[Federal Register Volume 61, Number 214 (Monday, November 4, 1996)]
[Notices]
[Pages 56716-56724]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-28223]
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NUCLEAR REGULATORY COMMISSION
Notice of Issuance of Branch Technical Position on Screening
Methodology for Assessing Prior Land Burials of Radioactive Waste
Authorized Under Former 10 CFR 20.304 and 20.302 for Interim Use and
Comment
SUMMARY: This notice is to advise the public of the U.S. Nuclear
Regulatory Commission's issuance of a Branch Technical Position (BTP)
which provides a screening methodology that the staff finds acceptable
to determine the need for further characterization and/or remediation
of prior low-level radioactive waste disposal conducted under the
provisions of former 10 CFR 20.304 and 20.302.
Burial of certain quantities of radioactive waste in soil, by
licensees, without prior NRC approval, was authorized on January 29,
1959 (22 FR 548). This authorization was codified in former 10 CFR
20.304. On January 28, 1981, the NRC concluded that it was
inappropriate to continue generic authorizations of burials pursuant to
10 CFR 20.304 without regard to factors such as location of burial,
concentrations of radioactive material, form of packaging, and
notification of NRC. Therefore, NRC rescinded 10 CFR
[[Page 56717]]
20.304 (45 FR 71761). As of January 28, 1981, licensees wishing to
perform on-site disposal of the type previously authorized under 10 CFR
20.304 were required to obtain prior NRC approval in accordance with 10
CFR 20.302.
Disposals made pursuant to former 10 CFR 20.304 and 20.302 at
facilities licensed under 10 CFR Parts 30, 40, and 70, and that have
been unused for NRC licensed operations for a period of 24 months, are
subject to the requirements of the ``Final Rule on Timeliness in
Decommissioning Nuclear Facilities'' (59 FR 36026, effective August 15,
1994) (hereinafter called the ``Timeliness Rule''). Licensees who have
unused outside areas (e.g., burial areas) containing elevated levels of
licensed radioactive materials, are required to notify NRC, that they
are in possession of these areas and must begin following a schedule
for decommissioning these areas. For timing provisions related to
decommissioning, see 10 CFR 30.36(d), 40.42(d), 70.38(d), and 72.54(d).
On August 19, 1996, NRC published Information Notice 96-47
``Recordkeeping, Decommissioning Notifications for Disposal of
Radioactive Waste by Land Burial Authorized under Former 10 CFR 20.304,
20.302, and Current 20.2002.'' This notice re-emphasized NRC's position
that former burials are covered under the Timeliness Rule, outlined the
decommissioning schedule required by the rule, and stated that NRC
would develop a screening methodology for assessing former burials.
This screening methodology is being issued as a draft BTP and is
attached to this notice.
Because of the deadlines associated with the Timeliness Rule, this
BTP is being issued for public use and comment for 90 days. At the end
of the 90 day period, the comments received will be evaluated to
determine if the BTP should be revised. Since there is a possibility
that the comments could result in a substantial change to the BTP, NRC
will not make any decisions regarding the assessment of prior burials
until after the comments can be evaluated.
All comments should be addressed to Heather Astwood, Mail Stop T-
7F-27, U.S. Nuclear Regulatory Commission, Washington, DC 20555. A copy
of the BTP is also located in the NRC's Public Document Room, 2120 L
Street NW., Washington, DC 20555. A copy is also on the NRC homepage
which can be accessed at www.nrc.com.
FOR FURTHER INFORMATION CONTACT: Heather Astwood, Division of Waste
Management, Office of Nuclear Material Safety and Safeguards, U.S.
Nuclear Regulatory Commission, Mail Stop T-7F-27, Washington, DC 20555,
telephone (301) 415-5819.
Dated at Rockville, MD this 25th day of October 1996.
For the U.S. Nuclear Regulatory Commission.
Michael F. Weber,
Chief, Low-Level Waste and Decommissioning Projects Branch, Division of
Waste Management, Office of Nuclear Material Safety and Safeguards.
Draft--Branch Technical Position
Screening Methodology for Assessing Prior Land Burials of Radioactive
Waste Authorized Under Former 10 CFR 20.304 and 20.302
October 1996
Low-Level Waste and Decommissioning Projects Branch, Division of Waste
Management, Office of Nuclear Material Safety and Safeguards
Table of Contents
1.0 Purpose
2.0 Introduction
3.0 Discussion
4.0 Regulatory Position
4.1 Scope
4.2 Screening Methodology
4.2.1 General Approach
4.2.2 Step 1--Records Review
4.2.3 Step 2--Ingestion
4.2.4 Step 3--Exhumation Concentration
4.2.5 Results
4.3 Dose Screening Level and Basis
Appendix A Analysis of Other Pathways
Appendix B Metric Conversion Table
Appendix C Sample Calculations
Draft--Screening Methodology for Assessing Prior Land Burials of
Radioactive Waste Authorized Under Former 10 CFR 20.304 and 20.302
1.0 Purpose
This Branch Technical Position (BTP) provides a screening
methodology that the staff finds acceptable to determine the need for
further characterization and/or remediation of prior low-level
radioactive waste disposals conducted under the provisions of former 10
CFR 20.304 and 20.302. This BTP is intended to be a final evaluation
for former burials. Decisions made based on this BTP are not expected
to change because of the issuance of future rules or standards.
2.0 Introduction
Burial of certain quantities of radioactive waste in soil, by
licensees, without prior NRC approval, was authorized on January 29,
1959 (22 FR 548). This authorization was codified in former 10 CFR
20.304. On January 28, 1981, NRC concluded that it was inappropriate to
continue generic authorizations of burials pursuant to 10 CFR 20.304
without regard to factors such as location of burial, concentrations of
radioactive material, form of packaging, and notification of the
Nuclear Regulatory Commission. Therefore, NRC rescinded 10 CFR 20.304
(45 FR 71761). As of January 28, 1981, licensees wishing to perform on-
site disposals of the type previously authorized under 10 CFR 20.304
were required to obtain prior NRC approval in accordance with 10 CFR
20.302.
On May 21, 1991, 10 CFR Part 20 was revised (56 FR 23360) and 10
CFR 20.302 was replaced by 20.2002. According to 10 CFR 20.1008(b),
licensees were required to comply with the new 10 CFR 20.2002
exclusively on January 1, 1994. The requirements of 10 CFR 20.2002 are
similar to the original requirements in former 10 CFR 20.302, with the
addition of requirements for submitting analyses and procedures for
maintaining doses within established dose limits and as low as
reasonably achievable (ALARA).
Disposals made pursuant to former 10 CFR 20.304 and 20.302 at
facilities licensed under 10 CFR Parts 30, 40, and 70, and that have
been unused for NRC licensed operations for a period of 24 months, are
subject to the requirements of the ``Final Rule on Timeliness in
Decommissioning Nuclear Facilities'' (59 FR 36026, effective August 15,
1994) (hereinafter called the ``Timeliness Rule''). Licensees who have
unused outside areas (e.g., burial areas) containing elevated levels of
licensed radioactive materials, are required to notify NRC, that they
are in possession of these areas and must begin following a schedule
for decommissioning these areas. For timing provisions related to
decommissioning, see 10 CFR 30.36(d), 40.42(d), 70.38(d), and 72.54(d).
The evaluations required before the Commission terminates a license
or releases a former burial area from a license related to disposed
material were discussed in the supplemental information to the final
rule on the ``General Requirements for Decommissioning Nuclear
Facilities'' (53 FR 24021), published June 27, 1988. In the statement
of considerations for the final rule, NRC stated that it ``. . . will
take a hard look at the extent to which the site has been previously
used to dispose of low-level radioactive waste by land burial and
decide what remedial measures, including removal of such soil off-site,
are appropriate before the site can be released for unrestricted use
and the license terminated.''
On August 19, 1996, NRC published Information Notice 96-47
``Recordkeeping, Decommissioning
[[Page 56718]]
Notifications for Disposals of Radioactive Waste by Land Burial
Authorized under Former 10 CFR 20.304, 20.302, and Current 20.2002.''
This notice re-emphasized NRC's position that former burials are
covered under the Timeliness Rule, outlined the decommissioning
schedule required by the rule, and stated that NRC would develop a
screening methodology for assessing former burials.
3.0 Discussion
During decommissioning, NRC will evaluate disposals authorized
under former 10 CFR 20.304 and 20.302, to determine whether they are
acceptable for release for unrestricted use, based on their potential
impact on the health and safety of the public. The acceptability of a
disposal will depend on the potential for significant exposure to
members of the public who may, at some time in the future, develop and
use the disposal site for a private residence, farm, business, or other
purpose.
This methodology is intended to be used by the licensee as a
screening tool to determine which burial sites, in general, are
acceptable for release for unrestricted use, recognizing that
exceptions may be identified by NRC and/or the licensee. This screening
tool will be based on the total activity disposed of in the burial
ground and the potential for that activity to produce a significant
dose to a member of the public. Although this methodology estimates
doses, they are very conservative estimates. Actual doses produced by a
site would be a fraction of the doses estimated using this screening.
For those sites which pass this screening, in general, the staff
will require no further characterization or remediation effort. Those
sites that do not pass the screening would require more detailed
analysis. This may consist of site characterization and dose
assessments by the licensee and NRC. Remediation may also be necessary.
This is not to say that sites that do not pass the screening will be
required to remediate. This process is intended to screen out simple
sites with small inventories. More detailed evaluations can then be
performed for the more complex sites, or sites with unique
circumstances (i.e., no records, or burial located under a building).
It is recognized that spot concentrations in the waste may exceed NRC's
radiological criteria for decommissioning (57 FR 13389, ``Action Plan
to Ensure Timely Cleanup of Site Decommissioning Management Plan
Sites''), but the overall risk to the public is limited by the total
inventory, site characteristics, or other factors. It is also
recognized that these burials may not be the only residual activity
contained at a site. This screening is intended to evaluate the risks
posed by an on-site burial independent of any other evaluations of dose
contributions from other areas of the site. A facility which contains
larger quantities of contamination would be required to complete a site
and facility characterization program and a detailed dose assessment
that accounts for doses from all sources. Because such a site/facility
could conceivably have residual contamination levels that result in
doses that are just below the unrestricted release criterion, it is not
justified to exclude a former burial site or sites. Therefore, this
screening cannot be used for sites that have surface soil or building
contamination outside of what is contained in the burial site and sites
where members of the public would be exposed concurrently to both the
burial and other residual radioactivity. It is restricted for use at
those sites where a former burial is expected to be the only source of
residual contamination at time of decommissioning.
The Timeliness Rule, published August 15, 1994, outlines a schedule
for licensees to follow in performing decommissioning activities and
requires licensees to notify NRC of plans to meet this schedule. It
also requires licensees to decommission portions of their site,
including ``unused outdoor areas,'' which have not been used for a
period of 24 months. These outdoor areas include former 10 CFR 20.304
and 20.302 disposals, and are, therefore, subject to the Timeliness
Rule.
There are several issues associated with the assessment of prior
burials. Many licensees considered these burials to be permanent
disposals at the time of placement. Licensees did not budget the time
nor monetary resources to evaluate these sites at the time of
decommissioning. There is also a concern about the cost benefit of
evaluating these sites for decommissioning. Many universities and
hospitals disposed of small quantities of wastes associated with
research and medical applications. The cost to characterize and
remediate small burials of byproduct materials may outweigh the hazards
avoided. However, some burials may pose greater risks to the public,
such as those containing significant quantities of source and special
nuclear material wastes. At these sites, characterization and/or
remediation may be needed and costs of remediation will be considered
for sites that are below 100 mrem/yr and have an adequate ALARA
analysis. In addition, there are concerns about the quantity and
quality of available disposal records. At the time of decommissioning,
complete records of 10 CFR 20.304 and 20.302 disposals are necessary
for NRC to evaluate the acceptability of the disposals. Former 10 CFR
20.401(c)(3) stated that records of disposals made pursuant to 10 CFR
20.302 and 20.304 should be maintained until NRC authorizes their
disposition. However, for many of the older sites, these records are
scarce or unavailable. The sites that have no burial records, may be
required to evaluate and/or characterize the burials. Then, if NRC
determines that the site does not pose a risk to the public, the site
could be released for unrestricted use. If, however, it is determined
that the site could pose a significant risk, the licensee may be
required to remediate the burial. This analysis is based on the
radiological risks associated with the burial. If the burial areas
require characterization and/or remediation, other applicable local,
state, or federal radiological and non-radiological regulations should
be considered.
To help alleviate some of these concerns, the staff developed this
screening methodology to determine which former burials require
additional characterization and assessment and which burials are
acceptable for unrestricted use. To perform this screening, the
licensee will need a copy of Part 20, Appendix B, and NUREG-1500
``Working Draft Regulatory Guide on Release Criteria for
Decommissioning: NRC Staff's Draft for Comment.'' 1 The NRC will
defer decisions on releasing former burials based on this methodology
until this draft is finalized.
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\1\ NUREGs can be ordered by calling (202) 512-1800.
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4.0 Regulatory Position
4.1 Scope
The methodology of this BTP applies to prior burials of radioactive
material that were buried under 10 CFR 20.304 and 20.302. This
methodology is not intended to be applied to burial sites that are
currently in use or to evaluate former or proposed burials under 10 CFR
20.2002. The final rule on ``Decommissioning Recordkeeping and License
Termination: Documentation Additions,'' was issued on July 26, 1993 (58
FR 39628), and requires a single document listing: (1) All areas
outside restricted areas where current and previous wastes have been
buried, (as documented under 10 CFR 20.2108); and (2) other information
necessary to ensure that decommissioning is carried
[[Page 56719]]
out in accordance with the NRC's regulations. Therefore, for disposals
made pursuant to 10 CFR 20.2002, waste disposal records should be
sufficiently accurate and complete to demonstrate acceptability for
release in accordance with recordkeeping and decommissioning
requirements. In addition, recent approvals of 10 CFR 20.2002 disposal
requests have been based on the assumption that the site would be
released for unrestricted use. Guidance for evaluating these burials is
contained in NUREG-1101, ``Onsite Disposal of Radioactive Waste.'' As
stated previously, this screening is intended to be used for sites in
which the former burial is expected to be the only source of residual
contamination at the time of decommissioning. This screening is based
only on the radiological risks associated with the burial. If the
burial areas require characterization and/or remediation, or contain
hazardous and/or mixed wastes, other applicable local, state, or
Federal radiological and non-radiological regulations should be
considered.
This screening is intended to be used by both the licensee and NRC
to determine the ultimate disposition of the burial ground. Licensees
will perform the screening calculations, NRC staff will review the
calculations and make a final determination if the site passes the
screening. If the NRC's review indicates the site passes the screening,
no further evaluation or characterization of the site will generally be
required. The site can be removed from the license, if that is the wish
of the licensee, and the site will not need to be revisited during
license termination. Those sites that do not pass this screening will
require more detailed analysis to assess potential radiological risks.
The amount of analysis required beyond this screening depends on the
complexity of the site, the amount of available site characterization
information and site characteristics, and will be determined on a case-
by-case basis.
4.2 Screening Methodology
4.2.1 General Approach
This methodology consists of three steps. The first step involves
collecting information on the materials which were buried at the site.
The other two involve conservative dose assessments using this
historical information to determine the possible consequences from
human exposure to the buried material. The Step 2 calculations are
performed first because they require a minimal amount of information
about the site, and are easy to perform. If a site passes Step 2, there
is no need to collect additional information required to perform Step 3
calculations because Step 2 is more conservative. If the site does not
pass Step 2, then Step 3 calculations should be performed. If a site
fails both Steps 2 and 3, this site requires more detailed analysis to
determine whether it poses an unacceptable risk to the public.
4.2.2 Step 1--Records Review
The first step for the licensee should be a review of the burial
records. These records should indicate the activity and types of
isotopes that were disposed of at the site and the time period for
those disposals. All available and relevant records should be used to
develop a complete inventory for the burial area. The total activity of
each isotope in the entire burial site should be determined and
converted into microcuries (Ci). This total inventory should
be adjusted to account for radioactive decay which has occurred since
the time of burial.
It may be difficult to find records for some of the older burials.
Many of these sites may have had several changes in management or
location of record storage, and the records may have been misplaced or
lost. If no records are available, this methodology can be performed
using the original possession limits contained in the license for the
site for the actual or reasonable estimate of time in which the trench
was in operation and estimating the throughput resulting from the
licensed activity during that time. This approach would most likely
overestimate the quantities in the burial site because the activity
disposed of in a burial is typically only a fraction of the activity
allowed to be possessed under the license based on NRC staff
experience. This will only be allowed for estimating the total
inventory for use in Step 2. If there are no records, the trench size
could not be determined, and, therefore, Step 3 could not be
implemented. If using the original possession limits results in not
passing this screening criteria, the licensee should consult with NRC
for case-by-case guidance for evaluating the site. The maximum quantity
that was allowed to be buried in the trenches under rescinded 10 CFR
20.304, Appendix C cannot be used as an estimate for the quantity of
isotopes in the trenches because NRC has identified instances in
decommissioning burial sites where disposal limits were exceeded.
Without some evidence (i.e., disposal records) that these guidelines
were followed, the licensee and NRC can have little confidence in the
trench inventory.
If no records are available and the use of license limits result in
a failure at Step 2, the licensee can take some intrusive samples of
the burial ground to determine the general type and concentration of
isotopes at the site and then perform this screening. The level of
characterization necessary (i.e., number of samples) will be determined
on a case-by-case basis in consultation with NRC staff. NRC draft
``Branch Technical Position on Site Characterization for
Decommissioning Sites,'' dated November 1994, contains a description of
the type of site characterization information that could be required.
After Step 1 is complete and the total activity for each isotope in the
burial site is estimated, the licensee should continue with Step 2.
4.2.3 Step 2--Groundwater Pathway
Following the general screening model approach described in NCRPM
Report No. 123, this step assumes that the total activity for each
isotope is leached into the minimum quantity of water needed to meet a
family of four's average use in one-year (91 m\3\). Therefore, the
activity of each isotope (after decay) should be divided by 9.1E7
milliliters (ml) to obtain a concentration (C) for each isotope as
follows:
[GRAPHIC] [TIFF OMITTED] TN04NO96.011
The concentration of each isotope can be compared to the effluent
release criteria contained in Part 20, Appendix B, Table 2, Column 2
for water. The concentrations contained in this table are estimated to
produce a dose of approximately 50 mrem/yr assuming an individual
consumes 2 liters/day. Because Appendix B lists concentrations in
Ci/ml for isotopes which result in a dose of 50 mrem, this
concentration/dose ratio can be used to estimate the dose produced from
a different concentration of that isotope. The potential dose from the
estimated concentration for the isotopes in the burial can be estimated
as follows:
[GRAPHIC] [TIFF OMITTED] TN04NO96.012
where:
C=the concentration of a burial site isotope in groundwater
Ci/ml;
B=the Appendix B, Table 2, Col. 2 concentration for the same isotope;
and
D=the dose from exposure to this isotope.
This calculation should be performed for all isotopes in the burial
site. After the doses are estimated for each isotope,
[[Page 56720]]
the doses should be totaled. If the total dose is less than the 100
mrem/yr screening level, the site passes Step 2 and, in general, the
site will require no additional evaluations. If the dose is greater
than the 100 mrem/yr screening level, then the analyses of Step 3
should be performed.
Note: Step 3 CANNOT be used for isotopes with atomic numbers of
88 or higher. Step 3 uses draft NUREG-1500, which is currently
undergoing revisions for these isotopes. If a site contains these
isotopes, licensees should consult with NRC staff for case-by-case
guidance for evaluating these sites. If a site passes Step 2, then
it passes the screening. If a site contains isotopes with atomic
weight greater than 88, and it fails Step 2, then the site fails the
screening and must be evaluated on a case-by-case basis.
4.2.4 Step 3--Exhumation Concentration
In this step, it is assumed that the total inventory of the site is
evenly distributed throughout the burial trenches. Most burial sites
consist of several burial trenches located at the same site. The
activity of each isotope should be divided by the total grams of
material in the trenches. This will produce a trench concentration
(Ci/gram of waste) for each isotope. This calculation should
only consider the specific burial area containing the waste and
contaminated soils. It should not include the soil cap, if one is
present, or the 6 feet of clean soil which was required to be placed
between burials conducted under the provisions of 10 CFR 20.304. For
example, if a 100 m\3\ site contained 6 burial trenches with each one
having a volume of 10 m\3\, the total inventory would be assumed to be
evenly distributed over the volume of the trenches (60 m\3\), not the
volume of the site (100 m\3\). For sites where the volume of the
trenches cannot be reasonably determined, licensees should consult with
NRC staff for case-by-case guidance for evaluating these sites.
This step of the methodology assumes that a member of the public
builds a house directly on the burial site. The Draft Environmental
Impact Statement developed for 10 CFR Part 61, ``Licensing Requirements
for Land Disposal of Radioactive Waste,'' dated September 1981 (NUREG-
0782), contains information concerning the dilution of waste caused by
exhumation of a building foundation. Appendix G of NUREG-0782 contains
the inadvertent intruder scenario and states that the waste
concentration should be reduced by a factor of 4 to account for
dilution during excavation (the contaminated material would be mixed
with the clean cover material as well as the clean soil surrounding the
burial). This concentration should be converted into picocuries per
gram (pCi/g) for comparison with NUREG-1500 values. NUREG-1500,
Appendix A, Table A-1, ``Total Dose'' column contains the total dose
calculated using a residential scenario, with default assumptions, and
is based on 1 Pci/g of an isotope. To calculate a screening dose for
the burial site, the above calculated exhumed concentration can be
multiplied by the Appendix A values.
[GRAPHIC] [TIFF OMITTED] TN04NO96.013
where
C=the concentration of a single isotope in the burial ground;
A=the NUREG-1500 Appendix A, Table A-1 dose for the same isotope; and
D=the dose from exposure to this isotope.
This calculation should be performed for all isotopes in the burial
site. After the doses are estimated for each isotope, the doses should
be totaled. If the total estimated dose is less than the 100 mrem/yr
screening level, the site passes the screening and no further analysis
is generally necessary for the site; however, extenuating circumstances
may warrant further review. If the estimated dose is greater than 100
mrem/yr screening level, the site fails this screening analysis and the
licensee will be required to perform additional site-specific analyses
(Section 4.3.5). Example calculations are provided in Appendix C.
4.2.5 Results
If the site passes one of the steps above, the site would generally
not require any further characterization or remediation. The licensee
should submit the results of this screening, including a description of
the site, as known, and copies of the calculations performed for this
screening. This should be submitted to NRC, along with a statement
concerning the licensee's intention to take no further actions at the
site. In accordance with recordkeeping requirements, the licensee will
be required to maintain these records until the NRC authorizes their
disposal. Assuming that the licensee submitted the notification and
analysis in a timely manner (as described in IN 96-47), NRC would then
issue a letter stating that the licensee has complied with the
Timeliness Rule and that the former burial is suitable for unrestricted
release. It will then be determined by NRC and the licensee when the
burial site would be released. This BTP is intended to be a final
evaluation for former burials. Decisions made based on this BTP are not
expected to change because of the issuance of future rules such as
NRC's radiological criteria for license termination.
There may be instances where the licensee's calculations indicate
the site passes the screening, but NRC determines the site requires
more evaluation to consider additional hazards that may be associated
with the waste. This would include sites which contain both radioactive
and hazardous wastes. This methodology may determine the site is
suitable for release based on the radioactive materials alone. However,
the presence of hazardous chemical wastes may warrant additional
evaluation to ensure protection of the public and the environment. This
could also include sites where it is known the burial will be excavated
in the future (i.e., the burial is in the path for a future road),
sites with very limited burial records, and sites where there is other
residual contamination outside of the burial area.
If the site fails Step 3 above, the licensee will be required to
perform more specific characterization of the site. The details of the
characterization process and the level of detail required will be
determined on a case-by-case basis. NRC draft ``Branch Technical
Position on Site Characterization for Decommissioning Sites,'' dated
November 1994, contains a description of the type of site
characterization information that could be required. In some cases, if
the characterization information indicates that total activity in the
burial site is less than the activity originally used in the screening
method, this more realistic total activity can be used in the screening
methodology. If the site then passes the screening using this new
activity, the site would not require further evaluation. If the site
fails again, then the licensee will have to work with NRC staff to
develop a plan for additional actions to be taken at the site.
Evaluations beyond this methodology may require site characterization
information and a dose assessment. More detailed assessment of the
environmental transport and potential doses should be conducted in
accordance with Policy and Guidance Directive PG-8-08, ``Scenarios for
Assessing Potential Doses Associated with Residual Radioactivity.'' In
such cases, sites will be acceptable for unrestricted release, if
projected doses are a small fraction of 100 mrem/yr and ALARA,
considering corrective actions. The staff will consider the magnitude
of the projected dose, and existing radiological criteria for
decommissioning, in conjunction with
[[Page 56721]]
the objectives of keeping residual contamination levels ALARA, to
determine if the waste may pose a significant risk to the public and
the burial requires remediation.
It should be noted that the results of this screening are most
affected by the quantity and quality of the records available to
determine total inventory, and the assumptions used in determining the
trench concentration. Slight variations in the trench size could be the
difference between a site failing or passing the methodology.
4.3 Dose Screening Level and Basis
This methodology uses the public dose limit of 100 mrem/yr in Part
20 as a screening level for determining if a site poses a significant
risk to the public. Although this is higher than the dose levels
previously imposed for on-site burials (i.e., a few mrem/yr), the staff
believes this is appropriate for screening these sites because of the
high degree of conservatism built into the methodology and limitations
of existing information.
Following the general screening model approach described in the
National Council on Radiation Protection and Measurements (NCRPM)
Report No. 123, dated January 22, 1996, Step 2 of this methodology
assumes the total inventory in the burial ground is leached into the
minimum quantity of water needed to meet the average water use of a
family of four for 1 year (91 m\3\). The dose is then calculated
assuming an individual member of the family drank 2 liters/day of the
91 m\3\ for 1 year. The use of 91 m\3\ is also the screening default
value used in NUREG/CR-5512, ``Residual Radioactive Contamination From
Decommissioning'' (Table 6.22).
NRC staff analysis in NUREG-1500, Table A-1 contains estimated
annual total effective dose equivalent factors. These dose factors
indicate that there are cases, in which the inhalation of an isotope in
a residential scenario would produce a larger dose than the ingestion
of an equal amount of activity. It also indicates that the direct
exposure pathway for some isotopes may be more limiting than either the
ingestion or inhalation pathway. However, Appendix A, of this BTP,
contains an analysis which demonstrates that the ingestion scenario, as
used in this methodology, is so restrictive that inhalation and direct
exposure calculations are not necessary.
The staff considers the assumptions used in this ingestion scenario
to overestimate likely doses to potential members of the public, such
as: (1) There has been no migration from the burial so that the total
inventory originally placed in the burial remains; (2) the entire
inventory leaches into the groundwater in a one-year period; (3)
someone moves onto the site, and places a well near the burial ground
that would capture all of the contaminated water; (4) there is no
sorption of the radionuclide during transport and only limited dilution
and dispersion; (5) a single individual drinks only well water from the
site for that year. As shown in the example given later in this
section, more likely doses to a hypothetical individual would be a
small fraction of the doses estimated in this methodology and would
likely be in the range of a few millirem per year if the dose using
this methodology is less than 100 mrem/yr.
Step 3 of this methodology assumes that a farmer lives on top of
the burial ground at some point in the future. This scenario also
contains several conservative assumptions such as: (1) There has been
no migration from the burial so that the total inventory originally
placed in the burial remains; (2) that an intruder inadvertently digs
into the waste and brings the entire inventory to the surface; and (3)
the intruder fails to recognize the waste. These are assumptions used
in developing the exhumed concentrations. There are also several
conservative assumptions contained in the dose conversion factors
developed for soils in NUREG-1500, which are used in this step to
estimate screening doses.
NUREG-1500 uses a family farm scenario, in which an individual
lives on the site, drinks water from an on-site well, and ingests 25
percent of his/her food from a garden, on-site. The resident's house
and garden are assumed to be in the contaminated area, and the garden
alone is assumed to be 2500 m\2\ (NUREG/CR-5512, Table 6.23).
Therefore, to contain the house and garden, the contaminated area has
to be larger than 2500 m\2\. Many of the on-site disposals that have
been reviewed by NRC in the past have had areas less than 2500 m\2\.
These sites are generally too small to contain a house and a garden,
and, since they are smaller than those used in NUREG-1500, would likely
produce a smaller dose than predicted using NUREG-1500 values.
Therefore, based on the conservative assumptions used in both
estimating the soil concentration, and estimating the doses, the actual
doses produced from a site are expected to be a small fraction of the
screening doses predicted using this methodology.
The following example of a Cs-134 burial is used to illustrate the
level of conservatism in these scenarios. Assuming a burial contains
270 Ci 2 of Cs-134, the resulting dose for the ingestion
scenario in Step 2 equals approximately 160 mrem/yr. If this same
inventory is evenly distributed in a trench which is 5m x 2m x 1m, the
exhumation concentration is calculated to be 4.2 pCi/g Cs-134 based on
Step 3. Using NUREG-1500, this results in a dose of approximately 13
mrem/yr. As an independent check, a RESRAD analysis was also performed
using a concentration of 4.2 pCi/g Cs-134 and a contaminated zone area
of 5m x 2m, but no other site specific information. This analysis
produced a dose of 7 mrem/yr (assuming no soil cover and that the
groundwater was within 2 meters of the bottom of the burial).
Therefore, although the scenarios in this methodology can predict
elevated doses, they are only for screening purposes and do not
necessarily reflect actual doses which could be produced from the site.
The projected doses calculated using a more rigorous approach are a
small fraction of 100 mrem/yr screening level.
---------------------------------------------------------------------------
\2\ NRC's standard metrification policy is to place metric units
first, followed by non-metric units in parentheses. However, the
supporting tables for this BTP (i.e., 10 CFR Part 20, Appendix B)
are presented in non-metric units, therefore, for comparison
purposes non-metric units are used in this BTP. A conversion table
is contained in Appendix B.
---------------------------------------------------------------------------
Appendix A--Analysis of Other Pathways
There are only a limited number of isotopes for which the
inhalation pathway is more limiting than the ingestion pathway for the
residential scenario in NUREG-1500, Appendix A, Table A-1. For all of
these, however, the direct exposure pathway is even more limiting than
either the inhalation or ingestion pathways. The staff created the
ingestion pathway scenario used in this methodology to be so
restrictive, that even for isotopes which are primarily an external
hazard (e.g., Co-60), the dose produced, based on ingestion, is higher
than one produced using an external scenario, as in NUREG-1500.
Based on calculations performed using Step 3 of this BTP and the
RESRAD, version 5.1, the dose modeling code, Step 2 of this methodology
produces a higher screening dose, and, therefore, is more restrictive
than the other two methods. Since both Step 3 and RESRAD consider all
pathways, including direct exposure, in the dose calculations, if Step
2 doses are high then the other pathways do not need to be considered
independently. To demonstrate this, it was assumed that there was a
burial trench which
[[Page 56722]]
contained a total activity of 270 Ci of Co-60. Co-60 was
chosen because NUREG-1500 indicates it produces the largest external
dose per pCi/g. It was assumed that the entire inventory of the burial
was contained in a relatively small trench, with an area of 10 m2
and depth of 1 meter. This area was used to be consistent with the
contaminated zone area used in the Step 3 screening of this BTP. It was
assumed that the groundwater was within 1 meter of the bottom of the
burial, and that there was no cover on the material. If the total
activity is used in Step 2, a screening dose of 48 mrem/yr is
estimated. Step 3 of the screening estimates a dose of approximately 40
mrem/yr, and a RESRAD analysis predicts 18 mrem/yr. A RESRAD analysis
using more site specific parameters (i.e., cover thickness, depth to
groundwater) would likely reduce this dose even further.
Appendix B--Metric Conversion Table
----------------------------------------------------------------------------------------------------------------
Quantity From To metric Multiply by
----------------------------------------------------------------------------------------------------------------
Activity............................ Ci (curie).................. MBq (becquerel)............. 37,000.0
Dose equivalent..................... rem......................... Sv (sievert)................ 0.01
Length.............................. ft (feet)................... m (meter)................... 0.3048
Volume.............................. ft3......................... m3.......................... 0.02831685
Volume.............................. gal (gallon)................ L (liter)................... 3.785412
----------------------------------------------------------------------------------------------------------------
Appendix C--Sample Calculations
1.0 Example Site No.1
This site contains 1-3 animal carcasses that were tagged with 41
millicuries (mCi) Cs-134, 10.5 Mci Fe-55, 60 Mci Zn-65, 2.7 Mci Co-60
and 25 Mci I-125. These animals were placed in a 5m x 2m x 1m burial
pit in 1980.
1.1 Step 1--Records Review
No burial records were available to determine how many of the
tagged animals were placed in the pits. There were records on the
number of animals tagged, and the maximum activity that was used to tag
these animals. Therefore, the maximum activity of each isotope was used
to estimate the total inventory. The burial has been in place for 15
years, which is sufficient time for Zn-65 and I-125 to decay to
insignificant activities. Therefore, they can be excluded from
consideration. The calculated activities for the remaining isotopes are
adjusted for decay.
------------------------------------------------------------------------
Isotope Ci
------------------------------------------------------------------------
Cs-134..................................................... 270
Fe-55...................................................... 233
Co-60...................................................... 376
------------------------------------------------------------------------
1.2 Step 2--Groundwater Pathway
The total inventory for each isotope was divided by 9.1E7 ml (91
m3) of groundwater. This represents the concentration in Ci/ml
of that isotope which could be ingested by a person in 1 year.
------------------------------------------------------------------------
Isotope Ci Ci/ml(water)
------------------------------------------------------------------------
Cs-134............................ 270 2.9E-6.
Fe-55............................. 233 2.5E-6.
Co-60............................. 376 4.1E-6.
------------------------------------------------------------------------
This concentration was then compared to Part 20, Appendix B, Column
2, limits. These limits represent concentrations in effluent releases
which could cause doses of approximately 50 mrem/yr assuming ingestion
of 2 liters per day. The Appendix B ratio of concentration to dose was
used to determine roughly the dose that could be produced from the
waste concentrations in groundwater. For example,
[GRAPHIC] [TIFF OMITTED] TN04NO96.014
161 mrem/yr from Cs-134
This calculation was preformed for the remaining two isotopes and
the results are included in the following table.
Appendix B
----------------------------------------------------------------------------------------------------------------
Ci/
Isotope Ci Ci/ ml/50 mrem/ mrem/yr
ml yr
----------------------------------------------------------------------------------------------------------------
Cs-134....................................................... 270 2.9E-6 9E-7 161
Fe-55........................................................ 233 2.5E-6 1E-4 1.25
Co-60........................................................ 376 4.1E-6 3E-6 68
----------------------------------------------------------------------------------------------------------------
The doses were summed and the result was a dose of over 230 mrem/
yr. This dose exceeds the 100 mrem/yr screening level, and, therefore,
this site fails Step 2 of the screening methodology. Since this burial
did not contain any isotopes greater than atomic number 88, Step 3 was
performed.
1.3 Step 3--Exhumation Concentration
In this step, the total inventory was averaged over the volume of
the burial ground, which is 5 m x 2 m and 1 meter deep or equivalent to
1.6E7 grams of waste and soil assuming a soil density of 1.6 g/cm3 to
determine an average concentration (activity per cm3). This
concentration is then converted into pCi/g for comparison with NUREG-
1500 values in Table A-1 and divided by 4 to represent expected
dilution from cover material and clean soil on the sides during
exhumation.
[[Page 56723]]
[GRAPHIC] [TIFF OMITTED] TN04NO96.015
Trench Concentration = 17 pCi/gram
[GRAPHIC] [TIFF OMITTED] TN04NO96.016
Exhumation Concentration = 4.2 pCi/g
------------------------------------------------------------------------
Isotope pCi pCi/gram
------------------------------------------------------------------------
Cs-134.............................. 2.7E8.................. 4.2
Fe-55............................... 2.3E8.................. 3.5
Co-60............................... 3.8E8.................. 5.7
------------------------------------------------------------------------
These concentrations were then compared to NUREG-1500 values in
Table A-1, Column 9, for the total dose in mrem/yr, as follows:
D mrem/yr = (4.2 pCi/g Cs-134)(3.06 mrem/yr), where NUREG-1500
relates 3.06 mrem/yr to 1 pCi/g Cs-134
D = 12.8 mrem/yr from Cs-134
This calculation was performed for the remaining two isotopes, and
the results are summarized in the following table.
NUREG-1500
----------------------------------------------------------------------------------------------------------------
mrem/yr/pCi/
Isotope pCi pCi/gram g mrem/yr
----------------------------------------------------------------------------------------------------------------
Cs-134.......................................................... 2.7E8 4.2 3.06 12.8
Fe-55........................................................... 2.3E8 3.5 1.65E-3 0.006
Co-60........................................................... 3.8E8 5.7 5.06 28.78
----------------------------------------------------------------------------------------------------------------
Based on the above calculations, the total dose is approximately 40
mrem/yr and is less than 100 mrem/yr. Therefore, this site passes
screening Step 3 and does not require any further characterization nor
remediation.
2.0 Example Site No. 2
This site contains process waste from the manufacture of uranium
fuel. The burial contains approximately 3 curies of uranium in several
trenches. The material was placed in trenches throughout the 1960s.
2.1 Step 1--Records Review
Burial records were available and reviewed to determine that
approximately 3 curies of uranium were disposed of in trenches. For
this example, it was assumed that there was 0.5 curies of U-234 and 2.5
curies U-238. Approximately 27 years have passed since the time of the
last burial, which is insufficient time for either uranium to have
decayed. Therefore, they cannot be excluded from consideration, and the
calculations will be performed with the quantities cited above.
------------------------------------------------------------------------
Isotope Ci
------------------------------------------------------------------------
U-234...................................................... 5E5
U-238...................................................... 2.5E6
------------------------------------------------------------------------
2.2 Step 2--Total Activity Ingested From Groundwater
The total inventory for each isotope was divided by 9.1E7 ml (91
m3) of groundwater. This represents the concentration in Ci/ml
of that isotope that could be ingested by a person in 1 year.
------------------------------------------------------------------------
Ci/
Isotope Ci ml
------------------------------------------------------------------------
U-234........................................ 5E5 0.005
U-238........................................ 2.5E6 0.027
------------------------------------------------------------------------
This concentration was then compared to Part 20, Appendix B, Column
2, limits. These limits represent concentrations in effluent releases
that could cause doses of approximately 50 mrem/yr. The Appendix B
ratio of concentration to dose was used to determine, roughly, the dose
that could be produced from the waste concentrations in groundwater.
For example,
[GRAPHIC] [TIFF OMITTED] TN04NO96.017
8E5 mrem/yr from U-234
This calculation was performed for the remaining two isotopes, and
the results are included in the following table.
----------------------------------------------------------------------------------------------------------------
App B Ci Ci/ m>Ci/ml mrem/yr
ml
----------------------------------------------------------------------------------------------------------------
U-234........................................................ 5E5 0.005 3E-7 8E5
U-238........................................................ 2.5E6 0.027 3E-7 4.5E6
----------------------------------------------------------------------------------------------------------------
[[Page 56724]]
The doses are well over the 100 mrem/yr screening level, and,
therefore, this site fails Step 2 of the screening methodology.
2.3 Step 3--Exhumation Concentration
This site contains isotopes that have atomic numbers greater than
88, and, therefore, cannot be used in Step 3. Since this site failed
Step 2 and cannot be used in Step 3, this site fails this screening
methodology.
[FR Doc. 96-28223 Filed 11-01-96; 8:45 am]
BILLING CODE 7590-01-P
