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NRC approves TerraPower construction permit
Today, the Nuclear Regulatory Commission announced that it has approved TerraPower’s construction permit application for Kemmerer Unit 1, the company’s first deployment of Natrium, its flagship sodium fast reactor.
This approval is a significant milestone on three fronts. For TerraPower, it represents another step forward in demonstrating its technology. For the Department of Energy, it reflects progress (despite delays) for the Advanced Reactor Demonstration Program (ARDP). For the NRC, it is the first approval granted to a commercial reactor in nearly a decade—and the first approval of a commercial non–light water reactor in more than 40 years.
Yuichi Niibori, Joonhong Ahn, Hitoshi Mimura
Nuclear Technology | Volume 175 | Number 3 | September 2011 | Pages 641-651
Technical Paper | NURETH-13 Special / Radioactive Waste Management and Disposal | doi.org/10.13182/NT11-A12512
Articles are hosted by Taylor and Francis Online.
Relative permeability kr is a practical tool to describe two-phase flow in the performance assessment of a geological disposal system of radioactive waste. So far, to avoid thermal alteration of an engineered barrier system such as bentonite, the maximum temperature in the conceptual design of a Japanese geological disposal system has been limited to <373 K. However, for a limited time period, even if the temperature exceeds 373 K or the boiling point at the underground level, the robustness of the system is expected to be sufficient. An upward revision of the permissible maximum temperature would reduce the total space of the repository and would result in more effective use of the space. Therefore, when two-phase flow is also considered, a more reliable estimate of the thermal impact on the repository system is needed.In general, the fluid flow velocities of two phases are described by Darcy's law including the relative permeabilities defined as the functions of liquid-water saturation (or steam saturation), e.g., Corey's equations. However, such saturation (e.g., liquid-water saturation Sw) is not always uniformly distributed in the grid cells of the numerical implementation. In this study, the uncertainty of kr due to the distribution of Sw was examined by using various kinds of probability density functions (pdf's). The results suggest that the apparent kr value can be numerically described by the arithmetic mean, the standard deviation, and the skewness of Sw. (In other words, the apparent value of kr does not depend on the types of pdf's.) Since the value of Sw is in the range of 0 to 1, the standard deviation and the skewness are limited. Therefore, the apparent values of kr also are in a limited range. Using the Lagrange multiplier method, this study examined the ranges of the kr value for each arithmetic mean of saturation Swa. Furthermore, by considering both the frequency distribution and the spatial distribution of saturation, this study quantitatively shows the degree of uncertainty of relative-permeability curves. These curves can explain the scattered data of two-phase-flow experiments.
