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Congress receives NRC report on unusual events
The Nuclear Regulatory Commission has published its annual report to Congress for fiscal year 2023 on abnormal occurrences involving medical and industrial uses of radioactive material.
The report, which was announced by the NRC on May 3, is available on the NRC website.
Ulrich Fischer
Fusion Science and Technology | Volume 22 | Number 2 | September 1992 | Pages 251-270
Technical Paper | Blanket Engineering | doi.org/10.13182/FST92-A30108
Articles are hosted by Taylor and Francis Online.
One-dimensional neutronic calculations in a simple geometrical model, which are used frequently in blanket design and shielding analyses, are qualified by a comparison with three-dimensional calculations in a realistic tokamak model. The Next European Torus (NET) reactor is used as an example of a well-developed design for a “next-step” tokamak machine. Various blanket concepts with different neutronic characteristics are taken into account: a helium-cooled solid breeder blanket with beryllium as neutron multiplier, a self-cooled liquid-metal blanket with the eutectic alloy Pb-17Li, or, alternatively, pure lithium as breeding material/coolant and an aqueous lithium salt solution blanket. The calculations are performed with the MCNP Monte Carlo code, both in the one- and the three-dimensional approach. It is shown that the use of the one-dimensional approach can be justified for design and shielding calculations, if the plasma source is normalized in a consistent manner and both its radial distribution and its angular dependence are chosen appropriately. The latter requirement necessitates the use of an anisotropic neutron source distribution in the one-dimensional calculation. The tritium breeding ratio is overestimated in the one-dimensional approach to a degree that depends on the neutronic characteristics of the blanket variants used. A blanket concept evaluation, therefore, is valid only on the basis of three-dimensional calculations in the actual tokamak geometry. One-dimensional shielding calculations on average agree rather well with three-dimensional ones, although they do not allow “safe” results to be obtained. As the safety margins for the shielding system in general are crucial, a proof by three-dimensional shielding calculations in the real tokamak geometry is required.