Cirene reactor

The Cirene reactor was a 40-MWe prototype power plant constructed at Latina, 80 km south of Rome. Construction start in 1976 and completion was scheduled for 1984. Commissioning stopped in 1988, before work to reduce the positive void reactivity coefficient was complete, by the general moratorium on nuclear reactor operation imposed by the Italian Government following the Chernobyl accident. 

Feasibility studies have been carried out to evaluate to feed a CIRENE type reactor with slightly enriched uranium (1.1%) and also on the use of CIRENE reactor for dual purpose plants -(desalination and electricity). 

On another point. In our studies on the natural uranium fuelled CIRENE reactor, where we only consider continuous axial refuelling, we also found that a unidirectional scheme tends to over-compensate for the roof-topped flux distribution, A reasonable scheme seems to be one with two bottom feed channels and one top feed channel. Following your studies, what would be a reasonable scheme in the case of multi-segmented fuel ... 

Two possible control schemes for the station, the coupled and decoupled have been presented. During the study of a general control of the CIRENE reactor, we have found that a co-ordinated scheme of the forcing type, in which a load demand signal is fed to both the reactivity control and to the turbine valve, allows a considerably better dynamic behaviour, with time constants of the turbine power of the order of 1-2 s. Is this type of scheme being studied ... 

SYNOPSIS The main characteristics of a typical l600 MW(th) CIRENE reactor design are discussed and some data reviewed in comparison with similar reactor concepts, namely the SGHWR and the CANDU-BLW. 

The development of the CIRENE reactor is eventually Justified on the economic ground, in the frame of long-term forecasts for the growth of power demand in Italy. 

Fig. 1 Flow diagram of the cooling system for a typical CIRENE reactor... 

As it can be seen from the table, the CIRENE reactor is foreseen to operate with the highest steam exit quality 25 by weight. 

The fast control system of the CIRENE reactor, which ensures also the spatial stability of the core, consists in a number of special control tubes placed vertically through the core. 

A CIRENE reactor of 16OO MW thermal would require 19 control tubes like that here described, acting at a rate of about 30 pcm/s and covering an overall reactivity range of 6OO-8OO pcm. 

The scram system of the CIRENE reactor consists, as previously mentioned, in a number of tubes passing through the core and allowing injection of a poisoned liquid. Each of these tubes is a branch of a U-shaped duct, the other branch being placed outside the core. In operation the liquid column is maintained in the outside branch by an overpressure of the cover gas inside the in-core branch, which balances the hydrostatic head. 

The less stringent requirements as for the insertion time in comparison with the SGHWR, which permit the scram system to rely on gravity only without the need of a pressure drive, are due to a different approach to some safety problems. In fact, for the CIRENE reactor, one does not admit the sudden loss of flow due to pump failure since the pumps are provided with fly-wheels. Other emergency cooling means are also foreseen in case of pump failure,... 

Due to the strong influence of the coolant density on reactivity, the basic operating programme taken into consideration for the CIRENE reactor is such as to keep constant at different loads the coolant density, its value being the same as in nominal conditions, l.e., about 0.28 g/cm5. Such a programme differs from... 

In default of a practical experience (because no examples exist of what really happens when charging and discharging on power a full-scale boiling channel) and due to the relatively small economic differences among the various schemes, offload refuelling - possibly in unpressurized conditions - is presently considered very seriously for adoption In the CIRENE reactor. 

Several improvements may lead in the future to more advanced versions of the CIRENE reactor design. 

The CIRENE reactor is being presently designed for natural uranium fuel, but it cannot be excluded that a very slight enrichment may Improve its overall economy under particular circumstances. Very slight enrichment means here that the U-235 content in spent fuel is still so low as to exclude the economic convenience of its recovery. 

Both the development expenditures occurred before 1979 and the net savings obtained in power generating costs by operating a number of CIRENE reactors after 1979 tnay be referred to the year 1979. 

In order to evaluate the economic benefit deriving from power generation through CIRENE reactors, some assumptions have to be made about the total Installed capacity with reactors of this type and about the rate of installation. 

Nuclear power plants would allow a substaintial reduction of this expenditure nearly 6o% for enriched fuel elements imported as a finished product or even 90 for natural uranium imported as uranium concentrate to be processed by domestic Industry. The CIRENE reactor being fed by natural uranium, would give thus a substantial contribution in reducing expenditures for fuel importation. 

It has to be mentioned at this point that feeding CIRENE reactors, like other heavy water converters, requires relatively low urainium amounts. Some comparative... 

Furthermore generating costs with CIRENE reactors, as with other heavy water converters, are not very sensitive to price... 

In the period foreseen for the Installation of CIKENE type reactors, beginning only in 1979, fast reactor systems are likely to have reached industrial maturity. It is therefore Interesting to examine the Impact that CIRENE reactors could have on fast reactor penetration. In comparison with light water reactors. 

To have an idea of the advantages which may derive from a good converter like CIRENE with respect to a light water reactor, let us compare two mixed fast plus thermal reactor systems, in which the thermal share consists entirely of either CIRENE reactors or light water reactors respectively. 

If we assume for fast reactors a load factor of Q0%, an overall fuel inventory of 5.2 kg fisslle/MWe and an integral conversion ratio of I.30 their penetration would correspond respectively to 40 of the total nuclear capacity in the first case and to about 56 in the second case. These data refer to an overall nuclear load factor of 65 and a plutonium production of 0.55 kg/MWe - year for CIRENE reactors and 0.28 kg/l We - year for light water reactors. 

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