Data Relating to Hanford Mined Graphite (2273-D) Samples Annealed at NAA

Page 2

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Page 3

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

Page 4

AEC RESEARCH AND DEVELOPMENT REPORT DATA RELATING TO HAN FORD SAMPLES ANNEALED AT NAA This report was prepared as an account of Government sponsored work. Neither the United States, nor the Commission, nor any person acting on behalf of the Commissions A . ftAakes any warranty or representation, express or implied, with respect to the a c - curacy, completeness, or usefulness of the informstion contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not i n - fringe privately owned rights? or B. Assumes any liabilities with respect to the use of, or for domages resulting from the use of any information, apparatus, method, or process disclosed in this report. As used in the above, "pereon acting on behalf of the Commission" includes any e m - ployee or contractor of the Commission to the extent that such employee or contractor prepares, handles or distributes, or provides access to, any information pureuant to his e m - ployment or contract with the Commission.

Page 5

On February 8? 1950 there was mined from process tube 2273 in D pile at Haaford a quantity of graphite powder, which was expected to sho"«? the roost extensive radiation damage of any graphite available at that time. A series of saiapies of this powder were annealed in 100° increments front 100° to 2000° C at this laboratory. These were returned to Hanford and shipped by them to the National Bureau of Standards for total stored energy ineasurements. ~ The present memorandum is comprised of a description of the annealing procedure used here, curves giving the detailed annealing his-tory of each sample, and various curves derived from data obtained from these samples at Hanford and at the National Bureau of Standards. IL PROCEDURE USED IN THE ANNEALING OF MINED It was desired to anneal a series of two-gram samples in steps of 100° C from room temperature to 2000® C or above, A vacuum furnace of about L5 cm^ capacity was available for this work. The furnace is shown in Fig» 1. The furnace has a range from roono temperature to perhaps 2400® C, at which temperature appreciable sublimation of the graphite components begins to take place* It was found that by packing the powdered graphite tightly^ approximately 2 grants could be placed into a crucible of the dimensions shown in Figo 2. In order to maintain as uniform a temperature as possible throughout the sanaplej it was desirable to keep the length of sample short and to pack the graphite tightly to improve the thermal conductivity^ A. PRELIMINARY TESTS OF FURNACE A few simple tests of heating times and temperature gradients in the furnace were made before the annealing was begun. The first of these tests consisted in placing one of the empty crucibles in the furnace with a platinums platinum-10 per cent rhodium thermocouple in the crucible at the bottom^ The furnace was then turned on and temperature was determined as a function of time. This is shown in Fig^ 3, After the furnace came to equilibrium, there was a variation of about t l ^ C.At the equilibrium temperature, optical meas - urements were made of the heater temperature through the holes designated 2,

Page 6

3 and 4 in the furnace shield. Tie temperature reading through the upper hole These data have been corrected assuming an em is siv it y of 0. 9 and 10 per cent loss due to the bell jar. It appears,therefore, that the temperature of the heat - e r is not a good indication of the crucible temperature. The crucible was then loosely filled with powdered graphite^ The P t / P t - R h thermocouple was buried in the graphite near the center of the cruci - ble.A pyro meter was ^.rranged to look at the top of the crucible through a hole in the top shield. The furnace was turned on, allowed to approach equilibrium, and s nea sure ment s then made simultaneously with the thermocouple and the pyro meter. The results of these measurements are tabulated below. Due to errors in setting the pyrom.et@r and in the assumptions used to make the corrections, one might expect the accuracy of the pyro meter reading to b© only within about ilO ° C» In view of this, the readings agree surprising - ly well. One would expect the agreement to be at least equally good with tightly The same measurement was made without the top shield„ Temperature variations of about 40® Cwere noted between the top and the amiddle of the cru - cibleo The furnace was set to various voltages and the temperature was noted as a function of time.A measurement of the rate of cooling was m.a.de also. These measurements are plotted in Fig. 4. B. ANNEALING OF THE HANFORD GRAPHITE The Hanford graphite was tamped firmly into the crucibles and ade - press ion about 3/16 of an inch deep was forined at the top for the thermocouple. Figs.5 through 14 show the temperatures to which the various samples were subjected. The tem.perature was raised gradually over a period of 10 to 20 minutes to avoid a sudden release of stored energy which might cause over - shooting<, The sample was held at the desired temperature for about 15 to 20 m.inutes and then cooled rapidly. Temperatures were observed continuously throughout each run and were recorded at convenient times during the rise peri - od. During the steady period, high and low points were recorded.

Page 7

A thermocouple was used to measure temperatures to 1400® C A Leeds The accuracy of the thermocouple xnea.sur€tnent$ is probably ± 5 Cj and that of Small overshooting of temperature was observed at 100°, 200° and which we observed which might have been due to the release of stored energy. Temperature was controlled manually on all runs. It was difficult to maintain tion losses stabiliased the furnace very effectively. Above 1400° C, small vmriations (< 3 C) could not be observed with the pyrometer which was used* The highest temperature reached was ZQOO'^ C^ Higher tenapcratures with the power available would have required much better shielding along the axis of For completeness, three curves. Fig. 15, Ifi^ and 17, are included ia tively and Fig. 17 was derived from HW-19621. The greatest release of stored energy appears to be in the neighborhood ol 1400° C.

Page 8

ENDS OF GRAPHITE HEATER ARE COPPER TOP SUPPORTING TUBE HEAT SHIELD TO PROTECT GASKET FROM DIRECT

Page 23

NOMINAL ANNEAUNG TEMP. C^XIO'^I Figtire li,Calo ti metric Memsiiremeiits of Total Stored Energy in Mined Graphite {iZ't/i-'j)