氮气-水体系多组分辐解平衡计算模型

Multi-component Radiolysis Equilibrium Calculation Model in Nitrogen-water System

氮稳压相比于蒸汽稳压而言有机动性强、结构简单、体积小等优点。在使用氮稳压的核反应堆中,氮气在堆芯区域受辐照后分解,与水的辐解产物发生反应,生成氮氢、氮氧化合物,影响一回路冷却剂的水化学控制。目前,针对氮气在一回路冷却剂辐解产物产量的计算模型,采用反应动力学方法,需求解大量非线性病态方程,计算量大,数值不稳定,计算误差范围在-50%~100%之间,误差较大。为建立一种计算量小、数值稳定的计算模型,本文从反应热力学角度,使用辐射化学产额g与平衡常数法,基于反应平衡方程、物料守恒及电荷守恒方程建立了含氮水的辐解计算模型,假设在单个时间节点上反应达平衡并求解非线性方程组,通过更改每个时间节点的初始条件以模拟时间的影响,最终的稳态计算结果在288~473 K温度范围内,与已有实验数据的相对误差在-60%~10%之间。本文计算了反应堆工况下的冷却剂离子浓度变化情况,并分析了关键因素对结果的影响,发现辐照产生的亚硝酸根离子含量较高,使平衡时溶液呈酸性,反应条件中的温度和氮气浓度对最终结果的影响较大,剂量率对平衡结果无影响。研究结果对使用氮稳压的反应堆水化学设计有重要指导意义。

In contrast to a steam pressure regulator,a nitrogen pressurizer offers several advantages,including enhanced maneuverability,a straightforward design,and a compact size.Within nuclear reactors utilizing nitrogen pressurization,nitrogen gas in the reactor core area undergoes decomposition under radiation and interacts with radiation-induced byproducts of water,resulting in the formation of nitrogen hydrides and nitrogen oxides,which impacts the management of water quality within the primary cooling circuit and may leading corrosion intensification.The present numerical model of nitrogen decomposition product yields in the primary circuit is predominantly dependent on a computational model rooted in the kinetics of reactions.This approach involves tackling an extensive set of non-linear equations,which,in turn,hinges on unknown experimental factors.As a result,the current methodology leans heavily on a multitude of conjectures,and the condition number of its Jacobi matrix is notably high,giving rise to substantial calculation inaccuracies,spanning from-50%to 100%.Therefore,this paper aims to establish an accurate and well-convergent numerical computational model to guide the water chemistry control of nitrogen-pressurized reactor systems.From a thermodynamic perspective,the paper employed the radiation chemical yield(g-value)and equilibrium constant method to construct a decomposition calculation model for water dissolving nitrogen in a radiation filed.Specifically,the work employed point-by-point steady state hypothesis,considering that the chemical state reaches equilibrium at each time point.The model solved ten chemical equilibrium equations,an atom conservation equation and an electronic conservation equation at each time point,and simulated the time effect of radiation by changing the primary conditions at each step.Within the temperature range of 288 K to 473 K,this model exhibited relative errors from reported experimental data ranging from-60%to 10%.Employing this model,calculations to ascertain changes in coolant ion concentrations were conducted under reactor operating conditions.Furthermore,the paper presents an in-depth analysis of how calculation parameters influence the obtained results.The research reveals a consistent trend in the pH value,showing a gradual decrease under irradiation until it reaches a slightly-2acidic state,which comes from a relatively high concentration of NO ions,emphasizing the need for the addition of alkalizing agents during practical reactor operation to maintain suitable water quality.Additionally,the paper delves into an analysis of how different reactor parameters affect the equilibrium state.Notably,a linear relationship is identified between temperature/nitrogen concentration and the concentrations of typical ions.In contrast,the radiation dose rate does not exert a substantial influence on the final outcomes.This work carries significant reference value for the design of nitrogen pressurized reactors.