[Federal Register Volume 72, Number 84 (Wednesday, May 2, 2007)]
[Notices]
[Pages 24279-24281]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E7-8374]


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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

[[Page 24281]]

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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