ORNL-4191 - the Molten Salt Energy Technologies Web Site

olten- I rr
Molten-salt breeder reactors are expected to
operate with a high rate of production of fission
products as a result of fuel salt power densities
in excess of 200 w/cc. The effects of long-term
exposure under such conditions on the stability
of fuel salt, the compatibility of salt with graphite
and metal (Hastelloy N), and the fate of the fission
products are of interest. Undue buildup of
fission product poison on core graphite, for example,
could reduce the breeding efficiency of t.he
reactor if not mitigated. Initial loop experiments
are being directed largely at understanding the
fate of important fission products.
The second thermal convection in-pile loop experiment
was terminated by the appearance of a
Results of the first in-pile molten-salt convection
loop experiment in this program have been
reprted. Irradiation of the second molten-salt
convection loop in beam hole HN-1 of the Oak
Kidge Research Reactor began' January 12, 1967,
and was terminated April 4, 1967, after development
of 8.2 x 10 ' * fissions/cc (1.2% ' 5U burnup)
in the 7LiF-BeF ,-%rF,-UF , (65.3-28.2-4.8-1.7
mole %) fuel. Average fuel power densities up to
150 w per cc of salt were attained in the fuel
channels of the core of MSRE-grade graphite.
'H. C. Savage, E. L. Compere et al., MSR Program
Serniann Progr. Rcpt Feb 28 1967, ORNL-4119,
pp. 167---73.
E. G. Bohlmann
crack in the core outlet pipe, probably caused by
radiation embrittlement of the alloy and stresses
encountered during a reactor setback. Sufficient
operating time had, however, been achieved to
produce fission product concentration levels
equivalent to those estimated to be present at
processing equilibrium in a breeder; therefore, an
exhaustive evaluation of the experiment is in
progress.
Future loops will be fabricated of Hastelloy N
modified by titanium additions shown to inhibit
the radiation effects. Experiment objectives in-
clude study of materials compatibility, fission
product behavior, and effects of operation at off-
design conditions.
E. L. Compere H. C. Savage J. M. Baker
176
The experiment was terminated after radioactivi-
ty was detected in the secondary containment sys-
tems as a result of gaseous fission product leak-
age from a crack in the core outlet tube.
Operation and postirradiation examination of
the second loop are described below.
A diagram of the second in-pile molten-salt con-
vection loop is shown in Fig. 15.1. The core
section of the loop consists of a 2-in.-diam by
6-in.-long cylinder of MSRE graphite. Eight
vertical 'G-in.-diarn holes for salt flow are bored
through the core in an octagonal pattern with