ORNL-5388 - the Molten Salt Energy Technologies Web Site

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trons in the Zircaloy cladding and the coolant of conventional PWRs (~4% of all
neutron absorptions in PWRs result from hydrogen absorption).
2. Low 233Pa burnout due to the low (7-8 W/cm3) power density.
The combination of low power density and large core heat capacity associated with
the graphite moderator and the ceramic fuel largely mitigate the consequences of HTGR loss-
of-coolant accidents. Loss of cooling does not lead to severe conditions nearly as quickly
as in conventional LWRs or FBRs since the heat capacity of the core is maintained, there-
fore allowing considerable time to initiate actions designed to provide auxiliary core cooling.
The HTGR offers a near-term potential for realization of tmproved U308 utilization.
The 330-MWe Fort St. Vrain plant has been under start-up for several years with a current
licensed power level of 70% and the plant has operated at the 70% power level for limited
periods. A data collection program is providing feedback on problem areas that are becoming
apparent during this start-up period and will serve as the basis for improvements in the
comsercial plant design.
An advantage of the HTGR steam cycle is that its commercialization could lead to
later commercialization of advanced gas-cooled systems based on the HTGR technology. These
include the HTGR gas turbine system which has a high thermal efficiency of 45 to 50% and
the VHTR (Very High Temperature Reactor) system for high-temperature process heat appl i-ca-
tion.
Mass balance calculations have been performed by General Atomic for several a1 ternate
HTGR fuel cycles,l and some additional calculations carried out at ORNL have verified certain
GA results.2 Their results for the following fuel cycles are presented here:
Dispersible Resource-Based Fuels
1. LEU, no recycle.
a.
b.
Carbon/uranium ratio (C/U) = 350.
C/U = 400, optimized for no recycle.
2. MEU/Th (20% 235U/U mixed with 232Th), C/Th = 650, no recycle.
3. MEU/Th (20% 235U/U), C/Th = 306 for initial core, C/Th = 400 for reload segments,
23311 recycle.
Dispersible Denatured Fuel
4. MEU/Th (15% 233U/U), C/Th = 274/300 (initial core/reload segments), optimized
for uranium recycle (23% t 2351)).
Energy-Center-Constrai ned Fuel
5. Pu/Th, C/Th = 650 (batch-loaded core).
Reference Fuels
6. HEU(235U)/Th, C/Th = 214/238 (initial core/reload segments), no recycle.
7. HEU(233U)/Th, C/Th = 150, high-gain design, uranium recycle.
8. HEU(235U)/Th, C/Th = 180/180 (initial core/reload segments), uranium recycle
(from ref. 3).