Tank Waste Retrieval Lessons Learned at the Hanford Site
- CH2M HILL Hanford Group, Inc., Richland, Washington (United States)
One of the environmental remediation challenges facing the nation is the retrieval and permanent disposal of approximately 90 million gallons of radioactive waste stored in underground tanks at the U. S. Department of Energy (DOE) facilities. The Hanford Site is located in southeastern Washington State and stores roughly 60 percent of this waste. An estimated 53 million gallons of high-level, transuranic, and low-level radioactive waste is stored underground in 149 single-shell tanks (SSTs) and 28 newer double-shell tanks (DSTs) at the Hanford Site. These SSTs range in size from 55,000 gallons to 1,000,000 gallon capacity. Approximately 30 million gallons of this waste is stored in SSTs. The SSTs were constructed between 1943 and 1964 and all have exceeded the nominal 20-year design life. Sixty-seven SSTs are known or suspected to have leaked an estimated 1,000,000 gallons of waste to the surrounding soil. The risk of additional SST leakage has been greatly reduced by removing more than 3 million gallons of interstitial liquids and supernatant and transferring this waste to the DST system. Retrieval of SST salt-cake and sludge waste is underway to further reduce risks and stage feed materials for the Hanford Site Waste Treatment Plant. Regulatory requirements for SST waste retrieval and tank farm closure are established in the Hanford Federal Facility Agreement and Consent Order (HFFACO), better known as the Tri- Party Agreement, or TPA. The HFFACO was signed by the DOE, the State of Washington Department of Ecology (Ecology), and U.S. Environmental Protection Agency (EPA) and requires retrieval of as much waste as technically possible, with waste residues not to exceed 360 ft{sup 3} in 530,000 gallon or larger tanks; 30 ft{sup 3} in 55,000 gallon or smaller tanks; or the limit of waste retrieval technology, whichever is less. If residual waste volume requirements cannot be achieved, then HFFACO Appendix H provisions can be invoked to request Ecology and EPA approval of an exception to the waste retrieval criteria for a specific tank. Tank waste retrieval has been conducted at the Hanford Site over the last few decades using a method referred to as Past Practice Hydraulic Sluicing. Past Practice Hydraulic Sluicing employs large volumes of DST supernatant and water to dislodge, dissolve, mobilize, and retrieve tank waste. Concern over the leak integrity of SSTs resulted in the need for tank waste retrieval methods capable of using smaller volumes of liquid in a more controlled manner. Retrieval of SST waste in accordance with HFFACO requirements was initiated at the Hanford Site in April 2003. New and innovative tank waste retrieval methods that minimize and control the use of liquids are being implemented for the first time. These tank waste retrieval methods replace Past Practice Hydraulic Sluicing and employ modified sluicing, vacuum retrieval, and in-tank vehicle techniques. Waste retrieval has been completed in seven Hanford Site SSTs (C-106, C-103, C-201, C-202, C-203, C-204, and S-112) in accordance with HFFACO requirements. Three additional tanks are currently in the process of being retrieved (C-108, C-109 and S-102) Preparation for retrieval of two additional SSTs (C-104 and C-110) is ongoing with retrieval operations forecasted to start in calendar year 2008. Tank C-106 was retrieved to a residual waste volume of 470 ft{sup 3} using oxalic acid dissolution and modified sluicing. An Appendix H exception request for Tank C-106 is undergoing review. Tank C-103 was retrieved to a residual volume of 351 ft{sup 3} using a modified sluicing technology. This approach was successful at reaching the TPA limits for this tank of less than 360 ft{sup 3}and the limits of the technology. Tanks C-201, C-202, C-203, and C-204 are smaller (55,000 gallon) tanks and waste removal was completed in accordance with HFFACO requirements using a vacuum retrieval system. Residual waste volumes in each of these four tanks were less than 25 ft{sup 3}. Tank S-112 retrieval was completed February 28, 2007, meeting the TPA Limits of less than 360 cu ft using salt-cake dissolution, modified sluicing, in-tank vehicle with high pressure water spray and caustic dissolution. Tanks C-108 and C-109 have been retrieved to 90% and 85% respectively. Modified sluicing was no longer effective at retrieving the remaining 5,000 to 10,000 gallons of residual. A Mobile Retrieval Tool (FoldTrac) is scheduled for installation early in 2008 to assist in breaking up chunks of waste and mobilizing the waste for transfer. Lessons learned from application of new tank waste retrieval methods are being documented and incorporated into future retrieval operations. They address all phases of retrieval including process design, equipment procurement and installation, supporting documentation, and system operations. Information is obtained through interviews with retrieval project personnel, focused workshops, review of problem evaluation requests, and evaluation of retrieval performance data. This paper presents current retrieval successes and lessons learned from retrieval of tank waste at the Hanford Site and discusses how this information is used to optimize retrieval system efficiency, improve overall cost effectiveness of retrieval operations, and ensure that HFFACO requirements are met. (authors)
- Research Organization:
- WM Symposia, 1628 E. Southern Avenue, Suite 9 - 332, Tempe, AZ 85282 (United States)
- OSTI ID:
- 21319752
- Report Number(s):
- INIS-US-10-WM-08179; TRN: US10V0441061943
- Resource Relation:
- Conference: WM'08: Waste Management Symposium 2008 - HLW, TRU, LLW/ILW, Mixed, Hazardous Wastes and Environmental Management - Phoenix Rising: Moving Forward in Waste Management, Phoenix, AZ (United States), 24-28 Feb 2008; Other Information: Country of input: France; 4 refs
- Country of Publication:
- United States
- Language:
- English
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