[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 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.