7-3]
THE HOMOGENEOUS REACTOR EXPERIMENT (HRE-1)
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at this point was composed mainly of excess oxygen plus the highly active fission gases, mainly xenon, krypton, and their decay products . The activity of these gases was many orders of magnitude greater than the activity which can be discharged directly to the atmosphere without the construction of a very expensive stack ; therefore it was desirable to provide some inexpensive means of storage for the dissipation of the radioactivity . This was accomplished by passing the gases through cold traps to remove moisture and adsorbing them onto water-cooled activated-carbon beds which were buried underground outside the reactor building . It is estimated that the equilibrium activity of the gases held on the carbon bed was 400,000 curies . The adsorption efficiency of the charcoal, even at ground temperature, was good enough to prevent a discharge of activity greater than a few curies per day . However, even this amount of activity had to be diluted so that the atmospheric concentration at ground level was not greater than 10-13 curies/cc of air . Dilution was accomplished by feeding the active gas into a 1000-cfm ventilating air stream from the reactor shield and then to a 100-ft-high stack . During operation the gaseous activity inside the stack barely exceeded inhalation tolerance . 7-3 .5 Fuel concentration control . The condensate which was removed from the vapor-gas mixture upstream of the recombiner was returned either to the fuel storage tanks or to weighed holding tanks . The accumulation of water in the holding tanks provided a means of increasing the concentration of fuel in the storage tanks underneath the reactor . Since fuel was pumped continuously from the storage tanks to the high-pressure system by means of a duplex-diaphragm type pump at a rate of 0 .8 gpm, it was possible to vary the concentration of the fuel which circulated through the reactor . Figure 7-5 shows how the core temperature varied with fuel concentration, in g/kg H 20 . Furthermore, since the operating temperature of the core was controlled by the fuel concentration as shown in this figure, the operator had a convenient means of adjusting the solution temperature to the desired level . This feature of variable concentration was employed during startup of the reactor when the concentration had to be changed by large amounts, and also during steady operation for small changes in temperature . When sudden dilution of the fuel was desired, as in the case of a complete shutdown, the condensate holdup tanks were quickly emptied through a drain valve into the fuel-storage tanks, or condensate was pumped directly into the core . The steep slope of the curve in Fig . 7-5-i .e ., the large negative temperature coefficient-was a feature which was extremely important from safety *One curie equals 3 .7
X
10 10 disintegrations per second .