Pulse Jet Mixing at the Waste Treatment and Immobilization Plant, 81250-81253 [2010-32365]

Agencies

• Defense Nuclear Facilities Safety Board

[Federal Register Volume 75, Number 247 (Monday, December 27, 2010)]
[Notices]
[Pages 81250-81253]
From the Federal Register Online via the Government Printing 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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