[DNFSB
LETTERHEAD]
October 17, 2005
The Honorable Samuel W. Bodman
Secretary of Energy
1000 Independence Avenue, SW
Washington, DC 20585-1000
Dear Secretary Bodman:
A key function of the Defense
Nuclear Facilities Safety Board (Board) is to review the design and
construction of new Department of Energy (DOE) defense nuclear facilities and recommend
such modifications as the Board considers necessary to ensure adequate
protection of public health and safety. The Board has considered the treatment of high-level
waste at the Hanford Site as a system, including the high-level waste tanks,
new treatment facilities, and interfaces. As such, the Board believes that a
conservatively designed Waste Treatment Plant (WTP) that will remain operable
following any natural phenomenon hazard is essential to the treatment and
disposal of this waste. The Board
continues to review nuclear safety aspects of the design and construction of
the WTP on this premise. The bases for
our oversight reviews are DOE’s orders, standards, and directives, supplemented
by industry standards and the state of the practice. The Board believes it would be useful for you
to have a benchmark understanding of the state of our nuclear safety reviews at
WTP.
For the past several years, the
Board has performed safety-related reviews of the WTP design and construction
efforts. The Board has communicated to
DOE a number of safety-related issues in the areas of seismic ground motion,
structural engineering, chemical process safety, fire protection, waste feed
delivery, electrical distribution, instrumentation and control, and ventilation
for confinement and process systems. The
Board believes DOE has responded to these issues, though not always in a timely
manner, and has provided technically sound paths forward for their resolution. The following paragraphs summarize the primary
remaining safety issues identified by the Board to date, as well as the status
of DOE’s efforts to address these issues.
These nuclear safety issues can
be divided into four major areas:
Seismic
Ground Motion. In letters to DOE dated July 30,
2002; January 21, 2003; July 29, 2004; and April 19, 2005,
the Board identified numerous issues regarding the earthquake ground motion
criteria specified by DOE for WTP. The
approach used to develop these criteria is based on probability theory and
provides a “design basis event estimate” for plant design. Furthermore, original WTP ground motion
criteria assumed that the response of the site’s soil and rock characteristics
would be similar to that in California (i.e., the California attenuation
relationship). The geotechnical ground
motion community considered that approach acceptable in the early 1990s. By 2002, however, more representative,
site-specific attenuation relationship approaches had become available and were
in use at other DOE sites, based in part on the use of measured on-site soil
and rock properties.
Shortly after the Board began to
exercise safety oversight of the WTP project in late 2001, the Board questioned
the use of the California attenuation relationship, with the belief that it
could result in an increase in the ground motion at the Hanford Site. The Board requested that DOE address this
issue. In response, DOE chose to
estimate site-specific attenuation while allowing its contractor for WTP,
Bechtel National Incorporated (BNI), to continue with the plant design. In studying this issue, DOE found that the
soil column below WTP was reduced relative to that originally assumed, which
accounts for a significant increase in ground motion. DOE’s efforts eventually led to the
development, in February 2005, of significantly more demanding interim ground
motion criteria (interim criteria).
Although the Board believes that
the interim criteria provide a reasonably conservative basis for continuing
with the plant design, some important uncertainties remain. The only means of reducing these uncertainties
is to measure soil and rock properties under the WTP site. These measurements would allow development of
a site-specific attenuation relationship. DOE has decided to measure site-specific
properties using a deep drilling program and estimates that effort will require
up to 2 years before final ground motion design criteria can be determined.
BNI is in the process of
updating the structural model for the building and preparing to reanalyze the
High Level Waste and Pretreatment facilities using the interim criteria. This effort will determine the impact of the
ground motion increase on the already constructed slabs and walls. Based on its understanding of the existing
design margins in these two facilities, the Board does not believe significant
reconstruction of existing slabs or walls will be necessary. However, the planned reanalysis is required
to substantiate this belief.
BNI is also evaluating
safety-related facility and chemical processes equipment to determine the
impact of using the interim criteria. In
contrast to potential impacts on the already constructed slabs and walls, the
impact of the increased ground motion on equipment is not as well understood. The Board is aware that DOE is using a peer
review team to assist in its review of BNI’s evaluation. The Board views the continuing involvement of
these technical experts as a crucial aspect of DOE’s oversight and believes the
review team will provide the expertise necessary for successful and economical
resolution of any technical issues that remain.
The Board believes that:
Structural
Engineering. To address safety issues raised
by the Board, BNI is currently revising the structural design bases, as well as
the structural models, for the High Level Waste and Pretreatment facilities. These revisions address issues related to the
mesh density used in the structural models, application of thermal loads, and
unique aspects of the High Level Waste building design. The Board has also asked DOE to identify how
loads are distributed throughout the structural members for each facility so
the local and global behavior of the structural components during seismic
loading can be understood. Based on
information provided by DOE and BNI, the Board expects that its review of the
design bases, acceptance criteria, and model revisions should be reasonably
straightforward since only a few issues remain unresolved. In addition, once re-analyses of the
facilities have been completed, the design basis documentation and the summary
structural reports, which provide load distributions in the High Level Waste and
Pretreatment facilities, can be revised.
Chemical
Process Safety. Three issues related to chemical
process safety need to be addressed: hydrogen
generation rate estimates, hydrogen in pipes and ancillary vessels, and pulse
jet mixing of non-Newtonian fluids.
Hydrogen
Generation Rate―In its letter of November 4, 2002, the Board informed DOE of
its concerns regarding the hydrogen generation rate estimates being used to
design WTP hydrogen mitigation systems. These concerns were based on BNI’s use of the
generation rate for the Hanford Tank Farms as the WTP design basis. The Board suggested that the markedly different
processing and accident conditions in WTP were not accurately reflected in that
generation rate. DOE undertook studies
to address this issue and revised its design basis generation rate equation to
reflect the WTP process more accurately. The new generation rate equation appears to
represent a conservative means of predicting hydrogen generation for WTP.
DOE has also revised the design
basis for the waste feed to be consistent with an updated forecast of waste
feed characteristics. Preliminary
calculations indicate that the actual amount of hydrogen generated in WTP
processes will be significantly lower than previous estimates. This, however, does not eliminate the hydrogen
hazard from WTP. BNI is in the process
of revising its final estimate of the quantity of hydrogen that will be
generated during WTP operations and will incorporate this information into the
design and safety bases. The approach
being undertaken by BNI appears reasonable to the Board.
Hydrogen
in Pipes
and Ancillary Vessels―The Board believes that BNI has
correctly identified hydrogen hazards associated with pipes and ancillary
vessels. The Board’s preliminary review
indicates that BNI has developed some engineering solutions that will successfully
prevent hydrogen-related accident scenarios. The exception appears to be BNI’s desire to
accept the risk associated with hydrogen deflagrations and detonations when a component
failure would not adversely impact the public, collocated and facility workers,
or other safety-class and safety-significant systems. If this is BNI’s strategy, the Board expects
that DOE will demonstrate that the likelihood of these accidents is extremely
remote and that the public and collocated and facility workers will be
protected. Additionally, the design
needs to meet all applicable codes and standards and minimize the potential
impact on WTP safety-related systems and site risk reduction objectives (e.g.,
timely treatment of tank waste).
The Board recognizes that DOE
has just begun its review of BNI’s strategy for dealing with these
hydrogen-related issues and has not approved the final hydrogen mitigation
design criteria or the final design. The
Board believes DOE must not rush its evaluations of BNI’s proposals and must
demand a full understanding of the potential impacts of this design approach. DOE also needs to consider the entire spectrum
of risk associated with these types of accidents (e.g., safety and mission
risk) before approving a design with any inherent weaknesses. The Board believes this will be a difficult
undertaking.
Pulse
Jet Mixing of non-Newtonian Fluids―In its letter of March 24, 2004,
the Board identified issues associated with the research and development test
data being used to design the equipment for mixing non-Newtonian high-level
waste. Although BNI has not completed
the final mixing design, the research completed by BNI’s research organization
and Pacific Northwest National Laboratory indicates that BNI has developed a
sufficient understanding of the requirements for mixing non-Newtonian fluids. The Board is aware of a number of design approaches,
such as not requiring redundancy in certain cases, that
will require careful DOE review before final designs can be approved. However, the Board believes BNI can develop a design
that meets existing safety requirements upon completion of remaining research
activities and ongoing engineering work.
Fire
Protection. In its letter of July 21, 2004,
the Board identified issues related to BNI’s proposal to minimize the
protection of structural steel against potential fires at WTP. After that letter was issued, BNI changed its
approach, and it is currently preparing the technical basis for meeting
applicable code requirements related to fireproofing structural steel. It is the Board’s
understanding that BNI now wishes to provide fire protection for
selected structural steel members based on their role in supporting the
structure during and after a fire, instead of protecting every member. This strategy is acceptable if it can
reasonably be shown that unprotected structural members with reduced material
properties due to a fire would not be relied upon to support the building. BNI is in the process of preparing the
appropriate structural design criteria and implementing this strategy across
the project. If this strategy is to be
effective, the Board believes DOE must understand precisely how loads are
distributed throughout each facility and account for degradation of the steel’s
material properties as the result of a fire. The Board notes that developing a well-defined
load path in the High Level Waste facility is difficult.
Conclusion. The
Board believes that the issues discussed above can be resolved on a timely
basis and do not preclude continuing with the design and construction of the
High Level Waste or Pretreatment facility. With the exception of the issue of hydrogen in
pipes and ancillary vessels, DOE has committed to appropriate paths forward for
addressing these issues. At the same
time, however, it is important that DOE provide in-depth oversight of WTP to ensure
that these issues are adequately resolved. DOE should continue to obtain and use expert peer
review groups to supplement and extend its technical capabilities as required
during the design, construction, startup, and operation process.
The Board will continue its
reviews of the design and construction of this important project. Please contact me if you have any questions on
the matters raised above.
Sincerely,
A. J. Eggenberger
Chairman
c: The Honorable James A.
Rispoli
Mr.
Roy J. Schepens
Mr.
Charles E. Anderson
Mr.
Mark B. Whitaker, Jr.