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NETS registration now open
The time has come to sign up for Nuclear and Emerging Technologies for Space (NETS 2026), which will be held in Dayton, Ohio, on April 27–30.
Hosted by the American Nuclear Society and the University of Dayton Research Institute (UDRI) and sponsored by ANS’s Aerospace Nuclear Science and Technology Division, NETS 2026 is an opportunity to exchange ideas and knowledge, develop strong relationships across organizations, and establish collaborations to solve challenging problems across the many space-related applications of nuclear science and technology.
M. R. Zika, T. J. Downar
Nuclear Science and Engineering | Volume 115 | Number 3 | November 1993 | Pages 219-232
Technical Paper | doi.org/10.13182/NSE93-A24051
Articles are hosted by Taylor and Francis Online.
Accurate solutions of the advanced nodal equations require the use of “discontinuity factors” (DFs) to account for the homogenization errors that are inherent in all coarse-mesh nodal methods. During the last several years, nodal equivalence theory (NET) has successfully been implemented for the Cartesian geometry and has received widespread acceptance in the light water reactor industry. The extension of NET to other reactor types has had limited success. Recent efforts to implement NET within the framework of the nodal expansion method have successfully been applied to the fast breeder reactor. However, attempts to apply the same methods to thermal reactors such as the Modular High-Temperature Gas Reactor (MHTGR) have led to numerical divergence problems that can be attributed directly to the magnitude of the DFs., In the work performed here, it was found that the numerical problems occur in the inner and up-scatter iterations of the solution algorithm. These iterations use a Gauss-Seidel iterative technique that is always convergent for problems with unity DFs. However, for an MHTGR model that requires large DFs, both the inner and upscatter iterations were divergent. Initial investigations into methods for bounding the DFs have proven unsatisfactory as a means of remedying the convergence problems. Although the DFs could be bounded to yield a convergent solution, several cases were encountered where the resulting flux solution was less accurate than the solution without DFs. For the specific case of problems without upscattering, an alternate numerical method for the inner iteration, an LU decomposition, was identified and shown to be feasible.