Computational modeling of accelerating corrosion in primary coolants of a typical PWR
High temperature and pressure environment along with large neutron and gamma-ray flux lead to significantly large corrosion in the stainless steel used in the primary coolant circuit of pressurized water reactors (PWRs). The corrosion products become activated in the reactor core upon circulation. Corrosion rate depends on reactor power and it can be a linear as well as a nonlinear function of time. Computer simulation offers a novel approach to study the effect of corrosion acceleration on coolant activity under transient conditions. We present two related mathematical models for corrosion acceleration under high temperature and flow rate transient conditions. In the first part of the work, we have formulated a mathematical model based on a system of coupled first order ordinary differential equations governing the isotopic concentration. In the second part, flow rate transients have been forced through non-homogeneous conditions. Numerical simulations show that for Na-24, Mn-56, Fe-59, Co-60 and Mo-99, the values of specific activities approach the equilibrium value fairly rapidly under normal operating conditions. Spikes are observed in the specific activity values of the primary coolant when corrosion acceleration and flow rate transients are employed in the model. Both the height and time of these spikes has been found to depend on the value of acceleration in corrosion.
Modeling and simulation of corrosion product activity in pressurized water reactors under power perturbations
Abstract 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 24 Na, 56 Mn, 59 Fe, 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 is due to 56 Mn. 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.
Assessment of orifice effects on dose rates at the reactor bridge due to coolant activation in typical MNSRs
Using the multigroup diffusion theory, the effect of the core outlet orifice on the dose rates at the reactor bridge of a typical MNSR has been studied under normal and flow rate perturbation conditions. A one-dimensional simple flow model is used for natural circulation of coolant to calculate the activity reaching the upper layers of water in the reactor tank. Results show that under normal operating conditions the dose rate at the reactor bridge increases owing to all of the coolant activation products as the orifice to the core cross-sectional area ratio is decreased. The total dose rate changes from 9.3 to 190.3 μSv/h as the orifice area to the core area ratio is decreased from 1.0 to 0. 25. Under the flow rate perturbations the dose rate remains less than 60 μSv/h when the orifice ratio (A orifice /A core ) is greater than 0.33