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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.
Tarek Zaki, Peter Yarsky
Nuclear Science and Engineering | Volume 184 | Number 3 | November 2016 | Pages 346-352
Technical Paper | doi.org/10.13182/NSE16-14
Articles are hosted by Taylor and Francis Online.
In a related paper (L. Cheng et al., “TRACE/PARCS Analysis of Anticipated Transient Without Scram with Instability for a MELLLA+ BWR/5,” Nucl. Technol. Vol. 196), the results of TRACE/PARCS calculations for representative anticipated transient without scram (ATWS) events leading to core instability (ATWS-I) were presented. In that analysis, instability onset was observed in response to changing plant conditions of power, flow, and feedwater temperature. The baseline calculations were performed without using a PARCS feature to simulate noise in the reactor.
When a simulated reactor is unstable but is in a steady-state condition, an analytical tool may not show the onset of instability because there would not be a perturbation to excite oscillation. Such a condition of artificial stability could not persist in an actual reactor where subtle variation of local conditions (e.g., void fraction) would provide a constant source of perturbation, or “noise.” The regulatory purpose of the current work is to study the reliability of the TRACE/PARCS prediction of instability onset and oscillation growth during ATWS-I by providing a source of noise in the simulation. In addition, the results of this study support a generic methodology recommendation for any future studies.
PARCS has a feature that can simulate the reactivity effect of perturbations in the local void fraction. This feature, referred to as the white noise feature, is used to provide an artificial source of constant, local perturbation that would more closely mimic the actual reactor condition where local void fractions are constantly changing. Sensitivity of the onset timing and growth was studied by varying the magnitude, frequency, and contour of the perturbations applied by the white noise feature.
The study concludes that the onset timing and growth of both the initial corewide and subsequent bimodal oscillation stabilized at a certain combination of perturbation magnitude, frequency range, and frequency resolution. With the appropriate range of these parameters, the instability onset occurs ~20 s earlier, and peak oscillation amplitude is achieved ~15 s earlier when compared to the baseline calculations. Given the importance of oscillation onset and growth on potential fuel damage, this study recommends a specific methodology with respect to white noise to ensure reliable prediction with TRACE/PARCS for future studies.