Release from defective fuel rods during reactor transients

2 Release from defective fuel rods during reactor transients 

Iodine spiking in pressurized water reactors was first analyzed in detail by Neeb (1971) using data obtained by measurment during several reactor shutdowns at the Obrigheim PWR plant. The time-behavior of the activity concentrations of the iodine isotopes in the coolant, which is exemplarily shown in Fig. 4.9., is fully consistent with the results reported by other authors, e. g. by Chubb et al. (1977), from Westinghouse PWR plants. 

By a more detailed analysis of the available experimental data, further effects can also be detected. The increase in activity concentration of the shorter-lived is considerably less pronounced than that of I, with the maximum of its activity concentration in the primary coolant during the spike being higher by only a factor of 10 to 30 than the level during the preceding steady-state operation phase. During 

Observations in some PWR plants showed that no shutdown spiking occurs when defective fuel rods are present exclusively in regions of low heat ratings, e. g. at the outermost periphery of the reactor core. 

As was discussed above, the maximum iodine activity concentrations attained in the course of a PWR shutdown spiking apparently depend on the type, position and number of defects present in the reactor core. When these parameters are 

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