Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
2002-04-26
2003-12-02
Phasge, Arun S. (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
active
06656338
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for reducing cationic impurities in the cooling-water loop of a light water reactor, and to the application of the method, the cooling-water loop containing a cationic solution. Furthermore, the invention relates to a method and the application of the method for dosing lithium in a cooling-water loop, containing cationic impurities, of a light water reactor. The invention also relates to a device having an electrodialysis unit that is connected on one side to a water loop, and connected on the other side to a concentrate loop. Finally, the invention relates to a cooling-water system of a light water reactor. In nuclear power plants having a light water reactor, boron in the form of boric acid (H
3
BO
3
) is added to the reactor coolant (water) for the purpose of absorbing neutrons. It serves to protect the reactor components against radiation and is practiced both in the case of boiling water reactors and, in particular, also in the case of pressurized water reactors. The boric acid has a side effect in that it lowers the pH of the cooling water, an effect that is not desired for reasons of protecting the components against corrosion, and it must be at least partially compensated for by adding an alkalizing agent. Isotopically pure lithium-7 (
7
Li) is normally used as alkalizing agent because it, on one hand, has virtually no undesired nuclear reactions with the neutrons present in the reactor core and, on the other hand, is continuously formed itself in the reactor by the nuclear reaction
10
B(n,&agr;)
7
Li proceeding during the neutron absorption by the active boron isotope
10
B.
The isotopic purity of the lithium used is necessary because the other isotope,
6
Li, present in the natural composition of the lithium has a very strong reaction with the neutrons, which produces tritium as reaction product. The excessive enrichment of tritium in the cooling water is undesired. The
7
Li is added in the form of lithium hydroxide solution (LiOH) and is present as a monovalent cation
7
Li
+
as a consequence of the dissociation of LiOH. It is expensive to produce isotopically pure
7
Li. Isotopically pure
7
Li is, therefore, very valuable and it is desirable to handle it economically.
The continuous reformation of
7
Li as a consequence of the nuclear reaction of the
10
B, and the only slight losses due to cooling water leaks cause an increase in the
7
Li concentration in the cooling water in the course of a fuel cycle of a light water reactor. This relates, in particular, to cooling water in the primary loop of a light water reactor, in particular, cooling water in the primary loop of a pressurized water reactor. The
7
Li concentration in the cooling water increases, in particular, at the start, that is to say, in an early time domain of a fuel cycle. Because, upon overshooting a concentration of approximately 2 ppm, lithium can cause corrosion on reactor components, it is necessary to withdraw a sufficient quantity of
7
Li
+
again from the cooling water. The result is chiefly to reduce corrosion of fuel rod cladding tubes that enclose the nuclear fuel in the fuel rod.
Because, however, the density of fissile material in the fuel also reduces in the course of a fuel cycle, it is also necessary to reduce the concentration of neutron-absorbing boron in the cooling water in the course of a fuel cycle. The reduction is usually achieved by extracting the boron-containing cooling water from the cooling-water loop and the feeding in of an equally large quantity of boron-free water. In such a process, lithium is also removed from the loop with the boron-containing cooling water, and is not supplemented by the feeding in of the normally completely demineralized water. As a result, therefore, the reduction in boron concentration also lowers the lithium concentration. At the end of a fuel cycle, the cooling-water exchange masses are substantially enlarged, in order to achieve an adequate lowering of the boron concentration. Normally, LiOH solution is then fed into the cooling-water loop to maintain a required lithium concentration, in particular, into the primary loop of a pressurized water reactor.
It is, therefore, necessary, depending on the operating cycle of a light water reactor, to dose the content of lithium in the cooling water of the light water reactor. The dosing feeds lithium to the cooling water, in particular, chiefly at early times in the fuel cycle, and withdraws it from the cooling water, in particular, at later times in a fuel cycle.
Because radioactive materials are continuously produced by the nuclear fission in the reactor and by the activation of material as a consequence of the neutron emission, it is unavoidable that the materials pass partly into the cooling water and contaminate the cooling water. These materials can be present in the cooling water in a different chemical form and be partially undissolved and partially dissolved as anions or cations. This relates, in particular, to emitting nuclides, chiefly cesium and cobalt, which are present as cations. Because the separation of lithium from the cooling water is normally performed by employing the positive electric charge of the lithium cation, a portion of the cationic, radioactive impurities is also separated from the cooling water together with the lithium. The valuable, isotopically pure, separated lithium is, thereby, contaminated and can, therefore, not be reused, as a rule.
For example, to lower the lithium concentration, the cooling water is normally led through ion exchangers that include cation exchanger resins. These cation exchanger resins bind the lithium ions contained in the water flowing through virtually completely to the resin and simultaneously output an equivalent quantity of hydrogen ions to the water. However, they also bind the cationic impurities, and, therefore, concentrate emitting nuclides. If they are saturated and finally ineffective for the lithium withdrawal, they are replaced by new resins. A regeneration of the exchanger resins, in the case of which the very expensive
7
Li could be recovered and, if required, fed into the cooling-water loop again, has already foundered on the fact that, in such a case, the concentrated impurities are also released together with the
7
Li. The depleted exchanger resins are, therefore, to be disposed of as highly emissive special waste.
The invention proceeds from the fact that the ion concentrations in two solutions can be set if an electrodialysis is performed between the loops of the two solutions. In this case, electrodialysis means ion transport through a membrane configuration having at least one membrane separating the loops, it being possible to control the direction and throughput of the ion transport by applying an electric voltage. Examples of such electrodialysis methods are described, for example, in German patent applications 19747077.7 and 19747076.9. However, the method described in German patent application 19747077.7, in particular, has the disadvantage that there is a lowering of the boron concentration at the same time as a lowering of the lithium concentration.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and device for reducing cationic impurities and for dosing lithium in the cooling water of a light water reactor, and a cooling-water system of a light water reactor having such a device that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that improves methods and devices that operate using such electrodialysis.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for reducing cationic impurities in a cooling water including the steps of providing a light water reactor having a cooling-water loop containing a cationic solution, a concentrate loop containing a medium in which a heightened cation concentration is produced, and a selective ion exchanger dis
Bolz Michael
Enkler Günther
Meintker Manfred
Rühle Wilfried
Framatome ANP GmbH
Greenberg Laurence A.
Mayback Gregory L.
Phasge Arun S,.
Stemer Werner H.
LandOfFree
Method and device for reducing cationic impurities and for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for reducing cationic impurities and for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for reducing cationic impurities and for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3175128