated the pro-to make any immediate changes in our ately disengaged. NRC officials want to rection gisen by containment buildings regulatory basis," Denton said.
review the chemisty of severe accidents, for De debate on molten fuel will intensifs He was seconded by Themis Speis, the Chernobyl released a far greater volume of now, spurred on by Chemobyl and b re-3 l
director of safety technology for NRC and lethal fission products than U.S. scenarios search coming out of the agencv's " source another member of the delegation that went forecast, even for the worst accidents. Final. terms" study. This is an industn~ inspired to Vienna. "We didn't see anything telhng ly, the gasernment may take a look at the effort to define more precisely the damage i
us immediately to make radical changes," quahry ofits evacuation plans. The Soviets that could be done by the worst possible Speis said in an inteniew. "But we have a had to scrap all of theirs because none accident.
l number of candidate issues that we are anticipated the sescrity of the accident.
By happenstance, Chernebyl bicw up just going to take a look at."
The prevaihng view is that a Chemobyl-as the source terms project was coming to an ao strrtuntst 1986 hIk-hhlN Ntws & CO.stst F NT li*s SI N
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end The industn belicied thn re carth containment to go around sush a w stem'*
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would show that the oM damage of tmatn he asks himself 'I doubt that you can '
opmnim of thc hkhhw d.it a srcam drn vi were too large It hoped SRC would use Accordmp to Speis, the fuel u as subjeced catastropft Without doing new rewars h less carachsma terms to desenbe nuclear ro an as erage heat of ar Icast 300 calories per ther concluded m 1985 that it was atmost accidentwa hope that mas base gone up m gram, with some areas gemng much hotter impmuble. In unting the repon. thn ado the smoke abmc Chernobl it shattered and u as ejeacd m paruc!c form ed that n would be hc!ptut <<a condus some The Chemobl acadent.c eral phmcists mto the surrounding u ater, w hich unmedi.
esperiments to confirm thn ripinnin sav, must has e included a prompt neutron" ately flashed to steam The pressure shar-Berman thers urore a memo descnbmg pou er bunt. The Souets apparenth did not tered the 1000 ton concrete hd of the reac-SERG's data as " gambler's esumares stress this fact but referred to the accident tor and towed hot graphite and bits of fuel essentiall, guenes'that "cannot be suppon-simph as a steam nplosion -
through the roof of the building. In this ed on technical grounds
- He found the Reaaor fuel emns two Linds of neutrons, sense, the Souets are justi6cd m calhng the method of pothng experts for their per>una:
the " prompt
- ones that appear in a mdhsec. blast a steam esplosion But Speis and Wil-opinions to be nonscienti6c.
ond, and the "delated' ones that may take son. argue that what happened was verv In a separate memo, NRC staff scientnt up to tens of seconds to appear. Reanors are ditTerent from any steam explosion that is Joram Hopenfeld rated the espert opiruons designed to operate so that delayed neutrons considered posuble in a U.S. reactor.
for credibihrn He noted that "none of the sustain the chain reaction, for without the 13 expens prosided an estimate of contain-time lag thev provide, it wou'd be impossi-ment failure w hich is technica!h defensible "
ble to throttle the system up and down. No Str7Han (Ont/#dtd that he fuel core contains more 'than enough mechanism for controlhng tons of fuel 7gg jjggfjgggg ggg y7gg,g enugno Nou se mp of the reanor sessel mcnes in fracions of a mierosecond. For J
and send it through the containment. So the this reason, all reaaors are designed to (Xp/OSMn hrc4 king 4 proNem, Hopmfeld explams, is sat to an muimize the total neutron aux mithout gO7f fn 4 g.g. Mnt7(4r gue this cannot happen, one must has e some allowing prompt neutrons to dominate the faith credible physical evidence. Yet, Ho-contg [npngntygnggd penfeld wrote,"There is no indicanon that reaction in the core. In contrast, an atomic bomb rehes striaj on prompt neutrons.
the rnembers fullt utihred the available y
The big weakness of a Chemobylepe httWttn ht !Mp0SS!h/t large. scale industri steam explosion expen-reaaor (RBMK 1000) is that when the gngthgfngp/pgpfg, ence
- He found that verv firtle con 6dence system loses water, the pow er increases-so could be placed in the SERG estimates rnuch so, it now appears, that prompt neu-The S asi difference," Speis says, is that Ne enheless. the NRC forged ahead, cu-trons may take over. last Apn], after dis-the fuel at Chemobyl mtxed with the water ing SERG's opinions in a source term docu-abhng nearly all mechangal controls oser in a 6ne particle form. w hereas in.the worst ment issued m July (NCREG 0956)- It the 6ssion process, the operators at Chemo-U.S. scenano, it would pour into the water states that a catastrophic steam explosion byl reduced the water flow. The inevitable as a large mohen blob. Haung a greater inside the reactor vessel is " considered to (c$11 owed: the water heated and allowed the surface area, particles transfer energy more have a low probabihty and its analysis is no power to increase. The reaaor went into a eEciently than blobs. U.S. research has con-included" in computer programs that are rapid power surge, ending m an uncontrol-centrated entirely on blobs on the assump-used to estimate the impact of a soere table prompt neutron bunt." This blurs tion that in a U.S. reactor, the overheated accident.
somewhat the distinaion beracen a reactor fuel would have to take that form. Speis This issue may hase to be reexamined accident and a bomb. But the disuncion notes that this research shows that it is vert now, along with others intohing the remains strong in terms of energy and speed, unkkely that a steam explosion could breach strength of containment buildings. One for the discharge from the fuel was far less a contamment structure. This is the settled who miends to see the debate rnised is energetic than a TST blast.
NRC tiew, and. as a result, Speis says,-We Daniel Hirsch a critic of SRC pohev at the Once the prose >5 w as set in monon, neu.
u ere A ing uct.m cylosion research, u e are Unnersity of Cahforn a at Santa Crui tron emissions n th; core grew oponential-now phasing it out
Hirsch claims that "U.S. conuinm.:nts, ty for several seconds, rapidly oserheating Some disagree with this pohcv, one being hke the pressure boundaries for Chemobyl, the fuel Then the power dropped as heat the scientist whose budget for steam re-are not required to be designed to w ithstand slow ed the chain reaction (due to the Dopp-search is being phased out. This is Marshall the challenges of core melt accidents
- He ler effea) and vapor pressure burst the core Berman of the Sandia National 1 abora-ticks off some of the problems Chemobyl apart.
tories. In an NRC financed analysis in will bring forward: the risk of molten fuel A Sosiet mathematical reconstruction of 1984, he declared that the cata wcre too reacing with concrete to produce an explo-the event shows the core rising from below variabic to support a clear.uswer. Some sion,the possibihn that melted fuel sprayed one tenth power to 120 nrnes normal in steam expkisions com ert less than 1% of the from a reactor vessel might merstress the seconds (full power being 3200 megawatts energy present to mechanical force. Other containment, the pamcular weaknesses of thermal). It then dropped momentanly and expenments show a more c5cient partem of the Mark i boihng uater containment sys-finally surged up to 480 times full power. conversion, enough to drive the pressure tem tident:6ed by the NRC as minerable),
Speis thinks the second power surge may be vessel head through the roof.
and the discrepancy berueen the farge vol-the result of an error in Sonet calculations.
Berman concluded that the likelihood of a ume ofiodine released from Chemobvl and Howner, R2 chard Wilson, a Harvard steam explosion brealung a hole in a U.S.
the low amcunts assumed to be released in physicist who chaired the Amencan physical nuclear containment ranged between the U.S accident models.
Society's source term study and w ho went to impossible and the ine stable. The NRC was This is hardly an uphftmg agenda from Vienna as an NRC consultant, does not rule dissatis6ed with this answer, and therefore the nuclear industn s point of siew. But e
out the possibihty that the reaaor surged to commissioned a new panel of experts, the after Chemobv', it may prove unasoid-m er a mi!! ion megawatts. -Can you design a Steam Explosion Review Group.
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l use teflure was so low that it wasn't knowledge is gained, however, and j
rth worrying about, steam explosions may agaM become a i
4 1r45 report by the American prominent concern. Wright noted the i
yrical Society's source tem panel NRC is about to embark on new work i
d snuch the same thing, Edst a 'er Sandia to esplor( the 1mpact of l
this year by the Eeropean convection withis the reactor vessel.
iort clear Agerm y.
Oser na port yese aad a half, i group of 13 steam explosion concern has sesented that convectico serts gathered by the NRC reported withla the vessel folkwing a meltdown t year that they also believed the afght heat the vessel's head bolts, hemode failure was very unlikely, waaben'nt thant If that's the ceae, a rman, in a February 1985 memo to steam explosion may not brie se be as NRC. contended the probabihty vigorous as aos totaved to turn the imates made by the gnup's enem vessel's Imad into a containment.
's were
- essentially guesses" wit!> threatedng miami 1* Wright said.
scientific basis.
Dough the Chernobyl areMant has se uma pietos terman's view was shared by at ret caused a massesanent of steam at some NRC staff members. For explosions, Wright said it will cause This esquence of photos, spanning a in a Janua=y 1985 memo, the NRC to review the chemistry of quarter of a second, illustrates a Sandla f the reactor ers-severe accidents because the radaoac. Labs experiment C*~ ~ * -
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ranch said be assigned tive coaraminants spewed from the i
tow level of confldcoce to the crippled reactor was far granter than gggjogyng, p;p"y
... to a bability estimates, based on his had been forecasted. De commission motten nucles' r ^"
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.lustion of the experts' techedcal also w111 review evacuacon plans.
which proved inadequate at Caer-eq9pe j im9 m
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Albuquerque h FenA-64-70 Chernobyl Stokes C6ntrovi Despite Cutbacks, Sandia Seeks Clues to Steam Exj By Byron Spice This may then have been followed by detonation of hydrogen gss released JounhaL scasses wntran during the accident, further damagmg the reactor building.
PRENOhENON caDed a
-he conditions were exactly right R4appened steam explosion is being for t5e very quick, intimate mixing of h srie blamed for ripping apart very hot fuel and water," noted Wil-the Chernobyl nuclear liam Stratton, a nuclear power consul-Canes seawri reactor, but Nuclear Regulatory Com,.tantand retired Los Alamos National yps j
missir.n officials say that doesn't laboratory physicist.
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changs their minds about downplaying Such a rapid rise in poweris consid-research into steam explosions.
ered virtually impossible in the At Sendie National Laboratories, pressuriasd-water and boiling-wa;tt GresMe f f where the bulk of the NRC's steam reactors used in most U.S. nuclear
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explosion work is performed, budgets power plants, he explained. De surge f
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'l g for the program plummeted more than at Chernobyl was caused by an b 80 percent the past year.
temption in the flow of calant; U.S.
A steam exploelon that blows a hole reactors, by contrast, Rose power when,
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is, scientificaDy,a quhe differ-
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son -haslong been recognized as one eat process than what we ese la of the most catastrophic of potential. core-melt accidents?anMW4ht,
- 1N% weier e reactor accidents, but years of research have an official within the NRC's accident
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led many experts to conclude that its evaluation branclL "De Chernobyl Heats meer vie seen occurrence in a U.S. reactor is highly experisce doesnt ready I nd eny.
- unlikely, thing new to our understandtn of The events and conditions leading to steam explosions?
the Ct,ernobyl steam explosion last In a core-melt accident, Berman
(
April were f&r different than those explained, it's asrtmed that the molten w
W red that could exist in commercial power core material will first pool and then
- roos e,swwste reactors here, NRC officials contend, fallinto the wsteras a giant slut Much 3 ng,,,cgan so that accident has little relevance to of the current scientific debate con.
I the steam explosion threat.
cerns whether this falhng slug sepe-
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But some scientists, tactuding Mar-rates into BB and gravel. size blobs shad Berman, who directs Sandia's that wmld permM an efficient mixing e o steam exploelon research, maintain of core material with the water.
that more needs to be understood Such a " coarse mixture"is thought before anyone writes off the threat to be necessary for a containment-posed by steam explosions.
threatening steam explosion to occur.
"I don't know the likelihood of Ms mixing occurred at Chernobyl sJphe-mode faDure," Berman wrote because of the sudden deterioration of last year in a memo to the NRC. the fuel
- Neither does anyone else. It is possi-Berman said be doesn't yet know ble that research will show that such enough about the Chernobyl accident p.,4,,,,
failures are impossible. It is also to say whetherit has any relevance for Coeurs uwnsn paaets possible that the research will ahow U.S. reactors. But recent Sandia re-usiergeog rassner Asaan that a large steam explosion mig occur during a core melt accident..ht anarch sussests that molten core mate-rial separates into a coarse mixture A steam explosionis water that boils much are readily than previously so fast that shock weves develop, much assumed.
as the detonation of a chmical explo.
That reeaarch is pregnesin stn generates abock r /et slower rata now, however, g at ahaving Mpha. mode faunteis a scenario that dropped from mors than 81 milhos in might occur foDowing the mahdawn of 1985 to about $400,000 this year.
a reactor's fhel core. GeneraDy, it's ne overell cut in NRC steem exple ' westh wierybus about,made enBare un l
described this warrMolten core mate-senem empl rch was not that severe, A aft $ report by the Astericas prominent rial, bassed to perhaps 5 000 deg
- Wcblef of the Physiast geciety's suuree term panel NRC is abr Fahrenheit, fa!!s into weier paaa rees,
30 the as"om' rF tant Imtamany went so a at sL some of said much the samme thdug,es 'did a es gendia the hottom of the reacsor vessel, Mrwrt idnio year by the Ety e.
a, ant 4w resulttog in a steam a plosia, that 1msas was savetted foe weet at blows off the top or er re1meL T1ns F*M laborneory.
hcieur Agaw t-Om at bunk of steel becomeo a afune that
@taa research has been A post of 13 seesta expWe cos.,x e he enrede gathered by the h8tC ref rted eli!J: rhei breaks through the cant Emant wens, out back, however. "We have taugh last year that they also behered :he might hee d3i888 permitting radioactive g* era sad aero-reau' ties,to make in the face of budget alphe-enadr Amihue was ver7 ur.likely sols to escape and endast dat public, Sunr6ers said, and the What happened April 16 at Cher, E bas seen Ng cuts is the severe Berman, ta a February 1945 men-to st.aan e.pl nobyl was quite differem, exording to accidet reenarch budget-the NRC, contended the prooability vtgorous a j
the latest Soviet reports of the accp Dough officials may feel uneasy estimates made by the group's mem-vessel *e b dent. During an experiment in which about sums of the cuts, they have to bets were *eseentiaDF guseses* sith-thie.att.ning out scientific besit 7hsh i the power statice's operators had de-aDocate anoney to the moet critical Berman's view was shared by at not caused liberately disengaged many coetml, problems and, he added, steam explo-least some NRC staff memb and safety systems, power levels stone do not fallin that category.
sudderily surged from one-tenth of An American Nuclear Society com-uary 1985 memo, the NRC t norma: rower to 120 times permal afttee studying " source terme % the f the reactor sys. severe acc tema ranch said be assigned tive conta I
power, causes de reramic fuel rods amount and types of radioactive con. a low level of confidence to the crippled re to dantegrare and mit with the water tamiaants that could escape from a probability settmates, based on his ha l
t: sed to cool the reactor cors. De CrfPpled reactor and chaired by Strat. evaluation of the experts' technical also will n w.as steam espksson blew the top tan - reported in 1984 that they rsoonales.
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TITLE:
A DISCUSSION OF STEAM EXPLOSIONS AND COMMENTS ON RELAT PAPERS 4,6,7,8,9,10,21,26, etc.
Marshall Berman Sandia National Laboratories My knowledge of the Chernobyl accident comes primarily from articles in the lay and technical press, and from References 1-3.
There are many aspects of the accident that seem uncertain and speculative, especially the chronology of the last few seconds before the " explosion."
The prevailing descriptions of these seconds are quite inconsistent (e.g. see 1, p. 21; 2; 3].
Several assumptions pervade the' discussions at this conference:
The fuel was not molten at the time of the steam explosion; the solid fuel was prefragmented into "small" pieces before it contacted the " coolant;"
It is not clear to me which,the " coolant" was predominantly steam.
if any, of these assumptions are true.
The following discussion provides my speculations concerning possible scenarios at Chernobyl, based primarily on the computer generated parameter histories prepared by the Soviets and my own extensive experience in this field.
High Ambient Pressure The modelling histories show that the ambient pressure was at least 90 bars, and could have been much higher.
is correct in stating that if there was a steamSteve Sholly (message 4) explosion at Chernobyl, it would contradict what some experts have claimed - that such events are incredible at such high pressures.
The RIA-ST-4 accident discussed by R. Hobbins (message 7) explosions at high ambient pressure. lends even more credence to the poss insertion of 350 cal /g " melted" a fuel rod "and the meltHe states that an energy interacted explosively with the water."
His description of the post-explosion debris is very similar to debris we have observed in some of our experiments (4).
This experiment also leads me to question the Soviet statement that the fuel did not melt, though their calculated energy insertions of 300 cal /g (mean even value? +/- how much?) could easily have been sufficient to melt much of the fuel and the cladding, considering the power asymmetries.
Coolant Quality It is difficult to read the P (mass steam quality, 0-6%)(volumetric steam quality, 1.2X) and O 0-curves in the plots of the codp' uter simulation.
these quantities imply that a great deal of liquid water couldHowever have been present in some fuel channels at the time of the " steam explosion."
If one takes into account asymmetries in the fur.1 channels and the potential errors in the computer simulatiorr, don't see how a large amount of liquid water can be precluded.
I The computer histories also show that the main circulation water flow began to increase during the last two seconds before the explosion.
Therefore, it is possible (or likely) that some poi A -S(, '43
.3 33 I
't i
1 channels were beginning to refill with water.
clad could have fallen into these " puddles" cf water. Molten fuel and explosions in adjacent channels, explosion in one channel would h An resulting in a coherent explosion.
In summation, subsequent contact of these materials with liquid waterI believ l
i resulting steam expl'o'sion is a credible sequence of events
, and a R. Hobbins (message 7) materials contacted water at TMI without an explosion.says that large am however, that a 2 MPa pressure spike was observed He notes, 4
the vessel lower plenum region)
(far away from.
I submit that such a spike could easily have been createdab MPa.
by one or more steam explosions, or by a highly energetic fuel coolant interaction.
Furthermore, the supposition that large particle sizes" is,"relatively large streams were involved" resultin i
in fact, just supposition.
vely experiments at Sandia indicate that streams of diameters Current 4
could indeed break up into small particles. comparable to the d l,
i calculational model of-jet breakup.
Ref. 5 presented a disintegrato after falling only 27 cm through water "10 "a
i j
o diameters for the various TMI support and grid plates rang d f Hole about 8 to 16 cm.
e rom 3
\\
involving melt masses ranging from 50 mg to 50 kgWe I
ons and for coolant pouring onto quiescent molten poolsob We have i
i scale, occurrence of explosions sometimes appears ra.
At large i
variability has been observed extensively both for ' controlled ndom.
This i
experiments and industrial accidents.
]
We have also observed fuel-coolant interactions withpr of intensities, from benign boiling, a wide range to mild explosions, to extremely violent explosions.
not vulnerable to steam explosions based on the "presumeTo conclu absence of an explosion at TMI is to make a grave error.d" Feynman said (6):
the first shot got off safely is little comfort for th"When playing Richard i
e next."
explosions, which contains a plethora of modifiers. Ariel S own definition given in Ref.
7 I prefer my defined as a boiling process ra:pid enough 'to generate' shock"A ste waves." Man explosions. y people have profferred complex definitions of steam I think that such definitions tend to cloud the safety issues our primary co,ncern is to prevent damage to the reactor.and i
i Artificially restrictive definitions should not be used to creat i
k e
}
l
logical and semantic barriers to understanding the Chernobyl explosion and assessing its relevance to Western reactors.
L. Leach (message 10) time to generate hydrogen for the second explosion. questions whether th We recently presented a paper (8) that included models for predicting the rates and amounts of hydrogen that could be generated during steam explosions.
Two different models were used; one model assumed that molten retal reacted with a steam environment, the other with an environment composed primarily of liquid water and In both cases, large quantities of hydrogen were predicted to be generated on the time scale of the steam explosion, 0.5 to 5 ms.
j R. Hobbins (message 7) feels that one should add as much water as possible to a Western LWR as soon as possible.
address this comment I will in my paper in the Accident Management Conference.
In summary, Chernobyl is a plausible scenario:I believe the following sequence of events at i
leads to melting of some of the zirconium and fuel.The reactivity transient material is expelled into the fuel channel where it contacts The molten water, or it falls into water residing at the bottom of the i
channel.
One of the channels spontaneously triggers a steam explosion, and the generated shock triggers a large number of other channels to explode.
The steam explosions produce large quantities of steam and hydrogen which lift off the reactor roof.
The steam and hydrogen mix with the ambient air initially in a mixture too rich to explode.
fuel / metal spreads into the building,As the hydrogen-steam-air-hot finally reaches a detonable concentration.from metal-steam 3
initiated by the hot fuel and hot oxidizing cladding.A detonation is then would hear these events as one explosion after another, Witnesses the Soviets have reported.
just as REFERENCES 1.
Accident at the Chernobyl Nuclear Power Plant and ItsUSSR "The Consequences," Draft, August 1986.
- 2. "Chernobyl: The Soviet Report,"
Sept. 11, 1986.
Nuclear News Special Report,
- 3. " Chronology of a Catastrophe," Nature, Vol. 323, No, 6083, 4-10 September 1986,
- 4. L. S. Nelson and P. M.
- Duda, Single Drops of Iron Oxide Melted with a CO" Steam Explosion Experiments with 2 Laser," SAND 81-1346, NUREG/CR-2295, September 1981.
n o
5.
M.
- Epstein, H.
K. Fauske, " Steam Film Instability and the Mixing of Core-Melt Jets and Water," ANS Proceedings of 1985 National Heat Transfer Conference, Aug.
4-7, 1985, Denver, Co.
6.
R.
P. Feynman, Contribution to the President's Commission Investigating the Challenger Accident,.1986.
7.
M. Berman, Section E-1 in " Steam Explosion Review Group Report: A Review of-the Current Understanding of the Potential for Containment Failure Arising from In-Vessel Steam Explosions," NUREG-1116, February-1985.
- 8.. M.
F. Young, M.
- Berman, L. T. Pong, " Hydrogen Generation Curing F!ael-Coolant Interactions," presented at the American Chemical Society Meeting, Anaheim, California, Sep. 12, 1986.
l
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