钠-水型快堆蒸汽发生器中腐蚀氢传质的物理模型

V. Smykov, S. Kanukhina, K. Legkikh
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摘要

为了及时及时检测二回路“钠-水”型蒸汽发生器的回路间降压情况,在所有运行模式下对钠与水相互作用的产物氢的含量进行连续监测。然而,在现实中,第二回路钠中氢的主要来源是10X2M蒸汽发生器钢在蒸汽-水介质中的电化学腐蚀过程,该过程的速度永远不会为零,并通过第三回路的水-化学机制控制在可达到的最低水平。同时,蒸汽发生器在运行过程中,从第三回路侧面腐蚀产物沉积在结构钢表面。沉淀物的清除是在操作化学冲洗(ECPs)的帮助下进行的。然而,在ECP过程中,钢的腐蚀速度不可避免地显著增加(大约三个数量级),这导致水和钠中氢的浓度增加。这一现象以前曾引起核电站运行服务的关注,因为在常规ECP(每年清洗三个蒸汽发生器中的一个)期间可能发生穿透腐蚀。但是,蒸汽发生器不经ECP处理是不可接受的,为了降低蒸汽发生器管道钢在蒸汽-水环境中的腐蚀速率,在ECP处理后,采用不同配方进行化学钝化,其效果不同。本文建立了蒸汽发生器化学洗涤、钝化和启动过程中腐蚀性氢在蒸汽发生器内传质的物理模型。提出了BN-600蒸汽发生器后续启动过程中,通过第二回路钠中氢浓度的增幅来评价钝化效果的操作准则:如果第二回路中氢浓度的增幅小于0.05 ppm/h,则钝化是有效的,如果大于则需要修改钝化公式。对于BN-800型蒸汽发生器,ECP后钝化工艺尚未确定,本文提出了其效率为0.015 ppm/h的计算准则。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
THE PHYSICAL MODEL OF MASS TRANSFER CORROSIVE HYDROGEN IN FAST REACTOR STEAM GENERATORS OF THE SODIUM-WATER TYPE
For timely and prompt detection of the inter-circuit depressurization of the steam generator of the “sodium-water” type in the 2nd circuit, continuous monitoring of the content of hydrogen, as a product of the interaction of sodium with water, is carried out in all operating modes. However, in reality, the main source of hydrogen in the sodium of the 2nd circuit is the process of electrochemical corrosion of 10X2M steam generator steel in a steam-water medium, the speed of which is never zero and is controlled at the minimum achievable level by means of the water-chemical regime of the 3rd circuit. At the same time, during the operation of the steam generator, deposits of corrosion products accumulate on the surface of the structural steel from the side of the 3rd circuit. The removal of deposits is carried out with the help of operational chemical flushes (ECPs). However, during the ECP, the corrosion rate of steel inevitably increases significantly (by about three orders of magnitude), which leads to an increase in the concentration of hydrogen in water and in sodium. This phenomenon has previously caused concern to the operational services of nuclear power plants due to the likely through-corrosion during regular ECP (every year, one of the three steam generators is washed). However, it is unacceptable to operate a steam generator without ECP, and to reduce the corrosion rate of steel of steam generator pipes in a steam-water environment, after ECP, a chemical passivation stage is carried out with different formulations, the effectiveness of which is different. This article presents a physical model of the mass transfer of corrosive hydrogen in a steam generator during chemical washing, passivation and start-up of the steam generator. An operational criterion for evaluating the effectiveness of passivation by the rate of increase in the concentration of hydrogen in the sodium of the second circuit during the subsequent start-up of BN-600 steam generators is proposed: if the rate of increase in the concentration of hydrogen in the 2nd circuit is less than 0.05 ppm/h, then passivation is effective, if more than the passivation formula requires revision. For BN-800 steam generators, the technology of passivation after ECP has not yet been determined, the article proposes a calculated criterion for its efficiency of 0.015 ppm/h.
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