operational life of nuclear reactors Commonly we tend to think that the cost of producing nuclear energy depends mainly on the cost of system construction, but there are various factors that determine the cost per kWh produced. Among these, very important is the operational lifetime of the plant. In this fascinating article, Domenico Coiante, from his experience as a physical scientist and manager for 35 years at the Aeneas, not only sheds light on this crucial issue, but also tells us perhaps a little known part of the energy history national.
Written by Domenico Coiante
Cost per kWh and lifetime
In estimating the cost of kWh produced in power stations have an integral role in the full duration of the operation efficiency of the production facilities. This time period is referred to as "useful life" or "lifetime". It begins at the time of production start-up and ends when the annual cost of operation and maintenance is above the revenue from the sale of energy (maintenance costs grow with the aging of facilities). This event causes the permanent closure activities.
Fixed nominal power generator, the longer the lifetime the higher the cumulative energy production. So, for the same cost of the plant, the cost of the unit of energy produced will be much lower than the longer its life.
nuclear reactors I and II were designed to build an operational lifetime of 30 years, the same as in conventional thermal power plants. The depreciation expense for the plants was spread over the entire life cycle and that determined through the current discount rate, the production cost per kWh. Therefore, existing conditions, both for the cost of the plant, both for governmental incentives, together with the operational life of at least 30 years, ensuring the competitiveness of nuclear electricity market dominated by thermal generation convenzionale.
Per lo meno ciò è stato vero fintanto che è esistito il mercato parallelo, militarmente protetto, del plutonio estratto dagli elementi di combustibile bruciato. I proventi del plutonio, come sottoprodotto della produzione atomica pacifica, ammontavano in quegli anni a circa 30 $/g e questo prezzo d’acquisto da parte del governo USA era così alto da rappresentare per le imprese nucleari la “fonte più alta di profitto” (Loizzo, 1994). Ricordo che con il plutonio si sono realizzate nei Paesi Alleati (ed ex Alleati) migliaia di testate nucleari durante il periodo della guerra fredda. La quota di ricavo proveniente dalla vendita del plutonio costituì il sussidio principale di sostegno al costo del kWh nucleare fino al 1977. In quell’anno il Presidente J. Carter, preoccupato per la proliferazione atomica, fece approvare dal Congresso un decreto che proibiva l’estrazione del plutonio dagli elementi di combustibile bruciato. Improvvisamente, per i gestori delle centrali nucleari, venne a mancare il principale provento. Le centrali già in funzione da anni, a cui il sussidio ‘plutonio’ aveva consentito praticamente di ammortizzare la spesa di costruzione, poterono continuare a produrre i kWh in attivo, mentre, per le ultime nate, sorsero seri problemi economici. Le cose peggiorarono ulteriormente nel 1978, quando il Presidente G. Ford fece privatizzare completamente il settore dei reattori nucleari, togliendo gli altri public incentives, including government guarantees for loans requested to carry out the installations. For the U.S. nuclear industry was grinding to a halt: the orders in the pipeline were blocked and no new plant was more ordered in the U.S. to this day. The industry was drastically cut back and some have survived by taking advantage of some designs of nuclear reactors in developing countries, mainly China, India, Pakistan, Korea, where there were ambiguous plans for the "peaceful nuclear energy."
Italy also strongly affected by this situation. The nuclear program, launched by the Minister of Industry Donat Cattin effort in 1975, which included the construction of 20 power plants nuclear 1000 MW each, for a total cost of 20 trillion lire, had to be reduced to only 6 plants, of which only two were built: Three Vercelli and Caorso. As evidence of the seriousness of the crisis, this writer can remember that in the days of the decision of President Ford, the training course on reactor safety of PWR Westighouse, which was being held in Rome and which he participated, was stopped abruptly during a lesson and all teachers, specialists of the company, were recalled in the U.S. immediately.
Apart from the question of plutonium in reactors in the transition from the first generation of the '50s and '60s with those of the second generation of the '70s had been a considerable increase in construction costs of the plants, mainly because of the need for greater security imposed by the governmental control. These higher costs were partly offset by the large margin of profit, which came from the sale of plutonium. Once locked this source and liberalized the sector, the competitiveness of the nuclear kWh was significantly affected. Nuclear power was no longer a "cost so low that it can not be measured" as the slogan recited in vogue in the '50s.
We come to 2000, when the nuclear industry has survived started to announce the "nuclear renaissance", to be implemented with third-generation reactor, the present one, pending a fourth generation still in the minds of researchers.
What's new? The competitiveness of
kWh can be recovered, despite higher costs due to equipment installation of security systems through improved conversion efficiency and the prolongation of life.
The improvement of materials and technologies has made it possible to bring the average annual productivity of the plant from 6500 kWh / kW of the 80 in 7500 to 7800 kWh / kW at present.
The experience of second generation plants, which have now reached in our day to 30 years of operation, has shown the possibility to extend the operational life of up to 40 years, while the third generation reactors are designed with the technical criteria such as to provide an operational lifetime of 60 years. With a life span so long, the discount factor plays a minor role in the capital and produce the lowering of cost per kWh. What has
reliability prediction of the doubling of operating life from 30 to 60 years? The situation
First, try to understand why the operating life of reactors I and II generation was set at 30 years.
E 'known that the practical experience gained in over a century of conventional thermal power plant management, have established their life around 30 years. After this period, the number of failures of the relevant parties becomes so high as to bring the cost of maintaining such a value to zero profit. For this reason, an operational lifetime of 30 years is usually assumed for the thermal budget of the enterprise.
Since a nuclear plant, apart from how to heat the primary thermal fluid is substantially similar to a conventional thermal power plant, it was considered that the aging process of the main components were similar. Indeed, in the case of nuclear power, it is known that the presence of neutron radiation produces embrittlement of all materials, including steel. Thus, the aging process is accelerato e, di conseguenza, si sono dovuti adottare provvedimenti d’irrobustimento dei materiali per garantirsi almeno 30 anni di vita operativa. Questo ha prodotto, indipendentemente dai requisiti dei sistemi di sicurezza, un generale aumento del costo degli impianti rispetto a quelli convenzionali, ma tale aumento era compensato dal bassissimo costo del combustibile nucleare. In definitiva, i 30 anni previsti per la vita utile erano sufficienti per portare al profitto l’impresa.
Per molti reattori nucleari 30 anni sono ormai trascorsi dal loro avvio. Ci chiediamo se la previsione della vita operativa è stata rispettata.
Certo, non ci possiamo basare sull’esperienza italiana, che, a prescindere dal blocco a seguito del referendum del 1987, è stata abbastanza travagliata. Infatti, i due reattori della I generazione, costruiti alla fine degli anni ’50 ed avviati nei primi anni ’60, avevano mostrato una serie di malfunzionamenti, che difficilmente avrebbero permesso il raggiungimento dei 30 anni di vita operativa.
- Il reattore di Latina, della filiera inglese a gas-grafite, poco dopo essere stato portato alla massima potenza di 210 MW, ebbe un grave guasto a causa della dilatazione termica dei blocchi di grafite. Alcuni dadi che serravano i bulloni di contenimento della grafite saltarono via, facendo oscillare pericolosamente il nucleo del reattore e provocando l’intervento del sistema di blocco. L’esame del guasto e la sua riparazione consigliarono di esercire il reattore a potenza ridotta a 140 MW, onde impedire una eccessiva dilatazione della grafite, e così fu fatto fino al blocco del 1987. E’ chiaro che, in tali condizioni di funzionamento a regime ridotto, la vita operativa sarebbe stata poco significativa in ogni caso.
- Il reattore ad acqua bollente (BWR) da 160 MW della General Electric del Garigliano ebbe una vita altrettanto travagliata. Avviato nel 1963, il suo funzionamento fu spesso interrotto durante i primi 10 anni a causa di guasti. Chi scrive partecipò, come addetto ai controlli governativi previsti dalla legge, alle diverse ispezioni dei sistemi di sicurezza a seguito della richiesta del rinnovo decennale della licenza d’esercizio. Assieme ad alcuni malfunzionamenti minor, it was discovered on that occasion a leak of radioactive steam from a nozzle of the welding output of one of the primary circuits. The next test for all other unions emphasized the presence of cracks in the welds, which still did not go out steam. A survey done in Germany at some facilities equal to that of the Garigliano, allowed to ascertain the occurrence of similar failures. The technical and economic estimates made by ENEL not demonstrated the cost to repair the damage and, therefore, was made in 1981, the decision to shut down the reactor. When it was decided the suspension of nuclear power for the 1987 referendum, the Garigliano reactor was already shut down for years. Its operating life, wanting to be optimistic, was about 15 years.
- The other two reactors, the PWR Trino Vercelli from 260 MW and the BWR Caorso from 860 MW were shut down for political reasons in 1987, respectively after 25 and 12 years of operation.
We see, therefore, if we can bolster confidence in the prediction of 60 years of living with other experimental evidence from a significant base of the enlarged world.
The following table, published by the World Nuclear Association (WNA, 2010), gives a list of all the reactors have been shut down yet reached retirement age (because they become non-economic).
as can be seen, the vast majority of these 95 reactors went into service in the 60s and a small number of them was initiated in the early '70s.
The graph of Fig.1 shows the same data in the table in the form of distribution of the number of reactors in relation to life.
The arithmetic mean value of the life cycle, calculated for the entire distribution, is 23.1 years.
observing the histogram, you notice a group of cases are concentrated in the first seven years of the scale. It is almost always of cases of experimental prototype reactors, which have resulted in industrial clusters. Eliminating them from the base to the media because these cases are not significant, the value of media sale a 26,8 anni. Non possiamo, tuttavia, concludere che la vita operativa dei reattori della I e II generazione sia questa, perché non sappiamo quanti altri impianti, avviati negli anni ’70, siano ancora in funzione. Ad esempio, osservando il lato destro del grafico, possiamo vedere che una decina di reattori hanno operato per oltre 40 anni; ce ne potrebbero essere altri, entrati in servizio alla fine degli anni ’70 prima del blocco, che ancora sono in esercizio e che potrebbero portare la media della vita operativa ad un valore più alto.
Il grafico di Fig.2, sotto riprodotto da un recente rapporto dell’IAEA (IAE
A, 2009), è molto interessante. Esso mostra chiaramente che Most reactors in operation are between 20 and 30 years and another large group is in service for 30-40 years. Going back in time, the first group entered the service in the decade 1980-1990, and according to the chart, has statistically still faces a life span of another ten years, while the second, which was launched in previous decade 1970-1980, no longer has a future (always in statistical terms).
There are practically no longer in service reactors over the age of 40 years, that is built and launched before 1970.
Conclusion The conclusion to be drawn from these experimental data, is that the effective operational life can be placed with good certainty the value of 30 years and assumed that the extension to 40 years for the reactors of the latest technology, is probabilistically acceptable.
Regarding the further extension to 60 years, you have no feedback in the experimental data. References
- Loizou P., 1994, Nuclear power plants, or the devil who is not there, Ed Monteleone, Vibo Valentia 1994, p.98
- WNA, 2010, Decommissioning Nuclear Facilities, www.world-nuclear .org/info/inf19.html
- IAEA, 2009, Power Reactor Information System, www.iaea.org/programmes/a2
