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NRC Regulatory Issue Summary 2002-02
Lessons Learned Related to Recently Submitted Decommissioning Plans and
License Termination Plans
January 16, 2002
Addresses
All U.S. Nuclear Regulatory Commission (NRC) licensees.
Intent
To inform addressees of lessons learned from reviews of recently submitted
decommissioning plans (DPs) and license termination plans (LTPs). No specific
action or written response is required.
Background Information
NRC is issuing this regulatory issue summary (RIS) to provide licensees
with information that may help them develop more complete DPs and LTPs
which should result in more effective and efficient use of both licensees'
and NRC's resources.
This information is being provided to licensees as part of the NRC staff's
effort to implement the NRC Strategic Plan, specifically, our performance
goal of making NRC activities and decisions more effective, efficient,
and realistic.
On July 29, 1996, Title 10 of the U.S. Code of Federal Regulations (10
CFR) 50.82 was revised to define a new process for decommissioning power
reactors [61 Federal Register (FR) 39301]. This new process included a
requirement for licensees of power reactors to submit LTPs, rather than
DPs, when they wanted their facility licenses terminated. On July 21,
1997, 10 CFR Part20 was revised to include criteria for determining the
adequacy of remediation of residual radioactivity (62 FR 39088). This
revision to Part 20 affects most licensees. As a result of these revisions
to the regulations, certain licensees are required to submit either DPs
or LTPs to have their facility licenses terminated. These revisions to
the regulations require new information or different types of information
than previously required.
Since the implementation of these revisions to the regulations, several
licensees have submitted either the required DPs or LTPs for NRC review.
As a result of these reviews we have found common areas that have resulted
in NRC issuing several requests for additional information (RAIs) and
licensees performing additional analyses to address those RAIs. These
additional activities result in delays in completing these reviews. Further,
these additional RAIs resulted in increased costs to licensees, either
because of the costs associated with responding to these RAIs, or NRC
charges for additional staff time to complete these reviews.
The staff has reviewed, or is in the process of completing reviews of
several DPs or LTPs. As a result of these reviews, the staff has learned
the following lessons. A detailed discussion of each of these lessons
learned is provided in Attachment 1.
- Communications - Early and frequent discussions between NRC
staff and licensees are encouraged during the planning and scoping phase
supporting the preparation of the DPs or LTPs.
- Groundwater - Additional environmental monitoring data may be needed
because there may not be enough operational environmental monitoring
of groundwater for adequate site characterization and dose assessments.
- Data Quality Objectives - The data quality objectives process
is encouraged in planning and designing the final status survey plan.
- Inspections - In-process inspections are more efficient than
one-time confirmatory surveys.
- Flexibility - Continued communications between NRC staff and
the licensee during the staff's review is encouraged to help the licensee
take full advantage of the inherent flexibility in NUREG-1575, "Multi-Agency
Radiation Survey and Site Investigation Manual," and NUREG-1727,
"NMSS Decommissioning Standard Review Plan."
- Modeling Issues - Submittal of assumptions and justification
for parameters used in developing site-specific derived concentration
guideline levels (DCGLs) and application of those DCGLs is encouraged.
- Decommissioning Cost Estimate - The discussion should include
a clear relationship between the planned decommissioning activities
and the associated updated cost estimate.
- Records - Old records should not be used as the sole source
of information for the historical site assessment/site characterization,
because these old records may be inadequate or inaccurate.
- Environmental Assessments - Some environmental submittals have
not provided sufficient information addressing non-radiological impacts
of the proposed action, as required by the National Environmental Policy
Act.
- Classifications of Survey Units - DPs and/or LTPs should be
submitted only after sufficient site characterization has occurred.
- Embedded Piping - Some LTPs and DPs have not adequately described
the methods the licensee plans to use when surveying the embedded piping
planned to be left behind.
- Minimum Detectable Concentrations - Some LTPs and DPs have
not adequately described the methodologies the licensees plan to implement
to scan minimum detectable concentrations of mixtures of radionuclides
that may remain in given survey areas/units.
As a result of these findings, the staff has expanded its acceptance
review process for DPs and LTPs (typically an administrative review) to
include a limited technical review before a DP or LTP will be accepted
for detailed review. An expanded acceptance review facilitates the identification
of significant technical deficiencies early in the review process. This
limited technical review focuses on those areas in which experience has
shown technical deficiencies in licensees' submittals. In general, these
areas are:
- Site characterization (hydro-geological and radiological);
- Dose modeling;
- Final radiation survey;
- Cost estimate; and
- Institutional controls (applicable only to restricted release)
.
Backfit Discussion
This RIS requests no action or written response and is, therefore, not
a backfit under 10 CFR 50.109, 72.62, nor 76.76. Consequently, the staff
did not perform a backfit analysis.
Federal Register Notification
A notice of opportunity for public comment was not published in the
Federal Register because this RIS is informational and requires no
action or written response by addressees.
Paperwork Reduction Act Statement
This RIS does not request any information collection.
This RIS requires no specific action nor written response. If there are
any questions about this matter, please contact the person listed below,
the appropriate project manager, or the appropriate regional office.
/RA/
David B. Matthews, Director
Division of Regulatory Improvement Programs
Office of Nuclear Material Safety
|
/RA/
John T. Greeves, Director
Division of Waste Management
Office of Nuclear Reactor Regulation and Safeguards
|
Technical contact: |
Stewart W. Brown, NMSS
(301) 415-6605
E-mail: swb1@nrc.gov |
Attachments: |
- "Discussion of Lessons Learned"
- List of Recently Issued NRC Information Notices
|
DISCUSSION OF LESSONS LEARNED
The staff has reviewed, or is in the process of completing reviews of
several decommissioning plans (DPs) or license termination plans (LTPs).
As a result of these reviews the staff has learned the following lessons:
- Communications - Early and frequent consultations between
U.S. Nuclear Regulatory Commission (NRC) staff and licensees are encouraged
during the planning and scoping phase supporting the preparation of
the DPs or LTPs. In this context, a licensee may schedule a meeting
with the NRC Project Manager assigned to the site to discuss the planning
and content of the LTP or DP. The discussions would address, among other
topics, past and current licensed operations; types and quantities of
radioactive materials used or stored; activities (current or past) that
may have an impact on decommissioning operations; decommissioning goals
(restricted vs. unrestricted license termination); basis for cleanup
criteria and development of site-specific derived concentration guideline
levels (DCGLs), or commitment to use NRC default DCGLs; potential impact
on public health and safety or the environment; funding plan and financial
assurance; and the minimum information required to be contained in the
LTP or DP. Regarding the aforementioned topics, licensees are encouraged
to review NUREG-1727 ("NMSS Decommissioning Standard Review Plan,"
September 2000). The principal purpose of NUREG-1727 is to provide guidance
on review of DPs. However, the guidance in NUREG-1727 supplements that
in NUREG-1700 ("Standard Review Plan for Evaluating Nuclear Power
Reactor License Terminations Plans") in such areas as site characterization,
dose modeling, final radiation survey, and institutional controls. NUREG-1727
provides a structure, using 16 modules, with which to provide information
for staff review. With the exception of the executive summary, each
module addresses very specific elements of the decommissioning process
and related data and information needs. Given that NUREG-1727 presents
the information in a generic context, it is the responsibility of the
licensee to go over each module and determine which technical elements
or regulatory requirements apply to the facility. Appendix A of NUREG-1727
provides a checklist ("Acceptance Review Checklist") to facilitate
this process. Given that the checklist is a brief summary of the material
presented in each module, it is recommended that each module be reviewed
to gain a full understanding of the requirements as the checklist is
being prepared. Before meeting with the NRC staff, a licensee is encouraged
to prepare a checklist that identifies technical elements that are applicable
(based on a preliminary review); areas that require clarifications from
the NRC staff before decisions can be made as to their applicability
to the site or facility; and scope and level of technical details addressing
technical elements and regulatory requirements. In addition, the licensee
may wish to make a brief presentation describing the past and current
use of the facility and its most current radiological status. During
the meeting, the NRC staff and licensee representative would go over
each item of the checklist and address specific questions. NRC would
present an overview of its review process, including discussions of
the time line and major milestones. The end product of the meeting is
a marked-up checklist that defines the technical elements and regulatory
requirements to be covered in the DP or LTP submittal. The staff believes
that this process will result in a better understanding of the type
of information to be included in either document and to familiarize
the licensee with the process that the staff will use to evaluate the
information contained in the DP or LTP. This approach is expected to
minimize the need for requests for additional information, reduce the
number of iterations and submittals, and expedite the staff's technical
review.
- Groundwater - Operational environmental monitoring of groundwater,
although adequate for its intended purpose, may not be adequate for
site characterization and to support dose assessments. As noted in NUREG-1727,
"NMSS Decommissioning Standard Review Plan," Section 4.6,
"Groundwater," "[T]he information supplied by the licensee
should be sufficient to allow the staff to fully understand the types
and movement of radioactive material contamination in groundwater at
the facility, as well as the extent of this contamination." The
actual number, location, and design of monitoring wells depend on the
size of the contaminated area, the type and extent of contamination,
the background quality, hydrogeologic system, and the objectives of
the monitoring program. For example, if the objective of monitoring
is only to indicate the presence of groundwater contamination, relatively
few downgradient and upgradient monitoring wells are needed. In contrast,
if the objective is to develop a detailed characterization of the distribution
of constituents within a complex aquifer as the design basis for a corrective
action program, a large number of suitably designed and installed monitoring
wells may be necessary. Power reactors normally have groundwater monitoring
programs as part of their radiological environmental monitoring programs
(REMPs). Although data derived from a REMP may provide useful information,
the data still tend to be insufficient to allow the staff to fully understand
the types and the movement of radioactive material contamination in
groundwater at the facility, as well as the extent of this contamination.
Therefore, a licensee may need to gather additional data to understand
the types and movement of radioactive material contamination in groundwater
at the facility, as well as the extent of this contamination.
- Data Quality Objectives - In developing the final survey design,
the licensee needs to identify all appropriate data quality objectives
(DQOs) in planning and designing the final status survey plan. The process
of identifying the applicable DQOs ensures that the survey plan requirements,
survey results, and data evaluation are of sufficient quality, quantity,
and robustness to support the decision on whether cleanup criteria have
been met using statistical tests. In brief, the major elements of the
DQO process are:
- A clear statement of the problem (i.e., a full understanding of
the radiological status of the facility and extent and magnitude
of the contamination);
- The identification of all related decision statements and alternative
actions, including selection of the most appropriate scenario for
the site and objectives (i.e., how will compliance be demonstrated?);
- The identification of the information needed to support the decision-making
process, such as radionuclide distributions and concentrations,
methods used to obtain the data, etc.;
- The definition of the site physical, temporal, and spatial boundaries
for all environmental media and structures, including reference
areas, that will be covered by the decision process and modeling;
- The development of a decision rule in defining action levels [e.g.,
DCGL-Wilcox rank (DCGLW); DCGL- elevated measurement comparison
(DCGLEMC); minimum detectable concentrations (MDCs)]; grid size
and layout; statistical tests; and hypothesis;
- Specifying limits for Type I and II decision errors in support
of the null hypothesis and impacts on sample size and use of prospective
and retrospective power curves; and
- Optimization of the data collection process and updating the design
of the survey plan, while meeting all DQOs. In purpose and scope,
the DQO process can include a flexible approach in planning and
conducting surveys and for assessing whether survey results support
the conclusion that release criteria have been met. The DQO process
can be an iterative process that continually reviews and integrates,
as needed, new information in the design of the final survey plan
and decision-making. Finally, the selection and optimization of
DQOs will facilitate the later evaluation of survey results and
decision-making processes during the data quality assessment phase.
The NRC staff has observed that licensees have had difficulties
in developing DQOs and have not taken full advantage of the DQO
process, especially the optimization step. Experience has shown
that the process is often rigidly structured by relying too much
on characterization data and not being readily open to the possibility
of incorporating new information as it becomes available. This approach
makes the implementation of any changes difficult and is an inefficient
use of resources, since it imposes time delays while determining
how to implement any changes.
- Inspections - In-process inspections are more efficient than
one-time confirmatory surveys. In one case, the confirmatory survey
was conducted after the licensee had completed most of the final survey
and many of the staff supporting the final survey were no longer available
to address questions and issues that were discovered while conducting
the confirmatory survey. Simply put, the confirmatory survey was conducted
too late in the process.
The in-process approach has allowed the licensee and NRC to take side-by-side
measurements, compare instrument readings and sensitivity, and address
survey issues early in the process rather than at the end of the process.
The in-process approach has resulted in significant savings in cost,
assured a more accurate survey, and helped the licensee in maintaining
its release schedule.
- Flexibility - Continued communications between NRC staff and
the licensee during the staff's review is to help ensure that the licensee
is able to take full advantage of the inherent flexibility in NUREG-1575,
"Multi-Agency Radiation Survey and Site Investigation Manual" (MARSSIM)
and NUREG-1727, "NMSS Decommissioning Standard Review Plan." In reviewing
LTPs and DPs, the staff has observed that licensees are often boxing
their approaches into rigid structures and formats, thereby locking
out any operational flexibility in implementing MARSSIM and negating
cost savings. This approach may reflect, in part, the interpretation
of NRC guidance as regulatory requirements. However, it is possible
to meet NRC requirements, while instilling operational flexibility into
the overall decommissioning process. For example, large waste volumes
alone do not necessarily make a remediation project a complex one, assuming
that adequate resources are available to accommodate the higher disposal
cost. What makes a decommissioning project complex includes such considerations
as groundwater contamination; the presence of hard-to-detect and transuranic
radionuclides (TRU); heterogeneous distributions of contaminants; the
presence of mixed waste; onsite disposal using engineered features;
and reliance on institutional controls to maintain doses within NRC
limits under restricted-release scenarios, among others. Even under
such conditions, there still is an opportunity to simplify the process,
maximize operational flexibility, and benefit from economies of scale.
Another example involves how final surveys are structured and designed
around survey units, in recognition that some sites may have literally
hundreds of survey units, with licensees perceiving that NRC needs to
approve the final status survey design of each one. NRC expects that
licensees will group survey units into a manageable number of categories,
taking into account the types of buildings, rooms, areas, built-in equipment,
and other specific features. This approach is expected to provide the
means to identify and address survey unit features and design requirements
that are specific for each category, while treating all other common
aspects of the survey design in a generic and systematic manner. The
staff suggests that the descriptions identify and address, as is applicable,
specific survey design requirements, data quality objectives, sampling
methodology, applicable plans and procedures, quality assurance requirements,
and data analysis and interpretation for each category. This approach
will relieve NRC of having to review and approve each survey design
package, before its implementation, and will expedite the final phases
of the remediation work, while leaving the development and implementation
of each final survey design package subject to periodic regional inspection
and enforcement actions. Finally, in structuring the final status survey
report, licensees are expected to identify and summarize the specific
characteristics of each survey unit and discuss their relevance in the
analysis of all survey results and interpretation supporting the conclusion
that each survey unit meets the cleanup criteria.
- Modeling Issues - The derivation of DCGLs should include the
assumptions and justification for parameters used, and justification
for how these DCGLs will be applied to various survey units on site.
DCGLs will be captured by license condition as part of the LTP approval
process, and will require NRC approval for changes to the approved DCGLs.
Area Factors
Area factors are needed in the final status survey to determine the
required scan MDCs and to develop DCGLEMC values that are needed to
identify small areas that may need further investigation. However, area
factors are typically not provided for residual radioactivity on building
surfaces. The primary reason for this is that such factors cannot be
calculated by using the DandD computer code. Therefore, when screening
DCGL values are used, which were derived from DandD, an alternative
approach must be used to calculate area factors for residual radioactivity
on building surfaces.
One approach that has been successfully used is to develop the area
factors by using the RESRAD-BUILD computer code and adjusting these
derived area factors to account for the fact that RESRAD-BUILD typically
gives less conservative dose estimates. With this approach, the screening
DCGL values are converted into the appropriate concentration unit for
RESRAD-BUILD (i.e., from "disintegrations per minute per 100 square
centimeters" to "pico-curie per square meter"). Area factors calculated
by RESRAD-BUILD can then be adjusted by the ratio of the dose from RESRAD-BUILD
to 25 milli-roentgen equivalent man per year (i.e., the equivalent dose
from DandD).
Volumetric Contamination
Nuclear power plants often have volumetric contamination (e.g., contamination
below the surface) in the containment structure from activation products.
Because the contamination occurs within a building structure, some licensees
have assumed that it is appropriate to use DCGL values developed for
building surface contamination for these areas, without additional justification
regarding the appropriateness of their use. However, DCGL values developed
for building surface contamination may not be appropriate for areas
with volumetric contamination, because the potential future exposure
routes may be different, especially if the structure is later torn down.
It is advisable for licensees to develop specific DCGL values, for volumetric
contamination, which consider the potential routes of exposure for residual
radioactivity in the material if the structure is eventually torn down.
As an alternative, licensees can demonstrate that the DCGL values developed
for surface contamination will bound the possible effects from exposures
for other configurations of the building structure.
Model Results
Licensees using RESRAD, DandD, or other computer codes to generate DCGL
values or perform dose analyses often do not include the printout from
these codes as part of the decommissioning submittal. This information
is typically omitted because the output results tend to be voluminous.
However, without this information it is difficult for staff to undertake
confirmatory analyses (if needed) or to complete its review of the licensee's
analyses.
It is advisable for licensees to provide output results from any analyses
used to develop DCGL values or used to perform dose analyses. If the
output results do not provide an echo of the inputs used in the analyses,
it may be necessary to also provide copies of the input files. Nondispersion
vs. Mass Balance Models
In using the RESRAD computer code to develop DCGL values or to perform
dose analyses, licensees often use a nondispersion model for evaluating
the groundwater pathways. This model is commonly used because it is
the default in RESRAD and therefore will be used unless specifically
changed. However, the nondispersion model makes certain assumptions
about the location of the future hypothetical well and will generally
give lower estimated doses than the mass balance model (if the groundwater
is an important pathway).
It is advisable for licensees to either use the more conservative mass
balance models or provide justifications for using nondispersion models.
Specific guidance on justification for using the nondispersion model
can be obtained from NUREG-1727 (pages C47-C50).
Parameters
Licensees often use a combination of default and site-related parameters
in their analyses to develop DCGL values or in dose analyses. In many
cases, little or no justification is provided for the reason for using
the specific parameter values used in the analysis. This can lead to
uncertainties in assessing the appropriateness of the DCGL values or
calculated dose in demonstrating compliance with the standard.
Given the large number of parameters that may have to be justified in
an analysis to develop DCGL values or a dose analysis, NUREG-1727 (Section
7 of Appendix C) discusses an approach for focusing on those parameters
most important to the results. This approach entails classifying parameters
as either behavioral, metabolic, or physical, as defined in NUREG/CR-5512,
Volume 3. Licensees may use default values for behavioral and metabolic
(primarily those prescribed for DandD) as long as the values are consistent
with the generic definition of the average member of the critical group,
and the screening scenarios are used. Site-specific physical parameter
values should be used and justified. The level of justification needed
is dependent on the significance of the parameter to the results. The
relative significance of parameters to the results can be determined
through a sensitivity analysis. In the sensitivity analysis, the default
statistical distributions provided in RESRAD 6.0 and RESRAD-Build 3.0
should be used, supplemented with what is known about the site (note:
default distributions should not be used as a substitute for known information).
Known parameter values should be treated as a constant in the sensitivity
analysis. The relative significance of the various parameters can be
determined based on the ranks listed in the regression and correlation
results in the uncertainty report. The default surface contamination
values for alpha-emitting radionuclides are rather low, and in some
cases below the detection limit. This results from a conservative resuspension
factor (RF) used in the DandD code. Therefore, the licensee may wish
to consider using a more realistic RF value for site-specific analyses.
- Decommissioning Cost Estimate - There needs to be a clear relationship
between the planned decommissioning activities and the associated cost
estimate. At the license termination stage, the Commission must make
decisions on the proposed actions described in the LTP. The Commission
typically considers: 1) the licensee's plan for assuring sufficient
funds will be available for final site release; 2) radiation release
criteria for license termination; and 3) the adequacy of the final survey
required to verify that the site release criteria have been met. 10
CFR 50.82(a)(9)(ii)(F) requires the licensee to provide, in part, an
updated site-specific decommissioning cost estimate. If little decommissioning
has been completed, and inflation and disposal costs have not changed,
the cost estimate required by 10 CFR 50.82(a)(8)(iii) may be acceptable.
NRC is not requiring the licensee to submit any contractual documents/agreements
that exist between the licensee and its decommissioning contractor,
and the cost estimate should not be impacted by the election of the
licensee to decommission the facility, or contract to decommission the
facility. However, for NRC to be able to make a finding that sufficient
funding is available to complete decommissioning, the updated cost estimate
of the remaining site dismantlement activities, and the remediation
plan that outlines how the decommissioning will be conducted, must correlate.
The updated cost estimate should be based on the remaining activities
and the plans on how the actions will be completed. The updated site-specific
cost estimate must address the remaining activities necessary to complete
decommissioning, to assure sufficient funds are available, because the
financial assurance instrument required under 10 CFR 50.75 must be funded
to the amount of the cost estimate, and during decommissioning, the
licensee has been allowed to withdraw the funds set aside for decommissioning.
- Records - Old records may be inadequate or inaccurate for the
purpose of developing either the historical site assessment (HSA) or
site characterization. The staff suggests that these records not be
relied on as the sole source of information for the HSA or site characterization.
Interviews with current and former staff and contractors play an essential
role in formulating the HSA. Experience has shown that old records and
results of operational surveys and post-shutdown scoping surveys have
been submitted as substitutes for characterization surveys. For example,
the results of operational surveys may represent radiological status,
describing conditions over a limited time span, or may have been conducted
to address specific events (i.e., post-spill cleanup assessment). In
a few instances, the results of personnel interviews and information,
which can only be considered as anecdotal, have been presented in the
HSA. It could not be determined whether this information, in fact, was
part of an unbroken chronological history of the site or contained time
gaps for which operational milestones or occurrences were missing. Although
NRC encourages licensees to review old records and conduct personnel
interviews (past and current employees and key contractors), there is
a need to present this information in its proper context and qualify
its usefulness and how it might be supplemented (e.g., via additional
data searches or characterization surveys). To achieve the purpose of
the HSA, a complete history of the residual contamination is needed.
Given their importance, the staff suggests that characterization surveys
be developed only after the licensee has conducted a thorough evaluation
of the information collected during the site historical assessment.
Based on the review of several LTPs and DPs, the staff has found that
licensees have generally done extensive characterizations of facilities
slated for decommissioning. A review of selected characterization files
(in support of decommissioning and turnover surveys) revealed that a
wealth of information is indeed available, but that it is not conveyed
or presented clearly in LTPs and DPs. The information NRC seeks can
be drawn from existing characterization records or supplemental analysis
of existing samples, thereby avoiding the need to conduct additional
surveys and to send workers into radiation areas -- all while minimizing
costs. The type of information that is needed to support the preparation
of LTPs and DPs focuses primarily on residual levels of contamination
remaining on building surfaces or in soils (surface and subsurface),
after the remediation work has been completed. The characterization
of elevated contamination levels typically found in radiation areas
is of no concern in addressing the design of final status surveys, since
these areas are contaminated at levels that obviously exceed any realistic
DCGLW. NRC is seeking a better presentation, and perhaps evaluation,
of existing data supporting specific DQO elements and justification
for the approach proposed in developing survey designs. In most instances,
it is not a question of generating more data -- rather, it is a question
of making use of all existing data. There may be some exceptions where
additional characterizations might be warranted. Such exceptions might
apply to the characterization of subsurface soils, ground water, and
TRU, since these may present unique challenges, but can be resolved
without unnecessary radiation exposures.
- Environmental Reviews - Environmental assessments need to address
non-radiological impacts of the proposed action. In accordance with
the provisions of the National Environmental Policy Act(1) all agencies
of the Federal Government are required to assess the environmental impact
of any major Federal action that may significantly affect the quality
of the human environment. As part of NRC's approval of either a DP or
an LTP, NRC is required to determine if that approval is a Federal action.
Therefore, the impacts on the human environment associated with NRC
approving either a DP or an LTP must be assessed. Further, this assessment
must include both radiological and non-radiological impacts. Although
most licensees normally provide sufficient information for the staff
to assess the radiological impacts on the human environment, some licensees
have not provided sufficient information related to current site-specific
non-radiological impacts.
Because actions associated with NRC's approval of a DP are different
than those associated with NRC's approval of an LTP, the information
required to assess the impacts on the human environment are different.
That is, when NRC approves a DP, NRC is approving the licensee performing
the activities necessary to remediate radiological contamination at
a site.
Therefore, a DP should include information addressing non-radiological
impacts on the human environment associated with these proposed activities.
Non-radiological impacts include, but are not limited to the following:
land use; water quality; transportation; air quality; ecological; historical
and cultural resources; hazardous material/waste; noise; visual/scenic
quality; socioeconomics; and public and occupational health. However,
under the provisions of 10 CFR 50.82, most if not all activities necessary
to complete site remediation can be completed under the provision of
10 CFR 50.59. Therefore, these activities will not require prior NRC
approval. Consequently, unless certain site-specific issues exist, NRC,
when it approves an LTP, is approving only: (1) the adequacy of the
decommissioning funding plan to assure that sufficient funding is available
to complete the remaining radiological remediation activities; (2) the
radiation-release criteria for license termination; and (3) the adequacy
of the design of the final survey to verify that the release criteria
have been met.
- Characterization Surveys and Classifications of Survey Units
- The staff recommends that submittal of the DP or LTP occur only after
sufficient site characterization has occurred. The staff suggests that
the LTP or DP provide sufficient information demonstrating the characterization
of the radiological conditions of site structures, facilities, surface
and subsurface soils, and groundwater. The staff has observed that some
LTPs and DPs have been submitted with incomplete or inadequate characterizations
of radiological conditions. A review of such LTPs or DPs has shown that
the lack of information makes it difficult to agree with the rationale
justifying the proposed classification of survey units. The staff suggests
that the following issues related to the use of characterization survey
results and classification of survey units be considered when developing
either a DP or an LTP:
- Use of operational, post-shutdown scoping, or turnover surveys
as characterization surveys - Characterization surveys are the
most comprehensive of all surveys, yield the most information, provide
the basis to design the final status survey plan, and are used for
dose modeling as well. Characterization surveys are conducted to
determine the current extent and magnitude, and variability (as
surface and depth profiles) of the contamination, and radionuclide
distributions and concentrations. Characterization survey results
are used to guide remediation efforts, provide information with
which to update waste volume and cost estimates, and develop DCGLs.
Given their importance, the staff recommends that characterization
surveys be developed only after the licensee has conducted a thorough
evaluation of the information collected during the HSA, and the
results of operational surveys and post-shutdown scoping surveys.
Accordingly, it is not appropriate to use the results of past operational
and post-shutdown scoping surveys as substitutes for characterization
surveys conducted using the guidance of MARSSIM.
For example, the results of operational surveys may represent radiological
status describing conditions over a brief operational time span or may have
been conducted to address specific occurrences (i.e., post-spill cleanup
assessment). Moreover, the results of both operational and post-shutdown scoping
surveys may be of limited use unless it can be shown that data quality,
instrument calibration methods, and detection sensitivities (fixed and scan
measurements) for the anticipated radionuclide mix are comparable to those
defined for the characterization surveys based on MARSSIM guidance. These
limitations also apply to turnover surveys conducted after the completion of
remediation. In all three instances, this approach is also a departure from the
MARSSIM methodology in that it defeats the statistical basis intended to confirm
that survey units meet the release criteria. As is noted in MARSSIM (Sect.
5.5.2.5), "Measurement locations based on professional judgement violate the
assumption of unbiased measurements used to develop the statistical test described
in Chapter 8" (of MARSSIM). If a licensee were to use turnover survey data for
part of the final survey, statistical samples and/or measurements would need to
be identified in addition to the turnover survey data. Also, the samples and/or
measurements would need to be collected or made in compliance with MARSSIM
guidance (i.e., random start and systematic.
- Reclassification of Survey Units - It may not always be
appropriate to simply separate out an area of elevated activity,
from a Class 2 or Class 3 survey unit, as an individual Class 1
survey unit since the initial basis for evaluating a Class 2 or
3 survey unit is based on specific criteria [i.e., 10 to 100 percent
scan coverage for Class 2, and judgement (typically <10 percent)
for Class 3 survey units]. Similarly, there is a need to provide
the basis in delineating Class 3 survey units as buffer zones around
Class 1 and 2 survey units and areas with insufficient justification
to be classified as non-impacted. If survey results were to reveal
elevated levels of contamination in an arbitrarily selected portion
of a Class 2 or 3 survey unit, then the classification of the entire
survey unit should be deemed suspect and re-evaluated, using MARSSIM
guidance. In this context, the staff suggests first, that there
should be considerations of: the assumptions made as to how the
survey unit was initially classified; most likely or known causes
of contamination; and the possibility that other similarly contaminated
areas within the original survey unit might have gone undetected.
The staff also suggests that a DP or LTP address these considerations
and describe the method, consistent with MARSSIM, that will be used
if a survey unit or portion of a survey unit must be upgraded to
a higher classification level. In general, increasing the coverage
of the scan is less expensive than finding areas of elevated contamination
levels later in the process. Finding areas with elevated levels
of contamination later in the process will require the conduct of
additional surveys, lead to delays in reconsidering the initial
classification of the survey unit, and will lead to additional regulatory
scrutiny. The staff recognizes, in many instances, that LTPs or
DPs are submitted at a time when some characterization work is still
ongoing and that supplemental data may lead to the reclassification
of some survey units. Accordingly, an LTP or DP should include the
flexibility to accommodate changes in the classification of survey
units as more characterization data are obtained and evaluated.
- Completeness of Characterization Survey Design and Results
- In some submittals, the NRC staff has noted that contamination
results for plant structures, systems, and components; surface and
subsurface soils; and groundwater are at times i ncomplete. For
example, the review of data characterizing such areas or media has
revealed that only limited information is being provided about the
presence of TRU (e.g., plutonium-239, americium-241) and hard-to-detect
radionuclides (e.g., hydrogen-3, carbon-14, nickel-63). In other
instances, the data fail to provide sufficient information in determining
the fraction of surface radioactivity that is fixed and removable.
Similar shortcomings were noted for removable alpha and beta radioactivity
found in embedded piping, usually contained in residues, sediments,
and internal film coatings. Although reporting histories of fuel
cladding failures, some plants have not provided information on
the presence of TRU in plant systems and at effluent discharge points.
The characterization of neutron activation products in concrete
and rebar is often limited in scope, and the presentation of the
results fails to address the significance of the reported radionuclide
concentrations and their applicability to other areas of the plant.
In summarizing characterization results, there are instances when
both the average and maximum surface beta activity results are below
the stated MDCs. Such results are misleading since it is not clear
if the stated MDCs are representative of all areas within a survey
unit or whether there might be multiple MDCs that could be unique
to distinct areas within each survey unit. Such results imply that
the variability may apply to all areas within a survey unit, when
perhaps the variability of the contamination might be multi-modal
if it were evaluated by separate and smaller areas. This problem,
in part, is attributed to how the data are edited for summarization.
In other instances, licensees have proposed radiological results
characterizing radionuclide distributions and concentrations using
smears/wipes, air filters, and debris, with no rationale as to the
relevance of the information. It should be noted that characterization
survey results provide the most important information [i.e., the
basis to design the final status survey plan; define radionuclide
distributions and concentrations; identify hard-to-detect radionuclides
and develop surrogate ratios; define survey area classifications;
and assign the sigma characterizing the variability of the contamination
(a key parameter in determining the number of samples in survey
units)].
Accordingly, the planning and execution of any characterization surveys should be
conducted in a manner that will generate technically defensible results with which
to design the final status survey plan.
- Embedded Piping - Nuclear power reactors and other types of
nuclear facilities contain embedded piping that may become radiologically
contaminated as a result of licensed operations. The staff suggests
that LTPs and DPs include a discussion on the methodology for conducting
surveys of embedded piping planned to be left behind. The staff suggests
that sufficient justification for the assumptions considered in the
computer modeling and dose analysis for embedded piping be described
in the basis. Also, the staff suggests that copies of relevant computer
code printouts be included for NRC evaluation.
One approach that has been approved for surveys of embedded piping is to establish a
separate site-specific dose criterion for external penetrating gamma radiation emitted
from the internal surface of embedded piping present in structures (e.g., walls, floors,
ceilings) which are also in the same survey unit. In this approach, the predominant
radionuclide of concern from a dose perspective (e.g., colbalt-60) is determined by
isotopic analysis of scale or residue samples collected within such piping during the
licensee's radiological characterization program. The dose criterion should be based on
bounding conditions developed from characterization data, computer modeling using a
radiation shielding computer code, and a detailed dose analysis of the exposure scenario.
In the model, grit blasting of the internal surface of embedded piping may need to be
considered to assess: (a) any gains from the removal of loose surface activity and (b)
whether the application of grout to immobilize and encapsulate fixed residual surface
contamination would reduce radiation exposures.
It is important to describe the mechanism in which the dose contribution from the
embedded piping and the non-embedded piping portion in a given survey unit is evaluated,
when the dose to either component is determined to be equal to/or greater than the respective
established dose limit, to ensure that the entire survey unit does not exceed the release
criteria. Further, the staff recommends that licensees discuss how adequate scan and
static investigation levels will be implemented and further evaluated, as needed, in
the final status survey. It is also advisable that radiation detectors used for embedded
piping surveys be properly calibrated for this specific geometry [including the use of
National Institute of Standards and Technology traceable radiation source(s)], which
are appropriate for types, energies, and residual concentrations expected in the final
status survey.
- MDCs - The decommissioning process typically involves sites
with multiple radionuclides present at the time the final status survey
is conducted. Although individual radionuclides and their respective
DCGLW values and initial-scan MDCs for the principal radionuclides of
concern have been identified, LTPs and DPs should describe the methodology
and basis on which to implement a scan MDC to account for a mixture
of radionuclides that may remain in a given survey area/unit. The staff
recommends that parameter values such as source (s) and instrument (i)
efficiencies, surveyor efficiency (p), and performance criteria (d'),
which determine the scan MDC, be evaluated before implementation; also,
changes in the default parameter values (e.g., p = 0.5, d' = 1.38) need
to be clearly justified in the LTP or DP.
In MARSSIM, decisions are made on selecting appropriate detection sensitivities or MDCs for
radiological survey and laboratory instruments in the DQO process. Static MDCs within 10 to
50 percent of the DCGLW of the individual radionuclide are often readily achievable; however,
the scan MDC involves a larger number of arbitrary assumptions and decisions. The NRC staff
generally considers the s values described in International Organization for Standardization
(ISO) 7503-1 and ISO 7503-3 guidance for alpha- and beta-emitters to be acceptable estimates,
absent site-specific information, for surface contamination detectors in the final status
survey design. The staff suggests that, in situations where surface contamination measurements
are planned on irregular and uneven surfaces such as scabbled concrete and embedded piping,
licensees determine an appropriate site-specific s value(s). Further, the staff recommends
that the methodology and basis for the s value(s) be provided for NRC review.
When multiple radionuclides are present in the survey area/unit, application of an i value,
the use of a representative, conservative, or beta-weighted average energy for the anticipated
radionuclide mixture, has been acceptable to the NRC staff.
Because the estimated-scan MDCs for open land areas (soils) (Table 6.7 of MARSSIM) are
premised on certain decisions and assumptions involving human factors and survey techniques,
detector characteristics and performance, and computer modeling, it is advisable that licensees
validate (e.g., a posteriori-scan MDC) the a priori-scan MDC used for design goals, as
information is collected and assessed, so that an actual-scan MDC can be calculated for
implementation in the final status survey, for demonstration of compliance.
ADAMS Accession Number ML013510432
- Public Law 91-190.
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