Article

Measurements of Radioiodine Species in Samples of Pressurized Water Reactor Coolant

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Abstract

Samples of primary coolant at two pressurized water reactors in the United States have been collected and analyzed to determine the fraction of the radioiodine present in volatile forms. The volatile species, I² and organic iodides, would be available for prompt release following a steam generator tube rupture (SGTR) accident, which overpressurizes the secondary coolant system and causes venting to the atmosphere. Coolant samples were collected at full power, during power reduction at the start of an outage, and up to 48 h after shutdown. Radioiodine concentrations spiked as power was decreased, and an increase in the volatile species fraction to â¼20% was seen with 2 h of shutdown. A second peak of 30 to 40% volatile species occurred at â¼ 1.5 days after shutdown, but is not significant for SGTR accidents.

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... According to the measurements carried out by Voillequé (Voillequé, 1990), the addition of boric acid did not cause a significant increase in the volatile fraction. The author emphasized that I 2 variations were observed during the course of the cooling process and following the depressurization phases but not following the boric acid injection. ...
... Average measurements contributions for each iodine specie during full power operation (%) (DL: detection limit) (Martucci, 1973) ( Mandler, 1985) ( Voillequé, 1990) ( Lin, 1996) ( Ravi, 1992) ( Volent et al., 1996) on the failure and the oxidation state of the fuel inside the gap, the primary radiolysis products (OH) from the water enter during the transient periods. This can favour I À oxidation in the gap (I À þOH . ...
... Average measurements contributions for each iodine specie during shutdown (%) (Martucci, 1973) ( Mandler, 1985) ( Voillequé, 1990) (Lin, 1992(Lin, , 1996 ( Ravi, 1992) ( Volent et al., 1996) their mutual interactions. Therefore, the possibility of performing the oxygenation phase at a low temperature to optimize the iodine management should be evaluated prudently, taking into account the impact on the other domains, such as the risk of corrosion product contamination in the RCS and in auxiliary systems, operating constraints and shutdown schedules. ...
Article
Iodine is one of the most important fission products due to its high fission yield, significant radiobiological hazard and potential volatility. Its environmental and biological risks have been extensively studied in case of a severe reactor accident. Nevertheless, little information is available about iodine behaviour under normal Pressurize Water Reactor (PWR) operating conditions.The work reported explores the behaviour of different iodine species (I−, I3, I2, HOI and IO−) during full power periods, transient periods (power reductions and depressurizations) and shutdowns. Thermodynamic calculations were conducted, and their results are compared with previous predictions and with the experimental data provided by nuclear power plants (NPP).Based on thermodynamic calculations and NPP feedback, it was concluded that iodine speciation depends primarily on the redox potential and water radiolysis.•The experimental values confirm that the iodine ionic form I− is the major species during normal operation (I2 < 2%) and shutdowns (I2 < 9%).•During shutdowns:-High [I2] (20–40%) can be observed in the presence of fuel failures following an iodine spike during power or pressure variations. The fuel oxidation by radiolysis products can lead to I2 formation inside the gap and its subsequent release through cladding defects.-Once in the primary coolant, I2 is transformed into I− or , depending on the water oxidation conditions.•The lithium concentration and the primary coolant temperature seem to have a secondary influence on iodine speciation, while the existence of a redox potential threshold appears to be the main factor controlling the formation of volatile and non-volatile iodine forms.This paper summarizes the major results of the iodine thermodynamic studies and PWR feedback, permitting some possible recommendations for inclusion in the NPP guidelines in order to master iodine’s behaviour. Future work is proposed. Redox potential measurements at high temperatures, coupled with thermodynamic estimations and radiolysis analysis, should be considered as useful tools to specify the optimal conditions for limiting iodine volatisation and I2 absorption.Highlights► Few data is available about iodine behaviour under normal PWR operating conditions. ► This study provides the characteristic iodine speciation in PWR primary coolant. ► The conclusions are based on thermodynamic calculations and experimental analysis. ► Iodine ionic form is the major specie during full power and shutdown. ► Iodine speciation mainly influenced by redox potential: secondary effect of [Li] and T.
... The maximum value of power and activity have a delay of about 9 h. Such activity spikes were measured in various studies (Mandler et al., 1985;Volleque, 1990). Mandler et al. (1985) reported coolant activity spikes when power was increased in studies conducted at four PWRs as a part of the in-plant source term measurement program. ...
... Mandler et al. (1985) reported coolant activity spikes when power was increased in studies conducted at four PWRs as a part of the in-plant source term measurement program. Also, when samples of primary coolant from two PWRs in USA were collected and analyzed to ®nd the fraction of radioiodine in them Volleque, 1990 concentraion spikes were measured as power was perturbed. The width of the spike (H) obtained in the present studies, represents the time taken by the activity to reach back to its initial value (as shown in Fig. 9). ...
Article
An improved methodology is presented for simulation of coolant activation due to corrosion products and impurities in a typical pressurized water reactor (PWR) under power perturbations. Using time dependent production and losses of corrosion products in the primary coolant path an approach has been developed to calculate the coolant specific activity. Results for 24Na, 56Mn, 59Fe, 60Co and 99Mo show that the specific activity in primary loop approaches equilibrium value under normal operating conditions fairly rapidly. Predominant corrosion product activity is due to 56Mn. Flow rate has been assumed to follow power changes and different types of power perturbations are introduced after the equilibrium activity has been achieved. In particular the effects of linear changes in reactor operating power and power peaking on the corrosion product activity of the primary coolant have been studied.
... Its saturation value is 0.22 mCi/cm 3 and it makes the primary coolant as a 0.663MCi source within 150-230 h of reactor operation at full power. These are close to the values already reported by Mandler et al. (1985) and Volleque (1990) in their source term measurements. ...
Article
Computer simulation of behavior of coolant activation due to corrosion products have been investigated in a typical pressurized water reactor (PWR) under flow rate perturbations for linearly accelerating corrosion. The computer program CPAIR-P (Deeba et al., 1999) has been modified to accommodate for time dependent corrosion. Results for 24Na, 56Mn, 59Fe, 60Co and 99Mo show that the specific activity in primary loop approaches equilibrium value under normal operating conditions fairly rapidly. During reactor operation, predominant corrosion product activity is due to 56Mn and after shutdown cobalt activity dominates. These simulations suggest that the effect of flow rate perturbations on specific activity in the form of a depression in the activity curve can be smeared by a linearly rising corrosion. Such a dip can only be seen in activity when corrosion rate approaches to an equilibrium value well before the initiation of the transient. The time period to reach minimum coolant activity during transient is a function of the slope of flow rate perturbation parameter, g(t). The new saturation value for activity depends on changes in flow rate (Δw) and equilibrium value (Cs) for the corrosion rate. For linearly accelerated corrosion and a pump coastdown condition, the activity does not show an initial drop when flow starts decreasing. It monotonically rises and follows the slope of corrosion rate. If the slope is greater than 9×10−6 μg/s2, then the activity crosses the normal saturation value of 0.22 μCi/cm3 before the reactor scram occurs. These results also indicate that the pump coastdown does produce a coolant activity spike before the reactor scram; however it can only be observed when the corrosion acceleration is fast.
... Saturation activity values for primary coolant, on pipe scale and on core surface are 17.3, 12.9 and 74.1 mCi/cm 3 , respectively. These are close to already reported values by Mandler et al. (1985) and Volleque (1990) in their source term measurements. ...
Article
For nonlinear accelerating corrosion, calculation of activated corrosion products on inner surfaces of primary coolant pipes have been done in a typical pressurized water reactor (PWR) under flow rate perturbations. Computer program CPAIR-P (Corrosion Product Activity In Reactors) (Deeba et al., 1999) has been modified to accommodate for time-dependent corrosion rates. Results, for (24)Na, (56)Mn, (59)Fe, (58)Co, (60)Co and (99)Mo, show that the specific activity in primary loop approaches equilibrium value under normal operating conditions fairly rapidly. Predominant corrosion product activity during operation is due to (56)Mn, and cobalt isotopes dominate the activity after shutdown of reactor. Flow rate perturbations and different types of rising corrosion rates were introduced in the system and effects on saturation activity were studied. For a linear decrease in flow rate and a constant corrosion rate, the total coolant activity and activity on pipe scale approaches higher saturation values when compared to normal condition values. With a nonlinearly accelerating corrosion, the behavior of specific activity changes considerably. The flow rate perturbations on specific activity for pipe scale results in a new saturation value which depends on both the changes in flow rate (Delta w) and equilibrium corrosion rate (C(s)) values. However, the time taken to reach the saturation activity depends on the slope of corrosion rate. For a slow pump coastdown, the activity does not show an initial drop when flow rate starts decreasing. It monotonically rises and follows the slope of corrosion rate. The peak value and decay of activity after scram are strong functions of flow rate and removal efficiencies.
... Its saturation value is (-0.22 wCi/cm') and it makes the primary coolant as a 0.663MCi source within 150 to 230hours of reactor operation at full power. These are close to the values already reported by Mandler et al. (1985) and Volleque (1990) 117, 181 in their source term measurements. ...
Conference Paper
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