A dry criticality test was carried out to determine the minimum critical mass of the HNPF Core without sodium. A subcritical calibration of the central control rod was performed and the relative reactivity worths of the inner ring of six control rods were determined. The extrapolated critical loading for the various plots after each incremental fuel loading with all rods out is shown. A tabulation is presented of multiplication data taken throughout the dry critical test. In order to find the relative integral reactivity worth of the central control rod in the dry critical loading, subcrltical multiplication data were obtained. The test completion criteria as stated in the test procedure were met. (M.C.G.)

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The purpose of this study is to determine if a hazardous condition is created by accidental closing of the coolant loop isolation valves�while the reactor is operating.

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Core dimensions and nuclear parameters were calculated for a sodium- cooled fast reactor containing UC fuel elements in a skewed hexagonal array. (C.J.G.)

An evaluation of a modulator flux sensitive playback head to be used with an analog magnetic recorder for nuclear pulse information storage was made. The modulator head was found unsultable. A pulse stretching unit was constructed which takes pulses from a standard linear pulse amplifier and provides an output signal suitable for driving a recording head. (For preceding period see ARF-1151- 3.) (C.J.G.)

Descriptions are given of various procedures used in determining leaks in the tubes of the 1B heat exchanger. Air pressurization tests determined leakage and leak rate of nine tubes. The leak-location-detector-probe method was found promising for locating defects along the length of the tube. Results of the probalog, dye-penetrant, and ultrasonic tests proved inconclusive in determining leak locations. (B.O.G.)

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Alloys containing 55 wt.% iron--22 wt.% nickel-- 17 wt.% chromium--2.5 wt.% molybdenum- 1.0 wt.% niobium-0.03 wt.% carbon-- 0.5 wt.% manganese-- 0.5 wt.% silicon with nominal additions of from 0 to 1.5 wt.% yttrium, and 36 wt.% iron-37 wt.% nickel--18 wt.% chromium--2.5 wt.% molvbdenum- 1.5 wt.% niobium-- 1.0 wt.% aluminum-0.05 wt.% carbon--0.5 wt.% manganese-- 0.5 wt.% silicon with nominal additions of from 0 to 2.0 wt.% yttrium, were prepared by vacuum- induction melting. Alloys containing 55 wt.% iron were successfully forged in air at 1900 deg F, rolled at 1850 deg F to 0.060-in. sheet and cold rolled to 0.015in. sheet. Fabrication of alloys containing 36 wt.% iron with more than 0.5 wt.% yttrium was unsuccessful. Addition of yttrium had relatively no effect on the yield and ultimate strength from room temperature to 1850 deg F. The ductility of fabricable alloys studied was increased at elevated temperatures by increasing yttrium contents. The greatest increase in ductility occurred at 1.5 wt.% yttrium. (auth)