The MTR completed its ninth year of successful operation on March 31, 1961. During this period the reactor was operating at design power, or better, approximately 70% of the time, for a total cumulative thermal energy production of 82900 megawatt days. The operating power level, originally designed for 30 Mw thermal, was raised to 40 Mw in 1955. Although normally operating on a fully enriched uranium core, the MTR has also operated successfully for one fuel cycle on a 20% enriched core and a plutonium core. A total of 10500 individual irradiations was performed in the MTR under AEC sponsorship and 986 under commercial programs. The Engineering Test Reactor was in successful operation at full design power of 175 Mw thermal for approximately three years, except for down-time occasioned by loop installations, experiment insertions and removals, and refueling. Total accumulated energy production to March 31, l961, was 80900 Mw-days. Installation of major in-core loops is expected to be essentially complete by the end of 1961. A total of 1215 individual irradiations was performed in the ETR under AEC sponsorship and 2! under commercial programs. Roughly more » 41% of the associated with the civilian reactors program, 40% with classified programs, and 3% with privately financed irradiations. The remaining 16% represents general research and development activities and radioisotope production. Approximately 700,000 c (curies) of radiocobalt were produced in the MTR- ETR, mostly in the 20 to 50 c/g range. Highest specific activity produced thus far is 308 c/g. No serious reactor incident was encountered in either the MTR or ETR, and there were no serious overexposures of personnel to radiation. The basic operating philosophy is implemented by a continuously functioning safeguard review board with power of veto over all reactor operations; careful operator training and supervision; firm instructions to all operators that the reactors are to be scrammed ' promptly whenever any of the instrumentation or circuitry indicates abnormal behavior; prohibition against operating either reactor with any significant defects in control instrumentation, fuel elements, or shim rods; and strict limitations on permissible departures from standard operating parameters and procedures by reactor operators. (auth) « less