[Federal Register Volume 64, Number 181 (Monday, September 20, 1999)]
[Proposed Rules]
[Pages 50778-50781]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-24254]


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NUCLEAR REGULATORY COMMISSION

10 CFR Part 61


Proposed Compatibility Designation Change and Draft Emplacement 
Criticality Guidance for Low-Level Waste

AGENCY: Nuclear Regulatory Commission.

ACTION: Request for comment.

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SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is requesting 
public comment as to whether the compatibility designation of 10 CFR 
61.16(b)(2) should be changed. The compatibility designation relates to 
the extent which an Agreement State's regulations must be compatible 
with NRC requirements. The section of the Commission's regulations 
under consideration requires low-level waste (LLW) disposal facility 
licensees who receive and possess special nuclear material (SNM) to 
describe proposed procedures to avoid accidental criticality for 
storage of SNM waste prior to disposal and after disposal in the 
ground. In addition, NRC also is requesting comment on draft guidance 
on emplacement criticality at LLW disposal facilities.

DATES: Submit comments by October 20, 1999. Comments received after 
this date will be considered, if it is practical to do so, but 
assurance of consideration can only be given to comments received on or 
before this date.

ADDRESSES: Submit comments to David L. Meyer, Chief, Rules and 
Directives Branch, Division of Administrative Services, Office of 
Administration, U.S. Nuclear Regulatory Commission, Washington, DC 
20555. Hand deliver comments to 11545 Rockville Pike, Rockville, MD 
between 5:15 am and 4:30 pm on Federal workdays.
    You may also provide comments via the NRC's interactive rulemaking 
website through the NRC home page (http://www.nrc.gov). From the home 
page, select ``Rulemaking'' from the tool bar. The interactive 
rulemaking website can then be accessed by selecting ``New Rulemaking 
Website.'' This site provides the ability to upload comments as files 
(any format), if your web browser supports that function. For 
information about the interactive rulemaking website, contact Ms. Carol 
Gallagher, (301) 415-5905; e-mail [email protected].
    A copy of the draft guidance (NUREG/CR-6626, Emplacement Guidance 
for Criticality Safety in Low-Level Waste Disposal) can be obtained 
from the Internet at ``http://ruleforum.llnl.gov,'' or contact Mr. Tim 
Harris (see FOR FURTHER INFORMATION CONTACT).

FOR FURTHER INFORMATION CONTACT: Tim Harris, Office of Nuclear Material 
Safety and Safeguards, U.S. Nuclear Regulatory Commission, Washington 
DC, 20555, telephone (301) 415-6613, or e-mail at [email protected].

Background

    Section 274 of the Atomic Energy Act of 1954 (AEA), as amended, 
provides a statutory basis for discontinuance by the NRC, and the 
assumption by the State, of regulatory authority for byproduct 
material, source material, and SNM in quantities not sufficient to form 
a critical mass. As stated in the Commission's Policy Statement on 
Adequacy and Compatibility of Agreement State Programs (62FR46517, 
September 3,1997), NRC and Agreement States have the responsibility to 
ensure that there is adequate protection of public health and safety 
and that radiation control programs are administered consistent and 
compatible with NRC's program.
    Quantities of SNM not sufficient to form a critical mass are 
defined in 10 CFR 150.11 as enriched uranium not exceeding 350 grams, 
uranium-233 not exceeding 200 grams, plutonium not

[[Page 50779]]

exceeding 200 grams, or mixtures where the sum of the fractions is less 
than unity. These quantities of SNM can be regulated by the Agreement 
States. In both Agreement States and non-Agreement States, an NRC 
license is required for persons who possess quantities of SNM in excess 
of the Sec. 150.11 limits. As it pertains to disposal facilities, the 
possession limits apply to material above-ground. Once the SNM waste is 
disposed of (i.e., placed in the disposal trench), SNM waste is not 
restricted by the Sec. 150.11 limits.
    Currently 10 CFR 61.16 is not a regulation required for Agreement 
State adoption; therefore, there is no equivalent Agreement State 
regulatory requirement for Agreement State licensees of existing or 
future LLW facilities to follow the equivalent of Sec. 61.16(b)(2) and 
to evaluate emplacement criticality safety. This section of 10 CFR Part 
61 requires LLW disposal facility licensees who receive and possess SNM 
waste to describe proposed procedures to avoid accidental criticality 
for storage of SNM waste prior to disposal and after disposal in the 
ground. Although the SNM mass limits in Part 150 restrict above-ground 
possession and ensure criticality safety above-ground (during receipt 
and storage), there is no equivalent mass restriction or other controls 
which limit the amount of SNM waste that can be placed in a disposal 
trench; and therefore, the question of criticality safety below-ground 
after disposal is left open. A technical basis for NRC's concern 
regarding emplacement criticality safety is presented in the DISCUSSION 
section of this document.
    LLW containing SNM is currently disposed of at three facilities: 
Barnwell, South Carolina; Hanford, Washington; and Clive, Utah. All of 
these facilities are licensed by Agreement States. From the 1970's to 
1997, NRC licensed the Barnwell and Hanford facilities under 10 CFR 
Part 70, to receive, possess, store, and dispose of kilogram quantities 
of SNM waste. In 1997, these facilities requested that the SNM 
possession limits be reduced to the Section 150.11 limits, and that NRC 
licenses be transferred to the respective Agreement States. These 
actions have been taken for both (Barnwell and Hanford).
    The State of Washington incorporated NRC criticality controls for 
emplaced waste in license conditions in its Hanford license. Although 
not in the license, the State of South Carolina has required the 
licensee to implement the SNM waste emplacement procedures that address 
criticality safety. These procedures cannot be changed by the operator 
without State approval. NRC recently issued an Order to Envirocare that 
exempts Envirocare from the licensing requirements in 10 CFR Part 70 
for possession of SNM waste at concentration limits in the Order, which 
ensures criticality safety. The conditions of the Order have been 
incorporated into the State of Utah license.
    If NRC changes the compatibility designation for Sec. 61.16(b)(2), 
then LLW disposal facility licensees would be required to develop 
procedures for avoiding accidental criticality, during both storage of 
SNM waste prior to disposal and after disposal in the ground. These 
procedures would then be reviewed and approved by Agreement State 
staffs. Given that licensees and Agreement State staffs may not have 
experience in criticality safety, NRC has developed guidance that could 
be used by licensees and Agreement State staffs to demonstrate 
compliance with Sec. 61.16(b)(2). A summary of this draft guidance and 
how the guidance is envisioned to be used are provided in the 
DISCUSSION section of this document.

Discussion

    This section presents a discussion of the following: (1) the 
technical basis for requiring emplacement criticality controls; (2) NRC 
staff's assessment of the compatibility designation for 10 CFR 
61.16(b)(2); (3) a summary of the draft guidance; (4) the envisioned 
implementation if the compatibility of Sec. 61.16(b)(2) is changed; and 
(5) NRC staff's assessment of potential resource impacts on Agreement 
States.

Technical Basis

    Spontaneous nuclear fission occurs naturally in a very small 
percent of radioactive decays in some elements. When fission occurs, 
neutrons are emitted, along with fission fragments (e.g., cesium and 
strontium). The neutrons that are produced may be absorbed by an atom 
without causing a fission, may be absorbed by an SNM atom and cause a 
fission, or may not collide with any atoms. SNM (i.e., uranium-235, 
uranium-233, and plutonium) is unique from most materials in that a 
fission, not associated with a radioactive decay, can occur when a 
neutron collides with its nucleus. In natural materials such as soils 
containing natural uranium, neutrons produced by spontaneous fission 
are typically absorbed by uranium-238 atoms and do not collide with a 
uranium-235 atom possibly resulting in fission. Criticality is a chain 
reaction where large numbers of neutrons are produced, and can occur 
when sufficient SNM is present.
    For a criticality to occur, special conditions involving a number 
of factors must occur. Important factors that affect the criticality 
safety of a LLW disposal site are: (1) the isotope; (2) enrichment; (3) 
mass; (4) concentration; and (5) presence of neutron moderating and 
absorbing materials. Each of these is discussed below. (Following this 
is a discussion of these factors relative to possible scenarios).
    (1) Isotope: The SNM isotopes present in LLW are dependent on the 
waste stream. The vast majority of SNM waste is generated from the 
production of nuclear fuel for nuclear power plants and from LLW 
generated by nuclear power plants. Of the SNM isotopes, uranium-235 is 
the most common. Large quantities of plutonium and uranium-233 (the 
other SNM isotopes) are not present in the commercial waste. However, 
these materials are present in Department of Energy (DOE) facility 
waste, and some DOE waste is being shipped to commercial LLW disposal 
facilities.
    (2) Enrichment: Enrichment is a ratio of the weight of uranium-235 
to the weight of the total uranium and is commonly expressed as a 
percent. Natural uranium, found in most soils, has an average 
enrichment of 0.71 percent. In order to be used as nuclear fuel, 
natural uranium must be enriched in uranium-235. Most nuclear fuel is 
enriched to less than 6 percent, which is considered low-enriched 
uranium; however, some nuclear fuel for special reactors such as those 
in naval vessels is enriched to much higher values, which is considered 
high enriched uranium. At enrichments less than about 0.96 percent, 
criticality is not possible regardless of the mass or concentration. As 
enrichment increases, criticality becomes a greater concern. Although 
most of the SNM waste contains low-enriched uranium, some waste 
contains high-enriched uranium.
    (3) Mass: As discussed above, disposal facilities that are licensed 
by Agreement States and do not have an NRC license are subject to the 
SNM possession limits in Part 150 for above ground possession. These 
limits are based on a fraction of the minimum mass required to achieve 
a criticality. Under these limits, there is simply not enough SNM to 
cause a criticality regardless of the enrichment or concentration. 
However, these limits have been applied to above-ground possession, and 
SNM waste that has been disposed of is no longer be subject to these 
limits. Historic records at disposal sites indicate that some

[[Page 50780]]

disposal units (trenches) have a mass of uranium-235 in the hundreds of 
kilogram range. Therefore, it is reasonable to assume that large masses 
of SNM waste will be disposed of in disposal units in the future.
    In some cases, the mass of SNM in individual packages is limited by 
the requirements in Part 71 (Packaging and Transportation of 
Radioactive Material). The majority of SNM waste shipped to a LLW 
disposal facility is transported under 10 CFR 71.53 as ``fissile 
exempt.'' This means it does not have to comply with the fissile 
material package standards in Secs. 71.55 and 71.59. In order to be 
``fissile exempt'', the quantity of unusual moderators (beryllium, 
graphite, or deuterium) is limited as is either the mass per package, 
the amount of moderator (water), concentration, enrichment, or mass per 
consignment. For example, SNM waste can be shipped as fissile exempt, 
if it contains no more than 15 grams of SNM per package. However, some 
general licenses in Part 71 allow for SNM waste to be shipped at higher 
masses per package. For example,10 CFR 71.22 allows up to 500 grams per 
shipment, which could be in a single container, provided unusual 
moderators are limited to 0.1 percent of the mass of the fissile 
material. This general license does not restrict concentration or 
enrichment. Therefore, mass cannot be eliminated as a factor of concern 
based solely on packaging and transportation regulations. As mass 
increases, criticality becomes a greater concern.
    (4) Concentration: In some cases, the concentration of SNM received 
by a LLW disposal facility is limited by the requirements in Part 71. 
While significant quantities of SNM waste can be shipped under a number 
of general licenses, the majority of SNM waste shipped to a LLW 
disposal facility is transported as ``fissile exempt''. As noted above, 
in order to be ``fissile exempt'', the quantity of unusual moderators 
(beryllium, graphite, or deuterium) is limited, as is either the mass 
per package, the amount of moderator (water), the concentration, the 
enrichment, or the mass per consignment. For example, SNM waste can be 
shipped as fissile exempt, if it contains no more than 5 grams of SNM 
in any 10 liter volume. However, some general licenses in Part 71 allow 
for SNM waste to be shipped at higher concentrations per package. 
Therefore, concentration cannot be eliminated as a factor of concern 
based solely on packaging and transportation regulations.
    (5) Presence of neutron moderator and absorbers: Neutrons that are 
produced during a fission have a relatively high energy and are termed 
``fast'' neutrons. Moderators are materials that reduce the energy, or 
slow neutrons. This is important because uranium-235 is much more 
likely to be fissioned by slow neutrons than by fast neutrons. 
Therefore, the presence of moderator materials can increase the 
criticality concern. Elements such as hydrogen and carbon are 
particularly good moderators. Because water is abundant and is a very 
efficient moderator, assuming water is present is a common approach in 
evaluating the criticality significance of situations. However, there 
are certain materials such as beryllium, graphite, and deuterium that 
are more efficient moderators than water. These material are commonly 
termed ``unusual'' moderators.
    Absorbers are materials that absorb or capture neutrons. Because 
capturing neutrons prevents those neutrons from possibly causing a 
fission, the presence of absorber materials will decrease the 
criticality concern. Most materials act both as a moderator and an 
absorber to varying degrees.
    In some cases the presence of moderator material is limited by the 
requirements in Part 71. However, this is not always the case. It is 
reasonable to assume that moderators, such as water, will be present in 
the waste. In analyzing the criticality hazard of waste at LLW disposal 
facilities, it is conservative to assume that moderators will be 
present in optimal amounts. The presence of absorber materials is not 
limited by regulations. These materials, such as iron, calcium, etc., 
are present in LLW and in the waste containers. However, the amount and 
distribution of absorbers cannot be assured, so they are typically 
omitted in analyzing criticality hazards. For example, although a steel 
drum acts as an absorber, the drum will corrode within tens of years 
and can no longer be depended on to contain the waste and act as an 
absorber.

Possible Scenarios

    In order for a criticality to occur, several of the above factors 
must be above certain values. For instance, a criticality cannot occur 
if the mass of the SNM is below a certain value regardless of the 
enrichment or concentration. A criticality cannot occur if the 
concentration of the SNM is below a certain value regardless of the 
enrichment or mass. A criticality cannot occur if the enrichment is 
below a certain value regardless of the mass or concentration.
    Considering what can be controlled by Parts 71 and 150, several 
scenarios can be postulated. For waste shipped as ``fissile exempt'', 
concentrations can be limited to 5 grams of SNM per 10 liters. This 
translates to 104 grams of enriched uranium for a typical waste 
container (i.e., 55-gallon drum). In addition, under the fissile 
exemption unusual moderators are limited. Assuming a density of waste 
of 68 pounds per cubic foot, this concentration (4.6E-4 gram of 
uranium-235 per gram of waste) is smaller than the allowable 
operational concentration limit in the draft guidance (NUREG/CR-6626, 
Emplacement Guidance for Criticality Safety in Low-Level Waste 
Disposal) and therefore is considered safe. The limits in the draft 
guidance have been developed considering that absorbers are not present 
and that moderation with water is optimal to maximize the possibility 
of fissions.
    For waste that does not meet the fissile exemption criteria, 
concentration, enrichment, and mass are not controlled. Given that 
disposal facilities licensed by Agreement States can only possess 350 
grams, a package containing 350 grams of highly enriched uranium could 
be shipped to a disposal facility. Using the example of waste shipped 
in 55-gallon drums with a waste density of 68 pounds per cubic foot, 
the uranium-235 concentration is 1.5E-3 gram of uranium-235 per gram of 
waste. This concentration exceeds the limit for high enriched uranium 
in the draft guidance (8.3E-4 gram U-235/gram of waste for a 10-foot 
high disposal unit). While a single container would not represent a 
criticality concern, an array of such drums could represent a 
criticality concern.
    Using the criticality calculations in NUREG/CR-6505 Volumes 1 and 
2, ``The Potential for Criticality Following Disposal of Uranium at 
Low-Level Waste Facilities,'' an array of low-enriched uranium (10 
percent enrichment) drums stacked more than 15 feet high could pose a 
criticality concern. An array of high-enriched uranium (100 percent 
enrichment) drums stacked more than 11 feet high could pose a 
criticality concern. Trenches at burial sites are deeper than 15 feet. 
These calculations assume optimal water moderation and no absorbers. 
Although there is significant uncertainty associated with a waste 
facility receiving and disposing of numerous drums containing large 
amounts of SNM, there are no regulatory limitations to preclude this 
situation.

[[Page 50781]]

NRC Staff Assessment of Compatibility Designation

    At the time the compatibility designations were originally selected 
for Part 61 (1983), the NRC directly regulated SNM at LLW disposal 
facilities. Becuase the NRC is responsible for SNM in greater than 
critical mass quantities and regulated SNM at LLW disposal facilities, 
there was no need for Agreement States to adopt these requirements. 
These requirements were designated ``Not Required for Compatibility.'' 
As noted above, LLW disposal facilities reduced their SNM possession 
limits to those provided in 10 CFR 150.11 (350 grams or less). This 
authority was assumed by the respective Agreement State; thus, the NRC 
no longer directly regulates SNM at LLW disposal facilities, including 
the authority to administer waste emplacement criticality controls. 
Therefore, the NRC is considering changing the compatibility 
designation of Sec. 61.16(b)(2) to ensure these safety measures are 
applied in the disposal of SNM.
    NRC staff used the procedures outlined in Management Directive 5.9, 
``Adequacy and Compatibility of Agreement State Programs,'' and 
concluded that the compatibility designation for Sec. 61.16(b)(2) 
should be revised from category ``Not Required for Compatibility'', to 
category ``Health and Safety''. ``Health and Safety'' applies to 
activities that could result directly in an exposure to an individual 
in excess of basic radiation protection standards, if the essential 
objectives of the provision were not adopted by an Agreement State. If 
an inadvertent criticality were to occur at a LLW disposal facility, 
workers could receive doses in excess of the 10 CFR Part 20 limits. 
Under the ``Health and Safety'' category, Agreement States that have 
currently operating LLW disposal facilities and those States which will 
be establishing LLW disposal facilities in the future, would need to 
adopt legally binding requirements that encompass the essential 
objectives of 10 CFR 61.16(b)(2) within three years of the change of 
designation in compatibility. This requirement would continue to be 
designated as ``Not Required for Compatibility,'' for other Agreement 
States.

Summary of Draft Emplacement Criticality Guidance

    The draft guidance provides a general approach to emplacement 
criticality safety. Five different SNM isotopic compositions were 
studied: uranium-235 at 10 and 100 percent enrichment; uranium-233; 
plutonium-239; and a mixture of plutonium-239, -240, and -241. Three 
different graded approaches are presented. The first graded approach is 
the most conservative, and can be used easily for facilities that 
dispose of very low levels of SNM, or dispose of material with a low 
average enrichment. This approach relies on the calculation of average 
areal density, or grams of SNM per square foot, or on the average 
enrichment of SNM. The area over which averaging may be performed also 
is specified, but the emplacement depth and concentration are not 
limited.
    The second graded approach relies on limiting the average 
concentration by weight of SNM in the waste, and on limiting the depth 
of the emplacement. This method may be useful for facilities that 
emplace somewhat higher areal densities of SNM, but which do not use 
vaults or segmentation in the disposal emplacement.
    The third graded approach relies on limiting the average 
concentration by weight of SNM in the waste, and on the presence of 
segmenting barriers, such as vaults, that will prevent movement of SNM 
waste from one side of the barrier to the other. This method may be 
useful for facilities that use concrete vaults in their disposal areas.

Envisioned Implementation of Guidance and Change in Compatibility

    If the compatibility designation of 10 CFR 61.16(b)(2) were changed 
from ``Not Required for Compatibility'' to ``Health and Safety'', 
Agreement States would have three years to implement regulations or 
other legally binding requirements compatible with Sec. 61.16(b)(2). As 
noted earlier, the States of Washington and South Carolina currently 
have emplacement criticality controls. The compatibility change will 
assure that future LLW disposal facilities in Agreement States will 
have criticality safety controls for emplaced SNM waste.
    After these legally binding requirements have been implemented, the 
Agreement State regulatory program would require their licensees 
(disposal facility operators) to prepare and submit information 
demonstrating compliance with their equivalent of 10 CFR 61.16(b)(2).
    To assist the States and licensees, NRC has prepared emplacement 
criticality safety guidance. Licensees would review the types of waste 
and disposal operations and determine which of the graded approaches in 
the guidance were appropriate for its facility. For each of the graded 
approaches, the NRC draft guidance includes criticality safety limits 
and a description of how to calculate the limits based on readily 
available information. The draft guidance also indicates the type of 
procedures that would need to be developed for each of the graded 
approaches. This guidance would serve as a technical basis for 
preparing the license amendment requests submitted to the Agreement 
States.
    The Agreement State regulator would then review this amendment 
request and modify the license as appropriate. Again, the guidance 
would serve as the technical basis for the State regulator.

NRC Staff Assessment of Potential Resource Impact on Agreement States

    NRC staff has estimated the potential resource impacts on Agreement 
States to implement a change in the compatibility of 10 CFR 
61.16(b)(2). As indicated above, the first step would be to modify its 
regulations or other legally binding requirements to be compatible with 
Sec. 61.16(b)(2). We consider that only a minor modification would be 
necessary to the existing Agreement State Part 61 equivalent 
regulations, or that the compatibility change could be administered 
through other legally binding requirements. We estimate that this will 
take four to six-State staff weeks. The next step of an Agreement State 
would be to review the licensee's amendment request and/or procedure 
changes. We estimate that this will take two-State staff weeks. Some 
additional effort would be required for inspection of the facility; 
however, this effort is not estimated to be significant.

    Dated at Rockville, Maryland this 9th day of September, 1999.

    For the Nuclear Regulatory Commission.

Daniel M. Gillen,
Acting Chief, Uranium Recovery and Low-Level Waste Branch, Division of 
Waste Management, Office of Nuclear Material Safety and Safeguards.
[FR Doc. 99-24254 Filed 9-17-99; 8:45 am]
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