Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For properties of solid material
Reexamination Certificate
2000-12-18
2002-08-27
Warden, Sr., Robert J. (Department: 1744)
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For properties of solid material
C205S775000, C204S400000, C204S434000, C376S249000, C376S306000
Reexamination Certificate
active
06440297
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to the determination of noble metal concentrations in either a volume of water containing such noble metals or in components exposed to such water. More particularly, the present invention relates to a system and method for determining noble metal concentrations in either a volume of water or in components exposed to such water. Even more particularly, the invention relates to a system and method for determining the concentration of noble metals present in either nuclear reactor water during noble metal chemical addition to the water or in the surface of structural materials that have been exposed to the reactor water containing the noble metals.
Under the water chemistry conditions normally encountered during the operation of boiling water nuclear reactors (BWRs), strong oxidizing species, such as oxygen and hydrogen peroxide, are generated. The presence of such oxidizing species contribute to the intergranular stress corrosion cracking (IGSCC) of sensitized 304 stainless steel within the reactor. Naturally, IGSCC is known to be a major environment-related material performance problem within BWRs. It has been demonstrated that, by sufficiently lowering the concentrations of ionic impurities and oxidizing species in the reactor water, IGSCC can be mitigated. The electrochemical corrosion potential (ECP) of stainless steels and other active metals is known to be controlled mainly by the dissolved oxygen, hydrogen, and hydrogen peroxide concentrations in the BWR coolants and the hydrodynamic flow conditions within the coolant path. In order to evaluate or predict materials performance (including SCC as a function of time), it is extremely important to know the ECP value of the structural materials that are exposed to high temperature water within the reactor pressure vessel.
In hydrogen water chemistry (HWC), hydrogen is added to the feed water of a BWR to mitigate IGSCC. The primary purpose of the hydrogen addition is to reduce the concentrations of dissolved oxidants and thus lower the ECP to a value that is less than a critical value of −230 mV, measured against a standard hydrogen electrode (SHE), at which IGSCC susceptibility is markedly reduced. Hydrogen (H
2
) levels in the feed water are always in the excess of the stoichiometric amount needed to react with either O
2
or H
2
O
2
to form H
2
O. However, several side effects of the HWC application, such as increased N
16
carry-over to the turbine and higher Co
60
deposition rates, have been reported. Also, the critical ECP value that is needed to prevent IGSCC is difficult to achieve in highly oxidizing and/or high water flow regimes.
Subsequent to the development of HWC, noble metal technology (NMT) was developed. By improving the catalytic properties of metal surfaces for the recombination of either hydrogen/oxygen or hydrogen peroxide/hydrogen to form water, NMT allows low ECP values to be achieved at much lower H
2
addition rates. This catalysis reduces the oxygen concentration at the metal surface to zero, thus causing the ECP to drop to its thermodynamic minimum (about≈−550 mV
SHE
in pure water at 288° C.). To achieve a stoichiometric excess of hydrogen, a H:O molar ratio of greater than 2:1, or a H:O weight ratio of greater than 1:8, is needed. This condition has been demonstrated to occur not only for pure noble metals and coatings, but also for very dilute noble metal alloys (NMA) or thermal spray coatings with powders of NMA. Recently, a technique for in-situ noble metal chemical addition (NMCA) on the oxide surfaces of various structural materials in high temperature water has been developed and applied to commercial BWRs in the United States, Europe, and Japan. Using NMCA, chemicals containing noble metals are injected directly into the reactor water and then are deposited onto the surfaces of reactor components that are exposed to the feed water. The surfaces of the reactor components are typically covered with an oxide outer layer. The noble metals are deposited onto the oxide layer, thus providing a catalytic site for both the H
2
/O
2
and H
2
/H
2
O
2
recombination reactions. The ECP value needed to ensure protection of components from IGSCC can then be achieved through the addition of smaller amounts of hydrogen, thus avoiding many of the negative side effects that are frequently encountered at higher H
2
concentrations.
In order to control the loading levels of noble metals such as platinum (Pt) and rhodium (Rh), the NMCA application process that is currently used requires that the concentration of noble metals on both the surface of the reactor components and in the reactor water can be determined. In order to measure the noble metal concentration present on the surface of the reactor components both during and after the NMCA application, the oxide surfaces that have been treated with noble metals (such as Pt and Rh) are first immersed in aqua regia to dissolve the oxide layer containing the noble metals. A sample taken from the aqua regia solution is introduced into an inductively coupled plasma-mass spectrometer (ICP-MS) to determine the noble metal concentration. Because of the relatively long time required to dissolve the oxide layer containing the noble metals in aqua regia, about 3-4 hours are needed to obtain valuable information on the Pt and Rh concentrations by this analytical method. As the NMCA process normally takes about 48 hours to deposit the desired amount of noble metal on the surfaces of BWR components that are exposed to high temperature feed water, the ICP-MS method of analysis is unable to provide a timely determination of the noble metal concentration in either the feed water or the component surface.
In addition to the long period of time needed to dissolve the oxide layer containing the noble metals, the use of ICP-MS to determine the noble metal concentrations during the NMCA process has other disadvantages. One such disadvantage is the high cost of ICP-MS hardware. In addition to cost, an ICP mass spectrometer typically requires a dedicated lab environment, provides no in-situ analytical capability, and requires the use of hazardous reagents such as aqua regia solutions. Furthermore, the sharing of ICP-MS resources by multiple users is precluded by scheduling concerns. All commercial BWRs are treated using the NMCA process during reactor shutdowns and most follow a common regular shutdown schedule. Thus, ICP-MS instruments are in high demand during the periods when such shutdowns take place.
The ICP-MS method of determining the noble metal concentration in BWR feed water and on component surfaces is slow, costly, and logistically awkward. Therefore, what is needed is a cost-effective system for determining the concentration of noble metals in the feed water of a BWR and BWR components that are exposed to the feed water. What is also needed is a timely, cost-effective method for analyzing the noble metal concentration in the feed water of a BWR. Finally, what is also needed is a timely, cost-effective method of determining the noble metal concentration in surfaces of BWR components exposed to feed water containing noble metals in solution.
BRIEF SUMMARY OF THE INVENTION
The present invention meets these and other needs by providing a new system and method for detecting and quantifying the amount of noble metals, such as platinum and rhodium, either dissolved in a volume of water or deposited onto a solid that has been exposed to the volume of water. More particularly, the present invention provides a system and method for determining the noble metal concentration in either the reactor water or the surface of reactor materials that have been exposed to reactor water containing noble metals. The system and method are capable of determining noble metal concentrations during periods of noble metal addition or during plant operation following such addition.
Accordingly, one aspect of the present invention is to provide a system for determining a noble metal concentration in a collection sample, the collection s
Andresen Peter Louis
Diaz Thomas Pompilio
Gui John Yupeng
Hettiarachchi Samson
Kim Young Jin
Johnson Noreen C.
Olsen Kaj K.
Santandrea Robert P.
Warden, Sr. Robert J.
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