ML20247K418

Assessment of Us Regulations for Fissile Exemptions & Fissile Matl General Licenses

ML20247K418
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Issue date:	05/10/1998
From:	Phil Brochman, Easton E, Parks C NRC, OAK RIDGE NATIONAL LABORATORY
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NUDOCS 9805220093
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l ASSESSMENT OF THE U.S. REGULATIONS FOR FISSILE EXEMPTIONS AND FISSILE MATERIAL GENERAL LICENSES J

C. Y. Parks (1), C. M. Hopper (1), J. J. Lichtenwalter (1), E. P. Easton (2), and P. G. Brochman (2) l (1) ORNL,* P. O. Box 2008, Oak Ridge, TN, USA 37831-6370 l

(2) USNRC, M/S-06F18, Washington, DC, USA 20555 l

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To be presented at PATRAM'98 Conference The 12th International Conference on the Packaging and Transportation of Radioactive Materials Paris, FRANCE May 10-15,1998; to be published in the Proceedings.

The submitted manuscript has been authored by a contractor of the U.S. Government under contract No. DE-AC05 960R22464. Accordir. gly, the U.S. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.

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' Managed by Lockheed Martin Energy Research Corp. under contract DE-AC05-960R22464 with the U.S. Department of Energy.

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ASSESSMENT OF THE U.S. REGULATIONS FOR FISSILE l

EXEMPTIONS AND FISSILE MATERIAL GENERAL LICENSES

• C. V. Parks (1), C. M. Hopper (1), J. J. Lichtenwalter(1), E. P. Easton(2), and P. G. Brochman(2) l (1) ORNL, P. O. Box 2008, Oak Ridge, TN, USA 37831-6370 l

(2) USNRC, M/S-06F18, Washington, DC, USA 20555 l

SUMMARY

The paragraphs for general licenses for fissile material and exemptions (often termed exceptions in the international community) for fissile material have long been a part of the U.S. Code of Federal Regulations (CFR)-10 CFR Pan 71," Packaging and Transportation of Radioactive Material." Although Part 71 has been revised to provide consistency with the 1985 Edition of the IAEA Regulationsfor the Safe Transport ofRadioactive Material (IAEA 1985), general licenses i

that provide for transport of fissile material in nonapproved packages or controlled shipments l

remain a part of Part 71. More recently, the Nuclear Regulatory Commission (NRC) issued a j

final mle on Part 71 via emergency rule-making procedures (Federal Register 1997) in order to address an identified deficiency related to one of the fissile exemptions. To address the specified deficiency in a general fashion, the emergency rule adopted the approach of the 1996 Edition of r

the IAEA: Regulationsfor the Safe Transport ofRadioactive Material (IAEA 1996), which places restrictions on certain moderating materials and limits the quantity of fissile material in a consignment. The public comments received by the NRC indicated general rgreement with the need for restrictions on certain moderators (beryllium, deuterium, and graphite). The comments indicated concern relative to both the degree of restriction imposed (not more than 0.1% of fissile material mass) and the need to limit the fissile material mass of the consignment, particularly in light of the subsequent NRC staff position that the true intent (consistent with l

draft IAEA advisory infonnation) was to provide control for limiting the fissile mass of the conveyance.

Even though the NRC emergency rule remains in place, staff at Oak Ridge National Laboratory l

(ORNL) are working with the NRC staff to perform a coherent review and documentation of the technical and licensing bases for the general licenses for fissile material and the fissile material l

exemptions. The pmpose of the review is to identify potential deficiencies that might be adverse to maintaining adequate subcriticality under normal conditions of transport (NCT) and hypothetical accident conditions (HAC). In addition, ORNL has been asked to identify changes that would address any identified safety issues, enable inherently safe packages to continue to be unencumbered in transport, and seek to minimize the impact on current safe practices. This paper will examine the complex issues that must be addressed in the assessment and will discuss potential recommendations under consideration.

• This work was performed by Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. for the U.S. Department of Energy under contract number DE-AC05 960R22464.

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BACKGROUND In 1992 the IAEA formed a Consultants Services Meeting (CSM) to review and address Member State comments and identified issues related to criticality safety requirements and criticality safety controls provided in the 1985 Edition of the IAEA Regulations. For the next three years issues related to fissile material exemptions were constantly on the agenda at the subsequent CSMs on criticality safety issues and the pertinent Revision Panel Working Groups. The identified problem that opened the discussion was the concem that carriers would be provided a large quantity of packages containing fissile-exempt quantities that, taken as a whole on one conveyance, could provide an unacceptable risk to criticality safety.

As one might imagine, the issue of changing basic exemptions that had been a part of the regulations since inception and which had not previously posed any known safety risk during transpon created some very intense discussions: How could the exempt fissile material be altered credibly be altered during loading and transport to cause a criticality concem? During the discussions it became apparent that there had been shipments where (intentionally or unintentionally) the accumulation of exempted 15-g packages had yielded an tmacceptable quantity of uncontrolled fissile mass on one conveyance. This identified case together with questions regarding credible changes to the loaded mr.terial during transport (normal and accident) led to the agreement to propose a method to control the quantity of fissile material in a shipment. Because of strong arguments against incorporating transport controls (e.g., a criticality safety index) in shipments of exempted packages, the 1996 Edition of the IAEA Regulations adopted wording that limits the quantity of exempt fissile mass per consignment.

This change was perceived as an ad hoc control that would minimize impact on existing operational practice while limiting the fissile mass per conveyance (since Member State experts did not envision multiple consignments being provided to a carrier for a single conveyance).

The second change in the 1996 Edition of the IAEA Regulations related to fissile material exemptions was that beryllium and deuterium were restricted to 0.1% of the fissile mass. This proposed change came very late in the revision process and was accepted because it was recognized that the mass concentration limits provided per consignment were inadequate if these two materials were present to any significant degree. There was no technical basis for the 0.1%

other than to ensure that the quantity was insignificant. Graphite, in its purest form, can also significantly reduce the mass concentration needed for criticality; however, concem over limiting waste shipments rich in carbon caused this material not to be considered until further study could be performed.

In 1996, an USNRC licensee informed the NRC staff of a potential situation where one of the fissile material exemptions in Part 71 would not have been adequate for criticality safety concerns if shipped in large quantities in the presence of beryllium (NRC 1996). The material being considered for transport was a uranium-beryllium filtercake, a waste product of a process involving weapons-grade uranium materials. The filtercake met the fissile material exemption i

l provisions of Part 71 and the 1985 Edition of the IAEA Regulations, but the presence of beryllium caused large volumes oflow concentration material to exceed safe values (Green 1997). Alerted to a potential practical transport situation where the regulations were deficient, the NRC initially issued an information notice (NRC 1996) and subsequently issued an eraergency rule (FederalRegister 1997) that effectively adopted the fissile material exemptions of the 1996 Edition of the IAEA Regulations and added graphite to the list of restricted I

moderators. The NRC emergency rule also modified the general licenses for limited quar.tities per package and per shipment to restrict the identified moderators.

REVIEW OF THE ISSUES One of the basic premises of the transport regulations is that subcriticality be maintained under normal conditions of transport (NCT) and hypothetical accident conditions (HAC). The regulations attempt to ensure that subcriticality by specifying requirements that must be met for l

packages containing fissile material and implementing operational controls (e.g., transport index) for the shipment. The package requirements seek to ensure that the chemical, physical, and material conditions of the package necessary for suberiticality are maintained under NCT and HAC. The operational controls have been implemented to allow straightforward procedures for sefe handling of the packages by transportation personnel who are not criticality specialists.

To be exempt from the requirements and controls for packages containing fissile material, both the NRC and the IAEA regulations specify that the fissile material must be less than certain quantities (e.g.,15 g per package) or meet prescribed conditions related to concentration (e.g.,

5 g in a 10-liter volume), homogeneity, enrichment etc. The general licenses for fissile material provided in the United States per Part 71 also dispense with the requirements for packages containing fissile material if the fissile material quantity is limited per package or controlled shipment and certain select conditions on the contents or package are met. Fissile material quantities with and without moderator limitations (beryllium, deuterium, and hydrocarbon oils excluded and carbon limited to 7.7 times the total mass of *U and plutonium) are provided in tables. A prescription for determming a transport index to provide shipment control is provided with the general license for packages.

The requirements and controls for certified packages containing fissile material are constantly under scrutiny as the knowledge base and experience are expanded because of the need to perform and submit package safety assessments for review and because of the oversight provided each shipment. Similar scrutiny has not been applied to the fissile exemptions or general license provisions, nor has there been a mechanism to expand the knowledge base or practical experience associated with allowed shipments. However, for years criticality specialists have postulated a number of situations where the conditions specified by the exemptions might not be sufficient in themselves to prevent a potential for a critical or near-critical situation (Mennerdahl 1996 and Shaeffer et al.1997) under NCT or HAC. For example, the basis of safety for the HAC is not theoretically justified for an exempt concentration of 5 g of fissile material per 10 liters of contaminated combustibles if one has a large volume and considers the effect C a fire, concentration of the fissile material, and moderation.

The potentially unsafe situations reviewed by Mennerdahl and Shaeffer et al. are generally characterized by large volumes, lack of absorbing impurities, and/or the presence of very selective materials. With the consignment mass limitation and the moderator restrictions in the 1996 Edition of the IAEA Regulations and the emergency rule issued by the NRC, there was an tempt to address these known situations that could compromise safety. However, although 3entified situations of potential safety concem have been addressed, some might question the need for the changes based on " practical" aspects of a shipment. Similarly, ShaefTer et al. present impacts of the changes that need to be considered: The applicability of using 0.1% of the fissile mass as the measure to restrict selected moderators (e.g., it could remove some small quantity, inherently safe packages from exempt status) and the increased number of shipments and/or measurement scrutiny that may be needed to abide by the consignment mass limitation.

The objectives of the current assessment are broader than simply addressing issues such as those discussed by Shaeffer et al. Instead, the assessment seeks to do the following:

1. Perform a review of the regulations (exemptions and general licenses) to document the technical basis and identify any potential deficiencies that might be adverse to criticality safety.

2. Address the question of whether shipments that use the fissile exemptions and general licenses provide similar ensurance ofpublic health and safety as that provided by shipments with packages meeting the requirements for fissile material contents.

3. Identify areas where regulatory wording might cause confusion among licensees and potentially lead to safety concerns.

4. Provide justifiable technical and licensing basis for either using the existing regulations or changing the regulations as recommended based on the findings ofitems 1 through 3. As appropriate, practical aspects of transportation or licensing that could mitigate, justify, or provide a historical basis for any identified potential deficiencies will be considered.

Recommendations to change the current regulations should seek to minimize the impact on current safe practice while correcting identified deficiencies.

The approach has been to consider the potential for simplifying the regulations on fissile material exemptions and fissile material general licenses, removing possible conditions that may present identified safety concems without excluding shipment conditions that are inherently safe, and providing a technical basis for future reference.

ASSESSMENT OF PRACTICES Discussions with various licensees have revealed that multiple consignments, individually qualifying as fissile material exemptions, have been offered (by single consignors) for transpo t on a single conveyance, thereby potentially exceeding a mmimum suberitical mass of fissile material. The logic behind the limit on fissile mass in a consignment was that a consignor would not typically provide multiple consignments to a carrier. In the United States the carriers have been dividing their waste material for transport into separate consignments because the receiving site that disposes of the material below ground can only handle 350 g on-site above ground.

Thus, multiple consignments on a transport allow the transport vehicle to remain at the site boundary while each single consignment is brought on site and disposed. This practice and the associated regulations that " encourage" it are beyond the scope of this paper, but note that the practice was perfectly legitimate under previous regulatory rules and could be interpreted as legitimate under the wording of the current rule. The occurrence of this practice would potentially indicate that shipment control should be extended to cover the conveyance and not be limited to the consignment.

In general, it has been difficult to obtain feedback on the recent NRC rule change, not because of a resistance from shippers, but because they do not seem to have fully assessed the impact of the changes and their effect on future shipments. It is suspected that U.S. Department of Energy (DOE) sites may have concem with the moderator exclusion portion of the rule change because they are more likely to transport small-quantity fissile packages with some amounts of the excluded moderators. Discussions of the changes in the regulations, together with interpretations of the nature of the implications have, as much as anything, invoked incredulous responses: Why has this been done? Haven't these types of shipments been made safely for years? Is there some other method wl.erebyl can ship this material and still be exempt?

b ASSESSMENT OF THE REGULATORY LANGUAGE The bases for and clarity of the general licenses for fissile material and the exemptions for fissile material in Part 71 (and correspondingly, the IAEA regulations) have become increasingly confusing with adjustments and accommodations of the regulations over time, as well as with shipper (consignor) interpretations and applications.

Although many of the specifications in the fissile material exemptions have a tie to readily available information on critical safe parameters, it is clear that an understanding of the tie between this information and acceptable practice has sometimes been obscured. For example, the advisory material developed (available as final draft; not published to date) for the 1996 Edition of the IAEA Regulations gives some background on the 15-g-per-package limitation in the fissile exemptions. The 15-g value was derived from analysis of 2501-liter packages considering only water moderation. Although 15 g in a package is safe, it is obvious from the latest regulatory changes that the need to prevent a large accumulation of packages was lost to the practitioner over the years.

It would be difficult to fonnulate a definitive argument that the transport safety criteria for fissile material general licenses and exemptions for fissile material conform to the transport safety criteria imposed by the standard requirements and controls for packages containing fissile material. Limiting conditiens for the general licenses and fissile material exemptions do not clearly correlate with subcriticality and safety for the packaging and transportation of fissile material under both NCT (where five times the number of undamaged packages per shipment is adequately subcritical) and HAC (where two times the number of damaged packages per shipment is adequately subcritical). In other words, it is easy to conceive ofinstances (perhaps not altogether practical, but nevenheless allowed by the regulations) where the margin of safety provided by a shipment exempted from classification as fissile material is less than that provided by the shipment of a package certified for transport of fissile material.

Various instances occur in the fissile material exemptions where the intent of both Part 71 and the IAEA regulations can be questioned or, perhaps worse, misunderstood, especially in the use of qualifying words. For example:

1. One must consider the presence of material with average hydrogen density less than or equal to water. What procedure should be used to determine the average?

2. The fissile material must be distributed homogeneously throughout the package contents and not form a lattice arrangement. The distinction between homogeneous and heterogeneous can be very difficult to ascertain, yet the classification can have a distinct impact on criticality safety.

In addition, in the United States, the licensee is subjected to possible confusion because of the differences between the wording used in the Department of Transponation regulations and the NRC regulations. Consistency in definition and stated intent needs to be provided.

j POTENTIAL CRITERIA MODIFICATIONS A fundamental question to address when considering criteria modifications is whether the exemptions for fissile material must be inherently safe based on improbable events and theoretical bases or can credible realistic arguments be formulated about what can and will be

shipped or what can and will happen. The latter approach seems to be the oasis for the initial formulation of the exemptions and general licenses for fissile material. The difficulty here is that "what can and will be shipped" changes with the needs of the industry and "what can and will happen" varies with the shipper and the conditions of shipment. Taking a strict theoretical approach leads one to criteria that are viewed as unreasonable based on historic practices and safety records.

As an extreme example, consider Part 71 and the 1985 Edition of the IAEA Regulations where 70 Bq/g is the radiation limit below which the regulations do not apply. Assumirig some 235 extrapolation of critical mass curves for uranium enriched to 93 wt %

U, one can estimate that about 800 liters (less than 1 m') of BeO can be brought to critical with a uranium concentration that would be less than the radioactive material exemption limit. Obviously, obtaining the purity of BeO and uranium needed throughout such a large volume is not a simple task and the practicality of having a safety problem is extremely remote, but it appears that the exemption limit was developed with little sensitivity relative to potential criticality safety concems. And to categorically state that such a system would not be considered for transport would be unfounded based on the recent issue surrounding the uranium-beryllium filtercake.

The approach currently being applied in this assessment is to develop theoretically defensible arguments that seek to incorporate practical constraints and consistency with the licensing concepts of the requirements and controls for packages containing fissile material. The first phase of the work is to investigate the technical basis of the existing criteria for the fissile material exemptions and general licenses. The review indicates that the criteria for the exemptions are valid for the 1996 Edition ofIAEA Regulations and the recently revised Part 71. The technical bases for the criteria are discussed in the advisory material that will soon be published for the 1996 Edition of the Regulations. As indicated earlier, the criteria assume water moderation and no change of conditions during transport. Additional work is needed to determine criteria for a revision of the 0.1% restriction on admixing of materials such as beryllium, deuterium, or graphite.

Some of the existing criteria for the general licenses for fissile material are somewhat more 235 tenuous. For example, the permissible mass limits based on U enrichment and uniformity (homogeneous vs heterogeneous) appear to be consistent with early reference material (Paxton et al.1964) but not with more recent revisions of the same report (Paxton and Pruvost 1986).

Obviously, if nothing else is altered, these criteria should be investigated and changed as needed based on the most recent technical information related to critical systems.

To this end ORNL has initiated work to calculate concentration and mass criteria that will maintain suberiticality for homogeneous and heterogeneous systems. Potential criteria are being derived by considering the following combination of parameters:

fissile nuclides: 23'U,235U, 2Pu,2 cpu, or a combination thereof; typical moderator materials: CH, H 0, D 0, BeO, soil (SiO ), Be, or a combination thereof; 2

2 2

2 2"U enrichment; infinite systems and finite systems; heterogeneity / homogeneity; and packaging materials (iron, wood, etc.).

235 Initial considerations have been directed towards infinite homogeneous systems of U metal with the listed moderating materials. Insight gained from infinite system calculations has been

6 applied to finite-system calculations in order to narmw the number of calculations. The finite systems will be used to consider recommended changes to the general licenses. For homogeneous systems of finite volume, the volume is taken to be limited by that available in a typical tractor trailer and the calculated effective neutron multiplication factor is limited to 0.93 after consideration of appropriate bias and uncenainties. Optimum interspersed moderation and close-water reflection are being considered for all finite system calculations. Package-specific calculations of arrays of damaged 110-gal.,20-gauge steel, tight-head steel drums are being evaluated to ascertain the effect of packaging materials on reactivity. Wood boxes may also be considered as needed. With the exception of uranium and water, the contents of the damaged package are assumed to be compacted and to constitute a more realistic 60% of the bulk volume, leaving a void fraction of at least 40% available for water flooding.

The initial set of analyses focus on fully enriched uranium as the prototypic system that can be used to formulate and test possible recommendations for future revisions to the regulations.

Subsequent to selecting final recommendations, this process will be repeated using other uranium enrichments and fissile materials beside 23nU, and for heterogeneous systems as the need arises.

CONCLUSIONS The 1996 Edition of the IAEA Regulations and the recent changes to Pan 71 provide some needed modifications that will help ensure that fissile material transponed under exemption and general license clauses will not present a potential criticality safety concern. However, the reduced regulatory oversight provided to exempt and general license shipments makes it imponant that the technical and licensing basis for these portions of the regulations be well documented and understood by the transport community. The need for clear, unambiguous, and straightfonvard specifications and language in the regulations is ofparamount importance.

The current assessment has confirmed that there are no routine or significant criticality safety hazards associated with the practical applications of the general licenses and exemptions. The reason for this conclusion is that the typical qualifying fissile material matrix in a general license or exempt consignment is relatively stable as dry, activated waste or in a nearly noncombustibk form. The primary concern is that the fissile material general licenses and exemptions do not have a theoretically defensible equivalency of safety with shipments that must meet the requirements and controls for fissile material. In addition, confusion over what is intended by the general provisions and exemptions could lead to unsafe practices. Countering these concems is the fact that the tight restriction on deuterium, beryllium, and graphite is so low as to exclude inherently safe packages of fissile material from being exempt. In fact, the restriction of deuterium to 0.1% of the fissile mass can even prevent some inherently safe, water-moderated shipments from being made as an exempted shipment.

The assessment work to date indicates that consideration needs to be given to providing some type of transport control (e.g., a transport index or criticality safety index) on exempt shipments in order to ensure adherence to a conveyance limit. It appears from a review of existing practices in the United States that a consignment limit is not altogether satisfactory for limiting quantities on a conveyance. Funhermore, it is obvious that restricting certain low-neutron-absorbing materials to less than 0.1% of the fissile mass is not a satisfactory approach because of the deuterium noted above and the potential to restrict transport of some inherently safe packages of very small fissile material quantities. There will also surely be a desire to provide for simple and easy transport of very small quantities of fissile materials for which any type of consignment or conveyance limit would not seem applicable. To provide defensible and straightforward limits

for the general licenses, additional analyses may need to be performed to develop and justify criteria that are consistent with current information on nuclear data and critical systems.

In light of both recent domestic and intemational situations where the transport community has presented practical examples that challenge the safety criteria of the regulations, it is felt that the current assessment of fissile material exemptions and general licenses will benefit future deliberations related to potential needs for regulatory changes.

This paper was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Govemment nor any agency thereof, nor any of their i

employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third party's use, or the results of such use, of any information, apparatus, product, or process disclosed in this paper, or represents that its use by such third party would not infringe upon privately owned rights. The views expressed in this paper are not necessarily 1

those of the U.S. Nuclear Regulatory Commission.

REFERENCES Federal Register. Fissile Material Shipments and Exemptions,10 CFR Part 71, Vol. 62, No. 27, February 10,1997.

Green, R. Nuclear Criticality Safety Concerns Related to Transport of U-BE0 Waste, Trans.

Am. Nucl. Soc., 76, pp. 256-257, Orlando, Fla., June 1-5,1997.

l IAEA Safety Series No. 6. Regulationsfor the Safe Transport of Radioactive Material,1985 Edition (As Amended 1990),Intemational Atomic Energy Agency, Vienna,1990.

IAEA Safety Standards Series No. ST-1, Regulationsfor the Safe Transport ofRadioactive Material,1996 Edition. Requirements. Vienna,1996.

Mennerdahl, D. Fissile Package Design Basis: Regulations or Analysis?, Proceedings oiThe 11* Intemational Conference on the Packaging and Transportation of Radioactive Materials (PATRAM'95), Las Vegas, Nev. (1996), pp. 449-456.

NRC Infonnation Notice 96-63. Potential Safety Issue Regarding the Shipment of Fissile Material, U.S. Nuclear Regulatory Commission, Washington, D.C., December 5,1996.

Paxton, H. C. et al., CriticalDimensions ofSystems Containing U'", Pu, and U'", Los. Alamos National Laboratory report TID-7028, Criticality Studies, June 1964.

Paxton, H. C. and Pruvost, N. L., Critical Dimensions ofSystems Containing U, Pu, and l

U, Los Alamos National Laboratory LA-10860-MS,1986 Revision.

l Shaeffer, M. K. et al., Recent Developments in Fissile Material Exemptions for Shipping Packages, Proceedings of the Criticality Safety Challenges in the Next Decade, American Nuclear Society, Chelan, Wash., September 7-11,1997, pp. 214-218.

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