Team:Lyon-INSA-ENS/Project/Industrialization

Team brainstorming

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

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- Major preocupation of nuclear industry is the reduction of waste volume and a previous modelization estimated that the "Cobalt Buster" strain is very efficient :

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. Biofilter production 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- Stocking stations of moderately radioactive waste are rapidly full, and our bacteria could help in the downgrading of these waste to low radioactive waste, which are stocked in other stations, usually more spacious.

Why not in the primary circuit ? (Experts advice)

During the project development we organized a lot of meetings with nuclear industry actors.

To know more about the operation of nuclear power plants we visited the nuclear power plant of Tricastin and we met a Chemist of the nuclear power plant of Bugey

We also visited the Nuclear center for processing and conditioning low-level radioactive waste (CENTRACO) to learn more about the constraints of nuclear waste processing.

Thanks to our partner Assystem we met nuclear experts who provided us additional and accurate informations on the issues of nuclear industry and assessed feasability of the project.

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" biolfilter, 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.

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.

Other prospects for the "Cobalt Buster" project ?

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