Chemical compatibility of B4C/Na/S.S.. Pt.1: The effects of temperature and B/C ratio

B4C pellets with different B/C ratio and nuclear purity grade sodium were put into a stainless steel cladding tubes and the out-of-pile tests were carried out at 550, 650 and 750 degree C. The test period is 82 d. After compatibility test, the appearance of B4C pellets is integral, and crack or break are not found. However, the surfaces become rough and original metal luster is lost. The chemical reaction product NaB5O8 deposits and adheres to the surface of B4C pellets. This results in the volume increasing of B4C pellets. No considerable change in microstructure and grain size of B4C pellets are observed. There are B, Na and C penetrate into cladding inner surface. The amount of B and Na penetration increases with the temperature and B/C ratio increasing, but C penetration is opposite. The chemical reaction products among Na, impurities in sodium, B4C and cladding are NaBO2 , Cr2B, Fe2B and Ni3B. The formation of the borides made increasing considerably in microhardness at the cladding inner surface