Additional Flux Measurements on the Raleigh Reactor

%MurNBflux110154; ]> Additional Flux Measurements on the Raleigh Reactor Machine readable transcription Waltner, A. W. Dayton, I. E. Creation of machine-readable version: Russell S. Koonts Creation of digital images: Russell S. Koonts Conversion to TEI.2-conformant markup: Russell S. Koonts ca. 19 kilobytes NCSU Libraries Raleigh, NC Modern English, MurNBflux110154

Available from: NC State University Archives

Publicly-accessible

URL: http://www.lib.ncsu.edu/archives/etext/engineering/reactor/murray/

18 November, 2000

Nuclear Reactor Digitization Project

Raymond L. Murray Reactor Project Notebook

Illustrations have been included from the print version. Scanned by Russell Koonts with Photoshop 5.0 software. Additional Flux Measurements on the Raleigh Reactor A. W. Waltner I. E. Dayton

5 pp. Manuscript copy consulted UA 105.16

Prepared for the North Carolina State University Science and Technology Electronic Text Center

The lineation of the manuscript has been maintained and all end-of-line hyphens have been preserved.

Keywords in the header are a local Science and Technology Electronic Text Center scheme to aid in establishing analytical groupings.

Library of Congress Subject Headings November 1, 1954 English LCSH manuscript 24-bit color: 400 dpi Additional Flux Measurements on the Raleigh Reactor Typescript 5 pp. November 1, 1954 MurNBflux110154

Murray NCSC-90 A. W. Waltner I. E. Dayton November 1, 1954

ADDITIONAL FLUX MEASUREMENTS ON THE RALEIGH REACTOR

During the past several weeks a series of flux measurements have been made on the Raleigh Reactor. These measurements followed no comprehensive plan but were rather intended to supply information useful to anyone working with the reactor. Unless noted, conventional foil activation techniques ware used and will not be discussed further.

1. Effect of Poison Near PCP Chamber. A BF3 counter was set up opposite beam hole No. 15 to monitor the actual power level of the reactor. In beam hole No. 13, the hole nearest the controlling PCP, a volume 10.5 cm long was left empty and than filled successively with graphite and with textile samples, To within 1% counting statistics the reactor power level remained the same in all three cases. A weekly absorbing sample or a void thus exerts a negligible effect on the power level calibration. The reactivity is, of course, altered by the presence of either a void or a sample.

2. Neutron Flux at Sample Positions. In order to make possible more accurate calculation of exposures, relative flux measurements were made at the positions of all samples then in the reactor. Those data are not of general interest since they apply only to the particular loading. They are omitted from this report but are available to anyone who is interested. It is of interest to note that with these weakly absorbing samples the flux depression is very slight, certainly loss than 25%.

For subsequent measurements all samples were removed from the reactor. The graphite stringer in Upper No. 8 was made identical to that in Upper No. 7 by drilling holes for foil holders. The eight sample holes in the inner graphite

stringers of No. 13 and No. 15 were provided with graphite plugs, thus restoring the reactivity to its original value.

3. Flux Asymmetry Produced by Control and Shim Rods. The profile of the neutron flux in the graphite was measured by means of a set of foils in Upper No. 7 and Upper No. 8, which are on opposite sides of the core. A control and shim rod con- figuration which would produce a maximum asymmetry was chosen. A second run with the same foils in each position and a mirror image of the control and shim rod con- figuration was made to check the possibility of asymmetries due to poison in a beam hole. To within the accuracy of the measurement the neutron profiles obtained in the two runs were mirror images. A third run designed to separate the effects of shim and control rods was made by balancing the shims so that the reactor was critical at the same control rod position as used in the two preceding runs. The results are exhibited in Figure 1. The maximum asymmetry varied from 15% next to the core to 10% in the last position. With the shims balanced, the safety rod all out, and the control rod out 4.1", the asymmetry varied from 4% to 2%. This is not the maximum asymmetry that could be produced by the rods alone, since the shims could be raised and the control rod run in. It might be valuable to extend those measurements over a series of control rod positions.

4. Neutron Flux in Beam Hole. In order to design experiments using an external neutron beam it is necessary to know neutron fluxes and cadmium ratios under various conditions. Measurements were made in No. 13 with two, one, and no graphite stringers in position. The results were normalized to unity at the center of the core and are summarized in Table I. It should be noted that all those fluxes were measured with bare In foils and hence include both thermal and epithormal neutrons.

5. Glory Flux by Wire Activation. The measurement of neutron flux in a region which has sharp discontinuities requires a more continuous record than that ordinarily available from foil data. In the reactor core there arc two such discontinuities near each other, the surface of the fuel and the top of the reactor

Table I. Beam Hole Measurements2 graphitestringers 1 graphitestringer no graphitestringersCenter of core 1.00 1.00 1.00Edge of core .42 .43 .35End of 1st graphite .118 .093 End of 2nd graphite 4.7 x 10-3 Beam hole opening 7.6 x 10-6 3.9 x 10-5 1.17 x 10-4In/ Cd/In/Cd -1]at beam opening 11.5 5.5 3.2

vessel. To measure the flux through this region Ca wire was placed along the axis of the glory hole and activated. The counting was delayed until the 5.2 min Cu66 activity became negligible leaving only the 12.9 hour Cu64 activity. The wire was counted in a load shielded GM counter assembly which exposed about 1/4" of the wire. Counts were taken at 1/4" intervals.

The resulting flux profile showed the expected general behavior but exhibited unexplained "fine structure". Confidence in the results is also diminished by the fact that it was difficult to reproduce a given point--rotation of the wire seemed to have some effect. The copper thermocouple wire used was presumably pure and had desirable nuclear properties, but its physical properties were unsatisfactory in that it was very soft, kinked easily, and was probably non-uniform.

In order to obtain a wire with more desirable physical characteristics, a number of likely samples were irradiated to check their nuclear properties. Of those tried, pure nickel and piano wire both exhibited a single half life of suit- able magnitude. Constantan, nichrome, tinned copper, and pure copper all seemed less desirable.

If this technique were developed farther and automatic data recording intro- duced, it might prove valuable in other flux measurements.

We would like to thank Mr. C. W. Terrell for assistance in the foil counting and Professor E. J. Brown for help in plotting the data.

Visiting Fellow from the Atomic Energy Division of the Babcock and Wilcox Company, Akron, Ohio.