Reactor stability index

Figure 2.2 Effect of temperature and conversion on reactor stability index.

Figure 2.4 Reactor stability index with 50% higher feed flowrate.

Effect of Heat Of Reaction Figure 2.5 shows what happens if the heat of reaction is 10 or 20% higher than the base case value. The conversion is 80% for all these cases. As expected, the heat of reaction has no effect on the reactor volume, diameter, or area. These parameters are set by throughput, temperature, and conversion. Higher heats of reaction require higher heat transfer rates Q, which lower the jacket temperature and increase the cooling water flowrate. As shown in Figure 2.6, the result is an increase in the reactor stability index, which indicates more difficult control problems. 

However, the circumferential wall heat transfer area increases as the aspect ratio increases. So, from a heat transfer, dynamic stability perspective, a large aspect ratio is desirable. Figure 2.8 shows the effect of aspect ratio on the various design and operating parameters for a design conversion of 80%. Increasing L/D increases heat transfer area, which decreases the required AT driving force and raises jacket temperature. The reactor stability index improves substantially. 

Pellets of UO2 have been pressed, sintered, and reprocessed several times via the AIR0X process(10,11,12). In one series of tests, stable fission products equivalent to 20,000 MWd/MTU burnup were added during each of five cycles until the fission products content of the UO2 was equivalent to 100,000 MWd/MTU burnup. No difference in behavior of the fuel was detected as the material was repeatedly processed. During these tests, it was found that tap density was a better index of sinterability than sieve-size distribution. In some of these tests, AIR0X processed UO2 that contained stable fission products equivalent to 100,000 MWd/MTU was refabricated and irradicated to 5,000 MWd/MTU excellent reactor stability of these pellets was obtained. 

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