[DNFSB
LETTERHEAD]
July 21, 2004
Mr. Paul M. Golan
Acting Assistant Secretary for
Environmental Management
U.S. Department of Energy
1000 Independence Avenue, SW
Washington, DC 20585-0113
Dear Mr. Golan:
Enclosed is a report detailing
observations made by members of the staff of the Defense Nuclear Facilities
Safety Board concerning ventilation systems being designed for the Hanford Site’s
Waste Treatment Plant. These
observations were developed through document reviews and discussions with
representatives of the Office of River Protection and Bechtel National, Incorporated.
In general, the design requirements for
the ventilation systems in the Waste Treatment Plant facilities are sound. Several specific areas were noted, however,
that warrant increased attention as the design progresses. Of particular note is the design of the
ventilation system for the safe haven, which is manned during an accident to
allow for remote process shutdown, located in the Pretreatment facility annex. Other specific comments are discussed in the
enclosed report, which is forwarded for your information and use, as
appropriate.
Sincerely,
John T. Conway
Chairman
c: Mr. Roy J. Schepens
Mr. Mark
B. Whitaker, Jr.
Enclosure
DEFENSE
NUCLEAR FACILITIES SAFETY BOARD
Staff
Issue Report
June
14, 2004
MEMORANDUM FOR: J. K. Fortenberry, Technical Director
COPIES: Board Members
FROM: R. Kasdorf and R. Zavadoski
SUBJECT: Hanford Waste Treatment Plant—Ventilation Systems
This report documents a visit to
the Hanford Site made by the staff of the Defense Nuclear Facilities Safety
Board (Board) to continue its review of the design of various ventilation
systems for the Waste Treatment Plant. The previous ventilation review occurred in June
2002. Participants in the review
included the Department of Energy’s (DOE) Office of River Protection and it’s primary contractor, Bechtel National, Incorporated.
Confinement
and Process Ventilation Systems. The contractor provided the
status of the confinement ventilation systems in each of the Waste Treatment
Plant facilities—High
Level Waste, Low Active Waste, Pretreatment, and the Analytical Laboratory. The staff toured the first three partially
complete facilities. The review included
the confinement ventilation systems, as well as the process and melter off-gas
systems. The review focused on the
derived safety classification for each system in each facility, including the
criteria and standards applied to each. Additionally, the staff evaluated the seismic
and electrical power supply requirements specified for the ventilation systems.
Safety
Classification—The
safety classification of the various sections of the ventilation systems and
support systems was logical and consistent with requirements. The staff did note that one support system in
the Pretreatment facility supplying hot air to help protect safety-class high-efficiency
particulate air (HEPA) filters was classified as a nonsafety system. The staff requested the technical basis for
this classification.
Standards
Applied—The Code on
Nuclear Air and Gas Treatment, designated AG-1a-2001 by the
American Society of Mechanical Engineers, is the code of record for the Waste
Treatment Plant project. This code is
appropriate for most components of nuclear air-cleaning systems. The contractor noted that the code does not
address radial HEPA filters. The contractor
provided a comparison of the Waste Treatment Plant specifications with the requirements
of Section FC, HEPA Filters, of the AG-la-2001 code. The contractor also noted that the new DOE Nuclear
Air Cleaning Handbook, DOE-HDBK-1169, has been used
for guidance in complying with the authorization basis for the Waste Treatment
Plant project and the Washington Administrative Code.
Seismic
Design—The contractor has determined the
level of seismic robustness required for each component in the confinement and
process ventilation systems. The most
stringent level is designated Seismic Criteria I and the least Seismic Criteria
IV. The requirements for each
designation (the relevant portions of the AG-la-2001 code) are specified in
procedures and equipment specifications. The planned ventilation filter housing shaker
table tests are scheduled for this summer. The contractor stated that a
bounding seismic spectra will be used as input for the shaker table
tests. The staff will review the
bounding data for suitability.
Electrical Supplies—The contractor presented a
tabulation of the ventilation systems’ electrical components and their source
of electrical power. Those components
designated as safety-class received their electrical power from redundant,
independent, emergency diesel generator-backed power trains. Certain risk reduction class and
non-important-to-safety loads have power supplied from a power source that is
backed up by a standby diesel generator. The standby diesel generator is a single
commercial-grade generator that is rated Seismic Criteria III. The staff noted that the Analytical
Laboratory’s ventilation systems did not have a source of auxiliary power. The consequences of recovery after a loss of
power, which could result in a spread-of-contamination event, need to be
considered before the decision is made on whether a source of auxiliary power
is necessary.
Staff
Concerns.
Based on the review, the staff has the following concerns.
Habitability Systems—The Waste
Treatment Plant project will use anhydrous ammonia in amounts up to 12,000
gallons. Rupture of the storage tanks
could produce unacceptable concentrations of ammonia in about 2 minutes at the
unprotected control areas. The safe
haven for remote process shutdowns is located in the Pretreatment facility
annex. This safe haven comprises
approximately 100,000 cubic feet, with a cleanup recirculation unit that turns
over only 1,000 cubic feet per minute. A
turnover rate of once per 100 minutes does not appear adequate to protect the
personnel who are expected to remain in the safe haven.
The staff urged that more
attention be given to the design of the safe haven. Consideration ought to be given to experience
gained from control rooms at licensed nuclear power plants. This experience has been captured by the U.S.
Nuclear Regulatory Commission in regulatory guides (R.G.) entitled: R.G. 1.194, Atmospheric Relative Concentrations for Control Room
Radiological Habitability Assessments at Nuclear Power Plants; R.G. 1.196, Control Room Habitability
at Light-Water Nuclear Power Reactors; and R.G. 1.197, Demonstrating Control Room Envelope Integrity At
Nuclear Power Reactors. The commercial nuclear industry,
as represented by the Nuclear Energy Industry (NEI), has also distributed in
draft form NEI 99-03, Control
Room Habitability Assessment Guidance. In addition, the staff
questioned plans for protecting the workers not in the safe haven given the rapid
propagation of ammonia in a potential tank accident.
Damper bypass leakage is a
particularly important consideration for the habitability of the safe haven. With the potential for high concentrations of
anhydrous ammonia outside the facility and the current low turnover rate of 100
minutes, small amounts of bypass leakage through isolation dampers could
contaminate the safe haven with ammonia fumes. The capability to test for bypass leakage is
challenging. In view of the importance
of the habitability of the Pretreatment Annex Control Area, the staff will pay
particularly close attention to the resolution of this issue.
The structural adequacy of the
safe haven is still uncertain. At
present, a steel architectural clad siding is specified. This type of clad siding is currently not
designed to withstand a seismic event. The contractor noted that it was considering
extending the concrete so that the clad siding would not be used for this
portion of the structure.
In-Bleed
Filter Units from the C-3 to the C-5 Zones—In an earlier design, the in-bleed
filter units going from the lower-contaminated C-3 zone to the
high-contaminated C-5 zone had HEPA filters for backflow prevention of
contamination. The HEPA filters (rated
at 99.97 percent removal efficiency) have been replaced by a filter (rated at
85 percent removal efficiency) and a fire damper (about 97 percent efficient). This represents a factor of 15 reduction in removal efficiency. The safety basis analysis was not available
during the review, but will be examined by the staff to ensure adequate
protection is being provided for facility workers during an accident.
Vessel
and Process Ventilation Capacity—The contractor discussed the
impacts of pulse jet mixers and air spargers on the Process Vessel Ventilation
systems. At the Pretreatment facility,
the Process Vessel Ventilation system cannot handle the full flow of all five
non-Newtonian vessels being sparged simultaneously at full flow; in fact, the
sparger air flow for just the two lag storage vessels exceeds the Process
Vessel Ventilation system capacity. Changes
are required to accommodate the sparge air flow. Consideration is being given to sequencing the
sparging rather than using continuous sparging. The staff will continue to follow the
resolution of the limited capacity of the Process Vessel Ventilation system and
the need to sparge to safely reduce hydrogen levels.
In reviewing the Pretreatment
facility’s Process Vessel Ventilation system, the staff noted a hot air
in-bleed system was classified as nonsafety, commercial grade. This system protects the process ventilation
HEPA filters, which are classified as safety-class. The staff questioned the use of
commercial-grade equipment in this application. The contractor will provide the technical
basis for this classification.
Issues
Related to HEPA Filter Bypass
Leakage—During its previous review, the staff noted
that bypass leakage around the HEPA units in the C5 ventilation system, which
must be maintained remotely, could present a problem. The contractor has looked into the matter and
has identified the potential for leakage past dampers, which would bypass one
bank of HEPA filters. There is no clear
method for measuring this bypass leakage. The contractor has considered three potential
test methods for examining leakage during facility startups. The staff will review the test methods as they
are finalized.
Overhead
Sample Transfer System—During
discussions regarding the Waste Treatment Plant’s Analytical Laboratory, the
staff learned that the contractor currently envisions using a pneumatic,
overhead sample transfer system to move samples from the three facilities to
the laboratory. The staff noted that
this could prove problematical if the samples were to become stuck and suggested
that the contractor may wish to consider other methods of transferring samples.