**\[DNFSB LETTERHEAD\]**

March 18, 2005

The Honorable Linton Brooks

Administrator

National Nuclear Security Administration

U.S. Department of Energy

1 000 Independence Avenue, SW

Washington, DC 20585-0701

Dear Ambassador Brooks:

On November 3, 2004, the Defense Nuclear Facilities Safety Board (Board)
sent a letter to the National Nuclear Security Administration (NNSA)
requesting a report on actions being taken to identify and correct any
deficiencies in the Device Assembly Facility (DAF) structure, its
equipment, or its safety management programs to support the increased
scope and operational tempo of activities at the Nevada Test Site. The
Board has reviewed your response of February 8, 2005. While the response
does not appear to fully address the Board\'s concerns, follow-on
discussions are being held with NNSA to better understand the process
being used to identify and address deficiencies at DAF.

The enclosed report prepared by the Board\'s staff provides an example
of ongoing facility degradation that needs to be addressed.
Specifically, there is extensive rainwater leakage into the facility
through expansion joints and building penetrations, and possibly through
structural cracks. There is also extensive cracking of the facility
walls and floors. This latter condition was known, and a published
report indicates concrete shrinkage as the cause; however, this
interpretation appears to be incompatible with the locations of the
cracks and the duration of the construction period. A unique aspect of
DAF is that it was exposed to ground motion from several years of
underground testing, both during and after construction. Thus, DAF has
been subjected to an unknown level of vibratory ground motion that
should be quantified as part of any effort to understand the potential
cause of concrete cracking. The locations and extent of the structural
cracks must be investigated and documented more thoroughly before
confidence in the cause of the cracking is warranted. A comprehensive
review of the structural capability of the facility and any necessary
repairs cannot be completed prior to this condition assessment.

In light of these observations and your schedule for expanded nuclear
operations, an immediate condition assessment of DAF is warranted.
Therefore, pursuant to 42 U.S.C. §2286b(d), the Board requests a report
within 45 days of receipt of this letter providing the results of a
condition assessment and mapping of building leaks and structural cracks
at DAF.

The report should address the extent and paths of the rainwater leakage
problem, which should be investigated as soon as possible before the
evidence disappears with the end of the rainy season. The report should
also provide NNSA's plans for addressing any identified deficiencies.

Sincerely,

***John T. Conway***

***Chairman***

c: The Honorable Everet H. Beckner

Ms. Kathleen A. Carlson

Mr. Mark B. Whitaker

Enclosure

**DEFENSE NUCLEAR FACILITIES SAFETY BOARD**

**Staff Issue Report**

**MEMORANDUM FOR:** J. K. Fortenberry, Technical Director

**FROM:** J. Kimball

**SUBJECT:** Device Assembly Facility Seismic/Structural Review

The staff of the Defense Nuclear Facilities Safety Board (Board) met
with personnel from the National Nuclear Security Administration's
(NNSA) Nevada Site Office and its contractors and consultants on
February 23−24, 2005, to discuss the seismic/structural adequacy of the
Device Assembly Facility (DAF) at the Nevada Test Site. The purpose of
the meeting was twofold: to perform a walkdown of DAF to gain an
appreciation of the extent of concrete cracking on the walls and floors,
and to discuss the status of previous analyses of seismic hazards and
seismic structural adequacy.

The DAF manager provided an overview of the operations and safety basis
for DAF.

Construction of DAF occurred between about April 1988 and July 1989. As
noted below, these dates are important in understanding the cause of
observed concrete cracking. The facility manager summarized actions that
have been initiated to update the DAF seismic hazard assessment.
Lawrence Livermore National Laboratory (LLNL) has determined that the
existing probabilistic seismic hazard analysis (PSHA) is no longer
current and must be updated. LLNL has prepared a preliminary draft
project plan to initiate this work, and is in the process of securing
funding for project execution. In addition, a master equipment list is
being prepared for each DAF building. Such a list is important for
ensuring that seismic qualification of equipment is complete.

The DAF walkdown gave the Board's staff an opportunity to visit numerous
buildings within the facility (cells, bays, bunkers, etc., are referred
to as "buildings") to observe the size and spacing of cracks that have
been noted in the concrete walls and floors. The walkdown included
buildings on both the first and second floors. The staff made several
observations:

Cracking of the walls and floors generally occurs in regular spaced
patterns, with many cracks progressing circumferentially down one wall,
across the floor, and up the opposite wall. Observation of roof cracks
was not possible because of the existence of false ceilings.

-   The cracking is prevalent throughout the facility, including cell
    round rooms. Given the duration of construction, about 1 year, it is
    difficult to attribute the cracking to concrete shrinkage as
    concluded in a memorandum prepared by LANL dated July 1, 2003. Given
    the wide range of environmental conditions that most likely occurred
    during the 1 year construction period, certain sections of the
    building would be expected to remain relatively crack free. This was
    not the case. Moreover, cracks located about 10 feel from expansion
    joints are not likely due to concrete shrinkage, which should have
    occurred during the curing period when backfill was not yet in
    place.

-   There was some discussion regarding the cause of the observed
    cracking. The staff raised questions regarding the ground motion
    experienced by DAF as a result of the nuclear testing program,
    before such testing was halted in 1992. While DAF personnel appear
    to favor concrete shrinkage as the cause of the cracking, this
    interpretation is subject to debate. The staff encouraged DAF
    personnel to compile data on the ground motion from these events at
    DAF.

-   Forty-two of the cracks are being monitored. It was not clear to the
    staff why certain cracks were selected for monitoring and whether
    the worst cracks are being monitored. Some of the crack monitors
    could be challenged as showing minor amounts of rotation. However,
    surveys of crack widths indicate that little if any movement
    occurred between 1999 and 2005.

-   While an exact count was not made, numerous water leaks were
    observed. Prior to the staffs visit, the area in the vicinity of DAF
    had experienced a large amount of rainfall. While some of the leaks
    were aligned with expansion joints (there are four such joints),
    many were not. It was not clear whether water was also coming into
    the facility via penetrations and building cracks. The amount of
    leakage calls into question the integrity of the liner between the
    concrete roof and overlying soil. The conduct of nuclear operations
    under the current state of water leakage may not be appropriate.

The staff developed a list of underground nuclear tests that occurred
during and after construction of DAF. The data revealed that DAF has
experienced ground motion from at least 25 tests, 11 of which are within
about 25 kilometers of the site. One of these tests had energy
equivalent to that of a magnitude 5.9 earthquake. The staff will pursue
the estimation of ground motions for these events as part of the effort
to understand the cause of concrete cracking.

LLNL staff and consultants reviewed the previous simplified DAF PSHA and
structural analysis. The simplified PSHA was completed by Geomatrix
Consultants in 1996. A former Geomatrix staff member noted that the
original PSHA work was based on the assumption that detailed
documentation of the PSHA results would be provided in a follow-up
phase. This phase was not completed by LLNL. Given that the existing
simplified DAF PSHA is about 10 years old, LLNL personnel recognize that
an update is needed. This determination was prompted by changes in the
state of practice, particularly the modeling of earthquake ground motion
attenuation (results that have become available from the Yucca Mountain
Project PSHA), and the need to collect better DAF specific geotechnical
data to understand the site's response to earthquake ground motion.
Investigations are planned to obtain subsurface information such as the
shear wave velocity for subsurface soils. The staff was provided some
preliminary information suggesting that the thickness of soils at DAF
may be as great as 1,000 feet.

LLNL staff reviewed the original DAF static seismic design completed in
the mid 1980's, and results from a dynamic analysis completed in 1996.
The Board's staff noted that the 1996 dynamic analysis provided
insufficient information to judge the overall DAF seismic structural
adequacy. LLNL staff agreed that significant improvements should be made
to the dynamic analysis. LLNL plans to complete a dynamic soil structure
interaction analysis using results from the PSHA update.