Iodine spiking model for pressurized water reactors

Will $^{37}$Ar emissions from light water power reactors become an obstacle to its use for nuclear explosion monitoring?

“…After a power transient, notably for reactor shutdown, enhanced releases of volatile fission products from defect fuel rods into the cooling water are observed (Lewis et al, 1997).…”

“…Although marked peaks are apparent from release of the 37 Ar accumulated in the fuel rod gap and plenum, both when the defect develops and after a power transient, their concentrations in stack emissions are negligibly small and do not produce any detectable 37 Ar background within the atmosphere. This is a marked difference from xenon emissions of nuclear power reactors, which for its major radioactive isotope 133 Xe mainly result from fuel rod defects (Lewis et al, 1997), notably after reactor shutdown when the noble gas retention systems are bypassed (Saey et al, 2013). This discrepancy results from the fact that the concentration of calcium as the precursor of 37 Ar in the fuel is limited to trace levels (5 ppm) producing a small equilibrium activity of 1.7 • 10 6 Bq kg −1 compared to the high yield fission product 133 Xe with an equilibrium inventory of 8.3 • 10 13 Bq kg −1 .…”

Methods for Evaluating the Accuracy of Fission Product Concentration Measurements in Nuclear Reactor Primary Heat Transport Systems

“…These measurements were then compared and contrasted against direct measurements; agreement between the independent systems provided confidence in both measurements. Unlike the NRU reactor, in the case of LWR/ PHWR/WWER commercial reactors, shutdown iodine spiking requires a more detailed model and higher frequency sampling (effective half-life is much shorter) to measure effective halflives and examine purification capabilities [3,18,19]. Errors in purification flow rates and efficiencies appear as κ(t), and will impact long-lived FP (small λ) more readily, with minimal impact on short-lived FP.…”

A model for predicting coolant activity behaviour for fuel-failure monitoring analysis

“…With the entry of high-pressure coolant through the defect, the fuel may be oxidized that can potentially enhance the fission product release [6,7]. Iodine release can also occur on reactor shutdown when the temperature in the fuel-to-sheath gap drops below the saturation temperature, permitting liquid water to dissolve the soluble iodine species in the gap resulting in an 'iodine-spiking' phenomenon [8][9][10][11]. Iodine-rich water remaining in the gap on the subsequent startup can also be released as the size of the gap is reduced with fuel expansion [12].…”

“…However, a preponderance of coolant activity data involves a time dependence associated with reactor shutdown/startup and bundle-shifting operations, which particularly arise in the CANDU reactor with its ability for on-power refueling. Other theoretical treatments have only focused on the shutdown event in order to account for iodine-spiking phenomena (which again requires a fitting of the model to available coolant activity data) [8,10,11]. Hence, a more general treatment is needed which can make use of all available data and is applicable for all operating reactor conditions.…”