Importance of Various Factors in Causing Radiation Damage* 
Gamma Thermal Epithermal Fission Dose 
Radiation Neutrons Neutrons Fragments Rate 
Metals, nonfissile L Lt H Ht ? 
Ceramics L Lt H Ht 7 
Plastics and elastomers H Lt H L§ H? 
Fuels L H H H ? 
Control and shield elements L H H L§ ? 
Electrical components* H Lt H L§ H 
Liquids (except metals) H Lt H L§ L 
H, High; M, Medium; L, Low; ?, Unknown. 
materials.  t When in contact with fuel. 
* Permanent change only, for all except electrical components. 
§ Which are normally not in contact with fuel 
Environ- Temper- Initial 
ment ature Stress State 
M? M ? M 
u M ? M 
H H H H 
? H @ H 
? M 1 H 
H H M M 
L H L L 
t For low-cross-section 
Engineering Use 
of Damage Data 
By O. SISMAN and J. C. WILSON 
Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 
AT THIS EARLY DATE in the develop- 
ment of power reactors, interpretation 
of radiation-effects data is a most diffi- 
cult task for the engineer who must in- 
corporate the data into design. The 
problem is difficult because there is 
little data. Also, interpretation of the 
data in terms of unique conditions in re- 
actors and in terms of unfamiliar prop- 
erties bestowed on familiar materials by 
irradiation, must be made without the 
extensive background of service experi- 
ence upon which evaluation of engi- 
neering data usually is based. 
To compile a handbook of radiation 
effects for general use at this time 
would be misleading because the inter- 
pretation of the data, not the data 
itself, is the important consideration. 
This article points out the important 
variables and outlines a framework for 
interpretation of radiation-effects data 
for the engineer. 
Engineering Methods 
Normally the engineer makes an 
estimate of safe operating conditions. 
But to do this he must face such diffi- 
84 
cult-to-answer questions as: When will 
a pressure vessel be subject to brittle 
fracture? When will a gasket leak? 
When will a bearing freeze? When 
will a pump stop pumping? To find 
answers he must look at certain readily 
accessible properties of materials: ten- 
sile strength, impact strength, vis- 
cosity, corrosion, etc. 
The first step in establishing a toler- 
ance radiation dose is then obvious. A 
tolerance change in some property or 
properties of the material must be 
established. The tolerable change may 
be quite large for one application and 
extremely small for another. The 
tolerable change in viscosity of the oil 
in which a sensitive instrument runs 
would have to be very small. The 
tolerable change in tensile strength of a 
structural member might be fairly 
large. The important point is that 
some tolerance must be established, no 
matter how small. 
For unirradiated components there 
is usually available operating data from 
which to get the characteristics of oper- 
ation and the expected lifetime of the 
component. There is almost no data 
of this type for irradiated components, 
so the effect of radiation on the com- 
ponent must be judged by the effect on 
the materials from which it is made. 
Often there is insufficient data to estab- 
lish the radiation dose that is tolerable, 
but a limiting dose usually can be 
established below which the radiation 
effect is unimportant. For some mate- 
rials an upper limit can be established— 
above which the material is completely 
unusable. The approximate radiation 
doses for a few important effects are 
presented in Fig. 1. 
If it has been established that there 
is a problem—i.e., that the proposed 
irradiation dose is greater than that for 
which no damage has been observed 
and less than that for which there is no 
hope of using this material—then one 
can proceed to determine what can be 
done about it. In some cases the radi- 
ation-damage data may be good enough 
to establish a lifetime for the compo- 
nent in the radiation field. In other 
cases additional testing is indicated. 
Sometimes the particular material is 
