Fuel-cycle duration

With this simple plant layout, reductions in the safety systems and the long fuel cycle duration, the expected availability is higher than 91%. 

XXni-11] ALEKSEEV, P., et al.. Influence of nuclear fuel cycle duration and... 

Figure 10.8 Active control experiments to realize full tube fills in the Stanford PDE (a) indicates fuel filling duration, and (b) indicates cycle impulse for the cases of fixed valve opening duration and variable opening for active control 1 — fixed duration and 2 — active control.

It was decided to use some of FAs for the forth year of operation for the purpose of higher burnup, better fuel utilization, flexibility of core layout solutions that allows to vary the duration of the fuel cycles. Up to 1997 significant experience of the so-called experimental-industrial FAs operation in 4 annual fuel cycles was gained. It allowed the chief designer of the reactor and FAs to change design limits for the FAs ... 

If the consumption of uranium continues at the current level and is used only for LWRs, the uranium resources for energy sources will be available for less than 100 years. However, if the nuclear fuel cycles are established and fuel breeding is achieved in FRs, then the duration of the use of uranium resources will be extended to several thousand years. In addition, if uranium in seawater becomes usable, the duration of use will exceed more than a million years. To that end, it is important to build nuclear reactors that can breed fuel and to develop nuclear fuel cycles, which can efficiently extract reusable nuclear fuel materials after burning. 

With the fast reactor operating in a closed fuel cycle, the fuel quantity miming through the cycle is largely determined by the duration of the external (to the reactor) part of the CFG. Therefore, in order to reduce the time and costs required for cooling of irradiated fuel and for... 

Preliminary experiments on coupons which had been plated with a chromium layer and subsequently passivated by hot moist air treatment showed significantly smaller radionuclide deposition when inserted into a PWR steam generator for the duration of a fuel cycle (Asay et al, 1991 b). Other experiments with stainless steel coupons which were exposed over several fuel cycles in the hot as well as in the cold legs of a steam generator channel head showed that chromium-plated coupons exhibited very low levels of activity uptake, as Co and °Co were in all cases lower by more than an order of magnitude than on as-received or on electropolished/passivated coupons. The addition of a passivation step after the chromium-plating treatment had a detrimental effect by increasing the uptake of activity by up to a factor of two (Pick et al., 1992). 

Due to the current low costs of natural uranium and uranium enrichment, the use of uranium dioxide fuel with postponed reprocessing and spent fuel storage on the nuclear power plant site, are economically preferable for SVBR-75/100 at the moment. The duration of the benefits of this fuel cycle option depends on the available uranium resources and nuclear power deployment scale. In any case, the existing uranium resources are sufficient to achieve the realistic scenario of nuclear power development until the year 2050. The costs of natural gas could be expected to increase more intensively than the costs of natural uranium. This will ensure the NPP competitiveness even with a considerable increase in uranium prices, because the structure of electricity cost is different for NPPs and fossil-fuelled heat power plants. 

At this stage, the key to improving the economic parameters of the fuel cycle will be extending the core lifetime (to increase fuel burn-up), as experience in operability of the fuel elements is gained. Further on, the reprocessing and recycle of the uranium could be applied, and the plutonium, minor actinides and fission products could be extracted and then stored until their recycle becomes economically efficient. The duration of the uranium stage may be extended upon a transition to the uranium nitride fuel. 

For 1300 MW NPP, strategy will depend on fuel management (cycle duration) and on the treatment of CRDM functional problems. 

Some load shedders use a demand target that is not fixed but increases at a steady rate. Other devices allow the off-on setpoints to be adjusted independently for individual loads. Loads can be cycled based on the maximum demand target, time of day and day or week, rate of demand increase, heating and cooling temperatures, pressures, fuel flow and rates, occupancy schedules, inside and outside temperatures, humidity, wind direction and velocity and combinations of the above factors. Durations can be variable and changed automatically according to these parameters. 

Durability is a fundamental and necessary feature for PEM fuel cells to see a wide diffusion as a practical power source in any application field. The requirements for fuel cell lifetime vary with the specific application, in particular a duration of at least 5000 h is mandatory for use on cars, while even longer periods are needed for bus and stationary employments (for most applications an acceptable degradation rate is considered to be comprised in the range 2-10 pV/h [51]). However, the wide variability of operative conditions usually encountered in automotive applications, such as dynamic driving cycles, startup/shutdown phases, and freeze/thaw, makes also the target for car very difficult to be met with the current technologies. 

In Fig. 6.23a, b, the coefficient of variation is reported as function of time for R40 and R47 driving cycles, respectively. Fast and transient excursions outside the optimal region of Fig. 6.20 occur at fuel cell system minimum power of both cycles and for the highest power peak of R40 (170 s in Fig. 6.22a). However, for R40 cycle these excursions do not involve significant losses of cell voltage uniformity, as evidenced by values of coefficient of variation always below 2% (Fig. 6.23a), indicating that the short durations of shifts from the optimal region of... 

Table 4 Diesel bench aging cycle for NOx-catalyst (1.9 I IDI/TC diesel engine,diesel fuel S-content 0.15 wt.-% S lubricating oil phosphorous content 0.1 wt.-%P duration 50h) [19]...

D. W. Gibbons and K. J. Gregg, Closed Cycle Aluminum/Oxygen Fuel CeU with Increased Mission Duration, Proc. 35th Power Sources Symp., IEEE, 1992. 

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