Compositions – Radioactive compositions
Patent
1985-10-04
1987-11-03
Terapane, John F.
Compositions
Radioactive compositions
134 2, 134 3, 134 28, 134 29, 134 41, 210682, 210684, 210760, 252 80, 376306, 376310, G21F 900, C02F 508, C23G 102
Patent
active
047042354
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method by which radio active coatings on the walls of the primary heating system in nuclear reactors of the pressurized water type can be removed. More specifically, the invention relates to the decontamination of in acid insoluble or sparingly soluble corrosion products from these primary system surfaces. In this respect the invention is a development and simplification of the technique that includes a first step wherein the contaminated surfaces are contacted with an oxidation agent, for oxidation of the insoluble products to acid-soluble oxidation products, whereupon in a subsequent step the oxidized products are dissolved and removed by means of an acidic decontamination solution.
BACKGROUND ART OF THE INVENTION
Corrosion products stemming from the primary heating system, which to a major extent comprises the tubes and pipe-lines of the steam generators, are conveyed into the reactor core where they are deposited on the fuel elements.
After some time, the corrosion products, which are now radioactive after the neutron irradiation, are liberated from the fuel elements and are subsequently deposited on the parts of the primary system in contact with water which lie outside the reactor core. Then the radioactive corrosion products give rise to radiation fields outside the core and thereby to radiation doses to the operational personnel.
Another cause of the occurrence of radiation fields is fuel element leakage. In case of leakage in the encapsulating material of the fuel elements fission products are leached out by the circulating water. These products are then incorporated in the oxide layers on the parts of the system (primarily the steam generators) lying outside the reactor core.
The radiation doses received by personnel must be kept within prescribed limits. For reasons of health and operational economy, the doses should of course be kept as low as is reasonably possible.
Before undertaking major work on the primary system, it can thus be desirable to remove the radioactive corrosion and fission products which have been deposited on the primary system surfaces. By a partial or complete dissolution of the oxide layers, a substantial portion of the radioactive isotopes can be removed from the system surfaces. In nuclear reactor terminology this process is denoted decontamination. Most of the known processes within this technology have been described in detail in J. A. Ayres, Ed., Decontamination of Nuclear Reactors and Equipment, the Ronal Press Company, N.Y. (1970).
During the years from about 1961 and up to the first years of the seventies, only a very small number of decontaminations of reactor systems were carried out. The most discussed decontaminations during this period were those of the Shippingport PWR (PWR=Pressurized Water Reactor) in the USA and the PWR plant at Greifswald in the GDR. Modified versions of the APAC method developed during 1961 in the USA were used in these decontaminations.
There were two steps in this method, namely a first oxidizing step with alkaline permanganate followed by a second dissolving step with an acidic decontamination solution containing ammonium citrate.
Common to all modifications of the APAC process is that the contents of chemicals must be relatively high for acceptable decontamination factors to be achieved. The decontamination factor (Df) is defined in the following way: ##EQU1##
In occasional cases where the APAC process has been used, it has been necessary to repeat the decontamination a number of times to obtain a satisfactory result.
The radioactive solutions of chemicals from this process have either been purified by ion exchangers or been treated in special evaporators. The greatest disadvantage with the APAC process is the large volumes of waste occurring in the form of radioactive ion exchange masses or evaporator residues.
The above-mentioned disadvantages have resulted in that during 1970 work was started in several quarters on developing new processes. The aim then was to achieve processe
REFERENCES:
patent: 3803295 (1974-04-01), Cathers et al.
patent: 3873362 (1975-03-01), Mihram et al.
patent: 4162229 (1979-07-01), Loewenschuss
patent: 4172786 (1979-10-01), Humphrey et al.
patent: 4287002 (1981-09-01), Torok
patent: 4437999 (1984-03-01), Mayne
Locker Howard J.
Studsvik Energiteknik AB
Terapane John F.
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