[Congressional Record Volume 141, Number 42 (Tuesday, March 7, 1995)]
[Senate]
[Pages S3637-S3639]
From the Congressional Record Online through the Government Publishing Office [www.gpo.gov]


   ALLEGATIONS REGARDING POTENTIAL NUCLEAR EXPLOSIONS IN A GEOLOGIC 
                   REPOSITORY FOR SPENT NUCLEAR FUEL

 Mr. JOHNSTON. Mr. President, last Sunday, the New York Times 
published a front-page story alleging that geologic disposal of spent 
nuclear fuel in Yucca Mountain could result in an ``atomic explosion of 
buried waste.'' The story is based on a hypothesis proposed several 
months ago by two scientists at the Los Alamos National Laboratory, Dr. 
Charles D. Bowman and Dr. Francisco Venneri. Drs. Bowman and Venneri, 
neither of whom is a geologist, performed some crude calculations on 
what might happen to plutonium in a geologic repository. They assumed 
that 50 to 100 kilograms of pure plutonium-239 would slowly diffuse 
through nonabsorbing silicon dioxide--not any type of rock actually 
found under Yucca Mountain--and then gradually reach criticality as 
various neutron-absorbing elements in the nuclear waste diffused away 
over the millennia.
  We have been told by the New York Times and by both Senators from 
Nevada yesterday that three teams of scientists at Los Alamos ``have 
been unable to rebut the assertion'' of Drs. Bowman and Venneri. This 
is simply not true.
  The Los Alamos National Laboratory, in fact, did respond to these 
allegations. It formed three review teams. A ``Red Team'' was set up to 
serve in the role of skeptic. A ``Blue Team'' was set up to take the 
role of defenders of the Bowman-Venneri hypothesis. A ``White Team'' 
was set up to serve as a neutral judge of the work of the other two 
teams, and to render an overall judgment as to which was more credible.
  What was the conclusion of the White Team? I ask that a two-page 
``Summary Critique of Bowman-Venneri Paper by Internal Review Groups at 
Los Alamos,'' which was publicly released yesterday by the Los Alamos 
National Laboratory, as well as the complete text of the White Team 
report, entitled ``Comments on `Nuclear Excursions' and `Criticality 
Issues''' be printed in the Record at the end of this statement.
  The White Team report is a devastating critique of the hypothesis of 
Drs. Bowman and Venneri. It states that:

       The geological situations in the Bowman paper are too 
     idealized to validate the proposed scenario.
       The assumption of significant plutonium dispersion into the 
     surrounding medium is without justification.
       The amount of water is overestimated by a factor of 1000. . 
     . . There is no steam explosion.
       The assumptions about the behavior of the fissile mixture 
     near criticality are not credible.
       There is no credible mechanism for releasing energy on a 
     time scale short enough for even a steam explosion.

  Even when the White Team started assuming that the impossible would 
happen, it still could not find the Bowman-Venneri hypothesis credible. 
For example, the White Team concluded:

       Even if dispersion and criticality are assumed (which is 
     strongly objected to), the conclusion that an explosion would 
     occur is incorrect.
       Even if dispersion, criticality, and energy release are 
     assumed, there would be no serious consequences elsewhere in 
     the repository or on the surface.

  The florid story in the New York Times and the comments made on the 
floor yesterday by my distinguished colleagues from Nevada illustrate 
vividly how to misuse science in public policy debates.
  Step No. 1. Ignore peer review. The New York Times clearly knew that 
an internal laboratory review of the Bowman-Venneri hypothesis had 
taken place, but got the story of that review completely wrong. Is 
there any way to characterize the above statements as being ``unable to 
lay [the Bowman-Venneri hypothesis] to rest,'' as the New York Times 
reported? I don't see how. And, of course, no external review by a 
scientific journal of this paper has taken place--it isn't even clear 
whether Drs. Bowman and Venneri have submitted their calculations to 
any journal, other than the New York Times, for consideration.
  Step No. 2. Do not even bother to get your facts straight. The true 
story of the internal Los Alamos review of this paper was readily 
available yesterday to any Member of this body who would have taken the 
time to call anyone at the laboratory whose name was mentioned in the 
New York Times story.
  Step No. 3. Just jump on any news story that seems to support your 
preconceived view. Blow up the headline into a big chart, and head 
directly to the Senate floor.
  Unfortunately, this is not the first time that we have seen bad 
science injected into the debate over a permanent geologic repository 
for spent nuclear fuel. In 1989, another DOE scientist named Jerry 
Szymanski interpreted some mineral deposits adjacent to the Yucca 
Mountain site as evidence that ground water repeatedly had risen well 
above the level proposed for the repository in the geologically recent 
past. If such an event were to occur in the lifetime of the repository, 
it would flood the waste packages and could result in a release of 
radioactive material to the environment. But before this hypothesis 
could be properly reviewed by other scientists, Szymanski's report 
became a media sensation fueled by, among others, the New York Times. 
Eventually, a distinguished group of scientists from the National 
Academy of Sciences was asked to evaluate Szymanski's interpretations 
and the data upon which he had based those interpretations. This panel 
concluded what the vast majority of DOE and U.S. Geological Survey 
scientists had concluded already: that the mineral deposits were 
produced by rainwater at the surface and had nothing to do with 
fluctuations in the ground water table at all. That was in 1992. 
Notwithstanding the NAS conclusion, the State of Nevada continues to 
pay large sums of money to Szymanski, now an independent consultant, to 
continue beating a dead horse.
  So let me respond in detail to the specific charges made yesterday by 
my distinguished colleagues from Nevada.
  The distinguished junior Senator from Nevada charged that a 
``discussion has been going on for months and months and months'' 
involving ``three teams comprised of 10 scientists--that is 30 
scientists [that] have been unable to rebut the assertion that there is 
a genuine fear that an explosion can occur in a geologic repository.'' 
In fact, the scientists at Los Alamos were able to rebut the assertion, 
and did.
  The distinguished senior Senator from Nevada complained that the 
Bowman-Venneri hypothesis had not been 
 [[Page S3638]] mentioned in public hearings or debates. Well, that's 
how scientific review works. Scientific results ought to get careful 
peer review within the scientific community before they are served up 
in the Sunday New York times. If a scientific result can withstand 
neutral scrutiny--which is what Los Alamos was in the process of 
doing--then it should be published in the open scientific literature 
and we can start the debate as to what its relevance to policy might 
be. None of us is served by fragmentary and distorted accounts of 
scientific research in the public media.
  The distinguished senior Senator from Nevada characterized the 
Bowman-Venneri calculations as ``evidence by a scientific community 
that says an explosion could occur.'' Do my colleagues really believe 
that a crude, theoretical calculation, predicated on all sorts of 
inaccurate assumptions for example, that the rock under Yucca Mountain 
is pure silicon dioxide, constitutes evidence? Evidence usually means 
something real. You can make up any theoretical calculations you like, 
and if you are not going to be constrained by reality, you can come up 
with some pretty interesting answers. But you will not get any evidence 
that way.
  The distinguished senior Senator from Nevada stated that ``it is not 
as if it has not happened before. In the former Soviet Union, they had 
an explosion from nuclear waste.'' He would have us believe that the 
Soviet explosion is somehow relevant to geologic disposal of spent 
nuclear fuel. Not so. The Soviet explosion occurred in a nuclear waste 
tank at Tomsk, not in a geological repository. The explosion was caused 
by red oil--a byproduct of reprocessing spent nuclear fuel. The whole 
idea behind the current DOE waste program, and geologic storage in a 
location such as Yucca Mountain, is not to reprocess.
  The distinguished senior Senator from Nevada says that his 
information is ``not sensationalism'' and that it ``comes from the 
scientific community.'' Well, publication in the New York Times hardly 
constitutes peer review. It is sensationalism, pure and simple.
  Finally the distinguished senior Senator from Nevada said that these 
results came ``from one of the finest scientific labs in the world.'' 
Now that we can see what Los Alamos actually has to say about the 
Bowman-Venneri hypothesis, will the Senators from Nevada accept what 
the Los Alamos review team had to say?
  In summary, it is not true that, as both Senators from Nevada tried 
to tell us yesterday: ``Thirty scientists * * * have tried to prove it 
wrong for 10 months. They cannot.'' As it turns out, they can shoot 
this hypothesis full of holes, and they did.
  Before we call a halt to all attempts to find a solution to our 
nuclear waste problems, or before we set up mini-repositories for spent 
nuclear fuel at every nuclear plant in the Nation, let's see the 
Bowman-Venneri hypothesis for what it is--a preliminary calculation 
with a highly questionable connection to the real world. If scientists 
at Los Alamos want to pursue such calculations, that is their right. 
But we should not let ourselves be swayed by sensational reports based 
on sketchy theories. Good policy can and should only be based on good, 
peer-reviewed science.
  The material follows:

       [The attached paper is a summary of the work of the three 
     review teams that have examined the paper on possible 
     criticality at the planned Yucca Mountain Repository. It was 
     compiled by the senior manager at Los Alamos National 
     Laboratory who supervises the author of the original paper.]
  Summary Points of Bowman-Venneri Paper--``Underground Autocatalytic 
         Criticality of Plutonium and Other Fissile Material''

               (By Charles Bowman and Francesco Venneri)

       1. Underground storage as presently recommended could lead 
     to autocatalytic criticality and uncontrolled dispersal of 
     thermally fissile material with significant nuclear energy 
     release and possibly nuclear explosions in the 100-ton range.
       2. Fissile material when emplaced underground is 
     subcritical. However, once containment is breached, the 
     fissile material is free to disperse in the underground 
     matrix either through natural (diffusion, earthquakes, water 
     flow) or unnatural means (human intervention).
       3. The underground matrix contains good moderators such as 
     water and rock (silicon dioxide) in various proportions. 
     Under certain conditions of fissile material density, radius, 
     water and rock composition, the fissile material can reach 
     criticality due to neutrons moderated in the rock/water 
     mixture. The criticality can have either positive or negative 
     feedback. Negative feedback would mean that the nuclear 
     reactions would decrease as the mixture heated up and 
     expanded and hence go subcritical. Positive feedback means 
     that the nuclear fission is self-enhancing (autocatalytic). 
     Hence the nuclear reactions continue to grow to 
     supercriticality and possibly explosive conditions.
       4. Neutron poisons, such as boron, that are added to the 
     spent fuel when emplaced underground to prevent criticality 
     have different solubilities than fissile materials and thus 
     would be leached out from the fissile material area.
       5. Without water, 50-100 kg of fissile material is required 
     to reach autocriticality. As small an amount as 1 kg of 
     fissile material can reach autocriticality with water 
     present.
                                                                    ____


 Summary Critique of Bowman-Venneri Paper by Internal Review Groups at 
                               Los Alamos


                          geologic emplacement

       1. The geological situation in the Bowman paper are too 
     idealized to validate the proposed scenario. Pure silicon 
     dioxide, a weak neutron absorber, is not a common geological 
     material and has not been proposed as a repository material. 
     Other elements present in all proposed geological formations 
     absorb neutrons much more strongly than pure silicon dioxide, 
     which reduces the reactivity of the mixture.
       2. For periods less than 10,000 years, the presence of 
     Plutonium 240 (half-life of 6,500 years) would also reduce 
     reactivity strongly.


                    material dispersion underground

       1. The assumption of significant dispersion of plutonium 
     into the surrounding geologic medium is without 
     justification. Geologic processes take millions of years by 
     which time the plutonium-239 (half-life of 24,000 years) 
     would have decayed to 235 U which is less reactive.
       2. The Bowman paper argues that water flowing down through 
     the repository would dissolve glass logs in about 1,000 years 
     and leave a fragile powder of plutonium that could disperse 
     through steam ``explosions'' caused by criticality heating of 
     the water in the vicinity of the Pu log. However, the amount 
     of water is overestimated by a factor of 1,000 so that the 
     correct time scale is on the order of a million years. Also 
     the temperature gradient is over estimated by a factor of ten 
     so that there is no steam ``explosion.'' Also the leaching 
     process could leave a residue as strong as the original log.
       3. Material is not likely to be dispersed into symmetric 
     shapes by rather along fractures which would provide more 
     difficult geometries for criticality.


                              criticality

       1. The assumptions about the behavior of the fissile 
     mixture near criticality are not credible.
       2. As the fissile/rock/water mixture approached 
     criticality, it would slowly heat and expand which would drop 
     its reactivity below critical and mixture would cool. Thus 
     the mixture would have a negative temperature coefficient.


                       explosions/energy release

       1. Even if dispersion and criticality are assumed (which is 
     strongly objected to), the conclusion that an explosion would 
     occur is incorrect.
       2. There is no credible mechanism for releasing energy on a 
     time scale short enough for even a steam explosion. A nuclear 
     explosion must make the transition from critical to highly 
     supercritical in a fraction of a second. A credible means to 
     force this transition in a repository has not been found.
       3. Even if dispersion, criticality and energy release are 
     assumed, there would be no serious consequences elsewhere in 
     the repository or on the surface.
                                                                    ____

       [The attached paper is the preliminary work of a team of 
     scientists at Los Alamos National Laboratory. The team was 
     asked to review the papers that have been generated dealing 
     with the issue of possible criticality at the planned Yucca 
     Mountain Repository. Further analysis may be conducted, and 
     possible further modifications of the estimates contained in 
     this paper may occur, in the normal process of scientific 
     investigation. The paper of the review team as it stands now 
     does contain considerable work by the team.]
     Comments on ``Nuclear Excursions'' and ``Criticality Issues''

       The Laboratory provided a technical review of a paper by 
     Drs. Bowman and Venneri on the ``Nuclear Excursions and 
     Eruptions from Plutonium and Other Fissile Material Stored 
     Underground,'' which argued that the dispersal of plutonium 
     (Pu) stored underground could increase its reactivity to the 
     point where critically, auto-catalytic reaction, and 
     explosive energy release could occur.
       The review concluded that the probability of each of these 
     steps is vanishingly small and that the probability of the 
     occurrence of all three is essentially zero. Moreover, even 
     if these steps could occur, any energy release would be too 
     small and slow to produce any significant consequences either 
     in the repository or on the surface.
       [[Page S3639]] The authors of ``Nuclear Excursions'' 
     provided responses to the issues raised in that review in the 
     form of a paper entitled ``Criticality Issues for Thermally 
     Fissile Material in Geologic Storage.'' The white team and 
     the leaders of the blue and red teams reviewed the responses 
     in ``Criticality Issues,'' met to discuss them, determined 
     that they are flawed for essentially the same reasons as the 
     original paper, and concluded that they do not significantly 
     impact the conclusion of the review that the probability of 
     the chain of events postulated in ``Nuclear Excursions'' and 
     ``Criticality Issues is essentially zero and that even if 
     they could occur, any energy release would be too small and 
     slow to produce significant consequences.


                              Emplacement

       The geological situations discussed in ``Nuclear 
     Excursions'' were too idealized to provide a useful framework 
     for analysis or to validate the proposed scenario. That was 
     pointed out in the review, but those situations were still 
     used in ``Criticality Issues.'' ``Nuclear Excursions'' 
     postulates the emplacement of fissile materials in geologic 
     formations of pure silicon dioxide. Pure silicon dioxide is a 
     weak neutron absorber, is not a common geologic material, and 
     has not been proposed as a repository material. Other 
     elements present in all geologic formations that have been 
     proposed absorb neutrons much more strongly than pure silicon 
     dioxide, which reduces the reactivity of the mixture.
       Furthermore, ``Nuclear Excursions'' performs most of its 
     yield calculation for pure Pu-239; so does ``Criticality 
     Issues.'' The weapons plutonium of interest has a significant 
     fraction of Pu-240, which is a strong absorber that further 
     reduces reactivity. Even for the maximum loading postulated 
     in ``Nuclear Excursions,'' weapons plutonium could never 
     disperse to a condition of criticality in real, dry 
     repository materials. It is argued that the Pu-240 would 
     decay, leaving the more reactive Pu-239, but that would 
     happen over several times the 6,500 year half life of Pu-240. 
     Even then the Pu-240 would be replaced by its daughter U-236, 
     which is also a strong absorber. Moreover, as noted above, 
     the calculations in both papers ignore minor soil 
     constituents with very large absorption cross sections. When 
     they are properly included, it may not be possible to achieve 
     criticality for the assumed conditions even without the Pu-
     240.
       The assumption of significant dispersion of plutonium into 
     the surrounding geologic medium in ``Nuclear Excursions'' is 
     without justification. Geological processes would take 
     millions of years, by which time plutonium would have decayed 
     to uranium-235, which is less reactive than Pu-239. We have 
     not discovered a credible process that would produce more 
     rapid dispersal. Anthropogenic measures are unlikely and are 
     routinely accounted for in repository analyses. ``Criticality 
     Issues'' argues that water flowing down through the 
     repository would dissolve the glass log in 1,000 years and 
     leave a fragile powder, but its calculation overestimates the 
     amount of rainfall on and water in the repository by factors 
     of 1,000, so the correct time scale for dispersal is again 
     about a million years.
       It has also been noted that the temperature gradient 
     driving the process is overestimated by an order of magnitude 
     and that the leaching process could leave a residue as strong 
     as the original log.


                              Criticality

       The assumptions about the behavior of the fissile mixture 
     near criticality are not credible. ``Nuclear Excursions'' 
     assumed that the rock in which the fissile material is placed 
     is rigid and would prevent the expansion of the material and 
     permit the achievement of super criticality. That was based 
     on an improper interpretation of the published equation of 
     state. In reality, rock is compressible, and even at depths 
     of several kilometers, lithostatic stresses are small and 
     anisotropic, so that confining stresses are small. Even if it 
     fractured the rock, it would not do so in a spherically 
     symmetric manner. Even if the mixed material became critical, 
     it would slowly heat and
      expand, which would drop its reactivity below critical, 
     after which its neutron flux would drop, and the mixture 
     would cool. That is, the mixture has the negative 
     temperature coefficient of many fissile assemblies. This 
     was pointed out in detail in the review.
       Nevertheless, ``Criticality Issues'' again argued that 
     fissile material could diffuse through criticality, although 
     it shifted its argument to soils with very high amounts of 
     water, which have higher reactivity. However, the essential 
     physics is the same as for dry rock. The mixed material would 
     slowly heat and expand, which would drop its reactivity, 
     which would cause it to cool. Hydrated mixtures also 
     generally have negative temperature coefficients. Moreover, 
     the first time the mixture underwent this cycle, it would 
     drive off the water, after which it would be left far below 
     critical, dry, and with no mechanism for the reinsertion of 
     water. Thus, there is nothing new in ``Criticality Issues,'' 
     it simply repeats the stability errors made in ``Nuclear 
     Excursions.''
       There are some interesting tradeoffs between the negative 
     temperature coefficient of such mixtures from expansion and 
     the potentially small positive coefficient from absorption 
     and Pu-239 resonance broadening, but those effects are 
     delicate and comparable even at high hydration. 
     Unfortunately, they cannot be evaluated from the calculations 
     in ``Criticality Issues,'' which were apparently all 
     performed for cold soil, pure SiO2, and pure Pu-239. All 
     three of those restrictions would have to be removed to 
     provide an assessment beyond that in ``The Myth of Nuclear 
     Explosions at Waste Disposal Sites.'' Given the simplicity 
     and ease of monitoring for the development of the conditions 
     postulated, that is readily addressed.


                             energy release

       Even if dispersion and criticality are assumed, the 
     conclusion that an explosion would occur is incorrect. 
     ``Nuclear Excursions'' postulates ``auto-catalytic'' behavior 
     in which the release of energy leads to greater criticality, 
     but the discussion above shows that in dry repository 
     material, the release of energy instead reduces criticality 
     and shuts the reaction off. ``Criticality Issues'' postulates 
     autocatalytic behavior in hydrated mixtures, but the 
     discussion of the previous section shows that to the extent 
     that the phenomena has been quantified by earlier work, the 
     release of energy reduces criticality there, too.
       The postulated mechanisms for explosion are not credible; 
     the most that appears possible is heating and evaporation of 
     some water before a smooth shut down. There is no credible 
     mechanism for releasing energy on a time scale short enough 
     for even a steam explosion. A nuclear explosion must make the 
     transition from critical to highly supercritical in a 
     fraction of a second. A credible means to force the 
     transition in a repository has not been found. Thus, the 
     assertion that an explosion would occur is incorrect.
       Even if dispersion, criticality, and energy release are 
     assumed, which appear virtually impossible on the basis of 
     the arguments above, there would be no serious consequences 
     elsewhere in the repository or on the surface. Calculations 
     indicate containment volumes very small compared to the 
     nominal spacing between storage elements; thus, there could 
     not be any coupling between storage elements or any 
     possibility of greater energy releases through synergisms.


                        relation with other work

       That the critical mass may be reduced by dilution by 
     moderating material discussed in the paper is well understood 
     by the nuclear community. Fermi used it to full advantage 
     when he assembled the first pile under the grandstand at 
     Stagg Stadium.
       Fermi also used the advantages of heterogeneity in 
     minimizing resonance losses in natural uranium, although that 
     is irrelevant to the discussions of Pu reactivity here.
       The National Academy of Science report does not suggest 
     emplacement of weapons plutonium in the manner discussed by 
     ``Nuclear Excursions,'' although it did comment on the 
     advantages of higher fissile loading. The Academy was alert 
     to the potential for criticality and qualified its 
     recommendations by stating that further analysis and 
     discussion were needed before deciding on the best and safest 
     geologic disposition of weapons and reactor spent fuel.


                                summary

       We should always be alert to unintended consequences and 
     open to discussions that illuminate potential dangers in 
     nuclear waste storage. ``Nuclear Excursions'' argued that 
     there were serious dangers in proposed repository concepts. 
     We disagreed with the paper's major assumptions and found its 
     major conclusions to be incorrect for fundamental, technical 
     reasons, which were stated in detail and in writing. 
     ``Criticality Issues'' did not respond to those reasons, but 
     introduced a new scenario, in which it made the same 
     technical errors in a new context. We have pointed those 
     errors out above. At this point we find no technical merit in 
     either paper. However, the papers treat technical matters and 
     apparently contain no classified material; thus, in accord 
     with the laboratory's policy of open and unrestricted 
     research and discussion on unclassified matters, the authors 
     should be free to submit their paper for publication in a 
     peer reviewed journal.
       That said, we do not find any value in these two papers 
     that would justify publication in their current form, and we 
     do not see how to produce such a paper from them. They 
     contain fundamental errors in concept and execution. They 
     show no grasp of such elementary concepts as the time scale 
     for the approach to criticality and energy release and the 
     crucial role of the negative temperature coefficient of the 
     mixtures treated. Worse, they show no appreciation of these 
     points even after they were pointed out forcefully in the 
     review. That is compounded by the constantly shifting 
     scenarios in the papers and the alarmist estimates of 
     potential effects, which have become less credible and more 
     shrill throughout this process.
       The authors apparently show little interest in technical 
     suggestions or inclination to respond to it. Thus, it would 
     not appear to be useful to continue this one-sided 
     discussion, which we take to be concluded. If this program is 
     continued, and these individuals remain associated with it, 
     the laboratory would be well served by establishing a 
     permanent red team, funded by this program and composed of 
     independent members from the cognizant technical divisions, 
     and giving them the responsibility of checking each 
     calculation done by them.
  Mr. ASHCROFT. Mr. President, the following unanimous consent requests 
have been agreed to by the minority leadership, as well as the 
majority.




                          ____________________