Draft Interim Concentration Averaging Guidance for Waste Determinations, 74846-74850 [E5-7450]

Agencies

• NUCLEAR REGULATORY COMMISSION

[Federal Register Volume 70, Number 241 (Friday, December 16, 2005)]
[Notices]
[Pages 74846-74850]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E5-7450]


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NUCLEAR REGULATORY COMMISSION

[Docket No. PROJ0734, PROJ0735, PROJ0736, POOM-32]


Draft Interim Concentration Averaging Guidance for Waste 
Determinations

AGENCY: Nuclear Regulatory Commission.

ACTION: Issuance of Draft Interim Guidance.

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SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is issuing draft 
interim guidance on concentration averaging for public comment. The NRC 
is currently in the process of preparing a Standard Review Plan (SRP) 
to provide guidance to NRC staff regarding reviews of waste 
determinations

[[Page 74847]]

submitted by the U.S. Department of Energy (DOE). The NRC staff held a 
public scoping meeting on the draft SRP on November 10, 2005, to obtain 
stakeholder input on the contents of the SRP. The draft SRP is expected 
to be released for public comment in 2006 and will include, among other 
things, guidance on evaluating concentration averaging in those cases 
that are specific to the types of waste and situations typically 
evaluated in waste determinations. Because several stakeholders are 
interested in obtaining NRC guidance on concentration averaging as soon 
as practicable, the NRC is issuing this draft interim guidance prior to 
completion and public release of the entire draft SRP. This draft 
interim guidance is applicable only to waste determinations at DOE 
sites. This guidance will eventually be incorporated into the draft SRP 
and any comments received on this guidance will be evaluated at the 
same time as other public comments that are received following the 
release of the draft SRP.

DATES: The public comment period on the draft interim guidance begins 
with publication of this notice and continues until January 31, 2006. 
Written comments should be submitted as described in the ADDRESSES 
section of this notice. Comments submitted by mail should be postmarked 
by that date to ensure consideration. Comments received or postmarked 
after that date will be considered to the extent practical. Note that a 
subsequent public comment period will also be held after publication of 
the draft SRP in 2006.

ADDRESSES: Members of the public are invited and encouraged to submit 
comments to the Chief, Rules Review and Directives Branch, Mail Stop 
T6-D59, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001. 
Please note Docket Nos. PROJ0734, PROJ0735, PROJ0736, and POOM-32 when 
submitting comments. Comments will also be accepted by e-mail at 
NRCREP@nrc.gov or by facsimile to (301) 415-5397, Attention: Anna 
Bradford.

FOR FURTHER INFORMATION CONTACT: Ms. Anna Bradford, Senior Project 
Manager, Environmental and Performance Assessment Directorate, Division 
of Waste Management and Environmental Protection, Office of Nuclear 
Materials Safety and Safeguards, U.S. Nuclear Regulatory Commission, 
Rockville, MD 20852. Telephone: (301) 415-5228; fax number: (301) 415-
5397; e-mail: AHB1@nrc.gov.

SUPPLEMENTARY INFORMATION:

I. Background

    The Ronald W. Reagan National Defense Authorization Act for Fiscal 
Year 2005 (NDAA) provides criteria for determining whether certain 
waste resulting from the reprocessing of spent nuclear fuel is not 
high-level waste (HLW). Criteria 3(A) and 3(B) of Section 3116(a) of 
the NDAA require that the waste be disposed of in compliance with the 
performance objectives contained in NRC regulations at 10 CFR 61, 
Subpart C. The applicability of either 3(A) or 3(B) is dependent upon 
whether the waste exceeds Class C concentration limits, thus the 
classification of waste residuals must be determined in order to apply 
the NDAA criteria.
    NRC's regulation, ``Licensing Requirements for Land Disposal of 
Radioactive Waste,'' 10 CFR Part 61, provides waste classification 
tables (Tables 1 and 2 of 10 CFR 61.55) to ensure suitability of 
radioactive waste for near-surface disposal. The waste classification 
(along with other provisions such as waste segregation and intruder 
barriers) was developed in part to provide protection to individuals 
from inadvertent intrusion into the waste after disposal. To determine 
waste classification, 10 CFR part 61 allows for the averaging of the 
concentration of radionuclides in waste over the volume or weight of 
the waste, depending on the units used to express the limits for the 
radionuclides. The guidance provided in NRC's Branch Technical Position 
(BTP) on Concentration Averaging and Encapsulation (January 17,1995) 
represents acceptable methods by which specific waste streams or 
mixtures of these waste streams may be compared to the tabulated 
concentration values in Tables 1 and 2 of 10 CFR 61.55. The 
concentration averaging BTP was written to address a subset of 
acceptable classification or encapsulation practices and was not 
intended to address all cases. For example, the concentration averaging 
BTP was not written to address residual contamination of large 
underground or buried structures or systems.
    Waste classification was developed to ensure that waste 
concentrations would not exceed the values provided in Tables 1 and 2 
of 10 CFR 61.55, without special authorization, to provide protection 
of individuals from inadvertent intrusion into the waste. The waste 
classification tables were developed from performance assessment 
calculations for a variety of intruder scenarios considering the types 
of waste and disposal technologies that would likely be utilized for 
near-surface commercial disposal of low-level waste. The term ``near-
surface disposal'' indicates disposal in the uppermost portion, or 
approximately the top 30 meters, of the earth's surface. Waste that 
would decay to acceptable levels within 100 years was defined as Class 
A or B waste, and institutional controls were believed to be effective 
at limiting inadvertent intruder risk from these classes of waste. 
Waste that would decay to acceptable levels for an inadvertent intruder 
within 500 years was defined as Class C waste. Class C waste was 
envisioned to be segregated from other classes of waste, to be 
protected with 100 years of institutional control, to be disposed of 
deeper than Class A and B wastes, and to be disposed of with an 
intruder barrier that would prevent contact with the waste for 500 
years. It was also recognized that waste exceeding Class C limits for 
which form and disposal methods must be different, and in general more 
stringent, than those specified for Class C waste would not generally 
be suitable for near-surface disposal. However, it was recognized that 
there may be instances where waste with concentrations greater than 
permitted for Class C would be acceptable for near-surface disposal 
with special processing or design. These would be evaluated on a case-
by-case basis.
    Guidance on acceptable methods for performing concentration 
averaging to determine waste classification is presented in this draft 
interim guidance. Interpretation and examples of implementation of the 
BTP on concentration averaging and encapsulation as it applies to the 
types of waste and situations typically evaluated in waste 
determinations are provided. This guidance is only applicable to waste 
determinations at DOE sites; other uses may be authorized with 
permission of the NRC.

II. Proposed Concentration Averaging Guidance

    The guidance contained herein does not replace the guidance 
contained in the BTP on concentration averaging and encapsulation for 
the purposes of waste classification for the commercial disposal of 
low-level waste. The guidance is not intended to address all unique 
situations at DOE sites. However, the guidance contained herein is 
generally applicable to the following scenarios:
    (1) Underground waste storage tanks including heels, cooling coils, 
and residuals adhering to walls and other surfaces,
    (2) Infrastructure used to support underground waste storage tanks 
such

[[Page 74848]]

as transfer lines, transfer pumps, and diversion boxes,
    (3) Waste removed from tanks that is processed or treated for 
disposal in a near surface disposal facility, and
    (4) Other scenarios relating to waste determinations proposed by 
the DOE and accepted by the NRC.
    Although the concentration averaging BTP was not written to address 
residual contamination of underground or buried structures or systems, 
the fundamental principles contained within the BTP are applicable to 
these systems. This guidance clarifies the fundamental principles 
presented in the BTP and provides specific examples that may be 
pertinent to DOE waste determinations. The acceptable methods for 
concentration averaging for the purposes of waste classification for 
waste determinations are based on the following fundamental principles 
introduced in the BTP.
    (1) Measures are not to be undertaken to average extreme quantities 
of uncontaminated materials with residual waste solely for the purpose 
of waste classification.
    (2) Mixtures of residual waste and materials can use a volume or 
mass-based average concentration if it can be demonstrated that the 
mixture is reasonably well-mixed.
    (3) Credit can be taken for stabilizing materials added for the 
purpose of immobilizing the waste (not for stabilizing the contaminated 
structure) even if it can not be demonstrated that the waste and 
stabilizing materials are reasonably well-mixed, when the radionuclide 
concentrations are likely to approach uniformity in the context of 
applicable intruder scenarios.
    (4) Other provisions for the classification of residual waste may 
be acceptable if, after evaluation of the specific characteristics of 
the waste, disposal site and method of disposal, conformance of waste 
disposal with the performance objectives in Subpart C of 10 CFR part 61 
can be demonstrated with reasonable assurance.
    (5) Regardless of the averaging that is performed for waste 
classification purposes, the performance assessment or other approach 
used to demonstrate compliance with the performance objectives of 10 
CFR part 61, subpart C, must consider the actual distribution of 
residual contamination in the system when estimating release rates to 
the environment and exposure rates to inadvertent intruders. 
Conservative assumptions regarding the distribution of contamination 
are appropriate.
    The purpose of these principles is to prevent arbitrary or 
incorrect classification of materials that may result in near-surface 
disposal of materials that are not suitable for near-surface disposal. 
Appropriate concentration averaging may indicate that waste exceeds 
Class C concentration limits. Waste that exceeds Class C concentration 
limits may be suitable for near-surface disposal, but the evaluation of 
the suitability must involve independent analyses such as would be 
performed by the NRC under 10 CFR 61.58. The methods that follow can be 
used to determine the waste classification of waste residuals. As 
indicated by the first principle above, extreme measures should not be 
taken when performing concentration averaging to determine waste 
classification. Extreme measures include: (1) Deliberate blending of 
lower concentration waste streams with high activity waste streams to 
achieve waste classification objectives, or (2) averaging over 
stabilizing material volume or masses that are not needed to stabilize 
the waste per the 10 CFR 61.56 stability requirement or are not 
homogeneous from the context of the intruder scenarios. This guidance 
presents three categories of calculations of the concentrations of 
radionuclides in waste. The first pertains to cases in which the waste 
can be mixed and is fairly homogeneous. The second pertains to cases in 
which the waste cannot be removed or well mixed, and is stabilized in 
place to satisfy the requirements of 10 CFR 61.56. The third pertains 
to the concentrations used in performance assessment calculations to 
determine the suitability of near-surface disposal according to 10 CFR 
61.58 and does not pertain to the determination of whether a waste is 
Class A, Class B, Class C, or greater than Class C as defined in 10 CFR 
61.55.

Category 1. Physical Homogeneity

    In general, waste will have been processed to the maximum extent 
practical and will have been stabilized so that there is reasonable 
assurance that the performance objectives of 10 CFR 61, Subpart C, can 
be achieved. The concentrations of radionuclides in the waste for waste 
classification can be based on the average concentration calculated 
from the total volume or mass of the waste and processing or 
stabilizing materials if the materials are reasonably well-mixed. For 
Category 1, the weight or volume of the container should not be 
included in the calculation of average concentrations. The primary 
consideration is whether the distribution of radionuclides within the 
final wasteform is reasonably homogeneous. Technical basis should be 
provided (e.g., sampling results, engineering experience, operational 
constraints) to demonstrate that the waste is reasonably well-mixed. 
The preferred method to demonstrate homogeneity would be to provide a 
statistical measure of the variability of concentration within the 
waste, although it is recognized that this may not always be practical. 
For homogeneous mixtures, the classification of waste residuals may be 
based on the total volume or mass of the final wasteform. If additional 
averaging (e.g., as in the examples in Category 2) is not applied, 
waste with radionuclide concentrations after mixing that are greater 
than the values provided in Tables 1 and 2 of 10 CFR 61.55 would be 
considered to be greater than Class C waste.
    Mixing within waste or of waste with stabilizing materials may be 
needed for a variety of reasons. Mixing of waste and stabilizing 
materials may be advantageous to reduce release rates in order to 
achieve the performance objectives. As defined with respect to the 
principles of the BTP, mixing with excessive amounts of stabilizing 
materials solely to reduce the waste concentrations to alter waste 
classification should not be performed. In most cases, the ratio of the 
unstabilized to stabilized radionuclide concentrations would not be 
significantly greater than a factor of 10 for waste classification 
purposes. For unstabilized waste that can not be selectively treated or 
removed, mixing (within waste, not between waste streams) to facilitate 
homogenization of radionuclide concentrations is appropriate. For 
example, mixing may be used to reduce the variability in concentrations 
within a layer of tank waste that can not be removed for further 
treatment.

    Example 1-1. Liquid waste is removed from a tank and additional 
fluids are added in order to adjust the chemistry for processing. 
Cement and fly ash are mixed with the resultant liquid in an 
industrial mixer to form a grout that is placed in disposal 
containers. The concentration of radionuclides for determining waste 
classification is based on the total volume or mass of the final 
wasteform.
    Example 1-2. Reducing grout is added to stabilize a tank heel. 
The waste residuals in the tank are flocculated solids suspended in 
a liquid phase that can be mobilized with the tank transfer 
equipment. However, the solids can not be removed with the existing 
equipment. The reducing grout has a relatively high viscosity, such 
that the flocculated solid residuals and remaining waste liquids can 
be mixed with the grout prior to setting with the transfer 
equipment. The concentration of radionuclides for waste 
classification is based on the total volume or mass of the waste and 
the reducing grout in

[[Page 74849]]

which the waste is mixed. Additional reducing grout into which 
little or no waste is mixed should not be included in the total mass 
or volume used for concentration averaging.

Category 2. Stabilization To Satisfy 10 CFR 61.56

    Stabilization is a factor in limiting exposure to an inadvertent 
intruder because it provides a recognizable and non-dispersible waste. 
For solidified liquids and solids, Section 3.2 of the BTP provides for 
the concentration of the radionuclides to be determined based on the 
volume or weight of the solidified mass, which is defined here to be 
the amount of material needed to stabilize the liquids or dispersible 
solids to satisfy 10 CFR 61.56. Liquid waste must be solidified or 
packaged in sufficient absorbent material to absorb twice the volume of 
the liquid (10 CFR 61.56). However, the stabilizing material is not to 
be interpreted as bulk material added to fill void space. Stabilization 
is determined with respect to the waste and not the entire disposal 
system or unit. While stabilization of the entire disposal unit (e.g., 
a tank) may be necessary to meet the performance objectives, it 
generally would not be needed to make the residual waste recognizable 
and non-dispersible.
    Waste concentrations are calculated based on the volume or mass of 
material needed to be added to liquids or dispersible solids in order 
to solidify or encapsulate them. The concentration of the stabilized 
waste (waste plus stabilizing material) should generally be within a 
factor of 10 of the concentration on either a mass or volume basis in 
the unstabilized waste. The factor of 10 is derived from consideration 
that most stabilization techniques commonly envisioned use cementitious 
materials, and most cementitious wasteforms can readily achieve a ten 
mass percent waste loading. Additional stabilizing materials would in 
general not be needed for waste stabilization but may be needed for 
stabilization of the system or structures.
    For thin layers of contamination on surfaces, especially vertical 
surfaces, the average concentration may be based on the volume or mass 
of the structure in direct contact with the contamination plus a layer 
of stabilizing material that would be needed to stabilize the waste, as 
discussed above. This is not to be interpreted that averaging can be 
performed over all materials added to fill void space in the structure 
or over the portions of the structure that are essentially 
uncontaminated. This approach is justified because the concentrations 
would be expected to approach homogeneity with respect to the intruder 
scenarios, and the main justification for the classification system is 
to provide protection to the inadvertent intruder. The concentration 
values found in Tables 1 and 2 of 10 CFR 61.55 were derived assuming 
the total volume of waste exhumed by the intruder is at those 
concentrations, therefore a thin layer of more concentrated material 
averaged over the same exhumed volume would achieve a similar level of 
protection. Specific averaging volumes are not provided in this 
guidance because of the site-specific nature of the waste and site-
specific considerations for intruder scenarios.

    Example 2-1. A tank contains a heel that is 2.5 cm thick, and is 
composed of liquids and dispersible solids. A 20 cm thick layer of 
reducing grout is needed to stabilize the waste, and an additional 
300 cm of high-strength grout is added to fill void space and to 
provide an intruder barrier. The concentration of radionuclides 
would be calculated by averaging over the 20 cm thick layer of 
reducing grout. Use of a 20 cm layer of reducing grout in the 
concentration calculation is based on the amount of grout that would 
be needed to stabilize the waste if it could be removed from the 
tank and made into a stable wasteform. The concentration of the 
stabilized waste (waste plus stabilizing material) would generally 
be within a factor of 10 of the concentration in the unstabilized 
waste on either a mass or volume basis.
    Example 2-2. The walls of a waste storage tank have a thin layer 
(0.1 cm) of residual contamination that is not easily removed. The 
tank walls are 1 cm thick and the tank is contained within a 0.5 m 
thick vault. The contamination is distributed on the lower 5 m of 
the vertical surface. The contamination is not easily dispersed into 
the environment and is located underground. Closure of the storage 
tank will involve filling the tank and all void space with grout. 
The concentration of the waste for waste classification is 
calculated based on the thickness of the tank wall over the lower 5 
m of the tank, the thickness of the contamination, and a 1 cm thick 
layer of stabilizing grout. Use of a 1 cm layer of grout in the 
concentration calculation is based on the assumption that formation 
of a stable waste form is accomplished by incorporating the 0.1 cm 
layer of residual waste into a cementitious waste form at a mass 
loading of approximately 10%. The concentrations of the thin layer 
would be reduced by a factor of 20 for estimating waste 
classification if a volume basis were used.

Category 3. Other Provisions

    10 CFR part 61.58 allows the Commission to authorize other 
provisions for the classifications and characteristics of waste, if 
after evaluation of the specific characteristics of the waste, disposal 
site, and method of disposal, it finds reasonable assurance of 
compliance with the performance objectives in subpart C. Demonstration 
that the performance objectives can be satisfied would involve a site-
specific analysis (e.g., performance assessment). 10 CFR part 61.58 was 
intended to allow the NRC to establish alternate waste classification 
schemes when justified by site-specific conditions, and does not affect 
the generic waste classifications established in 10 CFR 61.55. Thus, if 
the results of concentration calculations performed in a manner 
consistent with the principles and examples described previously in 
this document indicate that radionuclide concentrations in the waste 
exceed Class C limits, then the waste is greater than Class C waste for 
waste classification purposes. If it can be demonstrated that the 
performance objectives of 10 CFR part 61.58 can be satisfied, then the 
waste would be suitable for near surface disposal.
    For the performance assessment calculations, the waste should be 
represented as it is physically expected to be present, and not 
averaged over the stabilizing and encapsulating materials unless the 
estimated doses to the public and inadvertent intruders were 
conservative as a result of averaging. Otherwise, every attempt should 
be made to represent the expected distribution of activity within the 
disposal system. If the 10 CFR 61 subpart C performance objectives can 
be met with reasonable assurance, then the waste is considered to be 
acceptable for near surface disposal.
    When performing the intruder calculations, it is not appropriate to 
calculate an average dose factoring in the likelihood of the occurrence 
of the scenario. The likelihood of the intruder scenario occurring is 
already represented in the higher limit (e.g., 500 mrem/yr) applied for 
inadvertent intruder regulatory analysis.

    Example 3-1. A waste heel remains in a HLW tank. Reducing grout 
is added to the heel, displacing some material to the center of the 
tank, while a fraction of the waste remains on the tank surfaces 
encapsulated by the reducing grout. A high strength grout is placed 
over the reducing grout as an intruder barrier and to limit water 
contact. The top of the waste residuals are 10 meters below the 
ground surface.
    An intruder scenario is evaluated in which a well-driller places 
a well through the disposal system. In this case, the intruder is 
exposed to drill cuttings (waste). The average concentration of the 
waste used in the performance assessment calculations should be 
calculated by assuming mixing over the volume of well cuttings 
exhumed because the cuttings are expected to be well-mixed when 
spread on the land surface. This average

[[Page 74850]]

concentration is applicable only to the performance assessment and 
not to the determination of waste classification.
    Because the rate of erosion at the site is relatively high, a 
second intruder scenario is evaluated in which most of the cover is 
eroded over the analysis time period. Some cover is expected to 
remain. The intruder constructs a home in the area over the tank. 
Because the direct exposure pathway is the only major contributing 
pathway for this scenario, the actual waste distribution can be used 
in the performance assessment. Alternatively, the average 
concentration of waste over the stabilizing materials can be used in 
the performance assessment because there would be less shielding for 
this calculation and the doses would likely be conservative.
    The doses to a public receptor who is offsite when institutional 
controls are in place and at the edge of a buffer zone near the 
closed tanks after institutional controls end is evaluated with an 
all-pathways performance assessment. The performance assessment 
represents expected degradation of the system over time. The 
modeling of the source term represents the waste as two zones, one 
zone of higher hydraulic conductivity and reducing conditions that 
persist for 500 years and one zone of lower hydraulic conductivity 
and reducing conditions that persist for the entire analysis period 
(10,000 years). The first zone represents waste between the tank 
surface and the added grout which may be exposed to increased 
moisture flow/oxidation because of shrinkage effects or degradation 
of the grout itself over time from various attack mechanisms. The 
second zone represents waste that was immobilized in the center of 
the reducing grout by the pour sequence of the tank closure 
operations. The concentrations of radionuclides in both zones should 
be represented in the performance assessment by the expected 
distribution of contamination within the zones, or distributions 
that can be demonstrated to be conservative with respect to release 
and exposure modeling. The potential pathways of water to the waste 
may depend on the discrete features of the system (e.g., cooling 
coils, shrinkage effects, fractures).

III. Further Information

    Documents related to NRC's reviews of waste determinations are 
available electronically at the NRC's Electronic Reading Room at https://www.nrc.gov/reading-rm/adams.html. From this site, you can access the 
NRC's Agencywide Document Access and Management System (ADAMS), which 
provides text and image files of NRC's public documents. Recent 
documents related to reviews of NRC waste determinations can be found 
under Dockets Numbers PROJ0734, PROJ0735, PROJ0736, and POOM-32. If you 
do not have access to ADAMS or if there are problems in accessing the 
documents located in ADAMS, contact the NRC Public Document Room (PDR) 
Reference staff at 1-800-397-4209, 301-415-4737 or by e-mail to 
pdr@nrc.gov.
    Documents may also be viewed electronically on the public computers 
located at the NRC's Public Document Room (PDR), O 1 F21, One White 
Flint North, 11555 Rockville Pike, Rockville, MD 20852. The PDR 
reproduction contractor will copy documents for a fee.

    Dated at Rockville, MD this 5th day of December, 2005.

    For the Nuclear Regulatory Commission.
Scott Flanders,
Deputy Director, Environmental and Performance Assessment Directorate, 
Division of Waste Management and Environmental Protection, Office of 
Nuclear Materials Safety and Safeguards.
[FR Doc. E5-7450 Filed 12-15-05; 8:45 am]
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