December 1, 2005
The Honorable A. J. Eggenberger
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.
Dr. Ines R. Triay
Chief Operating Officer for
cc: M. Whitaker, DR-1
R. Schepens, ORP
T. Smith, ORP