ORNL-5388 - the Molten Salt Energy Technologies Web Site

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The effect of applying the improving tails strategy to a nuclear system based on the
throwaway cycle is to increase the maximum installed nuclear capacity by approximately 60 GWe
and to delay the maximum by approximately five years (see Fig. 6.2-9). Mining the tails
stockpile accumulated prior to 2010 does not significantly change the result. The reason
that mining the past tails stockpile does not produce a significantly larger nuclear contri-
bution is explained by Fig. 6.2-11, which shows the cumulative amount of U308 processed
through the enrichment plants as a function of time. The amount is considerably less than
the amount of U,Ob committed at any given time, as shown in Fig. 6.2-6. It i s important to
note that the amount of U308 actually processed through the enrichment plants prior to 1990
is relatively small, and at this time the tails composition for the improving tails strategy
has been decreasing linearly for 10 yr. Thus, most of the U308 in the improving tails case
is processed at lower tails compositions, and mining the past stockpile does not produce a
significant improvement.
The most dramatic effect associated with the improving tails option
is the increase in the maximum annual enrichment requirement. As indicated in Fig. 6.2-9,
the maximum annual U308 requirement for this option is 67,000 ST/yr, while the maximum
annual enrichment requirement is 92 million SWU/yr. Thus, the principal limitation in this
case would be the availability of enrichment capacity.
The utilization and movement of fissile material per GWe of installed capacity in
the year 2035 for each of the converter options is shown in Fig. 6.2-12a-d, assuming the
high-cost U308 supply. These figures represent a snapshot of the system in time and include
the first core loadings for units starting up in the year 2036.
As can be seen, the U308 con-
sumption for Case 1L in the year 2035 is approximately 142 ST U308/GWe, with the LWRs having
an extended discharge exposure comprising 92% of the installed capacity. When the LWRs are
followed by SSCRs (Case lS), the annual U308 consumption is 135 ST U308, with the SSCR com-
prising 74% of the installed capacity. The fractional installed capacity of the SSCR is less
than that of the extended-exposure LWR in Case 1L because the extended-exposure LWR is intro-
duced'in 1981 while the SSCR is not introduced until 1991. In general, the fractional installed
capacity of a reactor concept in the year 2035 will decrease monotonically as the intro-
duction date for the concept increases. Similarly, the fractional installed nuclear
capacity of a reactor concept will increase monotonically as its U308 requirement decreases.
When the LWRs are followed by HTGRs (Case lG.), the U308 consumption in the year 2035
is 133 ST U308/GWe, with the HTGR comprising 54% of the installed capacity. The annual U308
consumption is lower than in Case 1s because the U308 requirement of the HTGR is less than
that of the SSCR (see Table 6.1-2 and Fig. 6.2-1). The fractional installed capacity of the
HTGR is less than that of the SSCR in the Case 1s because the SSCR is introduced in 1991
while the HTGR is not introduced until 1995.
When HWRs follow the LWRs (Case lH), U3O8 consumption in year 2035 is approximately
106 ST U308/GWe and the HWR comprises 79% of the installed capacity. The HWR in this case
and the HTGR in Case 1G have the same introduction date. The HWR, however, has a lower
U308 requirement and hence the total installed nuclear capacity is greater with this