265 where
Table 19.10. Estimated average corrosion rates in a frozen-wall fluorinator having a wall temperature of 450°C:
d = depth of nickel attacked by F,, mils;
t = t i m e of exposure of nickel metal to gaseous fluorine, measured from the time when no NiF, film exists; k = parabolic rate constant, mils hr-l/’.
Rate constants were calculated for 41 measurements for which the exposure times ranged from 5 hr to 960 hr. Most of the exposure times were in the range of 30 to 150 hr. Fourteen measurements had been made to determine the rate of corrosion of Ni-201 in the temperature range 380 t o 700°C; exposure times varied from 5 to 132 hr. The calculated rate constants are given elsewhere.’ The best least-squares representations of the data, which showed considerable scatter, are given below for Ni-200 and Ni-201 respectively: In k = 0.3773
In k = 4.3083
-
-
3691 T ’
Average life of film
12
1 month
1.4
0.47
52
1 week
2.9
0.97
365
1 day
7.66
2.5 8
satisfactory corrosion resistance if the NiF, film is kept intact for periods having an average length as great as one week. It appears that the anticipated corrosion rate would be influenced much more strongly by the length of time that a protective NiF, film is absent in the presence of fluorine and molten salt than by the frequency of destruction of the NiFz film in the absence of fluorine.
-
7836 T ’
19.8 AXIAL DISPERSION IN SIMULATED CONTINUOUS FLUORINATORS (3)
where k has units of mils hr-“’ and Thas units of “K. The largest deviations of individual data points from these two equations were about an order of magnitude higher and an order of magnitude lower. If n is the number of times per year that the NiF, film is destroyed, the extent of corrosion experienced each year (8760 hr) is given in mils by
(4)
-
Corrosion rate (mils/ year) Ni-200 Ni-201
n
and is the average corrosion rates for and one day are show were destroyed 52 times per year, the average corrosion rates at 450°C (the approximate wall temperature that will be used in a frozen-wall fluorinator) would be 2.9 mils/year for Ni-200 and 0.97 mils/year for Ni-201. If d 12 times annually, the average Id be 1.4 mils/year and 0.47 mil/year for Ni-200 and Ni-201 respectively. According to these results, Ni-201 seems to be more resistant to corrosion than Ni-200; however, either material shows
Molten Salt Breeder Reactor Processing No. 9., ORNL-TM-3259 (in preparation).
J. S. Watson
L. E. McNeese
Axial dispersion is important in the design of continuous fluorinators, which are envisioned as open columns through which fluorine is bubbled countercurrent to a flow of molten salt. We have previously reported showing the variation of dispersion coefficient with changes in gas and liquid flow rates, physical properties of the liquid, column diameter, and gas inlet diameter. During this reporting period, studies of the effect of column diameter were extended to a 6-in.-diam column, and additional data were obtained on the effect of the viscosity of the liquid. Most of the experimental data were obtained by students of the MIT Practice School. Dispersion coefficient data measured in a 6-in.-diam, 72-in.-long column are shown in Fig. 19.113. The dispersion coefficient values were about three times the values measured at the same superficial gas velocty in a 3-in.-diam column. The data show little dependence on superficial gas velocity. Although superficial gas velocities up to 10 cm/sec were used, the 6-in.-diam column was never operated in the “slugging” region. There was, 20. MSR Program Semiannu. Prop. Rep. Aug. 31, 1969, ORNL-4449, p. 240. 21. MSR Program Semiannu. Progr. Rep. Feb. 28, 1970, ORNL-4548, p. 307. 22. MSR Program Semiannu. Progr. Rep. Aug. 31, 1970, ORNL-4622, p. 216.