Experimental measurements of Na-24 activity in Tehran Research Reactor (TRR)

Experimental determination of coolant activity due to Na-24 produced as a result of 23Na(n,γ)24Na and 27Al(n,α)24Na reactions has been done for TRR. Activity of various water samples from the reactor pool was measured. Relative Source Strength Measurement (RSSM) technique was employed to measure Na-24 activity. It showed that the total activity per unit volume due to Na-24 in the reactor pool is 124.01 ± 3 Bq/cm3. The activity due to 23Na(n,γ)24Na reaction in coolant was also determined using the RSSM method and its value is 43.42 ± 0.8 Bq/cm3. Therefore the measured activity due to recoil Na-24 is 80.59 ± 1.1 Bq/cm3. It agrees well the theoretical predictions of 120.62 Bq/cm3 for same reactor operating conditions. These results validate assumptions made in development of coolant activation model, i.e., the fraction of Na-24 that enters the coolant as recoil product is 0.25 and about 90% of the water leaving the core mixes uniformly with the coolant in reactor pool whereas the returns immediately back to the core inlet.