Stress Mitigation Design of Tubesheets With Consideration of Thermal Stress Inducement Mechanism
Stress Mitigation Design of Tubesheets With Consideration of Thermal Stress Inducement Mechanism
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DOI：
10.1115/pvp2008-61320
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
M. Ando;Hideki Takasho;Nobuchika Kawasaki;N. Kasahara
中科院分区：
文献类型：
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作者：
M. Ando;Hideki Takasho;Nobuchika Kawasaki;N. Kasahara
日本下一代快堆计划采用Mo.9Cr-1Mo钢制的双壁直管蒸汽发生器。与SG相关的主要问题之一是管板的结构完整性。在反应堆的暂态运行中，热应力是由管板内的温度分布引起的，其大小取决于管板的结构。通过有限元分析，揭示了管板的应力产生机理。首次对半球型管板模型的热应力机理进行了研究。计算结果表明，半球型管板模型给出了最外层孔口附近广泛的峰值应力。认为半球型管板的热应力机理如下。(1)热应力主要是穿孔区域与周围区域温差引起的环向应力。(2)热应力对特定部位的大小不敏感，但以穿孔与周围区域的相互作用机制为主。(3)孔边应力集中产生峰值应力。(4)峰值应力的大小与管板穿透角度有关，在最外侧孔处应力集中程度较高。基于上述应力产生机理，作者提出了一种缓解应力的管板。改进结构为中心扁球型管板(FST)。计算的FST峰值应力小于半球型管板的峰值应力。进一步的研究揭示了FST在热瞬变过程中的详细应力产生机理。FST中存在两种不同的可比热峰值应力机制。最大峰值应力的位置和大小取决于热瞬变时的钠温度历史。一个取决于钠温度变化的范围(ΔT)。这种峰值应力是由结构不连续引起的径向应力，它位于最外面的孔洞。另一种则取决于钠的温度变化率(dt/dt)。这种峰值应力是穿孔区域与周围区域相互作用产生的环状应力，位于最外层孔的内层孔内。版权所有*2008由ASME
Adoption of double-wall-straight tube steam generators made of Mod.9Cr-1Mo steel is planned for next generation fast breeder reactors in Japan. One of the major concerns relevant to the SG is structural integrity of tubesheets. In the reactor transient operation, thermal stress is induced by the temperature distribution in tubesheet and the magnitude of it depends on configurations of tubesheet. Stress generation mechanism of tubesheets was revealed through Finite Element analysis. Semi-spherical tubesheet models were investigated for the first survey of the thermal stress mechanism. As calculated results, semi-spherical tubesheet model gave the extensive peak stress around the outermost hole. Recognized thermal stress mechanism of semi-spherical tubesheet is as follows. (1) Dominant thermal stress is hoop stress caused by temperature difference between the perforated region and surrounding region. (2) Thermal stress is insensitive to size of specific portion, although is dominated by interaction mechanism between perforated and surrounded regions. (3) Stress concentration around hole’s edge generates peak stress. (4) Amplitude of peak stress depends on the tubesheet penetration angle and stress concentration becomes high near the outermost hole. Based on the above stress generation mechanism, authors proposed a stress mitigated tubesheet. It is center flatted spherical tubesheet (FST) as improved configuration. Calculated peak stress of FST was smaller than that of semi-spherical tubesheet. Further investigation revealed the detailed stress generation mechanism of FST during thermal transient. There were two different comparable thermal peak stress mechanisms in FST. Both location and magnitude of maximum peak stress depend on sodium temperature histories at thermal transient. One depends on the range (ΔT) of sodium temperature change. This type of peak stress was radial stress caused by the structural discontinuity, and it was located at the outermost hole. The other depends on the rate (dT/dt) of sodium temperature change. This type of peak stress was hoop stress caused by interaction between perforated region and surrounding region, and it was located at the one inner layer hole from outermost layer holes.Copyright © 2008 by ASME