[Federal Register Volume 75, Number 247 (Monday, December 27, 2010)]
[Notices]
[Pages 81250-81253]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2010-32365]
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DEFENSE NUCLEAR FACILITIES SAFETY BOARD
[Recommendation 2010-2]
Pulse Jet Mixing at the Waste Treatment and Immobilization Plant
AGENCY: Defense Nuclear Facilities Safety Board.
ACTION: Notice, recommendation.
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SUMMARY: Pursuant to 42 U.S.C. 2286a(a)(5), the Defense Nuclear
Facilities Safety Board has made a recommendation to the Secretary of
Energy concerning the use of pulse jet mixing at the Waste Treatment
and Immobilization Plant located in Washington State.
DATES: Comments, data, views, or arguments concerning the
recommendation are due on or before January 26, 2011.
ADDRESSES: Send comments, data, views, or arguments concerning this
recommendation to: Defense Nuclear Facilities Safety Board, 625 Indiana
Avenue, NW., Suite 700, Washington, DC 20004-2901.
FOR FURTHER INFORMATION CONTACT: Brian Grosner or Andrew L. Thibadeau
at the address above or telephone number (202) 694-7000.
Dated: December 20, 2010.
Peter S. Winokur,
Chairman.
Recommendation 2010-2 to the Secretary of Energy
Pulse Jet Mixing at the Waste Treatment and Immobilization Plant
Pursuant to 42 U.S.C. 2286(a)(5).
Atomic Energy Act of 1954, as Amended.
Dated: December 17, 2010.
Introduction
Legacy wastes from decades of nuclear weapons production by the
Department of Energy (DOE) and its predecessor agencies include high-
level radioactive waste stored in 177 underground tanks at the Hanford
Site. The risk posed by the continued storage of wastes in these tanks
is considerable. Many of the tanks have a history of leakage, several
are more than 60 years old, and most will be far beyond their intended
service life by the time the wastes are retrieved and processed into
stable forms. DOE must ensure that the Hanford Waste Treatment and
Immobilization Plant (WTP) in conjunction with the Hanford tank farm
waste feed delivery system will operate safely and effectively for many
decades to eliminate the safety hazards posed by the wastes. This
imperative requires that the pulse jet mixing and transfer systems
relied upon in the WTP design perform reliably and effectively for
decades of WTP operations, and that technical issues with the
performance of these components be resolved in time to enable DOE to
meet its existing commitment to begin WTP operation in 2019.
Background
In a letter to DOE's Assistant Secretary for Environmental
Management dated January 6, 2010, the Defense Nuclear Facilities Safety
Board (Board) summarized its concerns related to WTP's mixing and
transfer systems; specifically, that the pulse jet mixers (PJMS) lacked
sufficient power to mix adequately and to transfer the most rapidly
settling particles expected to be present in the Hanford waste
inventory. In its letter, the Board identified three significant safety
issues related to pulse jet mixing: (1) Retention of fissile materials
in vessel heels would present a criticality safety concern, (2)
retention of flammable gas due to the presence of solids in vessel
heels, and (3) the presence of a large solids inventory could have a
detrimental effect on the vessel level instrumentation, which is
required to control the PJMs.
In its May 17, 2010, response to the Board's letter, DOE committed
to take actions to increase confidence in successful operation of WTP.
These actions included integrated testing of vessel mixing and transfer
systems at a larger scale. However, DOE did not provide details such as
the scope and schedule for this effort.
On July 1, 2010, the Consortium for Risk Evaluation and Stakeholder
Participation (CRESP), an independent technical review team under
contract to DOE, issued a report that identified concerns similar to
the Board's. Specifically, CRESP found that there was uncertainty in
PJM performance and that the absence of full-scale or near full-scale
testing represented a large risk for the WTP program. The CRESP report
presented DOE with thirteen recommendations that addressed topics of
Board concern, e.g., large-scale testing, reliance upon computational
fluid dynamics modeling, functional performance specifications for
inspecting and accessing vessel bottoms, heel removal needs and
operating strategies, and criticality safety.
On October 7-8, 2010, the Board held a public hearing on WTP
issues, of which one session focused on evaluating the state of the PJM
design. In advance of the public hearing, the Board asked DOE to
respond to written questions related to PJMs. These questions focused
on the scope of integrated testing at larger scale and DOE's actions to
address the concerns raised by CRESP. DOE provided written responses to
the Board's questions on September 8, 2010, but did not provide insight
into the scope or schedule of the large-scale testing. DOE's responses
stated that the objectives and schedule for the large-scale testing
were projected to be established by the end of calendar year 2010; this
has since been revised to January 2011. DOE's response also stated that
DOE and its contractors would address the recommendations from the
CRESP report, but that schedules for addressing most of the
recommendations had not yet been established.
The Board's written questions also asked DOE to describe each open
safety issue related to PJM performance. DOE responded that the primary
safety-related issue that remained open was associated with performance
of the integrated mixing and transfer system, which includes the PJM
mixing system and associated controls, the suction line, and the vessel
sampling system. DOE did not identify any concerns related to
accumulation of solids in WTP vessels.
In response to the questions posed by the Board, DOE included a
response from Pacific Northwest National Laboratory (PNNL) providing
its expert opinion on the adequacy of the PJM design. PNNL has
performed considerable testing and analysis in support of the WTP
mixing system design. PNNL noted in part:
Phase 1 testing performed by PNNL predicted inadequate
mixing in some vessels. The WTP project team subsequently changed the
mixing criterion from complete off-bottom suspension to a bottom-
clearing metric. This change represents a significant reduction of the
mixing criterion.
The WTP project team commissioned additional testing to
this new criterion using waste simulants. PNNL has several concerns
related to the simulants used in the WTP project team's tests, as the
simulants were not necessarily physically representative or bounding of
actual waste. PNNL expressed the concern that mixing performance
observed in the WTP project team's tests may be better than actual
plant performance.
The current design lacks an adequate scaling basis to
relate small-scale test results to full-scale plant performance. The
scaling of the mixing, transfer system, and pump-down process is
complex. The absence of an experimentally validated scaling basis for
pump-down represents a significant weakness of the current design
basis.
During the Board's public hearing, DOE and its contractors
acknowledged the need for large-scale testing and committed to complete
relevant portions of such testing before installing process vessels in
the WTP Pretreatment Facility, which is currently under construction at
the Hanford Site. DOE
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informed the Board that development of suitable waste simulants would
likely be the most time-consuming aspect of the preparations for large-
scale testing. DOE's commitment to complete applicable portions of a
large-scale testing program prior to installation of the Pretreatment
Facility vessels is a positive development.
Unresolved Concerns
The Board believes that the testing and analysis completed to date
have been insufficient to establish, with confidence, that the pulse
jet mixing and transfer systems will perform adequately at full scale.
The Board's unresolved technical concerns are summarized below:
Limitations of the small-scale testing program--The small-scale
testing program did not investigate the performance limits of the PJM
design. Rather, it demonstrated that the mixing system met a reduced
mixing criterion using simple simulant materials that were not fully
representative of the characteristics of Hanford's high-level wastes.
The testing program did not evaluate the entire range of WTP operating
conditions, used non-prototypic equipment for much of the testing, and
did not include multi-batch test runs to establish whether the mixing
and transfer systems could operate for long periods under a variety of
operating conditions. The program did not address the behavior of non-
Newtonian wastes, such as the effects of variations of viscosity within
a vessel, or the unique arrangement of PJMs in vessels containing these
wastes. Pump-out testing did not include prototypic simulant or
transfer system components, and lacked a well-established scaling
basis. Large-scale testing would remedy this issue.
Modeling of mixing performance--Computer simulations of mixing
performance, such as the Low Order Accumulation Model, have not been
verified and validated, yet have been used to advance the WTP mixing
design. DOE plans to use computer simulations in validating the final
WTP mixing design and is working to verify and validate a computational
fluid dynamics code (FLUENT) for this purpose. Any use of computer
simulations must be technically defensible, and the limits of each
computational fluid dynamics simulation need to be well understood to
prevent potential safety issues from arising during operations.
Waste characterization and feed certification--The WTP safety
strategy depends upon obtaining representative samples from the high-
level waste feed tanks to support WTP's waste feed certification
requirements, and from WTP process vessels to ensure safety-related
criteria are met. This capability has not been demonstrated in the
Hanford Tank Farms or WTP process vessels. Obtaining samples that are
sufficiently representative to support bounding estimates of the
composition and properties of both the solid and liquid fractions of
the high-level waste is required in order to demonstrate that the WTP
can be operated safely (e.g., prevent inadvertent criticality and
plugging of transfer lines).
The WTP project team has altered its mixing performance criterion
and made changes to the waste acceptance criteria, such as reducing the
allowable solids concentration for WTP feed to address unfavorable
mixing test results. DOE and its contractors have not yet been able to
explain the full impact of these changes on DOE's ability to qualify
WTP feed and process the entirety of Hanford's high-level waste using
WTP. Additionally, DOE and its contractors have not been able to
explain how representative samples from PJM-mixed tanks will be
obtained.
Planned WTP process vessel modifications--DOE is planning to add
capabilities for heel dilution, vessel pump-out, and visual inspection
to address potential risks and uncertainties remaining from small-scale
testing; however, the specifications for and capabilities of these
systems have not been established.
Limitations of PJM controller and instrumentation testing--DOE has
not performed PJM controller and instrumentation tests with a
combination of (1) A prototypic simulant; (2) a full-scale PJM system
driven by jet pump pairs; and (3) prototypic level/density
instrumentation and controllers. Pretreatment Engineering Platform
testing revealed that the level/density probes provided spurious data
because of plugging and interference resulting from hydrodynamic
pressures from the PJMs and transfer pumps. In addition, PNNL stated
that the PJM controller testing performed in 2009 had several
limitations and that ``any extrapolation of the data above and beyond
the scope of the present work should be done with extreme caution.''
Recommendation
Therefore, the Board recommends that DOE:
1. Develop a large-scale test plan, including a schedule and
milestones that addresses the issues raised by the Board in this
recommendation, by CRESP in its letter reports addressing pulse jet
mixing, and by PNNL. The objective of the test plan should be to define
the limits of the WTP pulse jet mixing and transfer systems given the
complete range of physical properties for the high-level waste stored
in the Hanford Tank Farms. The elements of the test plan should
include: (1) Design of simulants; (2) design of the prototypic mixing
systems, including PJM control and tank level control systems, and the
transfer system for the large-scale test; and (3) criteria for review
and interpretation of the large-scale test results. The test plan
schedule should be constructed such that results from the testing can
be used to inform WTP process vessel design decisions. The large-scale
test platform must integrate the scaling of the mixing and transfer
systems such that the scaling of the test platform is technically
defensible.
2. Develop waste simulants for the mixing and transfer system
testing that envelope the complete range of physical properties for the
high-level waste stored in the Hanford Tank Farms. The simulant
selection should include simulants representative of the waste's
Newtonian and non-Newtonian properties and particle shape, e.g.,
irregularly shaped simulant particles. The physical properties selected
for each simulant must reflect uncertainties in the existing
characterization of the high-level wastes.
3. Complete verification and validation of any computational models
used by the WTP project team (e.g., Low Order Accumulation Model and
FLUENT) based on the results from the large-scale testing.
4. Demonstrate the ability to obtain representative samples of the
solids and liquids in all of WTP's vessels, including demonstrating
that representative samples can be obtained even if the assumed WTP
design particle size or density is exceeded. This will ensure that the
sampling system does not exclude large, dense particles and
artificially bias the measured particle size and density distribution.
The representativeness of these samples must be statistically
defensible and meet appropriate confidence limits given the
significance of the safety-related issues in WTP.
5. Define the impact on the waste retrieval, feed delivery, and
feed certification processes due to any limitations of the WTP mixing
and transfer systems, and demonstrate the ability to obtain adequately
representative samples from the waste feed tanks to ensure the WTP
waste acceptance criteria can be reliably enforced.
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6. Establish functional design criteria for the heel dilution, heel
pump-out, and visual inspection functions, and demonstrate the
capabilities and limits of these systems through the large-scale
testing.
7. Identify the technical and safety-related risks that remain
unresolved upon completion of the large-scale testing and establish
suitable risk management strategies to ensure that each remaining risk
will have little, if any, potential impact on DOE's ability to begin
WTP operations safely and consistent with existing commitments.
In order to preclude unnecessary delay in the WTP project, the
Board urges the Secretary to avail himself of the authority under the
Atomic Energy Act (U.S.C. 2286d(e)) to ``implement any such
recommendation (or part of any such recommendation) before, on, or
after the date on which the Secretary transmits the implementation plan
to the Board under this subsection.''
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Peter S. Winokur, Ph.D.,
Chairman.
[FR Doc. 2010-32365 Filed 12-23-10; 8:45 am]
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