THE NEW NIST RAPID PNEUMATIC TUBE SYSTEM

The Nuclear Methods Group of NIST is developing a new rapid pneumatic tube irradiation system to be inserted into our 20 MW nuclear reactor. The terminal will be inserted into an existing horizontal pneumatic t ube location, the only one of five pneumatic tubes which has not been operational since the reactor upgrade from 10 to 20 MW ten years ago. This new terminal will contain two irradiation locations, one at the t ip in a void area between several fuel elements for epithermal fluence optimization, the second in a D2O tank midway in the terminal to opti mize the thermal fluence. Estimated neutron fluence rates (in n . cm(- 2)s(-1)) are 9E13 thermal/3E13 epithermal for the tip irradiation loca tion, and 3E13 thermal/5E12(or less) epithermal for the irradiation lo cation inside the D2O tank. Both locations will be served by the same night lines and a computer controlled send/receive system, with a 50 s ample auto-loader. This irradiation facility is expected to make radio activation products with halflives of 1 second to a few minutes availa ble for accurate INAA. However, difficulties occurring late in the con struction required modification and installation of a temporary in-cor e terminal with just the thermal neutron irradiation location. Additio nal effort will be made to produce and install the complete two-locati on terminal in the future. This modification will not adversely affect the design speed of the new facility.