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

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8%<br />

3.4 Reactor Materials<br />

Although special, high-quality materials probably would Re used<br />

throughout in <strong>the</strong> construction of a BMSR, most of <strong>the</strong>m Could be obtained<br />

from cowmerical sources that routinely supply such materials using cur-<br />

rently available technology. Two notable exceptions to this generaliza-<br />

tion are <strong>the</strong> Structural alloy that would have to be used for components<br />

normally exposed to molten salt and <strong>the</strong> graphite for <strong>the</strong> reactor core<br />

moderator and reflector. Both of <strong>the</strong>se materials would require specifi-<br />

cations peculiar to <strong>the</strong> MSW system.<br />

3.4.1.1 Requirements<br />

3.4.1 Structural allov<br />

The metallic structural material used in constructing <strong>the</strong> primary<br />

circuit of a molten-salt reactor will sperate at temperatures up to about<br />

700°C. The inside of <strong>the</strong> circuit will be exposed to salt that contains<br />

fission products and will receive a maximum <strong>the</strong>rmal fluence of about 6 X<br />

neutrons/m2 over <strong>the</strong> operating ldfetime of about 30 years. This<br />

fluence will cause some embrittlement because of helium formed by trans-<br />

mutation but will not cause swelling such as is noted at higher fast flu-<br />

ences. The outside of <strong>the</strong> primary circuit will be exposed to nitrogen<br />

that contains sufficient ajir from inleakage to make it oxidizing to <strong>the</strong><br />

metal. Thus, <strong>the</strong> m etal must (1) have moderate oxidation resistance, (2)<br />

resist corrosion by <strong>the</strong> salt, and (3) resist severe embrittlement by<br />

<strong>the</strong>rmal neutrons.<br />

In <strong>the</strong> secondary circuit, <strong>the</strong> metal will be exposed to <strong>the</strong> coolant<br />

salt under much <strong>the</strong> same conditions described for <strong>the</strong> primary circuit.<br />

The main differences will be <strong>the</strong> lack of fission products and uranium in<br />

<strong>the</strong> coolant salt and much lower neutron fluences. This material must have<br />

moderate oxidation resistance and must resist corrosion by a salt not eon-<br />

taining fission products or uranium.<br />

The primary and secondary circuits involve numerous structural shapes<br />

ranging from several centimeters thick to tubing having wall thicknesses<br />

of only a millimeter or so. These shapes must be fabricated and joined

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