Breeder penetration

Together these two ratios determine the degree of penetration of these reactor types into the total system nuclear capacity. The higher these ratios are the greater will be the breeder penetration, ratio (a) being more significant initially and ratio (b) on a long-term basis. 

Fig. 5. Breeder penetration in relation to the ratio between converter Pu-production and breeder inventory.

Table VI shows that the low excess Pu production of HTRs will result in a low fast breeder penetration and thus in less favorable fuel cycle expenditures. Because of the higher fuel cycle expenditures in the HTR compared with the LWR programs the capital investments for HTRs should be lower to make them compatible with LWRs. This effect will be more pronounced for increasing U prices.

Unilateral incompatibility is a phenomenon in which self-compatible species can be crossed as a female, but not as a male, to self-incompatible species (Abdalla and Hermsen, 1972). Pollen tubes fail to penetrate stylar tissue in self-incompatible (female) X self-compatible (male) crosses. Although most diploid Solarium species are self-incompatible, the Mexican species S. verrucosum is self-compatible. Dinu et al. (2005) found that S. verrucosum could be crossed as a female, but not as a male, to self-incompatible species. It is sometimes possible to find exceptional plants that do not exhibit unilateral incompatibility in self-incompatible X selfcompatible interspecific crosses (Pandey, 1962). The identification of such plants allows a breeder to overcome the unilateral incompatibility crossing barrier. For example, exceptional plants ( acceptors ) that accept S. verrucosum pollen and produce fertile hybrids have been reported (Eijlander et al., 2000). It is interesting that some acceptor plants will accept pollen... 

With the lower inventories of the thermal breeders it is possible, however, to install much more capacity in this reactor type as compared with the fast breeders, using the same amount of fissile material. This leads to much higher penetration rates into the total system nuclear capacity for the thermal breeders, or, in other words, a much higher fraction of the total system nuclear capacity will consist of thermal breeders. Furthermore, the low inventories of the thermal breeder reactors make it possible to start these reactors with even though this results in a higher... 

For the fast breeders the specific Pu inventory is rather high, the Pu production of the converters will thus have a large influence on the value of ratio (a) and on the initial penetration of the fast breeders, as shown in Fig. 5. This importance of the converter Pu production explains why a nuclear program with high temperature reactors (HTR) in combination with fast breeders will give results below expectations, compared with the other possibility—heavy water and fast breeder reactor. 

The second scale in Fig. 5 indicates that in most of the converter/ liquid fuel reactor cases ratio (a) will not provide any limitation for the initial liquid fuel reactor penetration because of the very low inventory of these thermal breeders. Although ratio (b) will become significant in the future because of the assumed value of 0 (no excess fissile material production) for the liquid fuel reactors, it does not limit LFR penetration in the cases that were considered. 

The last two rows of Table VII show finally the effect of a different introduction date for the breeders. To explain the effect of a delay in fast breeder introduction date it should be kept in mind that for those cases where a delay in breeder introduction results in the same penetration at the end of the period, the net effect will be nil (HWR + FB). The other cases give approximately 10% higher fuel cycle expenditures. For the converter/liquid fuel reactor cases the advance of the introduction date results in all cases but one in higher penetration of the LFR s and subsequently in a significant decrease in fuel cycle expenditures (25-30 % by 2010). The one exception is the LWR + LFR case in which the ratio (b) mentioned in Section V,F becomes a limiting factor for the further LFR penetration, thus resulting in the additional installation of light water reactors, and an increase in fuel cycle expenditures. 

The fissile material inventory of the breeders will be very important for the maximum rate at which breeder reactors can be incorporated in a nuclear program and thus the savings in fuel cycle costs and uranium requirements that can be obtained. In this respect the thermal breeder (the liquid fuel reactor) has a significant advantage over the fast breeder. In most nuclear programs the penetration of the latter reactor type is seriously limited by the vast amounts of plutonium required for the first reactor cores. 

To favor the maximum installation rate of the breeders it may be worthwhile to temporarily reduce the breeding ratio if this would result in lower fissile material inventories. These lower inventories would make a faster penetration of the breeders into the total system capacity possible. 

---