ML20064K473
| ML20064K473 | |
| Person / Time | |
|---|---|
| Site: | 05000142 |
| Issue date: | 12/23/1982 |
| From: | Dupont D COMMITTEE TO BRIDGE THE GAP |
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| NUDOCS 8301180417 | |
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Text
.
UNITED STATES OF AMERICA D
- NUCLEAR REGULATORY COMMISSION BEFORE THE ATCMIC SAFETY AND LICENSING BOARD %
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In the Matter of Docket No. 50-1!d* %k'-
THE REGE!ffS & THE UNIVERSITY
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& CALIFt)RNIA u-(Proposed Renewal
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(UCIA Research Reactor)
FacilityLicense)
DECLARATION OF_ DAVID R_.
DUpONT I, David R. Dupont, declare as follows:
1.
I am a chemist associated with the Southern California Federation of Scientists.
A statement of professional qualifications is attached.
2 I have reviewed certain safety matters pertaining to the UCLA reactor, primarily in the area of chemical reactions associated with potential accidents.
3 This review included a site visit and an examination of a number of documents associated with the application by UCLA for renewal of its license to operate its Argonaut type research reactor.
These documents have included:
the 1980 Application, and the 1982 amendments thereto; the original 1960 Hazards Analysis: Neill Ostrander's September 1,1982,~ declaration:
" Credible Accidents for Argonaut Reactors" hy Hawley, Robkin, and Kathren; and 'Tuel Temperatures in an Argonaut Core Following a Hypothetical Design Basis Accident" by G.E. Cort.
4 Based upon the above review, as well as independent calculations detailed herein, it is my conclusion that the above-mentioned analyses performed in l
support of the UCLA reactor are seriously flawed in their assessment of the l
potential for fire and other potentially destructive reactions in the UCIA l
reactor.
In particular, the esticates of Wigner energy that ray be stored in the reactor's graphite are vastly undervalued: the potential for a graphi.te, uranium metal, magnesium fire improperly assessedi the predictions of peak reactor temperature that can be attained in an accident are far too lows s.nd that consequently predictions of the magnitude of fission product release in case of a raximu'm credible accident are severely underestimated.
A discussion of these points follows.
5 ne UCIA reactor's primary material of construction is graphite, which serves both as moderator / reflector and provides some structural support.
The reactor is surrounded by a concrete biological shield, and the reactor's fuel plates are cooled and additionally moderated by light water.
The fuel is in the form of metallic uranium alloyed with aluminum, at 13 4 ut. % U, forming the low-melting eutectic.
The fuel is clad with aluminum, which also melts at a relatively low temperature; in fact, both meat and clad melt at considerably lower temperatures than the constituents of most other reactor fuels.
8301180417 830112 PDR ADOCK 05000 0
6.
Because there is no pressure vesssl, containment structure, exclusion zona, or radioactivity removal system for use in an emergency to prevent ficsion products from reaching the public if released from the fuel, the primary tarrier against fission product release is the fuel cladding,.015 inch thick aluminum. Because of the low melting temperature of the aluminum clad and the fuel meat, considerable attention has been given in analyses related to the UCIA reactor to the maximum temperature rise within the rzcctor that could acompany various credible accident scenarios.
7 Cne af the potential sources of heat in such an accident, either singly or as one of multiple contributors to a temperature rise in moderator or fual, is the energy stored in the graphite due to its long-term bombardment by neutrons.
Such bombardment causes damage in the graphite structure itself, knocking carbon atoms out of their normal positions, and in the process storing significant amounts of energy. This is known as the "Wigner effect," after Eugene Wigner who first predicted its occurrence.
8.
Bis stored energy can be rapidly released if the graphite is heated
, var a certain threshhold temperature, beginning around 170 C.
It thus poses a significant accident potential, because in the process of releasing tha stored energy, more of the graphite is brought to the temperature where it can release its energy, and thereby exists a potentially dangerous positive feedback mechanism.
The more graphite that is heated, the more heat is released.
9.
In addition to posing a simple thermal threat that could endanger the fuel's integrity, graphite is. combustible. At certain temperatures (estimated in the Hawley report to be approximately 650 C), it will ignite in the presence of air, in an exothermic reaction that releases large amounts of energy.
The Hawley report (p. 34) indicates that the combustien of 1 g of graphite will raise 38 g to the ignition temperature if no heat is lost, once again l
creating a dangerous positive feedback situation which, if started, could i
readily put the reactor fuel at risk of melting or of igniting.
(Theuranium i
in the fuel is also combustible.
It is reported that "In still air uranium oxidises, i.e. the reaction is self-heating at 350 C."
Nucleonics, Vol. 15, No. 12, December 1957.)
i 10 A very serious fire of the sort suggested above arose at a non-power reactor at Windscale, England, in which 20,000 curies of iodine-131 were released to the environment.* 2e fire-which involved both the uranium metal and the graphite--was initiated, in part, by release of the stored Wigner energy in the graphite. Although the reactor was a production reactor, it had a number of similarities to the UCLA reactor-fuel containing uranium i
metal, clad in aluminum, with a graphite moderator /. eflector, and normal l
operation at relatively low temperatures.
The operating temperature is l
very important because progressively larger amounts of self-annealing occur at higher operating temperatures conversely, significantly larger amounts of Vigner energy are stored at the lower operating temperatures.
11.
The Windscale accident in 1957 pointed to the importance of recognizing possible accident sequences involving stored energy in graphite.
It is thus necessary to have an accurate idea of the amount of such energy that might be stored in a reactor subject to irradiation damage in graphite, particularly reactors operating at low temperr.tures.
- Milk contaminated with I-131 had to be disposed of in an area of 200 square l
miles around the rmctor because of the accident.
_3_
12.
The Hawley, Kathran, and Robkin rr,visu treata ths Wign:r matter in tuo brief paragraphs on page 37 of their report.
Rey conclude that the amount of stored energy that may have accumulated in an Algonaut-type reactor lika UCLA's is approximately 5 cal /g, which they indicate is insufficient, if raleased, to heat the graphite by more than a trivial amount.
et al. ectimate. however is low by a factor of approximately
_The Hawley, 13 The true level of Wigner energy that may be stored in the graphite 25-40 of an Argonaut-type reactor such as that at UCIA is between 125 and 210 cal /g, given the calculational assumptions employed in the Hawley report and substituting numerical values that are more correct for the UCLA case than those used by Hawley.
Such a level of stored energy is sufficient, if released, to raise the graphite temperature 600 to 10000C above the temperature which had triggered the release, assuming adiabatic conditions.
In sum, an incident involving a relatively modest initial temperature rise in the graphite-of roughly 120"C--would be sufficient to trigger release of sufficient _Wigner energy to ignite the graphite or otherwise put the reactor fu11 at risk of igniting and/or melting.*
The Hawley report underestimation is caused by a series of cumulative 14 First of all, the value chosen for the rate of energy storage at 300C crrors.
is low by a factor of between 1.2 and 2.
Next, the ratio of energy storage at 50 C to that at 30 C is low by about 40%. In addition, Hawley uses 0
a thermal flux that is low by a factor of 3 3, based on empirical measurements at UCIA. And he estimates a total operating history of 12 W-days, whereas ths UCLA reactor has already run 19 sd in its first 20 years and, if ralicensed, can run an additional 37 Wd through the licensed period, This is a further error givcn the operatinc restrictions at the facility (1.2 x 1.4 x 3 3 x 4.7 = 26 of 4.7.
We cumulative effect of these errors to 2 x 1.4 x 3 3 x 4.7 '= 43), a factor of 26-43, depending on which initial value is chosen for the rate of energy storage at 30 0, is quite substantial.
0 Da errors are discussed in more detail below.
The Hauley report takes the value of.5 cal /s per Wd/At as the best 15value for the rate of energy storage in graphite irradiated at 3000, citing Nightingale's Nuclear Graphite, p. 328.
However, on page 345 of the same text, Nightingale states that "more accurate" values at low exposures range from.6 to 1.0 cal /g per Wd/At.
- 16. In order to correct these rates.for the somewhat higher temperature found in the Argonaut's graphite, cited to be approximately 500C, Hawley usssacorrectionfactorof3/5ths.
Data given by Nightingale (p. 328) for the change in the rate of energy storage with temperature, however, when graphed (see attachment) produce an actual ratio of 5/6ths (inverse 1.2).
0 Bis yields storage rates of.5 to.83 cal /g per Wd/At at 50 C, as opposed to the.3 assumed in the Hawley report at this stage of the calculation.
t
- 1.e., assume an initial temperature of 50 C and some incident which raises the temperature, not 600 C to the melting point of the fuel, but rather a mere 120 to the temperature at which Wigner energy is released. Assuming no heat loss, the released stored energy would be sufficient to raise the graphite to 770 to 11700C, well above the ignition temperature of the graphite or the ignition / melting temperature of the fuel.
_4_
- 17. Using the equation given by Nightingale relating thermal flux and EWd/At (p. 328 of Nightingale), Hawley then obtained a rate of energy storage in ths UCLA reactor.
The Nightingale approximation
- is:
Thermalnyt(BEPOequivalent) 17 6.4 x 10
=
mwd /At te of eg/g y storage for graphite Inserting the correct values yields a erg cal-ca' n, compared to Hawley's
~
in the UCLA reactor of 7 8 to 13 x 10-value at this stage of 4 7 x 10-19.
18 Hawley then atterpted to estimate integrated thermal neutron flux
, inn /cm) in order to convert, through the approximation provided above, into Toestimateintegratedflux,Hawleyassumedafluxrateof"about10g 2
cm -sec."
Thisorderofmagnigeestimatewasquitecrude,asHawleyassumed"the nsutrnnfluxashighas33x10gugmeasurementamadeatUCIAindicate flux to be 1.0 x 10, whereas a
- 19. Hawley then assumed thr t the reactor had logged 120 full power days, in order to estimate integrated flux (i.e., flux in n/cm2 persecong as determined in 18 above, times number of seconds, to produce n/cm integrated dose.) However, UCIA reports (Amended Application, p. III/8-7) that it had logged 19.4 mwd (or 194 full power days) in its first 20 years.
In addition, Hawley failed to consider the next 20 years for which UCIA has requested the license. At a 5% operating limitation, as in the Teqhnical Specifications, that would be approximately an additional 37 EWd, for a.
total of about 560 full power days to the end of the liceead period, l
in contrast to the 120 assumed in the Hawley report.
20 Inserting the more correct integrated thermal ' neutron flux into the j
relationship obtained from Nightingale in 17 above one gets a potential stored energy of 0
E 2
n/cm -s x 7.eto13x 10-19eal-cm /g-n 560 full powers days x e6,400 sec/ day x 3 3 x 10 yieldingapotentialstoredenergyof125to208 cal /gofgraphite.
This is in sharp contrast to the 5 cal /g estimated in the Hawley report.
21.
Integrating over the applicable range of temperatures the values for the epscific heat of graphite given by Nightingale on page 122, one determines that 125-208 cal / gram would correspond, if released and assuming no heat loss, to a temperature rise of approximately 600 to 10000C.
- Mawley dcas not demonstrate that this approximation.from Nightingale 10 universally applicable..It is used here only in following the Hawley m3thodology,in order to demonstrate that given the methodological assumptions employed, but using more correct numerical values, a substantially different rtsult is obtained.
- "Camma Flux Fapping of the UCIA Training Reactor" by George B. Bradshaw, Fasters Thesis,1965, p. 53 The study measured both gamma and neutron flux at a series of locations in the graphite.
The measurements were in limited locations ary' therefore even higher fluxes elsewhere in the core canrot be ruled out.
ate also that the earlier draft of my calculations referred to in Professor Warf's affidavit were lased on the assumption of a smaller flux because I had not then obtained the Bradshaw data.
~5-22.
Bus, using the Hawley nothodology and more appropriate numerical inputs, it is concluded that more than sufficient energy can be stored in the UCLA reactor's graphite to produce, if released, temperatures in excess of the ignition temperature of the graphite, magnesium, and uranium, and the melting temperature of the cadmium control blades and the aluminum-uranium fuel.
23.
Se lack of an emergency cooling system thus becomes quite significant from a safety standpoint, as does the lack of detailed fire response plans.
Furthermore, as Professor Warf has indicated in his declaration, use of water or carbon dioxide to fight such a fire could be disastrous because of the explosive chemical reactions possible.
(Metal-waterreactions,as Michio Kaku and Boyd Norton have indicated, can also be initiated by a power excursion at this facility. )
24 Mr. Ostrander in his September 1,1982, declaration asserts that it would take hundreds or thousands of years of operation of the UCLA reactor to produce enough Wigner energy storage to be of concern.
He bases that assertion on the experience of the Hallam reactor, which was shut down because of swelling and cracking of the graphite moderator, and asserts that such deleterious effects were observed at Hallam after a far greater integrated fast flux than could be generated in the UCLA reactor.
There are a number of flaws in Mr. Ostrander's assertion (among them, that it is not at all clear that the swelling was due to neutron bombardment as opposed to thermal or other effects), but one need only examine one of the errors-the ignoring of differences 4
in operating temperature--to dispose of the matter.
25 Mr. cstrander cites as basis for his assertion above an answer by C$G to an interrogatory about the Hallam flux, but fails to mention the graphite operating temperature at Hallam cited by CBG in that answer.
That normal temperature during operation is 600 C for the pphite, well above the annealing temperature for the graphite. Above about 200 C, virtually all of the radiation damage is constantly being annealed out of the graphite by the high operating temperatures.
That is why high temperature graphite reactors have essentially no Wigner problem.
It is the low temperature graphite reactors, 3
i.e. those reactors who operate at temperatures below which significant annealing of the graphite takes place, who must worry about stored energy. And UCLA's is a low temperature reactor.
Hallam was not.
We Critical Temperature for the UCLA Reactor 26.
De Cort and Hawley analyses, as well as the Staff and UCLA reiterations thereof, are lased on the premise that essentially no fission product release can occur should reactor temperatures remain in an accident below about 640 C, the melting temperature of the fuel meat.
Bey therefore conclude that if, in the case of Cort, airflow in the fuel boxes were cut off in a seismic event, the reactor would not be at risk because the maximum temperatures attained would be below that critical temperature likewise l
in the Hawley report, which indicates temperatures just below the melting temperature in case of power excursion, and concludes that no fission product release would occur.
However, all e,f these analyses ignore the crucial additional energy 27.
that could be added to the incident from release of stored Wigner energy in the graphite.
Whereag Hawley indicatas a power excursion could produce fuel temperatures of 590 C, just below that of the melting temperature, a graphite temperature rise of only about 1200C is sufficient to release what appears to be enough Wigner energy to push the reactor far over the threshhold temperature for ignition and melting. The same is true,with Even accepting all of Cort's other assumptions, peak the Cort analysis.
temperatures of about 360 C are predicted. While insufficient in and of itself 0
to melt the fuel, such temperatures would not necessarily be insufficient to push the graphite over the Vigner threshhold, releasing sufficient energy to melt the fuel or ignite the core.
Similarly, heat sources deemed in the Hawley study insufficient to ignite the graphite by themselves may not be insufficient to cause release of the Wigner energy, which could then Thus, a common-mode accident involving an incident bring about such ignition.
insufficient in itself to bring about ignition or melting could well trigger release of sufficient stored energy to bring about that result. And, in a sense, the concept of stored energy means this is an accident mode present throughout the lifetime of the reactor, just awaiting the triggerir4
. incident.
- 28. Thus, the critical temperature for the UCLA reactor is about 170 C, the Wigner threshhold, not 640 C, the melting temperature of the fuel meat.
I note that the Applic$ tion (p. ITT/8-9) indicates that fission fragment release frem aluminum / aluminum-uranium alloys is significant at temperatures C or higher. Furthermore, the Hawley study indicates the ignition of 4000 temperature of materials that may be placed in-core are substantially lower.
And than the maximum temperatures Hawley assumes for a power excursion.
none of the analyses examine the effects of cladding softening arai volumetric expansion that can occur at temperatures substantially below that of the eutectic melting temperature. Even were there no Wigner potential, the critical temperature for this reactor would thus be considerably below the melting temperature of the fuel or the ignition temperature of the graphite.
(Note also, as indicated earlier, that uranium may ignite in air at temperatures well below that of the U-Al melting temperature, and that, as Professor Warf indicates in his declaration, cadmium metal control blades melt at arourai 320 C).
Conclusions 29 Accepting the Hawley methodology and substituting numerical values more accurate for the UCLA case indicates substantial Wigner energy can be stored in the graphite of the UCLA reactor during the license period.
This energy, if released, could raise temperatures well above ignition and melting temperatures. The energy release can be triggered by a relatively small initial temperature rise; thereafter the reaction is self-heating.
Thus, a number of scenarios of credible accidents which result in temperatures asserted to be below the melting temperature of the fuel could actually result in putting the fuel at risk, due to release of the stored energy, through fire or melting, or both.
- Note that Er Cort assumes no effect on thermal conductivity of either the fuel or the graphite due to irradiation effects.
This erroneous assumption invalidates the final results, as they are highly dependent upon the values used for thermal conductivity.
_7_
I declare under penalty of perjury that the foregoing is true and correct
, to the best of my knowledge and belief.
k David R. Dupent Dated this 13 day of December,1982, at Ben Lomond, california t
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Professional qualifications DAVID R. DUFONT My name is David R. Dupont.
I am a chemist ascociated with the Southern California Federation of Scientists (SCFS).
I worked, in cooperation with Professcr James Varf, a colleague at SCFS, on an assessment of chemical reactions that might affect reactor safety at UCIA. This included assessment of the potential for combustion of the reactor's graphite, ma6nesium, and/or uranium constituents; the potential for explosive reactions with steam, water, or carbon dioxide should such a fire occur or elevated temperatures otherwise result: Wigner energy storage ani other effects of radiation upon the chemical and physical properties of the reactor materials: ani the chemistry of fission product release at temperatures above and below the melting point of the fuel meat.
I received a Bachelor of Science Degree in Chemistry from the State University of New York at Albany in 1977. From 1980-1982 I was a Research Associate in the Biological 21emistry Department at the University of California at Los Angeles'.
UCLA MISCELIANETS " FACTS" 4n
- 36. See response to UCIA fact 17, under contention XIX 9
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- 37. See response to NRC fact 3 under contention VII 9
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