ORNL-TM-7207 - the Molten Salt Energy Technologies Web Site

63
n e results of a program of solution themodynamics,25926 a ~ong-tem
program of in-pile irradiations,5’ atad a number of special experiments
gemmed genel~aiiy accurate preaietions, 63-65 but much of our detailed -
and still incomplete - understanding of fission-product behavior comes
from operation of the ~ ~ 1 ~ ~ me ~ ~ ability 9 2 of 2 the ~ fissfsn ~ 2 produets
to form stable compounds and to dissolve in the molten fuel serves to
divide them into the three distinct groups described in the following
dissussisn.
e . Krypton and xenon (which
is an important neutron absorber) fom no eorrapounds under conditions ex-
isting in a DMSR or other molten-salt reactor.19,73 Noreover, these
gases are only very sparingly soluble in molten fluoride mixtures. 74-76
As with all noble gases (see Fig. la), 76 their solubility increases with
temperature and with diminishfng size of the gaseous atom, while the heat
of solution increases with increasing atomic size. This low solubility
is a distinct advantage because it enables the ready removal sf krypton
and xenon from the reactor by sparging with helium.
The relatively sim-
ple sparging system of the MSRE served to remove more than 80% of the
13%e, and far more efficient spargbng was proposed for the MSBR.”
Stripping of the noble gases from the reactor after a short residence
time avoids the presence of their radioactfve daughters in the fuel.
Tritium qualifies as a fission product because mall quantities of
it are produced in ternary fissions. However, essentially all of the
tritium anticipated in MSBR’Q,~~ results from other sources, as shown in
Table 27.
A DMSW at similar power level and with a generally similar fuel must
be expected to generate tritium at approximately this same rate. This
tritium will originate in principle as 3 ~ however, ~ ; with appreciable
esneentrations of ~3 present, this ’HF will be reduced largely to %2.
A However, note that the pores in the moderator graphite can offer a
haven far &heSE? gases.