ORNL-4191 - the Molten Salt Energy Technologies Web Site

however, electric heaters are provided in thimbles
around the inner walls of the cells, as shown in
Fig. 5.7. The electric leads for the heaters are
brought out through sealed bushings i.n the thimble
caps.
The off--gas cells and the drain-tank cells have
double containment but do not need the thermal
shield tQ protect against the radiation flux. ’The
steam cells require only the thermal insulation
and cooling air, since the radiation levels will be
relatively low and double containment is not re-
quired in these spaces.
5.3 REACTOR
G. EL Llewellyn
W. C. George
W. 6. Stoddart
H. L. Watts
W. Terry
w. M. Poly
During the past report period, the new data dis-
cussed in Sect. 6.1 became available on the di-
mensional changes that occur in graphite as a
result of neutron irradiation. Because of this
experimenhl evidence, we decided to redesign
the reactor even though there is optimism that a
more stable graphite will be developed within the
next few years. The MSBR cost and performance
characteristics continue to be attractive even
though penalized by designing on the basis of
the immediate technology. We also decided that
the reactor should be designed in such a way that
major redesign or modification would not be re-
quired, to take advantage of a more stable graphite
when it becomes available.
Several new approaches were tried for the core
design, one of which was to put the fertile salt
in the flow passages through the core graphite
arid to allow the fuel salt to move through the in-
I____._
71
terstices. This so-called “inside-out” design
could probably accommodate the dimensional
changes in the graphite, assuming that suitable
adjustments were also made in the fuel etirichment.
A major disadvantage, however, is that the
fuel salt would also penetrate into the interstices
of the radial blanket, a position in which it IS exposed
to relatively low neutron flux and thus produces
relatively little power Since the flow in
this area would also be somewhat indeterminant,
this design of the reactor was not pursued further.
Attempts lo design a removable graphite core
for the reactor led to the conclusion that such an
arrangement would probably be impractical. OnP
major problem would be containment of the highly
radioactive fission products associated with removal
of u bare reactor core There would also
be the problem of assuring leak-tightness of a
large-diameter flanged opening which must be
sealed only by use of remotely operated tooling.
As previously mentioned, it was decided to replace
the entire reactor vessel.
Selection of 0 ten-year life for the reactor, or
about 5 ‘i 10” nvt (greater than 50 kev) total maximum
neutron dose for any puint in the cote, meant
that the power density would be reduced from the
40 kw/liter used in previous concepts to 20
kw/liter. ‘]This involved doubling the corc volume
from 503 ft to about 1040 ft 3, and also required
that the reactor vessel size be increased correspondingly.
The factors entering into selection
of these conditions are given in Table 5.1, which
shows the effect of power density on the performance
factors for the plant. At 20 kw/liter, it may
be noted that the fuel cycle cost is 0.5 niill/kwhr
and the yield is 4%/year. This appears to be the
most practical design point, although it is without
benefit of improved graphite. It should be pointed
out that the differences in capital costs shown in
Tuble 5.1. Performance Factors of MSBR as Function of Average Core Power Density
Power Density Core Size (ft) Yield Fuel Cycle Cost Capital Cost I.ilb
!kw /liter) u iame ter He iL:h t !.%/year) (mills /kwhr) [$/kw (electrical)] (years)
80 6.3 8 5.6 0.44
40 8 10 5.9 0.46
2 o 10 13.2 4.1 0.52
10 12 18 2.7 0.62
F is 5 ile Inventory
[kg for 1000 blw
(e lei- trica 1
117 2.5 880
119 5 1 w0
125 10 1260
I32 29 1650
)I