Fission Product Distributions

Up to this point, we have focused on describing the factors that control the probability of fission to occur. Now we will focus our attention on the distributions of the products in mass, energy, charge, and so forth. In doing so, we will mostly be discussing scission point or postfission phenomena. Our treatment of these phenomena is, of necessity, somewhat superficial, and the reader is referred to the excellent monograph of Vandenbosch and Huizenga (1973) for a more authoritative account. 

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Fission product distribution Radioactive waste activity distribution... 

These variations permit the separation of other components, if desired. Additional data on uranium, plutonium, and nitric acid distribution coefficients as a function of TBP concentration, solvent saturation, and salting strength are available (24,25). Algorithms have also been developed for the prediction of fission product distributions in the PUREX process (23). 

There is no structure for an elongated core intermediate between that shown in Fig. 11, with three inner-core spher-ons, and that shown in Fig. 12, with four. The transition between these structures is calculated by use of Eq. 1, with n, = 22, to occur at nt = 69, that is, at N = 138. It is accordingly an expectation from the close-packed-spheron theory that, as observed, 90Ac13a2- 7 (formed by bombardment of Re- 20 with 11-Mev protons) gives a three-humped fission product distribution curve (23), which has been interpreted (24) as showing that both symmetric fission and asymmetric fission occur. 

In parametric studies using this method, calculation of fission product distribution among the various particle size groups was found to be insensitive to size of the detonation and the quantity of soil picked up. It is, of course, somewhat sensitive to the thermodynamic and kinetic values used, but most of all, it is sensitive to the particle size distribution itself. This result is of considerable interest. 

Table V. Fission Product Distribution Parameters (Land Subsurface Detonation)...

J. D. Chilton, et al., Separation of Uranium from Thorium by Liquid Metal Extraction, Thorium Recovery, and Fission Product Distribution, NAA-SR-6666, AI(1962). 

More realistically, this material (Pu(>2 plus fission products) would require either some further decontamination from deleterious fission products or further treatment to obtain a product having the necessary characteristics for fuel recycle (particle size, chemical form of fission products, other ). This further treatment has not been investigated to date and probably will not be until we have a better knowledge of the fission-product distribution and chemical form. 

How can fission-product distribution be controlled during uranate precipitation and on subsequent dissolution or other treatment ... 

With the development of fast chemical separation techniques and physical techniques that allows one to differentiate between different elements of an isobaric decay chain, information could be obtained on the fission product distribution prior to P decay. The corresponding yields are called independent or primary product yields. 

For the determination of the fission product distribution over the cross section of a fuel pellet, autoradiography is the simplest method with regard to instrumental needs this technique, however, requires extensive experience in order to obtain optimum results at the very high radioactivity level of the materials. The distribu-... 

Figure 3.9. Fission product distribution as a function of the relative fuel pellet radius in a LWR high-bumup oxide fuel (Kleykamp, 1990 a)...

The second effect leading to an inhomogeneous fission product distribution, in particular in the radial direction, is migration in the thermal gradient. This effect mainly affects the gaseous and the volatile fission products its extent depends on several parameters such as the linear heat rating of the relevant fuel rod and, consequently, the temperatures in the pellets during reactor operation, as well as... 

These three effects lead to deviations from the originally homogeneous fission product distribution in the fuel pellet. If one considers the single crystallite as the reference volume in fuel internal chemistry, then these differences have to be taken into account. However, until now this fuel microchemistry has not yet been treated in detail. 

Fission product distribution will be different but performance should be similar... 

These characteristics define the state of the fuel pin for mechanical calculations. Temperature distribution and voidage redistribution are closely linked (5) so these, together with swelling and fission product distribution, can be conveniently simulated by fuel behavior computer... 

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