ORNL-1816 - the Molten Salt Energy Technologies Web Site

c.
. f
0
L
..
would mean that most of the energy associated
with the hard ca e gammas emitted from the
gadolinium would appear as heat in the surrounding
moderating material rather than in the gadolinium.
Thus a gadolinium rod would have the advantage
relatively little of the heat associated with
ron captures in the rod would appear in the
rod, and therefore little provision for cooling
would be required, On the other hand, if boron
were used, the very short range alpha emitted
from neutron captures in boron would cause
virtually all the energy associated with the
neutron capture to appear in the boron.
The principal heating in a gadolinium rod would
be that induced by gammas from the fuel region.
For a 60-Mw re r it appears that the power
density in the gadolinium from this source would
amount to about 20 w/cm3. Estimates indicate
that about 20 cm3 of gadolinium would be re-
quired. The total power generation in the rod
from gammas from the fuel region would amount to
approximately 400 w, or about one-sixtieth the
power generation in a boron rod. It should be
noted that gadolinium oxide is available at a cost
of about $4000/lb and that it can be fabricated
re~adily by using conventional ceramic techniques.
f- Looling of the rod presents quite a number of
problems. If the rod were immersed in flowing
sodium, cooling would present no problem. How-
ever, the control rod actuating mechanism would
have to operate, to some degree at least, in
sodium, and self-welding might present some
difficult problems. If the rod were placed in a
thimble in the center of the core and an atmosphere
PERIOD ENDING DECEMBER 70, 7954
mechanism could include a heat exchanger so that
the heat would be removed from the circulating
helium and transmitted to the shield water. Un-
fortunately, such a system would be dependent on
the satisfactory operation of quite a number of
moving parts, always a likely source of trouble.
FILL AND DRAIN SYSTEM
A good, reliable, relatively simple fill-and-drain
system incorporating a quick disconnect c:oupl ing
suitable for remote operation with high-temperature
liquid systems is clearly needed. In the design of
the ARE, fixed tanks with remotely operated valves
were used in order to avoid a remotely operated
coupling. This approach led to a quite complicated
collection of tanks, plumbing, and valves, and to
somewhat clumsy arrangements for system drainage.
The requirements of such a system ar1s fairly
straightforward. In the first place, a good c:oupling
that can be operated remotely and that will be
dependably pressure-tight is required. This
coupling must be relatively insensitive tl3 align-
ment both as to concentricity and to par3llelism
of the axes of the mating flanges or surfaces. A
reliable pressure-tight valve on either side of the
coupling must be provided so that, after the
coupling has been made, the space between the
valves can be evacuated and then purged with
helium. The valves on either side of the c:oupling
can then be opened and the filling or idraining
operation carried out. Upon completion of the
operation, the upper valve can be closed and the
space between the valves cleared of liquid by
several short blasts of helium. The lower valve
can then be closed and the coupling broken.
the sp
imDortant. Partlv
hat might be
is implies that