Period of reactor

The coke profiles in the reactor bed can be predicted excellently by the model as shown by the solid lines in Figure 1. Figure 2 shows good consistency is also obtained for the average coke content over the reactor bed versus time on stream. Note that within the time period of reactor startup plus one hour of operation, the average coke content of the reactor bed is already at about 5 wt%. The model cannot be applied to this startup and initial period with the rapid transients of temperature, activity "spike" and concentration. However, compensation for this interval can be made by a time translation of the model a model time of 36 hours is fixed at an experimental time of zero. A temperature difference of more than 20C between the center of the bed and outer wall of the reactor in the startup stage has been observed in our laboratory for some experiments. About three-fourths of this difference is across the catalyst bed itself. Startup of the reactor at reasonably lower temperatures in order to control the coke formation and to better maintain the catalyst activity is important, if not critical. 

There is an 8in. line connected to the 30-in. inlet line at a point upstream from the valve pits and to the 36-in. line near the reactor. This 8 in. line provides a flow parallel to the main flow stream and contains two block valves, a flow instrument, a strainer, and a control valve. It can carry 1000 gpm and is used in the event that the main water line valve is closed off, thereby assuring a continuous water supply t o the reactor at all tirne. particu 1 arly at shutdown. This same line, which allows 1000 gpm of process water to by-pass the main stream, can also be- used to carry 1000 gpm of fresh demineralized water during periods of reactor flushing, or 1000 gpm of seal-tank water for recirculation through the seal ta.nk and the reactor only. 

The HCR s have the advantage over control splines in that t.l ey are remotely operable. Fine adjustments in position can be made during all periods of reactor operation and the rod position is indicated in the control room at all times. The control rods have a relatively long lile, but repair or replacement can be a time consuming and expensive operation. 

Evidently periods of reactor operation at 800"C and 750 C increased catalyst activity for subsequent operation at 700 C with the level of enhancement dependent upon the frequency of operation at 750-800°C. The increase in activity induced in this manner decayed with time falling to the unactivated condition some 30-50 hours after activation. Increasing the frequency of operation at higher temperature reduced the rate of decline of activity at 700"C leading to increased activity at the lower temperature as shown in Fig. 5. However the temperature activation was not sufficient to restore the activity found in the earliest operations and it appears that the initial decline was irreversible. 

The period of reactor operation without refuelling may be more than 7.3 EFPY with 5% enriched UO2 fuel all fuel assemblies are to be replaced at the end of life. 

At the end of the core life, spent fuel assemblies are removed and transported to centralized fuel storage or reprocessing facilities. This will be required only every 7.3 EFPY and, therefore, fuel assemblies would be not easy to steal or transport. It is assumed that the reactor vessel cover is not opened during the whole period of reactor operation. 

The reservoirs marked 9 contain fresh micro fuel elements only during the period of reactor refuelling, which is to be performed under strict security measures. When the reactor operates, the reservoirs 9 are empty and it is impossible to discharge irradiated micro fuel elements from the reactor vessel, as the reactor has no equipment for hydraulic transport of micro fuel elements. Such equipment is delivered to a site along with the reservoirs for spent fuel just prior to a refuelling and moved away immediately after the refuelling is completed. 

It is also assumed that the reactor vessel lid would not be removed during the whole period of reactor operation. In these conditions and taking into account that the AFPR is essentially a reactor with thermal spectrum of neutrons, there would be no possibility for irradiation of undeclared fertile material within or around the reactor. 

Heat is released from the reactor vessel by natural circulation of sodium and air to enable effective heat discharge in the period of reactor shutdown after an accident ... 

The fuel lifetime is 10 years, coinciding with the period of reactor operation without on-site refuelling. 

The absence of on-site refuelling means that there are no fresh or spent fuel storage facilities on the site and no access to the core during the whole period of reactor operation with this, all accounting and verification procedures are concentrated at special refuelling sites ... 

The LSPR is a factory fabricated and fuelled reactor designed for operation without on-site refuelling. During the whole period of reactor operation and transportation to and from the site, the reactor vessel is always closed (sealed) and the fuel is confined in the vessel. Because of very small operation reactivity margin in the core, the fuel inside the reactor vessel cannot be removed and fertile materials cannot be inserted in the reactor to produce fissile materials. No refuelling equipment is provided in the reactor or at the site during the whole period of reactor operation, including its transportation to and from the site. 

Elimination of fuel handling operations during the whole period of reactor operation on a site and transportation to and from the site ... 

After the reactor re-start operation the amount of the He in the Be reflectors decreased. However, for the WWR-M Kiev reactor the reactivity increase resulting from the reduction of He was less than the reactivity decrease due to fuel bum-up. In this way the net excess reactivity was always decreasing for any power and at any period of reactor operation. 

Ill steady-state operation, the concentration of the various nuclides within the reactor system does not change with time. During the initial period of reactor operation this situation is not true, but is approached after some time interval if neutron poisons arc removed by fuel processing. Under steady-state operation it is necessary to consider the equilibrium isotope relationships. In thorium breeder reactors this involves rate material lialanccs on Th, Pa - fi.ssion-product poisons,... 

Two-region reactors. During the period following reactor startup, there is a buildup of fission-produet poisons and higher isotopes with time, which results in varying nuclear characteristics. This section presents some calculations relative to the IlRE-3 conceptual design for the initial period of reactor operation. 

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