April 6, 1953

In answer to your questions:

• 1. What are exact dimensions of Boron Column in Control and Safety Rod?
• • length 12.0" (three 4.0" cylinders)
  • outside diameter 0.630"
  • inside diameter 0.183"
• 2. What is Volume of Boron?
• • 18.7 cm³ per cylinder, total 74.8 cm³
• 3. density of Boron?
• • 1.94 grams/cm³
• 4. density of Boron containing material
• • 2.50 grams/cm³
• 5. Total weigh of Boron per rod
• • 145 grams
• 6. Total weight of boron Containing Material
• • 187 grams
• 7. What, if anything, is present besides B4C?
• • Comparing theoretical percentage B with actual, discrepancy of 0.6%. No
    information on what this is, but may be carbon. Does not matter, however.

Rod Values:
Critical condition will be achieved with solution at temperature
of cooling water, with one rod completely out (safety) and one
rod completely in (control). As one rod is removed, [delta]k increases,
the power rises, and the temperature rises. The rod value as best
we can compare with Los Alamos is 80 grams of U-235 or 0.016 [delta]k.
If either this rod is dropped or the safety rod falls, the reaction is
suppressed. The average change in reactivity is, for 5"/min removal
0.016/2 minutes = 0.008/min or 0.00013/sec
The maximum rate of change of reactivity is approximately twice
this value, when the rod is half way out.