Proton Reaction Determination of Lithium and Fluorine in Molten Salt Reactor Graphite

Nucleonics

“…Because of the possibility, offered by prompt charged-particle reaction analysis, both for scanning the surface of a sample and for studying its depth profile, the short name "nuclear microprobe" has become widely accepted for this method. Among the advances reported, protons were used to determine lithium by counting either prompt gammas (204) in the U.S.S.R. or neutrons (133) at Oak Ridge. The latter group also determined fluorine by the (p,a.y) reaction which, in turn, was used in England .…”

“…Profile (depth) scanning for hydrogen was performed at Grumman (148) by taking advantage of sharp resonances of the reaction 7Li + p in an original experiment; the Oak Ridge procedure (133) was reversed by using 7Li2+ ions as projectiles. Finally, the proton microprobe was applied successfully for the first time to biomedical samples to obtain 13C/12C ratios (170), the ultimate goal being the development of a scanning technique.…”

Progress Report on Graphite-Salt Intrusion Studies

“…From 1965 to 1969, the Oak Ridge National Laboratory (ORNL) Molten Salt Reactor Experiment (MSRE) demonstrated that graphite can be used as a moderator in nuclear reactors in which molten fluoride salts are used both as a coolant and liquid fuel carrier. In the MSRE reactor, graphite was in direct contact with the fueled salt, which was the mixture of 7 LiF-BeF2-ZrF4-UF4 (65.0-29.1-5.0-0.9 mole %), and with the nonfueled coolant, which was the 7 LiF-BeF2 eutectic (66-34 mole %), also known as FLiBe. At the operating temperature (650°C), the salt vapor pressure was less than 15 Pa, and the gas blanket (He) pressure above the salt was 700 Pa. 1 Graphite was the preferred choice for the moderator in contact with the molten salts due to its low wettability and better chemical corrosion resistance than most metals in molten fluoride salts.…”

“…In this high-temperature fluoride (HFR) design, the carbon matrix in pebbles and graphite in the moderator and reflector are in contact with non-fuel fluoride salt, and the fission products are retained in the TRISO microspheres. Two types of fluoride salts are frequently studied as prototypes: 7 LiF-BeF2 (66-34 mole %), also called FLiBe, and 7 LiF-NaF-KF (46.5-11.5-42 mole %), also called FLiNaK.…”

“…Postexamination results of graphite used in MSRE showed that the concentration of F and Li infiltrated in graphite exposed to molten fuel salt decayed exponentially with distance from the graphite surface, but F and Li had concentrations that were two and one orders of magnitude, respectively, higher after 9 months of exposure in a reactor than in unirradiated graphite with the same exposure length in molten fluorides. 7 According to recent results, Na and K ions (from FLiNaK) have different migration rates under irradiation, which might result in unbalanced distribution and damage graphite coherence in moderator and reflector components. 8 The solidification of salts in graphite's Mrozowski cracks could generate internal compression stress, which might increase the coefficient of thermal expansion and improve graphite crystalline stacking.…”