Team:Lyon-INSA-ENS/Project/IndustrializationFr

Industrialisation

• Remue-méninges


• Pourquoi un "Cobalt Buster" biofiltre dans les centrales nucléaires ?


• Pourquoi pas dans le circuit primaire ?


• Ou utiliser "Cobalt Buster" ?


• Autres perspectives pour le projet "Cobalt Buster" ?


• Pour aller plus loin: L'analyse économique du modèle électronucléaire

Remue-méninges

Après plusieurs mois de réflexion et de lecture de revues de littérature scientifique le "Cobalt Buster" biofiltre est né, filtre dédié au circuit d'eau primaire des centrales nucléaires!

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Pourquoi un "Cobalt Buster" biofiltre dans les centrales nucléaires ?

1- Il est connue qu'une émission de cobalt radioactive dans l'eau se produit dans le circuit primaire , lors de l'entretien des centrales nucléaires quand le cœur du réacteur est ouvert. Cette émission détériore les résines échangeuses d'ions permettant de filtrer l'eau et de réduire son niveau radioactif.

2- La préocupation majeure de l'industrie nucléaire est de réduire le volume des déchets. Une modélisation faire précédemment a estimé que la souche "Cobalt Buster" est très efficace (Appl Microbio Biotechnol 2009 81:571- 578):

4 kg de bactéries modifiées = 8000 kg de résines échangeuses d'ions

3- La réduction drastique des coûts de traitement des déchets et de conditionnement est également un enjeu majeur pour l'industrie nucléaire. La production de Biofiltre est moins cher et ce dernier peut prévenir des dommages causés aux résines. Il pourrait réduire considérablement les coûts de réhabilitation des eaux usées du circuit primaire.

4- Les phases d'entretien génèrent un manque à gagner de millions d'euros et la réduction de la durée des phases de maintenance représentent un enjeu majeur.

5- Les stations de stockage des déchets moyennement radioactifs sont rapidement plein, et nos bactéries pourraient contribuer à la dégradation de ces déchets afin de réduire les déchets radioactifs, stockés dans d'autres stations, généralement plus spacieuses.

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Pourquoi pas dans le circuit primaire ? (Experts advice)

Pour inclure notre projet dans une approche réaliste et proche des préoccupations de l’ingénierie d'aujourd'hui et de demain, nous avons discuté notamment de la réalisation de nos BioFiltres avec M. Brette (professeur adjoint à l'INSA de Lyon, docteur en sciences économiques), nos partenaires (Assystem, EDF ). Nous nous sommes fais une idée réaliste concernant les difficultés techniques existantes grâce aux visites faites dans des installations nucléaires (centrales de Tricastin, zone de Centraco) et les discussions que nous avons eu avec un chimiste de la centrale nucléaire du Bugey.

Pour obtenir une application industrielle techniquement réalistes, nos BioFiltres doivent être conçus comme une innovation modulaire, ce qui signifie que cette solution peut être appliquée sans aucune modification majeure de la structure de la Centrale ou du centre de traitement (plomberie, les circuits des différentes composantes , etc). En effet, si cette solution est conservée dans un endroit central, il pourrait être rapidement appliqué dans tous les centrales du même type. Ainsi, la conception de la cartouche du BioFiltre est fondamentale pour pouvoir être utilisé dans le circuit des effluents nucléaires, puis être traité comme des déchets radioactifs.

From those discussions we know that our project is plausible and could interest industrials but some changes are to be made regarding the uses of our biofilters.

1- Cobalt released during the opening of the nuclear reactor may represent 150 TeraBecquerel (TBq) of radioactivity (500 m3 of contaminated water with a radioactive Cobalt estimated level of 300 gigaBq / m3).

If the Cobalt biofilter is used as shown above, dose rate for only 1 of the 150 TBq will represent 0,4 sievert per hour (Sv/h) whereas the authorized rate is up to 20 mSv per year.

Calculation of dose rate:
Dose Rate = 0.54 * C * E * P / d²

with
C = the activity Curie
E = energy radiation in MeV
P = the percentage of emission
d = distance from the radiation source

To treat 1TBq of Co60 with d = 1m (1TBq = 30 Curie)
EP = 2.5

we can estimate Dose rate
DR = (0.54 * 30 * 2.5) / 1²
DR = 40 rad / h
DR = 0.4 Gy / h
DR = 0.4 Sv / h

This exposure rate supposed that if we want to use our "Cobalt Buster" biofilter, a concrete wall of at least one meter has to be built for each parallel biofilter, and every manipulations have to be automated.

These changes involve too important costs as in France, a modification in one power plant must be also done in the 58 other power plants of the nuclear fleet.

2- We also have to consider that during the conventionnal operation, pressure in the primary circuit is up to 155 bars, and temperature up to 327°C (621°F). As maximum rate of temperature dicrease is estimated at 28°C/hr (82°F/hr)and acceptable temperature for our biofilter is between 20°C to 45 °C, it implies waiting 4 to 5 hours after the opening of the nuclear reactor, before starting the cobalt decontamination.

It could be too long because stopping the reactor costs one million euros a day and the maintenance time has to be as short as possible.

3- In the primary circuit, cobalt is in form of ions and particles. Cobalt particles may represent the majority of cobalt and the initial bioremediation strain is design to capture ions of cobalt .

At this stage of the project we could not assess the ability of the biofilter to capture cobalt particles. However, the final "Cobalt Buster" strain will produce amyloid fibers (curli) that could allow it to fix cobalt particles on its surface.

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Where to use "Cobalt Buster" ? (Experts advice)

1- According to the experts, the "Cobalt Buster" biofilter could be used in the treatment of other effluents, such as those of dismantling stations (STEL, stations of treatments of liquid effluents).

In these stations the radioactivity is lower, but the problems related to the cobalt still exist, and temperature and pressure are compatible with the survival of our biofilter (atmospheric pressure and ambient temperature).

Moreover, our biofilter may be adaptated on an existing filter and a collaboration subjected to non-disclosure agreement is being discussed with our partner ASSYSTEM.

2- The filter could also be used in a bubbling type system to treat contaminated air during the decommissioning of power plants.

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Other prospects for the "Cobalt Buster" project ?

1-

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To go Further : Economic analysis of the electronuclear pattern

The electronuclear pattern

Because of the implied technologies, ways and the potential risks, nuclear and electronuclear pattern are strategic fields. There are four sectors :

The Upstream aims to supply centrals in nuclear fuel. It group together several links : mines (mining exploration and natural uranium extraction), chemistry (purification and conversion of uranium to uranium hexafluorure), enrichment (augmentation of isotope U235 content from 0,7% to 3-5%).

The Construction put together conception, studies and ingeneering for each project of central, fabrication of components, installation and starting of centrals.

The operators of Exploitation are watchfull on the well functionning of centrals daily, and calibrate the power of reactor according to the needings of electric network. Maintenance includes activities necessairy for upkeep, modernisation and extension of the lifetime of nuclear centrals. The outages are important points of this activity: indeed reactors are stopped sometimes during several weeks to refill in fuel and large-scale maintenance operations.

The Downstream of the pattern is divided in two different activities: treatment of used fuel (recycling in MOX for a reuse), and life-ending of nuclear installations (dismantling, redevelopment of areas).

Because of the huges financial and technological means needed for the development of a business in the electronuclear field, threat of new competitors (new businesses incoming into the market) is low. Consequently, just a few large groups share the four lines of business, even at the world scale (for example AREVA, EDF, GE Energy or Mitsubishi). Suppliers, operators and customers inside the pattern are interconnected, and are quite often subsidiaries of these multinational companies. Competition is very strong because contracts are rare and huge.

Thus, pressure on this field are numerous and varied. Political influence on the electronuclear field is quite importante: in France, nuclear holds a paramount place, but politics can at any moment decide to favour other ways of electricity production, as in Germany (solar, windmills, etc.). Therefore role of public power in different countries and of international organizations (for example AIEA, ANDRA) is crucial, because those are the ones which will decide, fix rules and directives. The application of agreements against the global warming by public power (Kyoto, Copenhague) can also impact directly and positively on the electronuclear field, this one giving out no CO2, to produce electricity. However, there are currently two main problems: the becoming of nuclear wastes (for now, stocking of wastes of low, medium and high activity), and the risk of an accident whose consequences would be disastrous for environment and population. Laws taht have been voted purely restrict this field to allow a permanent control, avoid accidents and protect population. Indeed, from a social outlook, the apprehension facing this strength and the different accidents which occured is still present. Nevertheless, because of the increase of the price of fossil energies (petroleum, gas) and thanks to the researches on new generations of reactors, more effecient, electronuclear field keep its competitivity on the energy market.

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