[DOE LETTERHEAD]
December 1,
2005
The Honorable A. J. Eggenberger
Chairman
Defense Nuclear Facilities
Safety Board
625 Indiana Avenue, NW, Suite
700
Washington, DC 20004-2901
Dear Mr. Chairman:
This letter provides you with
new information on Hanford Tank AN-107 chemistry concerns and the Department of
Energy’s (DOE) planned actions. Since
our meeting in September 2005, the Chemistry Optimization Expert Panel, Oversight
Committee (hereinafter called the Committee), has provided an assessment of
Tank AN-107 corrosion properties of the interstitial liquid in the solids layer.
This assessment (Enclosure 1) and CH2M
Hill’s assessment (Enclosure 2) conclude that Tank AN-107 waste chemistry is
benign from a stress corrosion cracking perspective, and will remain protected
during the minimal chemistry changes projected over the next decade or more. The Committee recently released additional
supplemental assessments (Enclosures 3 and 4) noting that Tank AN-107 chemistry
should not appreciably increase general or pitting corrosion during this same
extended time period. This information
has led DOE to conclude that Tank AN-107 is safe and will remain so for the
foreseeable future.
DOE is changing the Tank AN-107
chemistry limits for interstitial liquid in the solids layer to allow for a
hydroxide concentration roughly equivalent to pH 10 or greater in accordance
with the Committee’s assessment. This
change will be implemented by modifying the existing chemistry control table
(Table 5.16-1) in Administrative Control 5.16 of the Tank Farms Technical
Safety Requirements (TSR) (HNF-SD-WM-TSR-006) for Tank AN-107 interstitial
liquid. In accordance with these
changes, a mixer pump is not required and is no longer planned for installation.
As a defense-in-depth,
and in accordance with the committee recommendations, an in-tank multi-function
corrosion and corrosion potential monitoring probe is being procured and will
be installed in Tank AN-107. TSR
controls recognizing the corrosion probe as a key element in the corrosion
protection program will be implemented with the chemistry limit change. As noted
previously to the Defense Nuclear Facilities Safety Board, the tank surface
ultrasonic testing area has already been doubled and test frequency has been
increased in accordance with earlier Committee recommendations.
The existing Tank AN-107
chemistry technical safety requirement recovery plan will be revised
accordingly. We will continue to keep
your staff informed on this new path forward.
If you have any questions,
please call me at (202) 586-0738 or Dae Y. Chung, Acting Deputy Assistant
Secretary for Integrated Safety Management and Operations Oversight, at (202)
586-5151.
Sincerely,
Dr. Ines R. Triay
Chief Operating Officer for
Environmental Management
cc: M. Whitaker, DR-1
R.
Schepens, ORP
T.
Smith, ORP