1.1 本规程描述了根据铁的每原子暴露指数位移（dpa）表征铁（和低合金钢）中子辐照的标准程序。 1.2 尽管本规程的方法适用于位移横截面σ d ( E )已知（参见实践 第521页 )，此练习是专门为铁编写的。 1.3 假设铁的位移横截面是计算主要为铁（95至100 %) 在二次损伤过程不重要的辐射场中。 1.4 与此类似的程序可用于计算带电粒子辐照中的dpa。（参见实践 第521页 .) 1.5 该实践的应用需要了解总中子注量和通量谱。 参考实践 第521页 用于确定这些量。 1.6 辐射效应数据的相关性超出了本规程的范围。 1.7 本标准并不旨在解决与其使用相关的所有安全问题（如有）。本标准的使用者有责任在使用前建立适当的安全、健康和环境实践，并确定监管限制的适用性。 1.8 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《国际标准、指南和建议制定原则决定》中确立的国际公认标准化原则制定的。 =====意义和用途====== 4.1 压力容器监测计划需要一种方法，将加速监测位置中暴露的材料的辐射引起的变化与压力容器的状况联系起来（见实施规程 E853型 ). 一个重要的考虑因素是，辐照暴露以物理上与损伤机制相关的单位表示。 4.2 金属中中子辐射损伤的一个主要来源是原子从其正常晶格位置的位移。因此，一个合适的损伤暴露指数是一个原子在辐照过程中平均位移的次数。这可以表示为每单位体积、每单位质量或每原子材料的置换原子总数。每个原子的位移是表示这个量的最常见的方式。 与特定辐射相关的dpa的数量取决于中子在材料中沉积的能量，因此取决于中子谱。（有关更详细的讨论，请参阅实践 第521页 .) 4.3 一般而言，dpa与材料特性的特定变化之间不存在简单的对应关系。然而，对于不同中子谱中产生的性质变化的相对相关性，一个合理的起点是与每个环境相关的dpa值。也就是说，dpa值本身提供了可能是有用的相关参数的频谱敏感指数，或者dpa值的某些函数可能影响相关。 4.4 由于dpa是一种结构，它取决于材料晶格中中子相互作用过程的模型，以及每个过程的横截面（概率），如果使用改进的模型或横截面，dpa的值将有所不同。 本规程中给出的铁素体铁的计算位移横截面由 6.3 本规程中当前推荐的铁位移横截面( 表1 )使用ENDF/B-VI铁横截面生成 ( 1. ) . 3. 最近使用ENDF/B-VII.0进行的计算得出了相同的结果 ( 2. , 3. ) ENDF/B-VII.1中的铁横截面数据与ENDF/B-VII.0没有差异。尽管基于ENDF/B-VI的铁位移横截面与之前推荐的ENDF/B-IV铁位移横截面积不同 ( 1. ) 大约60 % 在大约10keV的能量区域中 % 对于100keV和2MeV之间的能量，由于横截面中反应通道的打开，在1keV附近增加了4倍，积分铁dpa值对横截面的变化不太敏感。 当应用于H。 B、 Robinson-2压水反应堆，导致“ ∼ 4. % 压力容器外表面附近区域的dpa率较高，“压力容器内壁附近的dpa比率稍低” ( 4. , 5. ) . 表2 与上一版本（实践 E693型 –94）和目前推荐的几种中子谱的dpa估计值。 （A） 能量代表下仓边界。上限为20.0MeV。 （A） 本表中的谱平均dpa值是使用 公式11 在640 SAND-II能量群表示和E的下积分界中 o = 10 –10 MeV。

1.1 This practice describes a standard procedure for characterizing neutron irradiations of iron (and low alloy steels) in terms of the exposure index displacements per atom (dpa) for iron. 1.2 Although the methods of this practice apply to any material for which a displacement cross section σ d ( E ) is known (see Practice E521 ), this practice is written specifically for iron. 1.3 It is assumed that the displacement cross section for iron is an adequate approximation for calculating displacements in steels that are mostly iron (95 to 100 %) in radiation fields for which secondary damage processes are not important. 1.4 Procedures analogous to this one can be formulated for calculating dpa in charged particle irradiations. (See Practice E521 .) 1.5 The application of this practice requires knowledge of the total neutron fluence and flux spectrum. Refer to Practice E521 for determining these quantities. 1.6 The correlation of radiation effects data is beyond the scope of this practice. 1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 4.1 A pressure vessel surveillance program requires a methodology for relating radiation-induced changes in materials exposed in accelerated surveillance locations to the condition of the pressure vessel (see Practice E853 ). An important consideration is that the irradiation exposures be expressed in a unit that is physically related to the damage mechanisms. 4.2 A major source of neutron radiation damage in metals is the displacement of atoms from their normal lattice sites. Hence, an appropriate damage exposure index is the number of times, on the average, that an atom has been displaced during an irradiation. This can be expressed as the total number of displaced atoms per unit volume, per unit mass, or per atom of the material. Displacements per atom is the most common way of expressing this quantity. The number of dpa associated with a particular irradiation depends on the amount of energy deposited in the material by the neutrons, and hence, depends on the neutron spectrum. (For a more extended discussion, see Practice E521 .) 4.3 No simple correspondence exists in general between dpa and a particular change in a material property. A reasonable starting point, however, for relative correlations of property changes produced in different neutron spectra is the dpa value associated with each environment. That is, the dpa values themselves provide a spectrum-sensitive index that may be a useful correlation parameter, or some function of the dpa values may affect correlation. 4.4 Since dpa is a construct that depends on a model of the neutron interaction processes in the material lattice, as well as the cross section (probability) for each of these processes, the value of dpa would be different if improved models or cross sections are used. The calculated displacement cross section for ferritic iron, as given in this practice, is determined by the procedure given in 6.3 . The currently recommended iron displacement cross section in this practice ( Table 1 ) was generated using the ENDF/B-VI iron cross section ( 1 ) . 3 A recent calculation using ENDF/B-VII.0 produced identical results ( 2 , 3 ) . The iron cross section data in ENDF/B-VII.1 does not differ from ENDF/B-VII.0. Although the ENDF/B-VI based iron displacement cross section differs from the previously recommended ENDF/B-IV iron displacement cross section ( 1 ) by about 60 % in the energy region around 10 keV, by about 10 % for energies between 100 keV and 2 MeV, and by a factor of 4 near 1 keV due to the opening of reaction channels in the cross section, the integral iron dpa values are much less sensitive to the change in cross sections. The update from ENDF/B-IV to ENDF/B-VI dpa rates, when applied to the H. B. Robinson-2 pressurized water reactor, resulted in “up to ∼ 4 % higher dpa rates in the region close to the pressure vessel outer surface” and in “slightly lower dpa rates. close to the pressure vessel inner wall” ( 4 , 5 ) . Table 2 presents a comparison of a previous edition (Practice E693 –94) and currently recommended dpa estimates for several neutron spectra. (A) Energies represent the lower bin boundary. The upper bin limit is 20.0 MeV. (A) The spectrum-average dpa values in this table were computed using Eq 11 in a 640 SAND-II energy group representation and a lower integration bound of E o = 10 –10 MeV.