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2025 ANS Winter Conference & Expo
November 8–12, 2025
Washington, DC|Washington Hilton
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Japan gets new U for enrichment as global power and fuel plans grow
President Trump is in Japan today, with a visit with new Prime Minister Sanae Takaichi on the agenda. Takaichi, who took office just last week as Japan’s first female prime minister, has already spoken in favor of nuclear energy and of accelerating the restart of Japan’s long-shuttered power reactors, as Reuters and others have reported. Much of the uranium to power those reactors will be enriched at Japan’s lone enrichment facility—part of Japan Nuclear Fuel Ltd.’s Rokkasho fuel complex—which accepted its first delivery of fresh uranium hexafluoride (UF₆) in 11 years earlier this month.
Coleridge A. Wilkins
Nuclear Science and Engineering | Volume 14 | Number 4 | December 1962 | Pages 346-357
Technical Paper | doi.org/10.13182/NSE62-A26241
Articles are hosted by Taylor and Francis Online.
This paper involves the application of some modern probability methods to the problem of the slowing-down of neutrons, and attempts to provide a framework both for the exposition and computation of various phenomena in this field. It is shown that under certain conditions, the slowing-down of neutrons is a renewal process and renewal theoretical results apply. For instance, if scattering is isotropic and all cross sections similarly varying, then (in lethargy) slowing-down is certainly a renewal process. After investigating some aspects of moderation in hydrogen, and some incidental extensions of results for hydrogen, it is shown that for renewal types of slowing-down from a monoenergetic source, the Laplace transform of the rth moment of the number of collisions at lethargies below u may be obtained by differentiating (with respect to t) a generating function of the form This form applies to some types of anisotropic scattering as well as to isotropic scattering. The expressions derived are then extended to a distributed source by a method from reactor theory, and some resulting expressions are checked against corresponding renewal formulas. The asymptotic distribution of the number of collisions to slow down is found from renewal theory, from which it is shown that when scattering is isotropic, the spread of the number of collisions to thermalize in a light moderator is relatively greater than in a heavy moderator, the coefficient of variation being proportional to for a light species and for a heavy one. The asymptotic form of the density of nth collisions is investigated, and the form derived is compared with another ascribed to Dancoff. The preceding theory is then applied to a particular case of anisotropic scattering which occurs above about 100 kev. Finally, an exact expression is obtained (for similarly varying cross sections and zero absorption) for the probability that, in a mixture of n species, a neutron has r collisions at lethargies below u, precisely k of which are with a given species. The given species is then taken to be very heavy and the exact expression approximated accordingly.
