Adaptation of WWR-K reactor for irradiation work at low power

According to INAA in Sept 2000 there were 288 research reactors in operation in the world. 67 % of these reactors were operating in power mode below 1.1 MW. The profile of an available scientific and technological program depends to a great extent on reactor power. High-power reactors are used mainly for isotope production and material testing, specially for needs of power generation programs. Low-power reactors are used mainly for education and for irradiation for purposes of activation analysis. TRIGA, Slowpoke and the Chinese Mini Reactor are typical instruments in this class. High neutron flux can also be utilized for activation analysis. In this case, samples for irradiation should be tightly sealed in aluminium or in quartz, and organic samples can be irradiated for a relatively short time only. Another important issue is that reactor operation on a high power level is connected with higher expenses for fuel, for electric power, for coolant and for general maintenance. Many reactor centers use to charge prices like USD 200 to 400 for 1 day irradiation of a single container 10-12 cm high and 2.5 to 5 cm in diameter. For many users this price is prohibitive. In a low-power reactor all the expenses are smaller and samples of organic origin can be much larger. The WWR-K is 6 MW light water research reactor with the maximum neutron flux 1.4·1014 n·cm-2·s-1 and, correspondingly, rather high operation expenses. However, it can be operated at lower power levels, with much less electric power consumption for cooling systems. To check a possibility of use of the WWR-K as a low-power reactor, to decrease expenses for activation analysis, three experimental runs were performed on 200 k W power. Samples were irradiated in a specially built aluminium container 6 cm in diameter and 60 cm high. Inside the aluminium container there were located 6·120 ml bottles (jars). The total volume available in one irradiation was 720 ml. Analysis of economical and technological aspects of such irradiation method will be presented, with some conclusions concerning the potential of low-power operation mode for future irradiation work programs