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

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and to salt containing tellurium to show that it will resist embrittle-
ment by these two processes aver long periods of time. Numerous mechan-
ical property tests must be run
needed for ASME Boiler and Pressure Vessel Code appr~val of the alloy
and to establish adequate design methods.
3.4.2.1 hquiKementS
the new alloy to develop the data
3.4.2 Moderator
The graphite in a single-fluid molten-salt reactor serves no struc-
tural purpose other than to define the flow patterns of the salt and, sf
course, to support its om weight. The requirements ~n the material are
dictated nost strongly by nuclear considerations, that is, stability of
the material against radiation-induced dist~rtion and nonpenetrability by
the fuel-bearing molten salt. Practical limitationas of meeting these re-
quirements impose conditions on the core design- specifically the neces-
sity to l imit the cross-sectional area of the graphite prisns.
quirements of purity and impermeability ts salt are easily met by several
hfgh-quality fine-grained graphites, and the main problems arise from the
requirement of stability against radiation-induced distortion.
3.4.2.2. Status sf development
The re-
The dimensional changes ~f graphite during irradiation have been
studied for a number of years. The dimensional changes largely depend
on the degree of crystalline isotropy, but the volume changes fall into
a rathear consistent pattern.
tion QCCUPS first during which the vslurae decreases, and a period of swell-
ing then occurs in which the vo%me increases.
concern only because of the dimensional changes that take place, and the
second period is sf concern because of the dimensional change and the
formation of cracks. The formation of cracks would eventually allow salt
to penetrate the graphite. Data shown in Fig. 18 are for 7%5"C, and the
damage rate increases with increasing temperature. Thus, the graphite
section size should be kept small enough to prevent temperatures in the
graphite frm greatly exceeding those in the salt.
As shorn in Fig. 18, a period of densffica-
The first period is of