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Transport of Beryllium-7 in a Lithium Loop

Hiroji Katsuta, R. P. Anantatmula, Rebecca A. Bechtold, William F. Brehm

Fusion Science and Technology / Volume 6 / Number 1 / Pages 118-124

July 1984


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A 7Be transport test was performed in the Beryllium-7 Experimental Lithium Loop with hot leg at 270°C and cold leg at 230°C. The “cold leg” test stringer was in a rising temperature region at 250°C. A total of 108 test coupons were included in the material compatibility and deposition test programs, containing AISI Types 304 and 304L stainless steels, Fe-2¼ Cr-1 Mo, pure iron, molybdenum, beryllium, zirconium, titanium, yttrium, three different aluminide coatings on Type 304 stainless steel substrates, and both tubular and flat butt-welds of Type 304 stainless steel. An average lithium velocity of 1.36 m/s was established during the test, which was terminated after 3718 h. The 7Be activity data indicated that the deposition of 7Be is a function of temperature. The cold leg positions displayed maximum 7Be deposition followed by the intermediate temperature locations (cold leg test stringer) and the hot leg locations. Two chemical forms of 7Be are expected in lithium, namely, unbonded 7Be at a low concentration, and a fine precipitate of 7Be3N2 at a high concentration. The deposit in the hot leg region is presumed to be primarily 7Be, while the cold leg deposit is mostly 7Be3N2. The cold leg specimens of a given material showed more 7Be deposition than the hot leg specimens of the same material, consistent with the 7Be activity data on the piping. Based on the present investigations and previous data, it is concluded that 7Be produced in the Fusion Materials Irradiation Test (FMIT) facility will have sufficient nitrogen in the lithium system to form 7Be3N2. It is expected that the majority of 7Be will be transported to the colder parts of the loop and deposited as 7Be3N2. However, a small amount of 7Be in the unbonded form will be in the hotter parts of the loop and is expected to diffuse into the steel piping. Thus, it is recommended that a cold trap be used to effectively remove most of the 7Be from FMIT lithium.

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