NIST Research Reactor Resumes Operation!

[B. Kamitakahara]

NIST REACTOR RESUMES OPERATION WITH NEW COLD SOURCE!!

The NIST Research Reactor (NBSR) was restarted on September 27, 1995, after a
16-month shutdown.  The startup was uneventful, and after a few days at 10 MW,
power was increased to 20 MW, our licensed power level.  The facility comes 
back on line with greatly improved capabilities for cold neutron research, 
principally because a new liquid hydrogen cold source has been installed.  Its
performance is outstanding, corresponding in detail to the simulations of
radiation fluxes, heat loads, and other criteria which guided its design.

The preliminary data shown in the following table indicate very substantial 
gains over the fluxes delivered from our old D2O-ice cold source.  Note that 
the gain includes the effect of a power increase (the reactor has been 
operated at 15 MW rather than 20 MW for a number of years) as well as the 
effect of the new cold source.

Overall gain at NG-7 from hydrogen source and 20 MW operation

Wavelength(A) /gain
  4.0          3.2
  5.0          4.7
  6.0          6.0
  7.0          6.8
  8.0          6.9
  9.0          7.1
 10.0          7.2
 12.0          7.1
 14.0          6.8
 16.0          6.7
 18.0          5.8
 20.0          5.6



Besides the installation of the cold source, much other work was accomplished 
during the shutdown.  The two main tube and shell heat exchangers were 
replaced by three new plate-type heat exchangers, providing redundancy (only
two heat exchangers are used at any time) and a more efficient system.  The 
new heat exchangers permit the reactor to be operated at its full licensed
power level of 20 MW.  The refuelling head over the reactor vessel was removed
and completely rebuilt, providing for better operation of the refuelling system.
   

The sections within the reactor confinement of the last three neutron guides  
which transport neutrons into the guide hall were installed. The exterior 
sections, i.e., those in the guide hall, will be installed during the next 
few months.  A new curved guide terminating in the confinement building has 
also been set up.  Thus, the entire system of eight guides, seven 
of which will terminate in the guide hall, is nearing completion.   


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