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Glass strategy: Hanford’s enhanced waste glass program
The mission of the Department of Energy’s Office of River Protection (ORP) is to complete the safe cleanup of waste resulting from decades of nuclear weapons development. One of the most technologically challenging responsibilities is the safe disposition of approximately 56 million gallons of radioactive waste historically stored in 177 tanks at the Hanford Site in Washington state.
ORP has a clear incentive to reduce the overall mission duration and cost. One pathway is to develop and deploy innovative technical solutions that can advance baseline flow sheets toward higher efficiency operations while reducing identified risks without compromising safety. Vitrification is the baseline process that will convert both high-level and low-level radioactive waste at Hanford into a stable glass waste form for long-term storage and disposal.
Although vitrification is a mature technology, there are key areas where technology can further reduce operational risks, advance baseline processes to maximize waste throughput, and provide the underpinning to enhance operational flexibility; all steps in reducing mission duration and cost.
B. C. Johnson, G. E. Apostolakis, R. Denning
Nuclear Technology | Volume 172 | Number 2 | November 2010 | Pages 108-119
Technical Paper | Reactor Safety | doi.org/10.13182/NT10-A10898
Articles are hosted by Taylor and Francis Online.
We consider the design of a sodium-cooled fast reactor (SFR) in the context of the risk-informed technology neutral framework (TNF) for licensing new reactors that has been proposed by the U.S. Nuclear Regulatory Commission staff. In lieu of design-basis accidents (DBAs), the TNF imposes limits on the frequency and consequences of accident sequences called licensing-basis events (LBEs). We present a method to define LBEs for a SFR using generic functional event trees. Very large consequence events are considered beyond the licensing basis in the TNF as long as their mean frequencies are less than 1 × 10-7 per reactor year.For SFRs, energetic accidents have historically represented a major regulatory hurdle in the traditional licensing system that is based on DBAs. As a result, key systems that prevent or mitigate these accidents may have been overdesigned. We propose a new importance measure, the Limit Exceedance Factor (LEF). It is the factor by which the failure probability of structures, systems, and components (SSCs) may be multiplied such that the frequency of a risk metric reaches a limit. LEF allows a designer to know how much margin exists to the safety limit for each SSC. Alternatively, in the case where a design does not meet the frequency limit, LEF can reveal which systems are candidates for improvement to satisfy the limit. Within the TNF, using a frequency limit of 1 × 10-7 per reactor year and LEF, we find that for some SSCs a wide margin exists to this limit. Therefore, these SSCs are candidates for simplification resulting in economic benefit. This simplification should be done under the frequency-consequence constraints and the deterministic defense-in-depth requirements described in the TNF.