Patent Number: 047042451
Section: summary

BACKGROUND OF THE INVENTION This invention relates to a method and an apparatus for monitoring an ability to remove impurities of an ion adsorption apparatus using ion exchange substances, etc., and particularly to a method and an apparatus for monitoring a desalting unit suitable for continuous monitoring of an ability to remove radioactive ion species of a desalting unit in a reactor cleaning system of an atomic power plant. It has been mentioned as a cause for increasing the dose rate of radiation in commercial atomic power plants that a very small amount of various ion species such as Co ions, Ni ions, Fe ions, etc. discharged from the materials of construction in the primary cooling system are deposited on the surfaces of fuel rods, and are made racioactive through exposure to neutron irradiation, and the radioactive ion species such as .sup.60 Co ions, .sup..quadrature. Co ions, .sup.54 Mn ions, etc. are released from the fuel rods and deposited on the surfaces of pipings outside the reactor core, as disclosed, for example, in "Boshoku Gizitsu (Anticorrosion Technology)" Vol. 32, pages 276-285 (1983). Thus, it has been proposed to provide a desalting unit with ion exchange resin to remove such radioactive ion species from the core water (the desalting unit may be hereinafter referred to as "desalting unit in a reactor cleaning system"). The desalting unit in a reactor cleaning system has played an important role in prevention of an increase in the radiation dose rate in the atomic power plant. Heretofore, monitoring of an ability to remove the radioactive ion species of a desalting unit in a reactor cleaning system has been carried out by sampling core water at the inlet and the outlet of the desalting unit and measuring concentrations (on ppm level) of ion species playing an important role in the radiation dosage rate in the plant, for example, concentrations of .sup.60 Co ions, etc., thereby detecting deterioration of the removal ability, for example, the ability of the desalting unit through a decrease in the ratio of .sup.60 Co ion concentration between the inlet and the outlet of the desalting unit. However, the conventional method requires 40 to 80 l of sampling water for measuring concentrations of impurity ion species on a ppm level, but the actual sampling rate is about 0.1 l/minute, and thus the required sampling time is inevitably prolonged to, for example, about 10 hours and rapid measurement is hard to conduct. Furthermore, sampling of core water is usually carried out once in a week, but the actual analysis of the sampled core water is carried out about one week after the sampling, because it is necessary to decay the radioactivity of radioactive nuclear species having a shorter half life in the sampled core water thoroughly to lower the background level. That is, it takes maximum two weeks from the start of .sup.60 Co ion leakage from the desalting unit to the actual detection. Thus, the radioactive ion species playing an important role in the radiation dosage rate in an atomic power plant, such as .sup.60 Co ions, etc. are concentrated and accumulated in the core water, resulting in an increase in the radiation dosage rate. SUMMARY OF THE INVENTION An object of the present invention is to provide a method and an apparatus for monitoring a removal ability of an ion adsorption apparatus by continuously monitoring the removal ability and detecting deterioration of the removal ability in advance. The present invention is based on such findings that a break timing of target impurity ion species from the adsorption apparatus can be detected in advance by using an ion species having a weaker selective adsorbability (affinity) to the ion exchange resin as an indicator than that of a target impurity ion species to be removed in the adsorption apparatus and analysing break behaviors of the indicator ion species. The break of target impurity ion species to be removed, such as Co ions, Ni ions, etc., can be detected in advance by using a very small amount of Na ion species contained in the core water as an indicator when the present invention is used as a desalting unit in a reactor cleaning system in an atomic power plant, where the Na ion species is made radioactive in the reactor and is converted to .sup.24 Na, .gamma. ray-emitting nuclear species of relatively long half period (15 hours), and its energy is on a higher level than those of radioactive ion species of Co, Ni, etc. (for example, .sup.60 Co.sup.2+ and .sup.55 Co.sup.2+), so that a concentration of .sup.24 Na.sup.+ at the inlet and the outlet of the desalting unit can be continuously measured with a good resolving power by .gamma.-ray scanning at the outside of the piping. The present invention provides a method for monitoring a break of an ion adsorption apparatus by detecting a break timing of an ion adsorption apparatus using ion exchange resin, thereby determining a regeneration or exchanging timing for the resin, wherein an ion species having a weaker selective adsorbability to the ion exchange resin than that of a target ion species to be adsorbed is added, as a sampling ion species, to water to be treated, and a leakage of the sampling ion species is detected at the downstream side of the adsorption apparatus, thereby determining a break timing of the ion exchange resin.