Characteristics of the ORR, LITR, and OGR that experimenters have found to be important are listed. The results of a survey conducted among experimenters on the utility of the reactors for various types of experiments are discussed, and some changes which might be made to improve the utilization are listed. A brief outline, with references, of most of the experiments currently being performed is included. (auth).

The ORR reactor operated at an average power level of 29.7 MW for 90 percent of the time during April, May, and June of 1976. Twenty-five fuel elements were declared spent (52.3 percent average burnup) during the quarter, while twenty-five new elements were placed in service. Two shim-rod elements were retired from service at an average burnup of 62.5 percent. The reactor was shut down on thirteen occasions, four of which were unscheduled. One end-of-cycle shutdown accounted for 61.1 percent of the total downtime. The remaining downtime was used principally for refueling and experiment work. Maintenance activities, both mechanical and instrument, were essentially routine in nature. A special test completed during the quarter was the visual inspection of the poolside facility. Operating data are presented.

The ORR operated at an average power level of 29.8 MW for 29.6% of the time during October, November, and December of 1977. Ten new fuel elements were placed in service. Two shim-rod elements were retired from service at an average burnup of 71.2%. The reactor was shut down on seven occasions, none of which were unscheduled. Reactor downtime needed for refueling, maintenance and checks was quite low, with the reactor remaining available for operation 88.2% of the time. Maintenance activities, both mechanical and instrument were essentially routine in nature. In-service inspections completed during the quarter included inspection of the ORR decay tank and the ORR pool heat exchanger.

The ORR operated at an average power level of 29.9 Mw for 84.9 percent of the time during October, November, and December of 1975. Eleven fuel elements were declared spent (52.5 percent average burnup) during the quarter, while twenty-nine new elements were placed in service. Four shim-rod elements were retired from service at an average burnup of 63 percent. The reactor was shut down on eight occasions, all of which were scheduled. Two end-of-cycle shutdowns accounted for 80.7 percent of the total downtime. The remaining downtime was used principally for refueling and experiment work. Maintenance activities, both mechanical and instrument, were essentially routine in nature. Special tests or measurements during the quarter included: (1) Flux mapping for core No. 129A; (2) Determination of minimum fuel content in ORR fuel elements prior to declaring the element spent; (3) Reactor vessel, ultrasonic test, and (4) Visual inspection of ORR primary pump.

The ORR operated at an average power level of 27.9 MW for 88.9% of the time during January, February, and March of 1981. The reactor was shut down on seventeen occasions, seven of which were unscheduled. Reactor downtime needed for refueling, maintenance, and checks was normal, with the reactor remaining available for use 92.6% of the time. Maintenance activities, both mechanical and instrument, were essentially routine in nature with the exception of one Reactor Instrumentation and Controls Design Change Memo and one Mechanical Design Change Memo. Special tests or measurements completed during this quarter are reported in a summary entitled, ORR Reactivity and Flux Comparisons between a 280 g, 45 Weight Percent Enriched Texas Instrument Fuel Element and a 265 g Standard 93 Weight Percent Enriched Texas Instrument Fuel Element.