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February 26, 1995

Dr. Hans Blix
Director General
International Atomic Energy Agency
Vienna, Austria

BY FACSIMILE: 43-1234-564

Dear Dr. Blix:

We are writing to express our deep sense of amazement and outrage that the IAEA is now apparently prepared to exempt fresh mixed-oxide (MOX) fuel from the strengthened ("Type C") packaging requirements for air transport which will be included in the 1996 revision of the IAEA Safety Series 6 (SS6), "Regulations for the Safe Transport of Radioactive Material." This exemption, which will be approved at a meeting of the TRANSSAC (successor to SAGSTRAM) Committee beginning on February 26 in Vienna, will clear the way for large quantities of MOX fuel to be transported by air in Type B casks, which are not designed to withstand the stresses to which they would be subjected in a high-velocity airplane crash. This dangerous loophole is to be formalized in SS6 through the Agency's adoption of Germany's flawed proposal to define a new category of "low dispersibility material" (LDM), which is likely to include fresh MOX fuel.

Given that the Agency has acknowledged the practice of shipping plutonium by air in un-crashworthy casks raises serious safety questions, and that it has spent a great deal of time and effort in developing a more stringent (albeit inadequate) air transport standard, it is bizarre that it would then propose exempting MOX fuel from the new standard unless a new and exceptionally compelling safety case could be articulated. However, the LDM concept proposed by Germany by no means serves this purpose. Our analysis of this proposal indicates that its "technical" basis is a potpourri of unsubstantiated assertions, hand-waving and crude back-of-the-envelope estimates, with no discussion of the large uncertainties that often render such calculations meaningless. Christian Kppers of the ko-Institut in Darmstadt has conducted his own analysis and concludes that "the German position on Type C casks and LDM cannot be accepted as the basis of a sufficient radiation protection standard." We concur with this assessment.

Furthermore, there is evidence that the LDM performance parameters were not derived from a safety analysis, but were set specifically so that MOX fuel would be able to qualify a priori as LDM. This makes the commercial impetus for adoption of the LDM concept even more obvious. Indeed, the Agency has made no attempt to conceal this motivation, as the following quote from the Fourth Technical Committee Meeting, held in September 1995, illustrates:

"The difficulties, (or the alleged impossibility in some cases,) of producing of [sic] Type C packages and their high production costs were cited as supporting the need for the adoption of the [V]LDM concept."

Given the apparent commercial bias of this regulatory proceeding, we ask, in the interest of protecting public health and safety, that you promptly circulate this letter (and accompanying technical note) at the TRANSSAC meeting, and request that a decision on the LDM proposal be deferred until it has undergone a thorough and independent peer review, which should include consideration of the issues raised here.

One of the chief flaws of the proposed definition of LDM is the maximum permissible airborne release of radioactivity from the material under aircraft accident conditions: 100 A2 in "gaseous and particulate forms of up to 100 m aerodynamic equivalent diameter (AED)." This value is not consistent with the permissible release from a Type C cask following an airplane crash (A2 per week, with no restriction on particle size). Therefore, it cannot be assumed that the level of safety associated with air transport of LDM in Type B casks would be equivalent to that of Type C casks.

Two lines of reasoning have been offered to reconcile this inconsistency, and neither of them is convincing. The first is the justification given by the German position paper, which is that dispersion of the initial release would lead to "acceptable" maximum radiation exposures of 50 milliSieverts (mSv) at 100 m downwind from the accident site. This is clearly incompatible with the Q- system methodology, which must take into account the possibility of an individual who may remain within 1 m of a damaged package for 30 minutes. Mr. Kppers points out that for a near ground-level release, the dose commitment at 50 m from the release site would exceed that at 100 m by a factor of 50. Furthermore, the dispersion calculations provided in the German paper do not take into account variations in the atmospheric conditions, which in the most unfavorable case could result in radiation exposures exceeding those given by two orders of magnitude.

The second argument is that credit should be assigned to the residual containment function that a Type B cask may retain following an airplane crash. The problem with this approach is that there is very little information about how Type B casks would perform if subjected to the mechanical and/or thermal stresses resulting from an aircraft accident. To verify this hypothesis, a Type B cask would have to be tested to Type C conditions to demonstrate the extent to which it is still able to provide containment. At a minimum, such a test must be included in the revised SS6 if the LDM concept is to have any validity. In the absence of technical data, the notion of "graceful failure", e.g. that Type B casks will probably survive much more severe accident conditions than those for which they are designed and tested, is merely speculation.1

Since the proposed LDM permissible release of 100 A2 has no apparent relation to to safety considerations, what then is its origin? In the technical note attached to this letter, we provide evidence that German federal safety authorities developed the LDM definition by adjusting it to conform to information they had regarding the dispersibility of MOX fuel, rather than by determining the maximum permissible release from LDM that would lead to a level of safety consistent with the other transport operations regulated in SS6.

We are disturbed that such a shoddy piece of work has already been approved by the SAGSTRAM committee, over the objections of the United States delegation, which also pointed out the arbitrary nature of the proposed 100 A2 release. We ask again that the IAEA submit this important issue to much more rigorous scrutiny before putting the world's public at risk from large-scale air shipments of plutonium in casks that cannot survive a high- velocity crash.



Paul Leventhal, President

Edwin Lyman, Scientific Director

Nuclear Control Institute

Technical Note: Origin of the LDM Definition

It is instructive to cite a paper from the German Gesellschaft fr Reaktorsicherheit (GRS) from 1993, "Comparative Risk Evaluation of Air and Highway Transport of Unirradiated FBR Fuel Elements," by D. Grndler and F. Lange (the latter being one of the co-authors of the German LDM proposal). In this paper, it is estimated that approximately 0.57 g of respirable plutonium (AED <10 µm) would be released from the crash of a plane carrying 184 kg of plutonium contained in 482 kg of FBR MOX fuel (35% Pu) due to the mechanical impact alone, assuming that the shipping cask is completely destroyed. Our calculations indicate that this would correspond to a release of approximately 3 g of dispersible plutonium (AED <100 µm) from a cargo of LWR MOX fuel (5% Pu) containing the same amount of plutonium (approximately 8 fuel assemblies), using a log-normal particle size distribution determined from impact tests of uranium dioxide,2 and assuming that the same quantity of fuel is released in both cases. This should be compared to the A2 value for reactor-grade plutonium given by the 1996 revision of SS6, 0.06 g. It is clear that according to the German estimates, MOX fuel could not qualify as LDM unless the maximum dispersible release permitted were set at a value on the order of 100 A2.

End Notes

1. It appears that the the "graceful failure" concept, used in IAEA TECDOC-702 ("The air transport of radioactive material in large quantities with high activity") to derive the very important exemption values from Type C requirements for "ordinary" and "special form" materials, is based on the results of a single paper which purports to show that a "representative" Type B cask will not release more than 5% of its contents even if subject to impact speeds over 130 m/s. Even if one accepts this questionable result, it has no bearing on the equally important issue of package response to thermal environments more severe than Type B conditions. Because of the widespread use of elastomer seals in Type B packages, which lose their sealing function in the 250-300 degrees C range, these packages may rapidly lose their sealing ability under such conditions. Back to document

2. T.L. Sanders, et al., "A Method for Determining the Spent-Fuel Contribution to Transport Cask Container Requirements," SAND90-2406, Sandia National Laboratories, November 1992, p.IV-12. Back to document

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