A smooth curve of T vs. the half-life of the parent nuclide from the data obtained in an operating BWR is shown in Figure 8–1. Qualitatively, the curve would be expected to flatten out for short half-lives as a limiting point is reached where only a single flow delay is significant, and all other delays are so long relative to the half-life that they do not contribute to the release. The apparent transit time for other gaseous activities can be obtained from this curve. If the transit time from the outlet of the reactor pressure vessel (RPV) to the SJAE is known, the gaseous activity release rate at the RPV can be estimated.

Similarly, using the parent-daughter relationship, the delay time in the condensate (hot-well) can be estimated from the noble gas daughter and granddaughter activities. In the reactor coolant, the delay time in the sample line or any specific system can also be estimated from the parent-daughter pair activities. Some major parent-daughter pairs and their decay constants have been summarized in Table 2–1.

Figure 8–1. Apparent Transit Time for Gaseous Activities from RPV to SJAE