**\[DNFSB LETTERHEAD\]**

April 25, 2007

The Honorable Samuel Bodman

Secretary of Energy

1000 Independence Avenue, SW

Washington, DC 20585-1000

Dear Secretary Bodman:

On April 25, 2007, the Defense Nuclear Facilities Safety Board (Board),
in accordance with 42 U.S.C. § 2286a(a)(5), unanimously approved
Recommendation 2007-1, *Safety-Related In Situ Nondestructive Assay of
Radioactive Materials*, which is enclosed for your consideration. This
Recommendation addresses the measuring of radioactive material holdup at
defense nuclear facilities in the Department of Energy (DOE) complex.

After you have received this Recommendation and as required by 42 U.S.C.
§ 2286d(a), the Board will promptly make it available to the public. The
Board believes that this Recommendation contains no information that is
classified or otherwise restricted. To the extent that this
Recommendation does not include information restricted by DOE under the
Atomic Energy Act of 1954, 42 U.S.C. §§ 2161-68, as amended, please
arrange to have it placed promptly on file in your regional public
reading rooms. The Board will also publish this Recommendation in the
*Federal Register*. The Board will evaluate DOE's response to this
Recommendation in accordance with the Board's Policy Statement 1,
*Criteria for Judging the Adequacy of DOE Responses and Implementation
Plans for DNFSB Recommendations*.

Sincerely,

***A. J. Eggenberger***

***Chairman***

c: Mr. Mark B. Whitaker, Jr.

Enclosure

**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 within DOE. This effort should involve at least two
    actions:

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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:

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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***