APPARATUS FOR MEASURING DISSOLVED HYDROGEN CONCENTRATION

Abstract: An apparatus for measuring dissolved hydrogen con­ centrations of sample water comprises a hydrogen electrode (4) having electrodes (10, 11, 12, 13, 17, 19) at its inside and a hydrogen-permeable membrane (3) on its surface and containing an electrolyte solution (18) as filled therein, provided with a bellows (20) communicating with the electrolyte solution (18), the back side of the bellows in contact with the sample water, and the entirety of the hydrogen electrode being soaked in the sample water. A dissolved hydrogen concentration in hot sample water can be directly measured without pressure reduction and cooling.

Description: APPARATUS FOR MEASURING DISSOLVED HYDROGEN CONCENTRATION BACKGROUND OF THE INVENTION This invention relates to an apparatus for measuring dissolved hydrogen concentrations in nuclear reactors such as light water reactors, heavy water reactors, etc. According to the art so far in the practical use, hydrogen is extracted into a gas phase from metallic sodium in the sodium loop of a fast breeder reactor through a hydrogen-permeable metallic membrane of Pd, Ni, etc. and a dissolved hydrogen concentration is detected by a heat conductivity detector, etc. Since the vapor pressure of metallic sodium is less than 0.1 MPa, there is no fear of breaking the membrane in the normal use. However, in measuring a dissolved hydrogen concentration of core water, the vapor pressure of water is so high (for example, 6.9 MPa at 285"C) that there is a fear of breaking the hydrogen-permeable metallic membrane. Thus, a dissolved hydrogen concentration cannot be measured without additional operations to sample water such as pressure reduction, cooling, etc. SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus for measuring a dissolved hydrogen concentration where a dissolved H2 concentration of hot sample water can be directly measured without additional operations to the sample water such as pressure reduction, cooling, etc. The object can be attained in the present invention by providing a hydrogen electrode having electrodes at its inside and a hydrogen-permeable membrane on its surface and containing an electrolyte solution as filled therein with a bellows communicating with the electrolyte solution, the back side of the bellows being in contact with sample water, and the entirety of the hydrogen electrode being soaked in the sample water. The other objects, characteristics and effects of the present invention will be apparent from the following description, referring to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a vertical cross-sectional schematic view of a basic structure according to the present invention. Fig. 2 is a diagram showing a relationship between the output current of an apparatus for measuring a dissolved hydrogen concentration according to the present invention and the dissolved hydrogen concentration of sample water. DESCRIPTION OF PREFERRED EMBODIMENTS To measure a dissolved H2 concentration of hot sample water, the present invention is based on the following structure. That is, in the present invention, a hydrogen electrode entirety with a hydrogen-permeable membrane, an electrolyte solution, electrodes, bellows, etc. is soaked in hot sample water. The bellows serves not only to absorb a thermal expansion of the electrolyte solution in the hydrogen electrode, but also to keep a pressure balance between the sample water in which the hydrogen electrode is dipped and the electrolyte solution in the hydrogen electrode, thereby preventing the hydrogen-permeable membrane, etc. of the hydrogen electrode from breakage. A reference electrode, an anode, a cathode, etc. are provided at parts in contact with the electrolyte solution in the hydrogen electrode, and the reference electrode is made from a material that will not undergo decomposition at a high temperature with a stable electric potential and a high reliability and will not require any presence of ions, substances, etc. having a lower oxidation potential than H2 in the electrolyte solution. The anode is kept at a constant potential with respect to the reference electrode. The dissolved hydrogen in hot sample water is extracted into the electrolyte solution in the hydrogen electrode through the hydrogen-permeable membrane, and is oxidized at the anode kept at a constant potential with respect to the reference electrode. A dissolved hydrogen concentration of sample water can be quantitatively determined from the resulting output current. One embodiment of an apparatus for measuring a dissolved hydrogen concentration according to the present invention will be described in detail below, referring to Fig. 1 and Fig. 2. In Fig. 1 a vertical cross-sectional, schematic view of an apparatus for measuring a dissolved H2 concentration of hot sample water under high pressure, which may be hereinafter referred to as "high temperature, high pressure type dissolved H2 meter", is shown. The high temperature, high pressure type dissolved hydrogen meter comprises a sensor body (hydrogen electorde) 4, a sensor-encasing container 2 and an outside electric circuit comprising a voltmeter A 5, a voltmeter B 14, a resistor A 7, a resistor B 16, a cell A 6, a cell B 15, an ammeter A 8, etc,, as connected to electrodes in the sensor body 4. The sensor body 4 has a hydrogen-permeable membrane 3 on its surface and an electrolyte solution 18 as filled therein. In the electrolyte solution 18, there are an anode 12, a protective electrode 13, a reference electrode A 9, a cathode A 10, a reference electrode B 11, and a cathode B 19. The sensor body 4 is also provided with a bellows 20 communicating with the electrolyte solution 18 to absort a thermal expansion of the electrolyte solution. Sample water is introduced into the sensor-encasing container 2 through a sample water inlet 1 and discharged through a sample water outlet 21. The sensor-encasing container 2 is filled with sample water, and the entirety of sensor body 4 is soaked in the sample water. Thus, a pressure balance is always kept between the sample water and the electrolyte solution, and there is no fear of breaking the sensor body 4 and the hydrogen-permeable membrane 3. H2 in the sample water introduced into the sensor-encasing container 2 through the sample water inlet 1 permeates a hydrogen-permeable membrane made from Pd and enters into the electrolyte solution 18 in the sensor body 4. An aqueous solution of H2S04 and CuSO4 is used as the electrolyte solution. The H2 in the electrolyte solution reaches the anode 12. The anode 12 is adjusted to a constant potential V1 which is lower than the oxidation potential of S04 and higher than the oxidation potential of H2, with respect to the reference electrode A 9 using Ag/Ag2S04 or Pb/PbSO4, by means of the cell A 6 while monitoring the voltmeter A 5 through the resistor A 7. The Ag/Ag2S04 or Pb/PbSO4 electrode will not undergo decomposition even above 2500C and has a high stability and a high reliability. At and by the anode 12, the hydrogen is oxidized into hydrogen ions according to the following reaction (1). At the cathode, the following reaction (2) proceeds at the same time. H2 + 2H + 2e (1) Cu2+ + 2e + Cu (2) 2- SO4 has a higher oxidation potential than H2, and thus has a potential region failing to undergo oxidation. That is, no disturbing current due to the oxidation reaction of S042 develops. An output current between the anode and the cathode is measured by the ammeter A 8, and a dissolved hydrogen concentration of sample water is quantitatively determined from this output current value. The current value depends upon the hydrogen permeating rate through the Pd membrane, and is proportional to the one-second (1/2) power of the dissolved hydrogen concentration of sample water. Thus, a proportional relationship is established between the output current value and the one-second power of the dissolved hydrogen concentration. In Fig. 2, relationship between the output current value and the dissolved hydrogen concentration is shown for measurements at the sample water temperature of 250"C with a 100 pm- thick Pd membrane. In Fig. 1, the sensor body 4 is further provided with a protective electrode 13 to remove other substances oxidizable at the anode than hydrogen, which may exist in the electrolyte solution 18 in the sensor body 4 or enter the electrolyte solution from the sample water. The protective electrode 13 is adjusted to the same potential V1 as at the anode, with respect to the reference electrode B 17 using an Ag/Ag2 SO4 or Pb/PbSO4 electrode, by means of a cell B 15 while monitoring a voltmeter B 14 through a resistor B 16. By the protective electrode 13, the substances oxidizable at potentials lower than the oxidation potential of H2 are oxidized in advance in the electrolyte solution to prevent any occurrence of disturbing current to the anode. At the cathode B 19 connected to the protective electrode 13 through the cell B 15, the said reaction (2) proceeds, corresponding to the oxidation reaction at the protective electrode 13, and an electric current flows between the protective electrode 13 and the cathode B 19. The protective electrode 13 and the anode 12 are made from a metal having a higher corrosion potential than the oxidation potential of H2, for example, gold, platinum, platinum black, etc. Anodes 10 and 19 are made from gold, platinum, or a metal equivalent to the metal to be deposited from the electrolyte solution, for-example, Ni in the present embodiment. In the present embodiment, PA having a distinguished radioactive resistance is used for the hydrogen-permeable membrane 3, but other hydrogen-permeable metals such as Ni, etc., and heat-resistant polymers such as tetrafluoroethylene resin, silicone rubber, polyimide, etc. can be used. In the present embodiment, a sulfuric acid-acidified CuS04 solution is used as the electrolyte solution, but in place of CuSO4, other sulfates such as FeSO4, NiS04, etc. can be used, or aqueous solutions of these sulfates containing no sulfuric acid can be also used. When the metal ion of a sulfate is represented by M and the sulfate by Mi (S042 )i the reaction occurring at the cathode A 10 and the cathode B 19 is given by the following equation (3): + + je + M ..... (3) The substance to be reduced at the cathodes is not limited to the metallic cations, but the coexisting anions, or substances inoxidizable at the anode, for example, 02 or (NH4+)2S042 dissolved in the electrolyte solution can be used. Any material can be used for the reference elecrode, so long as it will not undergo decomposition at a high temperature with a stable potential and a high reliability and will not require presence of substances or ions having a lower oxidation potential than that of H2 in the electrolyte solution. Any electrolyte solution can be used, so long as it contains ions, substances, etc. necessary for the reference electrode to be used at a high temperature, and contains no substances having a lower oxidation potential than that of H2. As examples of such "reference electrode-electrolyte solution system", an Ag/Ag3PO4 reference electrode using an aqueous solution of phosphoric acid and a phosphate as an electrolyte solution, an 02-Pt/H+, H20 reference electrode or 02-Pt/OH , H20 reference electrode using an aqueous solution of dissolved 2 as an electrolyte solution, etc. can be used. The present embodiment has been described as a dissolved H2 meter, which can be also applied to measurement of dissolved H (radical hydrogen) concentration. In the foregoing embodiment, a dissolved H2 concentration in hot sample water can be directly measured without cooling and pressure reduction of sample water. Since the dissolved hydrogen concentration of sample water can be directly measured without cooling and pressure reduction of hot sample water, there is no time lag in the order of minutes due to pressure-reducing and cooling operation. Thus, when the present invention is applied to a light water nuclear reactor, the conventional measuring procedure which has failed to conduct exact quantitative determination of a concentration due to decrease in hydrogen concentration owing to reactions proceeding in the order of seconds, such as recombination reaction of H2 with coexisting H202 in core water, can be greatly improved. Since a dissolved hydrogen concentration of core water can be exactly measured at a high temperature, the present invention is very effective for controlling a hydrogen dosage, water quality, etc.

Claims: WHAT IS CLAIMED IS: 1. An apparatus for measuring a dissolved hydrogen concentration, which comprises a hydrogen electrode (4) comprising an anode (12), a cathode (10), a reference electrode (9, 11, 17) and a hydrogen-permeable membrane (3) provided at parts in contact with an electrolyte solution (18) as filled in the hydrogen electrode (4), the hydrogen electrode (4) being soaked in sample water, the outer surface of the hydrogen-permeable membrane being in contact with the sample water, a bellows (20) communicating with the electrolyte solution (18) as filled in the hydrogen electrode (4) being provided at the hydrogen electrode (4), the back side of the bellows (20) being in contact with the sample water, and a means (8) for measuring an electric current generated by oxidation of hydrogen at the anode (12). 2. The apparatus according to claim 1, wherein the sample water is core water of a nuclear reactor. 3. The apparatus according to claim 1, wherein the hydrogen-permeable membrane (3) is made of Pd. 4. The apparatus according to claim 2, wherein the electrolyte solution (18) is an aqueous solution of H2504 and CuS04 or NiS04. 5. The apparatus according to claim 2, wherein the reference electrode (9, 11) is an Ag/Ag2S04 or Pb/PbSO4 electrode. 6. The apparatus according to claim 5, wherein the anode (12) is provided with a means (5, 6, 7) for adjusting the anode to a constant potential lower than the oxidation potential of S042 and higher than the oxidation potential of H2 with respect to the reference electrode (9). 7. The apparatus according to claim 2, wherein a protective electrode (13) is further provided at a part in contact with the electrolyte solution in the hydrogen electrode, and the protective electrode (13) is provided with a means (14, 15, 16) for adjusting the protective electrode (13) to the same potential as at the anode (12) with respect to the reference electrode (17, thereby oxidizing substances oxidizable at a potential below the oxidation potential of H2 in advance in the electrolyte solution (18). 8. The apparatus according to claim 7, wherein the anode (12) and the protective electrode (13) are made from a metal having a higher corrosion potential than the oxidation potential of H2.

Inventors: NAKAYAMA, NORIO, OZAWA, YOSHIHIRO, UCHIDA, SHUNSUKE
Applicants: HITACHI ENGINEERING CO., LTD., HITACHI, LTD.
Application year: 1983
Main classification: G01N27
IPC codes: G01N27, G21C17