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operation of the PISRE.
67
analyses for 1311 showed that a large fraction of
the iodine was present in the fue120~72 and that 1311 deposited on metal
or graphite surfaces in the core region. However, material balances for
were generally low. ~t is possible that some of the precursor, 131~e
(25 min), was volatilized and sparged with the krypton and X~H~QR. Fur-
ther, 1 3 1 ~ produced by decay of E ~ I T in ~ complex metallic deposits (as in
the heat exchanger) may not have been able to return to the salt.
Noble and seminoble fission products. Some fission-product metals
(~e, AS, Nb, m, RU, ~ h Pa, , Ag, cd, SW, and sb) have fluorides that itre
unstable toward reduetion by fuel mixtures with appreciable eoncentra-
tions of UPQ; thus, they must be expected to exist entirely %n the ele-
mental state in the reactor. Selenium and tellurium were also expected
to be present as elements within the reactor circuit, and this behavior
was generally csnfirned during operation of the MSRE. 19920 $72 he MSRE
fuel samples usually contained far less than the generated quantities of
these elements. Portions of the MSRE samples were found (probably as
metalPic particulates) in the helium sparge gas,* deposited on metal sur-
faces, and (a reasonably small fraction) deposited on graphite specimens.
However, the distribution and especially the inventory in the fuel at the
sampling point in the pump bowl showed major variations. Further study
will be necessary before details of their behavior can be predicted with
confidence for a DMSR.
~n general, the results from MSRE operations suggest the following,20
I. The bulk of the noble metals remain accessible in the circulating loop
but with widely varying amounts in circulation at any particular time.
2. In spite of this wide variation in the total amount found in a par-
ticular sample, the proportional composition is relatively constant,
indicating that the entire inventory is in substantial equilibrium
with the new material being produced.
2k
Much-improved gas-sampling techniques used in later stages of MSRE
operation showed the fraction carried in the gas to be less than 2% of the
quantity produced” (with the possible exceptton of il i: 3% of ko3~u).