Patent Number: 048062782
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus proposed by the invention and capable of carrying out the method of segregating radioactive iodine isotopes (FIG. 1) comprises a sampling unit MV interconnected with a pipeline transporting a fluid medium containing among others radioactive iodine isotopes. Such pipeline can be the primary liquid coolant circuit of a pressurized water reactor serving as heat energy source of a water-water-type nuclear power plant. The sampling unit MV continuously takes samples of suitable pressure and temperature and passes them into a degassing vessel G having an inlet for introducing gas as nitrogen (N.sub.2). The nitrogen bubbles ensure agitation of the treated sample and permit to control the liquid level in the vessel. The degassing vessel G is connected through a piping to a transfer pump P1 and thereby to a cock CS receiving appropriate reagent from a container R by means of a pump P2. The fluid sample mixed with the reagent in the cock CS is transported to a bubble removing cell BC wherefrom the mixture is transferred to a segregation column K containing a filling made of amorphous zirconium phosphate. The segregation column K is connected--again through a piping--to a continuously operating flow-type energy-selective gamma radiation detecting system GD and a signal processing and recording unit JR. Instead of nitrogen it is possible to apply other appropriate inert gas. The degassing vessel G serves for expelling the gases dissolved in the sample (among them the radioactive isotopes of the noble gases). The pH-value of the samples taken is adjusted always to a neutral or alkaline level if necessary by means of the appropriate reagent placed in the container R. The samples treated in the required manner (having e.g. the required pH-value adjusted, being free of bubble and noble gases) are transported into the segregation column K with a speed ensuring full contact time generally from at least about 5 minutes to about 15 minutes. The active filling of the column containing high specific surface absorbent as zirconium phosphate is capable of binding the cations, fluoride anions and different colloid-state corrosion products from the sample. Before detecting the sample treated it flows about 20 minutes in order to premits the decay of the very short and short half-period radioactive isotopes remaining in the effluent in spite of the previous segregation steps and capable of disturbing the measurements related to iodine. The samples are introduced into the radiation detecting system GD for detecting gamma radiation of different energy levels. In the fluid carrier medium they contain in considerable percentage the radioactive iodine isotopes only. The detection system includes calibrated counters operated in gated mode and adjusted according to the different gamma-energy levels of the different radioactive iodine isotopes in order to determine their radiation level. With reference to FIG. 2 the following non-limiting example should be helpful in better understanding the essence of the invention. EXAMPLE A laboratory model was constructed for carrying out the method proposed by the invention. This model takes into account the specific conditions of the water-water-type nuclear power plant built-up in Paks (Hungary) operating with pressurized water nuclear reactors. The method should serve for measuring the radiation levels of the radioactive iodine isotopes in the primary coolant circuit of the Paks plant and it was realised in an arrangement shown in FIG. 2. The measurement was carried out as described here below. The sample is cooled after taking and the cooled sample is led into a 1000 cm.sup.3 glass bubbling vessel 2 at a flow rate of about 3 cm.sup.3 /min. At a flow rate of at least 10 dam.sup.3 /min, air is passed across a glass filter arranged at the bottom of the vessel 2. The surplus of the air/liquid mixture leaves the vessel at its top and enters a degassing unit, from where the part of the water sample is recycled into the primary circuit. From the noble-gas-free and bubble-free part of the solution collecting under the filter, the sample is pumped into a delay pipe section 3 by a peristaltic pump 4 at a flow rate of about 1 cm.sup.3 /min. By another peristaltic pump 5 connected to an Y-pipe 7, suitable reagents can be fed from a reagent storage tank 6 into the sample, e.g. for adjusting its pH-value. Before segregation, a portion of the sample can be picked up in a sampling vessel 9 through a two-way cock 8 for the purpose of reference measurements. By setting the two-way cock 8 into its other position, the sample is led into a column 10 of 6 mm inner diameter, with the spaces between quartz wad filter beds being previously filled up with 10 g of amorphous zirconium phosphate. The effluent is led through a hollow NaI(T1) scintillation detector 11 consisting of a teflon tube of 2 millimeter inner diameter and provided with a spirally arranged flow cell. From said detector the effluent gets through a shut-off cock 12 into a sampling vessel 13. The scintillation detector 11 obtains its supply voltage from an analyser 14. The energy selective signals of the scintillation detector 11 are led in a differential gated mode into counters or ratemeters 15, 16, 17 adjusted to the characteristic gamma lines of the iodine isotopes 131.sub.I, 132.sub.I and 135.sub.I, then the signals of the counters or the analogue signals of the ratemeters are plotted in the function of time by recorders 18, 19 and 20. The segregation of iodine isotopes by means of the method and apparatus proposed by the invention is in several aspects more advantageous than other methods known so far. After segregation--having determined its efficiency through checking measurements using semi-conductor detectors--the sample solution containing iodine is--within the sensitivity limits of the measurement--free of N, O, Na and K matrix components, i.e. of cationoc radioactive components in general, and its content of noble gases and fluoride ions belonging to the matrix components is low enough to leave the sensitivity of the measurement uneffected even in reactor shut-down periods associated with very low radioactive iodine concentrations. The method leads itself to continuous and parallel measurement of preferably at least three iodine isotopes, and by inserting a required number of signal processing units (and respective circuit elements), simultaneous measurement of all occurring iodine isotopes is feasible. Also, the apparatus for implementing the method can be arranged to contain two segregating columns connected parallel, filled up with charges of identical composition, permitting regeneration of exhausted charge without interrupting continuity of measurement and continuous supervision of operation. The metod is economical, it is characterized by low demand on time and work, it is based on exclusively inexpensive and simple pieces of equipment, resulting in low installation and operating costs.