be) 
o 
oF 
° 
2.0 
Votume increase (%) 
6 4 8 
FIG. 3. Tensile strength and hardness of 
annealed Type-347 stainless steel increase 
with irradiation. Rate of increase becomes 
smaller (note that horizontal scale is loga- 
rithmic), but saturation is not reached at 
exposures shown (11) 
(8). Most investigators report no sig- 
nificant changes in dimensions or physi- 
cal properties, although a 27 % increase 
in hardness is reported for the greatest 
exposure. A loss in ductility also-is 
reported (see table). 
In connection with the proposed 
Daniels power pile (9), ANL studied the 
effects of radiation on beryllium oxide. 
Dimensions and mechanical prop- 
erties of BeO were relatively unaffected 
by several months exposure in a reac- 
tor, but thermal conductivity decreased 
by over 50%. 
Structural Materials 
Designers have used aluminum and 
steels for most reactor structures. 
Radiation damage is slight in aluminum 
and somewhat greater in steel. Zir- 
conium, too, has been extensively 
studied for the purpose of determining 
its properties as a structural material. 
Aluminum. All of the early reactors 
and many of the present ones have used 
aluminum as their principal structural 
material. Although the choice of this 
metal usually was dictated by the de- 
mands of low absorption cross section 
and good aqueous-corrosion resistance 
at moderately low temperatures, nu- 
merous subsequent tests have shown 
that selection of aluminum was wise 
90 
12 
Exposure (10#° nfem®) 
ig 20 
62 
59 
56 
Rockwell A Hardness 
53 
198 10'? 
Tensile strength ~_ 
FIG. 2. Volume of graphite increases con- 
tinvally with irradiation (4). The material 
also displays anisotropic dimensional changes 
“Hardness 
Tensile Strength (105 psi} 
1029 
Integrated Neutron Flux (n/cm®) 
from the radiation-damage point of 
view as well. Radiation damage gen- 
erally is slight, although some loss of 
ductility is observed, as shown in the 
table. An associated increase in yield 
stress also is reported (10). 
Steels. The changes found in ir- 
radiated steels are larger, as might be 
expected from their higher annealing 
temperatures. Typical losses in duc- 
tility are shown in the table. The 
EBR-1 reactor, with its high fast flux, 
has been used to obtain information on 
radiation damage to Type-347 stainless 
steel with fast-neutron exposures up to 
Ductilities Before and After Irradi- 
ation* 
Elongation at 
breakage (%) 
Material 
Before After 
280 aluminum 38 21 
2SH14 aluminum 22 20 
Normalized carbon steel 22 5 
Austenitic stainless steel 49 25 
QMV beryllium 1.4 0.2 
356 aluminum 2.7 0.6 
Molybdenum 44 0 
* From ref. 15. 
4.3 X 107° n/em? (11). As shown by 
Fig. 3, the rates of increase in tensile 
strength and hardness of annealed 
material steadily decrease with increas- 
ing exposure, but saturation was not 
achieved. The original tensile strength 
and hardness were 130,000 psi and 48 
Rockwell A. These specimens were 
exposed at temperatures in the range of 
225-315° C. Similar changes occur in 
steels irradiated at 80° C (12). 
Austenitic stainless steel shows a 
slight tendency to transform to ferrite 
(13, 14). One group of investigators 
states that it seems unlikely that the 
changes are large enough to affect the 
stainless quality of the alloys (14). 
Carbon steels of the type used for 
pressure-vessel construction also show 
hardening and loss of ductility (12-16). 
An additional disturbing observation is 
the increase in temperature of the duc- 
tile-to-brittle fracture as shown in 
Fig. 4. The implications of this are 
discussed in ref. 15, in which it is stated, 
“Tt appears possible to irradiate a steel 
(A-212 for instance) only sufficiently to 
keep the properties within the ASME 
Boiler Code materials specifications and 
yet have the impact properties shifted 
to an extent that may endanger service 
performance.” 
Zirconium. Another structural 
