DAMAGING EFFECTS 
OF RADIATION... 
By ROBERT HARRINGTON 
Hanford Atomic Products Operation 
General Electric Company 
Richland, Washington 
Stupy oF How radiation affects solid 
materials incorporated in various com- 
ponents of a reactor is necessary be- 
cause of the changes induced. The de- 
sign engineer is confronted with new 
materials selection problems. 
The solid constructional materials 
most susceptible to change under radi- 
ation bombardment are the molecular 
solids to which the plastics and elas- 
tomers or rubber-like materials belong. 
Radiation Source 
As it is believed that the changes 
induced in organic materials are essen- 
tially the same for any type of ioniz- 
ing radiation with respect to energy 
absorbed, gamma radiations from spent 
fuel elements and cobalt-60 isotope 
sources were used as being representa- 
tive of ionizing radiations in general. 
However, it may be possible that this 
relationship is not valid over a wide 
range of energy absorption levels and 
rates. 
Effects of irradiation rates are shown 
in Table 1. These imply that ma- 
terials in a radiation field of a few 
hundred r/hr would not be altered as 
much at any given total dose as they 
would be at the dose rates used here. 
Procedure and Results 
The experimental work was designed 
primarily as a screening process 
whereby promising materials could be 
selected for more comprehensive study 
as dictated by specific applications. 
However, in some instances sufficient 
data were obtained for design purposes. 
96 
On Plastics 
and Elastomers 
Ultimate elongation and tensile 
strength properties were measured in 
accordance with ASTM D 412-51T 
using three Die C specimens for each 
exposure. A 180-deg bend test was 
also made after the exposures by fold- 
ing the broken tensile specimen back 
on itself with positive finger pressure 
applied to insure the specimen sides 
were in contact. Hardness and elas- 
ticity measurements were not taken for 
the more rigid ethylene materials. 
Properties were measured at 25° C and 
50% relative humidity after a 1-hr con- 
ditioning period. 
Table 2 summarizes the changes in 
properties of plastics and elastomers 
induced by various doses of gamma 
radiation from spent fuel elements. 
Discussion 
The data show how plastics and 
elastomers degrade* from exposure to 
gamma (ionizing) radiation. In many 
instances, short doses will actually im- 
prove the properties of the materials, 
but with continued exposure severe 
property changes occur and the mate- 
rials are altered radically. 
Properties. The elongation appears 
to be the most sensitive property meas- 
ured and provides a fairly good index 
of the degradation of the material. 
However, the flexibility probably offers, 
for the longer exposures, a better means 
of determining the condition of the 
material. This is illustrated by com- 
paring the two silicone rubbers SE-361 
*‘‘Degrade’’ as used here denotes a 
reduction in the usefulness of a material as 
a result of its properties being changed by 
exposure to an environment. Degrade 
often denotes the decrease in molecular 
weight of a material from exposure to an 
environment. 
TABLE 1—How Polymer Properties are Changed by 5 X 10’ r from Co®? 
Compared with the Same Dose from Spent Fuel Elements* 
Percent change in properties 
Material and source Hardness Elasticity Elongation Tensile Weight 
Silastic 152 
Cobalt-60 46.0 —51.8 —77.3 3.7 —0.09 
Spent fuel elements 36.0 -40.7 —68.2 —8.8 —0.138 
Alathon 4BK20 
Cobalt-60 —= — —84.3 —10.8 0.17 
Spent fuel elements = — —59.0 —19.7 0.29 
SE-361 
Cobalt-60 Ore —60.0 —48.4 16.3 0.14 
Spent fuel elements 13 —40.0 —38.5 7.0 0.20 
Hycar 1001 
Cobalt-60 5.3 —7.7 —74.6 —16.7 0.17 
Spent fuel elements ies} —15.4 —68.2 —14.4 0.07 
* Incident rates: Co® ~ 3.7 X 105 r/hr in 25° C air; spent fuel elements ~ 10®r/hr in 
15° C air. 
eT 
