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.

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.)

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.

TABLE 1 ENDF/B-VI-based Iron Displacement Cross Section

Bin	EngA (MeV)	σd (barns)	Bin	EngA (MeV)	σd (barns)	Bin	EngA (MeV)	σd (barns)
1	0.100E-09	158.3543	2	0.1050E-09	154.6209	3	0.110E-09	151.1395
4	0.1150E-09	147.8895	5	0.120E-09	144.1054	6	0.1275E-09	139.9202
7	0.1350E-09	136.0860	8	0.1425E-09	132.5445	9	0.150E-09	128.7502
10	0.160E-09	124.7860	11	0.170E-09	121.1728	12	0.180E-09	117.8527
13	0.190E-09	114.8137	14	0.200E-09	111.9561	15	0.210E-09	109.3199
16	0.220E-09	106.8646	17	0.230E-09	104.5694	18	0.240E-09	101.8930
19	0.2550E-09	98.93331	20	0.270E-09	96.65981	21	0.280E-09	94.12717
22	0.300E-09	91.05218	23	0.320E-09	88.24872	24	0.340E-09	85.68787
25	0.360E-09	83.33912	26	0.380E-09	81.17265	27	0.400E-09	78.92472
28	0.4250E-09	76.63646	29	0.450E-09	74.53734	30	0.4750E-09	72.59930
31	0.500E-09	70.81827	32	0.5250E-09	69.14790	33	0.550E-09	67.59222
34	0.5750E-09	66.13822	35	0.600E-09	64.64189	36	0.630E-09	63.12039
37	0.660E-09	61.70157	38	0.690E-09	60.37332	39	0.720E-09	58.92732
40	0.760E-09	57.39681	41	0.800E-09	55.97892	42	0.840E-09	54.65984
43	0.880E-09	53.43220	44	0.920E-09	52.28703	45	0.960E-09	51.21545
46	0.100E-08	50.07727	47	0.1050E-08	48.89598	48	0.110E-08	47.79609
49	0.1150E-08	46.76870	50	0.120E-08	45.57125	51	0.1275E-08	44.25006
52	0.1350E-08	43.03653	53	0.1425E-08	41.91761	54	0.150E-08	40.71708
55	0.160E-08	39.46333	56	0.170E-08	38.32018	57	0.180E-08	37.26968
58	0.190E-08	36.30967	59	0.200E-08	35.40710	60	0.210E-08	34.57391
61	0.220E-08	33.79705	62	0.230E-08	33.06956	63	0.240E-08	32.22424
64	0.2550E-08	31.28942	65	0.270E-08	30.57002	66	0.280E-08	29.76999
67	0.300E-08	28.79791	68	0.320E-08	27.91048	69	0.340E-08	27.10139
70	0.360E-08	26.35879	71	0.380E-08	25.67357	72	0.400E-08	24.96309
73	0.4250E-08	24.23960	74	0.450E-08	23.57548	75	0.4750E-08	22.96268
76	0.500E-08	22.39920	77	0.5250E-08	21.87094	78	0.550E-08	21.37982
79	0.5750E-08	20.91994	80	0.600E-08	20.44705	81	0.630E-08	19.96509
82	0.660E-08	19.51724	83	0.690E-08	19.09670	84	0.720E-08	18.63984
85	0.760E-08	18.15581	86	0.800E-08	17.70708	87	0.840E-08	17.29049
88	0.880E-08	16.90205	89	0.920E-08	16.54074	90	0.960E-08	16.20166
91	0.100E-07	15.84242	92	0.1050E-07	15.46908	93	0.110E-07	15.12094
94	0.1150E-07	14.79594	95	0.120E-07	14.41855	96	0.1275E-07	14.00095
97	0.13050E-07	13.61661	98	0.1425E-07	13.26338	99	0.150E-07	12.88403
100	0.160E-07	12.48759	101	0.170E-07	12.12633	102	0.180E-07	11.79428
103	0.190E-07	11.49039	104	0.200E-07	11.20760	105	0.210E-07	10.94298
106	0.220E-07	10.69745	107	0.230E-07	10.46804	108	0.240E-07	10.20132
109	0.2550E-07	9.906717	110	0.270E-07	9.679449	111	0.280E-07	9.427035
112	0.300E-07	9.118745	113	0.320E-07	8.838819	114	0.340E-07	8.582926
115	0.360E-07	8.347962	116	0.380E-07	8.131618	117	0.400E-07	7.907534
118	0.4250E-07	7.678809	119	0.450E-07	7.468805	120	0.4750E-07	7.276812
121	0.500E-07	7.097598	122	0.5250E-07	6.930767	123	0.550E-07	6.775607
124	0.5750E-07	6.630701	125	0.600E-07	6.482083	126	0.630E-07	6.330435
127	0.660E-07	6.188963	128	0.690E-07	6.056631	129	0.720E-07	5.913148
130	0.760E-07	5.760298	131	0.800E-07	5.618617	132	0.840E-07	5.486900
133	0.880E-07	5.364337	134	0.920E-07	5.250029	135	0.960E-07	5.143171
136	0.100E-06	5.029254	137	0.1050E-06	4.911427	138	0.110E-06	4.801945
139	0.1150E-06	4.699714	140	0.120E-06	4.581585	141	0.1275E-06	4.450361
142	0.1350E-06	4.329614	143	0.1425E-06	4.218222	144	0.150E-06	4.099185
145	0.160E-06	3.974304	146	0.170E-06	3.860402	147	0.180E-06	3.756055
148	0.190E-06	3.660761	149	0.200E-06	3.571313	150	0.210E-06	3.488699
151	0.220E-06	3.411616	152	0.230E-06	3.339466	153	0.240E-06	3.256051
154	0.2550E-06	3.163276	155	0.270E-06	3.091628	156	0.280E-06	3.013147
157	0.300E-06	2.916945	158	0.320E-06	2.829403	159	0.340E-06	2.749808
160	0.360E-06	2.676750	161	0.380E-06	2.608835	162	0.400E-06	2.527930
163	0.4250E-06	2.440897	164	0.450E-06	2.374384	165	0.4750E-06	2.313606
166	0.500E-06	2.257462	167	0.5250E-06	2.205331	168	0.550E-06	2.154114
169	0.5750E-06	2.108733	170	0.600E-06	2.060134	171	0.630E-06	2.011735
172	0.660E-06	1.966045	173	0.690E-06	1.923586	174	0.720E-06	1.877395
175	0.760E-06	1.828596	176	0.800E-06	1.783008	177	0.840E-06	1.741254
178	0.880E-06	1.703417	179	0.920E-06	1.667792	180	0.960E-06	1.632082
181	0.100E-05	1.595754	182	0.1050E-05	1.558720	183	0.110E-05	1.522295
184	0.1150E-05	1.490200	185	0.120E-05	1.451554	1 1. Scope 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 σd(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 and health practices and determine the applicability of regulatory limitations prior to use. 2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard. ASTM Standards E170 Terminology Relating to Radiation Measurements and Dosimetry E521 Practice for Neutron Radiation Damage Simulation by Charged-Particle Irradiation E560 Practice for Extrapolating Reactor Vessel Surveillance Dosimetry Results, E 706(IC) E821 Practice for Measurement of Mechanical Properties During Charged-Particle Irradiation E853 Practice for Analysis and Interpretation of Light-Water Reactor Surveillance Results, E706(IA) Keywords atomic displacements; cross section; irradiation; materials damage; neutron; steel ; ICS Code ICS Number Code 77.080.20 (Steels) DOI: 10.1520/E0693-12 ASTM International is a member of CrossRef. ASTM E693 (Nuclear Technology Standards) Citing ASTM Standards [Back to Top]