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Early in December 1963 eighteen natural uranium columns were discharged from C Reactor. Fifteen (15) of these columns contained alternately charged HDS (test) and AlSi (control) fuel elements in the downstream half (positions 1--16); two columns were charged full length with HDS material; and one column was charged full length with AlSi material. All canned pieces were nominally C5NS dimensions except that the HDS pieces were slightly longer than the standard AlSi pieces. Uranium fabrication history, through heat treatment, was controlled ad equivalent for both test (HDS) and control (AlSi) material. For these eighteen columns average exposure was {approximately}960 Mwd/ton, average tube power was {approximately}1125 kw, and average tube outlet temperature was {approximately}100 C. Two striped charges were discharged in September 1963 @ 370 Mwd/ton. This report presents results of the post-irradiation measurements that have been completed and analyzed as of this date. A second set of measurements for a portion of the material is being programmed.

This report to the FEDC Working Committee details activities in N-Reactor fuel element fabrication and materials testing for the time period of September 1965 to January 1966.

Fuel element warp occurring during the irradiation period is considered to be one of the major fuel element dimensional stability problems. Warp has been shown to correlate with accelerated corrosion attack. and also can contribute to stuck fuel charges, particularly in bumpered or self-supported charges where the annular clearances are reduced due to the presence of the projection rails. Thus, any process which offers a potential for reducing the average warp should be evaluated. Preliminary tests offsite have indicated that the use of a commercially available oil for a quench medium following beta heat treatment produces a fuel core with less residual stresses and a slightly finer and more uniform grain size than that produced by the present HAPO method of water quench. Thus, adoption of an oil quench nay offer a means whereby warp can be reduced without incurring costly revisions to equipment or fabrication processes. This report presents an irradiation testing program to evaluate the performance of oil quenched cores and to determine the optimum core heat treatment.

In order to predict graphite damage rates for the NPE, it is necessary to have some knowledge of the neutron fluxes at various energy levels. In particular it is important to know flux levels relative to those existing where graphite samples have been irradiated experimentally. Three-group flux levels have been calculated for regions far from boundaries in the core of the NPR and of a K-reactor. The results reported here have been obtained from more detailed calculations using better cross section data than used in obtaining a previous set of values (for NPR only). The calculations of effective group cross sections for the reactor lattice still are not entirely satisfactory however, and it is hoped that some improvement can be made. Since any revision of the cross sections will affect the calculated flux levels, the values reported here should be regarded as preliminary. It is felt that the relationship between NPR and K fluxes should be fairly satisfactory, since identical calculational methods were used for both.

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A significant portion of the planned production.gain expected from the FY 60 Reactor Plant Improvement Program was directly related to overboring the existing graphite channels. The overbore contemplated was a modest 200 mil enlargement (which would not require enlarging the reactor shield penetrations) at those reactors which were the last to require tube replacement. This was all that appeared feasible in view of the developmental work which had been accomplished at the time the program was prepared. Recent studies have confirmed that large incentives exist for overboring the reactor process channels approximately 500 mils in the C and 5 old reactors. Conservative estimates of the incentives for overboring indicate a payout period of about two years for the proposed work based on an increase in plutonium production of 15--18% derived from increased conversion ratio, and a reduction in plant unit cost. The proposal to overbore the graphite channels approximately 500--550 mils in one or more of the present Hanford reactors will require fuel elements about 0.5 inch larger in diameter than the present I&E fuel elements. Since there is only limited experience at HAPO in fabrication and irradiation of large diameter fuel elements, parallel development of large fuel elements is …