[Federal Register: May 2, 2007 (Volume 72, Number 84)]
[Notices]
[Page 24279-24281]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr02my07-40]
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DEFENSE NUCLEAR FACILITIES SAFETY BOARD
[Recommendation 2007-1]
Safety-Related In Situ Nondestructive Assay of Radioactive
Materials
AGENCY: Defense Nuclear Facilities Safety Board.
ACTION: Notice, recommendation.
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SUMMARY: The Defense Nuclear Facilities Safety Board has made a
recommendation to the Secretary of Energy pursuant to 42 U.S.C.
2286a(a)(5) which addresses the measuring of radioactive material
holdup at defense nuclear facilities in the Department of Energy
complex.
[[Page 24280]]
DATES: Comments, data, views, or arguments concerning the
recommendation are due on or before June 1, 2007.
ADDRESSES: Send comments, data, views, or arguments concerning this
recommendation to: Defense Nuclear Facilities Safety Board, 625 Indiana
Avenue., NW, Suite 700, Washington, DC 20004-2001.
FOR FURTHER INFORMATION CONTACT: Brian Grosner or Andrew L. Thibadeau
at the address above or telephone (202) 694-7000.
Dated: April 27, 2006.
A.J. Eggenberger,
Chairman.
Recommendation 2007-1 to the Secretary of Energy
Safety-Related In Situ Nondestructive Assay of Radioactive
Materials
Pursuant to 42 U.S.C. 2286(a)(5); Atomic Energy Act of 1954, As Amended
Dated: April 25, 2007.
Overview
There are many situations in which the quantity and composition
of radioactive material must be determined. In some instances,
access to the material is impossible or undesirable, and
consequently, weighing, laboratory analysis, and calorimetry are not
viable options. In these cases, in situ nondestructive assay (NDA),
based on the measurement of signature emissions from a specific
isotope of interest, is used to provide an estimate of the type and
quantity of radioactive material present. However, large
uncertainties and inaccuracies have occurred in estimating the type
and quantity of radioactive material using in situ NDA. These
uncertainties and inaccuracies include incorrect assumptions about
shielding and the spatial distribution of radioactive material, as
well as poor measurement techniques. Measurement errors, in turn,
lead to potential criticality accident conditions, unexpected
radiation exposure to workers, and underestimation of radioactive
material available for release in accident scenarios.
In most nuclear safety areas, the Department of Energy (DOE) has
captured required elements for robust site programs through its
Directives system. These elements include requirements necessary for
proper functioning of the program, training and qualification
standards for personnel, assessment criteria to ensure proper
implementation of requirements, and feedback mechanisms for lessons
learned and continuous improvement. However, DOE has not established
programmatic requirements for NDA, even though this method is
heavily relied upon for nuclear safety throughout the complex and is
key to many DOE activities. The capability to perform accurate
measurements and use the results to determine compliance with
nuclear safety limits is absolutely essential.
Research and development efforts for NDA have historically
focused on the areas of material control and accountability and
nuclear material safeguards; advances in these areas have
peripherally benefitted in situ NDA measurement capabilities.
Current research and development efforts appear to hold little
promise for addressing needed improvements for in situ NDA
measurement. For example, development of instrumentation and
measurement techniques is needed to reduce overall measurement
uncertainties.
Examples
Three notable instances of recent errors associated with in situ
NDA measurement of radioactive material holdup are discussed below.
These errors resulted from the use of inaccurate correction factors
regarding material geometry assumptions or failure to perform
measurements at locations where the material was accumulating. In
each of these cases, the amount of radioactive material was
initially underestimated, resulting in a smaller-than-expected
safety margin and violations of criticality safety limits.
Material holdup in 6-inch diameter vacuum system pipe at the Hanford
Site's Plutonium Finishing Plant was assumed to be in the form of a
0.25 inch layer at the bottom of the pipe. Using a correction factor
for this geometry, the initial estimate of material was about 1 kg.
When workers then proceeded to remove the piping, it was found to be
filled with a solid plug of material, and the actual amount of
material present was nearly twice as high as the initial estimate.
Measurement of an exhaust filter at the Y-12 National Security
Complex assumed that fissionable material was loaded only on the
face of the filter. An estimate of a few hundred grams of material
was obtained using correction factors for this geometry. Subsequent
investigation showed that material was loaded throughout the filter,
and not just on the face. The actual amount of fissionable material
present was several times the initial estimate.
A second exhaust filter at the Y-12 National Security Complex was
measured periodically using NDA, but the measurement point was not
where the fissionable material was accumulating. Once this error was
discovered, follow-up measurements showed significant material
accumulation.
In each of these instances, site-specific corrective actions
were taken based on the specific problem encountered. Lessons
learned from these events do not appear to have been shared within
the DOE complex. Complex-wide corrective actions have not been
identified to minimize the occurrence of similar events at other
sites. The Board is concerned that undiscovered problems currently
exist at other facilities within the DOE complex. It is incumbent
upon DOE and its contractors to review current in situ NDA
measurements to determine whether the assumptions used to derive
results are sufficiently conservative to ensure compliance with
nuclear safety limits.
Issues
Three main issues dominate the current technical and regulatory
landscape regarding in situ NDA measurements: (1) Lack of
standardized requirements for performing measurements, (2) lack of
design requirements for new facilities that would facilitate
accurate holdup measurement, and (3) lack of research and
development activities for new instrumentation and/or measurement
techniques. Each of these issues is discussed below.
Lack of Standardization--DOE has not established requirements or
guidance for performing in situ measurements in its Directives
system. While the Board recognizes that measurement techniques can
be highly location specific, a requirement to follow methods
outlined in national consensus standards when performing in situ NDA
measurements would reduce the errors and uncertainty of results.
Commercial guidance for NDA is available in a series of standards
published by the American Society for Testing and Materials (ASTM).
This series addresses good practices for performing NDA
measurements, methods for performing specific types of NDA
measurements (for example, ASTM C-1133-03, NDA of Low-Density Scrap
and Waste by Segmented Passive Gamma Ray Scanning), and training and
qualification of NDA personnel. While this guidance has been used
informally at some sites, DOE has not required its use for NDA
measurements.
Lack of Design Requirements for New Facilities--Many of the
problems that require in situ NDA to determine radioactive material
holdup arose because facilities were designed and built before the
need for NDA technology was evident. As a result, no consistent
attempt was made to design facility systems to minimize holdup or
facilitate its measurement. This historical trend should not be
repeated in new facilities. The necessity of monitoring radioactive
material holdup must be considered in the design of new facilities.
For example, locations for monitoring can be selected during the
design phase on the basis of the most likely locations for holdup to
occur. Calibrations can then be performed at these locations before
the facility begins operations to provide a baseline for future NDA
measurements. Facilities can also be designed to minimize holdup in
areas where it may be of concern.
Lack of Research and Development Activities--Los Alamos National
Laboratory (LANL) conducted NDA research for more than 20 years.
LANL developed most of the NDA techniques in current use, and
conducts associated training programs. However, it is not clear that
any significant research and development for in situ NDA
measurements is currently being conducted within DOE to address
serious concerns with material holdup. Research and development
activities are focused in other areas, such as nuclear material
safeguards and homeland security, but these efforts have different
objectives and may not yield results that are beneficial for
measurements using in situ NDA.
Recommendation
The Board, therefore, recommends that DOE:
1. Evaluate the extent of condition regarding inaccurate in situ
NDA programs
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within DOE. This effort should involve at least two actions:
A. Identifying all cases within the defense nuclear complex in
which in situ NDA results are used to ensure compliance with nuclear
safety limits.
B. Reviewing the cases identified in step 1.A to validate that
the protocols, methodologies, calculations, and assumptions used to
obtain NDA results are sufficiently conservative. This review should
take into consideration lessons learned from recent events.
2. Establish requirements and guidance in a DOE directive or
directives. The requirements and guidance should focus on in situ
NDA programs that are used to demonstrate compliance with nuclear
safety limits. Particular issues to be addressed should include:
A. Training and qualification standards for personnel involved
in performing NDA measurements, interpreting and reviewing results,
and managing site programs.
B. Application of standard protocols and methodologies, such as
those given in the national consensus series issued by ASTM, for
performing NDA measurements.
C. Standardization of correction factors for common situations
(geometry and self-attenuation factors) and consistent application
of uncertainty values.
D. Reinforcement of the use of formal lessons-learned mechanisms
in the application of NDA programs so that information can be shared
easily among affected DOE sites.
E. Incorporation of features in the design of new facilities to
minimize radioactive material holdup and facilitate accurate NDA
holdup measurements.
F. Periodic assessments of the need for new NDA technology and
the status of ongoing NDA-related research and development programs.
G. Periodic assessments to ensure that NDA programs are using
the best available technology.
H. Incorporation of appropriate quality assurance elements into
in situ NDA measurements when used for compliance with nuclear
safety limits as required by 10 Code of Federal Regulations Part
830.
A.J. Eggenberger,
Chairman.
[FR Doc. E7-8374 Filed 5-1-07; 8:45 am]
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