Geometrical data and material composition of fuel and fuel follower elements. Table 1 Fig. 1. Present core configuration of the TRIGA reactor. Fig. 2. The radial view of the MCNP model of TRIGA reactor. Comparison between the calculated and experimental core excess reactivity. Table 2 where p is the reactivity value in units of dollar ($) and Peg is the fraction of effective delayed neutrons (fef=0.007 for TRIGA fuel types (Negut et al., 2006; Simnad, 1981)). Fig. 4. Flow diagram of NJOY99 processing for ACE format library construction Fig. 3. The axial view of the MCNP model of TRIGA reactor. where Akeg and Akeg, represent the fractional statistical error estimates for Keg and Keg, , respectively. The calculation of the control rods’ reactivity worth simulated explicitly the experiment, which was carried out by the positive period method (Matsumoto et al., 2000). Using this method, the worth of one control rod was measured in the presence of other rods used for compensating the excess reactivity. We started the simulation with the control in their critical position calculating the keg, of the core. Then one of the control rods was withdrawn at a certain position, calculating the new keg. The control rod worth represented by reactivity o for that position was deter- mined by comparing keg and keg, as denoted by Eq. (2). The error propagated is deduced from Eq. (3) (Dalle et al., 2002): id iad Figs. 5-9 show the MCNP calculated integral reactivity curves for Shim I, Shim II, Shim III, Shim IV, and regulating rod, respectively. From these curves it can be observed that the MCNP calculated integral reactivity worth of control rods Shim I, Shim II, and Shim III are consistent. The measured reactivity worth of Shim IV and regulating rod are slightly superior to the calculated results. Nevertheless, this small disagreement remains acceptable in view of the other published results for other TRIGA reactors (Huda et al., 2004; Dalle et al., 2002). Also, it can be seen that, in all control rods the largest differential reactivity worth occurred when the rods supposed fully withdrawn. The calculated and measured reactivity Fig. 7. MCNP calculations and experimental integral rod worth for Shim III. Fig. 6. MCNP calculations and experimental integral rod worth for Shim II. Fig. 8. MCNP calculations and experimental integral rod worth for Shim IV. Fig. 9. MCNP calculations and experimental integral rod worth for regulating rod. Fig. 10. Power distribution within the fuel and fuel-follower elements of the TRIGA reactor core at 2 MW. Fig. 12. Hot channel fuel radial power factor profiles. Fig. 11. Hot channel fuel axial power factor profiles.
