Tank Farm Nuclear Criticality Review

The technical basis for the nuclear criticality safety of stored wastes at the Hanford Site Tank Farm Complex was reviewed by a team of senior technical personnel whose expertise covered all appropriate aspects of fissile materials chemistry and physics. The team concluded that the detailed and documented nucleonics-related studies underlying the waste tanks criticality safety basis were sound. The team concluded that, under current plutonium inventories and operating conditions, a nuclear criticality accident is incredible in any of the Hanford single-shell tanks (SST), double-shell tanks (DST), or double-contained receiver tanks (DCRTS) on the Hanford Site.

In November 1999, the Deputy Secretary of the Department of Energy directed a series of actions to strengthen the Department's ongoing nuclear criticality safety programs. A Review Plan describing lines of inquiry for assessing contractor programs was included. The Office of River Protection completed their assessment of the Tank Farm Contractor program in May 2000. This document supports that assessment by providing a compliance statement for each line of inquiry.

The mission of this project is to provide a defensible technical basis report in support of the Final Safety Analysis Report (FSAR). This technical basis report will also be used to resolve technical issues associated with the nuclear criticality safety issue. The strategy presented in this project plan includes an integrated programmatic and organizational approach. The scope of this project plan includes the provision of a criticality technical basis supporting document (CTBSD) to support the FSAR as well as for resolution of the nuclear criticality safety issue. Specifically, the CTBSD provides the requisite technical analysis to support the FSAR hazard and accident analysis as well as for the determination of the required FSAR limits and controls. The scope of The CTBSD will provide a baseline for understanding waste partitioning and distribution phenomena and mechanistics for current operational activities inclusive of single-shell tanks, double-shell tanks, double-contained receiver tanks, and miscellaneous underground storage tanks. Although the FSAR does not include future operational activities, the waste partitioning and distribution phenomena and mechanistics work scope identified in this project plan provide a sound technical basis as a point of departure to support independent safety analyses for future activities. The CTBSD also provides the technical basis for resolution of the technical issues associated with the nuclear criticality safety issue. In addition to the CTBSD, additional documentation will be required to fully resolve U.S. Department of Energy-Headquarters administrative and programmatic issues. The strategy and activities defined in this project plan provide a CTBSD for the FSAR and for accelerated resolution of the safety issue in FY 1996. On April 30, 1992, a plant review committee reviewed the Final Safety Analysis Reports for the single-shell, double-shell, and aging waste tanks in light of the conclusions of the inadequate waste characterization with respect to fissile material. The review indicated that the conclusion in the FSARS, that a criticality is not credible, cannot be supported for a full range of potential tank constituents. Therefore, a USQ was declared. Development of a credible scenario leading to a criticality proved to be extremely difficult, given the paucity of data on the quantity and distribution of fissile material in the tanks. The objective of this project plan is to develop a strategy and technical approach to provide a CTBSD for the FSAR and for resolution of the nuclear criticality safety issue pertaining to tank farm waste storage and transfer operations. The strategy and technical approach identified in this project plan include definition of administrative and technical tasks. Technical analyses will include mechanistic studies, historical data review, and additional limited neutronics analysis. Completion of these studies will be documented in a CTBSD to support the existing criticality technical basis. The CTBSD will be incorporated in the criticality portion of the FSAR.

This paper describes the approach used to resolve the Nuclear Criticality Safety Issue for the Hanford Site high-level waste tanks. Although operational controls have been in place at the Hanford Site throughout its operating life to minimize the amount of fissile material discarded as waste, estimates of the total amount of plutonium that entered the waste tanks range from 500 to 1,000 kg. Nuclear criticality safety concerns were heightened in 1991 based on a review of waste analysis results and a subsequent U.S. Department of Energy 1399 review of the nuclear criticality program. Although the DOE review team concluded that there was no imminent risk of a criticality at the Hanford Site tank farms, the team also stated its concern regarding the lack of definitive knowledge of the fissile material inventory and distribution within the waste tanks and the lack of sufficient management support for the overall criticality safety program. An in-depth technical review of the nuclear criticality safety of the waste tanks was conducted to develop a defensible technical basis to ensure that waste tanks are subcritical. The review covered all relevant aspects of nuclear criticality safety including neutronics and chemical and physical phenomena of the waste form under aging waste conditions as well as during routine waste management operations. This paper provides a review of the technical basis to support the conclusion that given current plutonium inventories and operating conditions, a nuclear criticality is incredible. The DOE has been requested to close the Nuclear Criticality Safety Issue. The Defense Nuclear Facilities Safety Board is currently reviewing the technicalbasis.

This document provides a detailed matrix of specific Tank Farms nuclear criticality safety program elements indexed to primary requirements documents. These requirements are collected at a higher level in HNF-SO-MP-SRID-001, ''Tank Waste Remediation System Standards/Requirements Identification Document.'' The intended use of this document is to provide a roadmap for implementing procedures and assessments.

DOE Tank Waste: How clean is clean enough? The U.S. Congress asked the National Academies to evaluate the Department of Energy's (DOE's) plans for cleaning up defense-related radioactive wastes stored in underground tanks at three sites: the Hanford Site in Washington State, the Savannah River Site in South Carolina, and the Idaho National Laboratory. DOE plans to remove the waste from the tanks, separate out high-level radioactive waste to be shipped to an off-site geological repository, and dispose of the remaining lower-activity waste onsite. The report concludes that DOE's overall plan is workable, but some important challenges must be overcomeâ€"including the removal of residual waste from some tanks, especially at Hanford and Savannah River. The report recommends that DOE pursue a more risk-informed, consistent, participatory, and transparent for making decisions about how much waste to retrieve from tanks and how much to dispose of onsite. The report offers several other detailed recommendations to improve the technical soundness of DOE's tank cleanup plans.

This document provides the results of an internal management review of the Tank Waste Remediation System (TWRS) criticality safety program, performed in advance of the DOE/RL assessment for closure of the TWRS Nuclear Criticality Safety Issue, March 1994. Resolution of the safety issue was identified as Hanford Federal Facility Agreement and Consent Order (Tri-Party Agreement) Milestone M-40-12, due September 1999.

This document provides requirements for the nuclear cr[i]ticality safety program for the Hanford Tank Farms, 242-A Evaporator, and 222-S Laboratory.