Team brainstorming

After several months of reflection and review of the scientific literature, the "Cobalt Buster" biofilter was born as a filter dedicated to the primary water circuit of nuclear power plants !

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Why a "Cobalt Buster" biofilter in nuclear power plants ?

1- It is known that a pulse of radioactive Cobalt emission occurs in the primary circuit of water, during the maintenance of nuclear power plants when they open the reactor core. This pulse damages the ion exchange resins used to filter the water and reduce its radioactive level.

2- A major concern of the nuclear industry is the reduction of waste volume and a previous modeling estimated that the "Cobalt Buster" strain is very efficient (Appl Microbio Biotechnol 2009 81:571- 578):

4 kg of modified bacteria = 8000 kg of ion exchange resins

3- Drastic reduction of the costs of waste processing and conditioning is also a major issue for nuclear industry. The production of biofilters is less expensive and the biofilter may prevent damage caused to the resins. It could significantly reduce costs of rehabilitation of primary circuit wastewater.

4- Maintenance phases generate a shortfall of millions of euros and reduction of the duration of maintenance phases represent a major issue.

5- Storage stations of moderately radioactive waste are rapidly full. Our bacteria could help in downgrading the high volumes of high radioactive waste to low radioactive waste, which are stocked in other stations, usually more spacious. Radioactive cobalt would be concentrated in smaller volumes thanks to the increase of the efficiency of filtration.

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Why not in the primary circuit ? (Experts advice)

To include our project into a realistic approach and close to concerns of today and tomorrow's engineers, we notably have discussed the realization of our biofilter with M. Brette (Assistant professor in INSA Lyon, doctor in economic sciences) and our partners (Assystem, EDF). We also have a realistic idea of the technical difficulties thanks to the visits we made in nuclear installations (central of Tricastin, area of Centraco) and discussions we had with a Chemist of the nuclear power plant of Bugey.

To get an industrial application technically realistic, our biofilter has to be designed as a modular innovation, what means that this solution can be applied without any major modification of the structure of the power plant or of the treatment center (plumbing, circuits of the different components, ...). Thus, design of the cartridge of the biofilter is fundamental to be able to be used into the circuit of nuclear effluents, then be treated as radioactive waste.

From those discussions we know that our project is plausible and could interest industrialists but some changes have 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

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, human operators will have to be protected from this high level of radiation, which means that a concrete wall of at least one meter has to be built for each parallel biofilter, and all manipulations have to be automated. This would involve a major modification of the structure of nuclear power plants.

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, for standardization and safety reasons.

2- We also have to consider that during the conventional operation, pressure in the primary circuit can reach up to 155 bars, and temperature up to 327°C (621°F). As the maximum rate of temperature decrease 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 or stations of treatments of liquid effluents (STEL).

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, a collaboration subjected to non-disclosure agreement is being discussed with one of our partner to realise pilot testing.

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 ?

As shown by the number of teams interested in strain adherence (TU-Delft 2011), metal absorption (Peking 2010), or radioactivity (Osaka 2011; NYC_Software 2011), collaborations and common brainstorming may enhance future prospects.

We initiated a collaboration with TU-Delft team in order to compare the efficiency of our two approaches and determine if the overproduction of curli is the best strategy to optimize the adhesion of E. coli strains.

Collaborations with Osaka and NYC teams should be considered to optimize the radioactive cobalt bioremediation of our "Cobalt Buster" strain.

To go further, outside the context of electronuclear pattern, we considered a wider use of the biofilter. The system could involve a large variety of bioremediation strains, each optimized for the capture of one metal and why not other pollutants (hydrocarbons, antibiotics...). These strains could be associated in a complex biofilm to create a broad-spectrum biofilter, as shown in the following video !

schéma prospects par iGEM_Lyon_2011

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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 groups 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 engineering for each project of central, fabrication of components, installation and starting of centrals.

The operators of Exploitation are cautious about the well functioning of centrals daily, and calibrate the power of reactor according to the needs of electric network. Maintenance includes activities necessary for upkeep, modernization 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: used fuel (recycling in MOX for a reuse), and life-ending of nuclear installations (dismantling, redevelopment of areas).

Because of the huge 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,sources of pressure on this field are numerous and varied. Political influence on the electronuclear field is quite important: in France, nuclear holds a paramount place, but politics can at any moment decide to favor other ways of electricity production, as in Germany (solar, wind turbines, 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, Copenhagen) 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. Voted laws restrict this field to allow a permanent control, avoid accidents and protect populations. Indeed, from a social outlook, the apprehension facing this strength and the different accidents which occurred is still present (Safety). Nevertheless, because of the increase of the price of fossil energies (petroleum, gas) and thanks to the researches on new generations of more efficient reactors, the electronuclear field keeps its competitiveness on the energy market.

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ENS assystem Biomérieux INSA INSA