Samarium Production

Samarium Production and Removal

Samarium production and removalSamarium Production

Fission does not produce Sm 149 directly. The fission yield of samarium 149 is nearly zero. Sm-149 is in the decay chain of the the fission product neodymium 149, which decays to promethium 149. Because of the short half-life of Nd-149 (compared to the half-life of Pm-149), promethium may be considered as if it were formed directly from fission. The decay sequence is depicted on the figure.

Samarium Removal

An important difference between Xe-135 and Sm-149 is that samarium 149 is a stable isotope, and therefore remains in the core after shutdown. There are only two ways of samarium removal. One of these processes is the samarium burnup, when the reactor is at power operation. The rate of samarium burnup is dependent upon the neutron flux and the samarium 149 concentration (i.e. the reaction rate).

The second process is associated with refueling. During refueling usually one third or one quarter of the core is removed to spent fuel pool and replaced by fresh fuel assemblies, while the remainder is rearranged to a location in the core better suited to its remaining level of enrichment. Therefore refueling naturally leads to a decrease in the overall samarium content in the core.

Samarium 149 – Differential Equations

Assuming that fission does not produce Sm 149 directly, and neglecting the small amount of promethium burnup, allows the situation to be described as follows. The production and removal of samarium can be characterized by the following differential equations.

samarium - differential equations

 
References:
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Advanced Reactor Physics:

  1. K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.
  2. K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.
  3. D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2. 
  4. E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.

See above:

Samarium