Is stainless steel acceptable for this laboratory sink?

The choice of sink materials may
depend, at least in part, on the radiological characteristics of radionuclides
being handled, but you must also consider the effects that certain chemicals
will have on the sink material. Among the common materials used for laboratory
sinks, stainless steel may be a reasonable choice if you are not using
chemicals that are likely to present corrosion problems, such as halogen acids
(e.g., HCl and HBr) and sulfuric acid. In such instances other choices such as
polyolefin or epoxy might be preferred.

Regarding its applicability for
disposal of ³²P wastes, it is true that stainless steel will produce
somewhat more beta particle backscatter than nonmetallic sinks. This is because
the higher atomic number steel is more efficient at backscattering beta
radiation than are lower atomic number materials. Stainless steel might be
expected to produce backscatter that is two to three times greater than that
from synthetic materials such as polypropylene. The end result of this is that
if ³²P is on the stainless-steel sink surface, as opposed to being
on a lower atomic number synthetic-sink surface, the total dose rate at a fixed
point above the surface might be increased by about 25 percent. Also, there
will be a small increase in bremsstrahlung radiation from beta particle
interactions in the stainless steel compared to other typical synthetic
materials, because the bremsstrahlung radiation yield is proportional to the
atomic number of the medium.

In my opinion, the relatively small
potential increase in dose associated with the use of the stainless-steel sink
does not, in itself, mitigate against its use, especially if you implement reasonable
housekeeping rules. If you will be pouring significant amounts of waste ³²P
solutions into the sink, it is generally desirable to attempt to pour the waste
directly into the drain line in the sink so as to avoid spreading much
contamination over the sink surface and increasing exposure to people near the
sink. Sink surfaces should be monitored and cleaned on a regular basis. The
stainless steel has the advantage that, if chemical corrosion is not a concern,
the sink surface may be easier to clean, especially as the surface ages
compared to some synthetic surfaces. Many of the latter tend to be softer than
stainless steel and more subject to deep scratches and surface damage that can
trap radioactivity. Stone or ceramic sinks have good abrasion resistance but
they are more likely to get damaged if objects are dropped in them.

In the end, you will have to make the
judgment as to which sink best fits your needs and budget. Assuming that
reasonable housekeeping is implemented, I would not reject the stainless-steel
sink based on radiological considerations.

George Chabot, PhD