ORNL-5388 - the Molten Salt Energy Technologies Web Site

GRlBRLL 1
U-239
4-46
As can be seen, the 239Pu content peaks at
'~r 30 MWD/kg,decreasing thereafter. The
higher Pu isotopes tend to peak at higher
U-240 U-242 burnups so that at discharge 242Pu doniio.olG%,
, nates. Compared to an LLJR with LEU ftlel,
50 ,oo nwOlac the PBR v:ith HEU/Th fuel discharges only 8%
HI)(II.TLUC"I.l.RuE1rEW.rT. as much fissile plutonium. Furthermore, the
Fig- 4-4-10 Buildup of the Plutoniur fissile fraction of the discharged plutonium
Isotopic Composition in the MEU/Th Fuel.
is only 39% compared to 71% for an LWR.
Table 4.4-8 presents U308 requirements of the various once-through cycle^.^,^ The
30-yr cumulative U308 demands for the MEU/Th once-through cycle and the HEU/Th once-
through cycle were determined by explicit 30-yr calculations.8 The 30-yr cumulative U308
demands for the LEU, the seed-and-breed MEU/Th and the seed-and-breed HEU/Th cycles were
determined from the U308 demand for the equilibrium cycles and estimates of the inventory
of the startup core and of the requirements for the approach to equilibrium.8
As can be seen from Table 4.4-8, from the viewpoint of U308 utilization for oncethrough
cycles in the PBR, LEU fuel is the least favorable and HEU/Th fuel is the most
favorable with MEU/Th fuel having a U308 utilization between HEU/Th and LEU fuel. It should
be noted that the cases presented in Table 4.4-8 do not include recycle of the bred fissile
material. Under these no-recycle constraints the MEU/Th cases have a 30-yr U3O8 demand comparable
to a PWR operating with uranium and self-generated Pu recycle (see Case F, Table
4.1-3). Thus if recycle were performed with the MEU/Th PBR cases, significantly less U308
would be required than for the PWR with U and Pu recycle. One option for the recycle in the
seed-and-breed MEU/Th PBR case would be to cycle the fertile balls back into the feed stream
(without reprocessing) for an additional pass through the pebble bed if the irradiation
behavior of the fertile balls permits.
Table 4.4-8. U308 Requirements for
Once-Through PBR Cyclesa
~-
Case 1, Case 2, Case 3, Case 4, Case 5,
Seed and Ereed Seed and Greed
LEU 11 E U / T h MEU/Th HEU/Th HEU/Th
Eauilihriun cycle 143 135 137 126 126
U308 demand, ST/GWE-yr
30-year cumulative
U308 demand,b ST/GWE 45OOc 41 84d 4200' 4007d 40OOc
'The basis for these requirements is a lOCO-H'.le plant operating at 752 capacity
factor for 30 years; tails composition is assumed to be 0.2 w/o.
'Assures no recycle.
c
Estimated value; could differ from an explicit 30-yr calculation by 5 3%.
dExplicit 30-yr calculation.
L
L