US4705573A
Expired / Lapsed
US
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Descaling process
Assignee: Electric Power Research Institute
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Filing: 1985-08-06
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Granted: 1987-11-10
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Expires: 2005-08-06
Abstract
Abstract A process for the removal of deposits consisting essentially of the oxides of one or more transition metals from a surface, which process comprises contacting the said surface at a pH in the range of from 2.0 to 7.0 with a reagent comprising a one-electron reducing agent which is the complex formed between a low oxidation state transition metal ion and a complexing agent, for destabilizing the metal oxides deposited, thereby increasing their rate of dissolution, the complexing agent being thermally stable at the operating pH and present in order to form the necessary complex reagent and also to increase the thermodynamic solubility of the metal ions released.
Inventors
- 👤 Christopher J. Wood
- 👤 David Bradbury
- 👤 Timothy Swan
- 👤 Michael G. Segal
- 👤 Robin M. Sellers
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 13:03
CPC Classifications
C; C23; C23G; C23G1/00; C23G1/24; C02; C02F; C02F5/00; C02F5/08; C02F5/10; G; G21; G21F; G21F9/00; G21F9/001; G21F9/002; G21F9/004
Claims Analysis
Total Claims: 18
Claim 1
Independent Claim
108 words
A process for the removal of deposits consisting essentially of the oxides of one or more transition metals from a surface, which process comprises contacting the said surface at a pH in the range of from 2.0 to 7.0 with a reagent comprising a one-electron reducing agent which is the complex formed between a low oxidation state transition metal ion and a complexing agent, for destabilizing the metal oxides deposited, thereby increasing their rate of dissolution, the complexing agent being thermally stable at the operating pH and present in order to form the necessary complex reagent and also to increase the thermodynamic solubility of the metal ions released.
Claim 2
Dependent Claim
108 words
A process for the removal of deposits consisting essentially of the oxides of one or more transition metals from a surface, which process comprises contacting the said surface at a pH in the range of from 2.0 to 7.0 with a reagent comprising a one-electron reducing agent which is the complex formed between a low oxidation state transition metal ion and a complexing agent, for destabilizing the metal oxides deposited, thereby increasing their rate of dissolution, the complexing agent being thermally stable at the operating pH and present in order to form the necessary complex reagent and also to increase the thermodynamic solubility of the metal ions released.
Claim 3
Dependent Claim
151 words
A process for decontaminating the cooling system or a component associated with the cooling system of a water-cooled nuclear reactor, or contaminated plant items of certain deposited contaminants, which process comprises circulating a decontaminating reagent at a pH in the range of from 2.0 to 7.0 through the cooling system of the reactor, or contacting a component associated with the cooling system or containing other contaminated plant items with a decontaminating reagent at a pH in the range of from 2.0 to 7.0, the decontaminating reagent comprising a one-electron reducing agent which is a complex formed between a low oxidation state transition metal ion and a complexing agent for destabilizing said certain contaminants deposited, thereby increasing their rate of dissolution, the complexing agent being thermally stable at the operating pH and present in order to form the necessary complex reagent and also to increase the thermodynamic solubility of the contaminants released.
Claim 4
Dependent Claim
151 words
A process for decontaminating the cooling system or a component associated with the cooling system of a water-cooled nuclear reactor, or contaminated plant items of certain deposited contaminants, which process comprises circulating a decontaminating reagent at a pH in the range of from 2.0 to 7.0 through the cooling system of the reactor, or contacting a component associated with the cooling system or containing other contaminated plant items with a decontaminating reagent at a pH in the range of from 2.0 to 7.0, the decontaminating reagent comprising a one-electron reducing agent which is a complex formed between a low oxidation state transition metal ion and a complexing agent for destabilizing said certain contaminants deposited, thereby increasing their rate of dissolution, the complexing agent being thermally stable at the operating pH and present in order to form the necessary complex reagent and also to increase the thermodynamic solubility of the contaminants released.
Claim 5
Dependent Claim
23 words
A process as claimed in claim 1 or claim 2 wherein the reducing agent is based on Cr II or V II .
Claim 6
Dependent Claim
33 words
A process as claimed in claim 1 or claim 2 wherein the reducing agent is one based on Cr II and wherein the complexing agent when used with Cr II promotes spin pairing.
Claim 7
Dependent Claim
29 words
A process as claimed in claim 1 or claim 2 wherein the complexing agent is ethylene diamine tetra-acetic acid, citric acid, picolinic acid, 2,2'-bipyridyl, nitrilotriacetic acid or 2,6-dicarboxy pyridine.
Claim 8
Dependent Claim
35 words
A process as claimed in claim 1 or claim 2 which comprises a one-electron reducing agent based on the triscomplex formed between V II and a sufficient amount of picolinic acid as the complexing agent.
Claim 9
Dependent Claim
34 words
A process as claimed in claim 1 or claim 2 which comprises a one-electron reducing agent based on the tris-complex formed between Cr II and a sufficient amount of bipyridyl as the complexing agent.
Claim 10
Dependent Claim
29 words
A process as claimed in claim 1 or claim 2 wherein the decontaminating reagent is used as a temperature in the range of from ambient temperature to 200° C.
Claim 11
Dependent Claim
25 words
A process as claimed in claim 6 wherein the decontaminating reagent is used at a temperature in the range of from 60° to 95° C.
Claim 12
Dependent Claim
39 words
A process as claimed in claim 1 or claim 2 wherein the concentration of the one-electron reducing agent based on V II or Cr II in the decontaminating reagent is in the range of from 10 -3 to 2M.
Claim 13
Dependent Claim
36 words
A process as claimed in claim 10 wherein the concentration of the one-electron reducing agent based on V II or Cr II in the decontaminating reagent is in the range 10 -3 to 10 -2 M.
Claim 14
Dependent Claim
25 words
A process as claimed in claim 1 or claim 2 which is carried out at a pH in the range of from 3.5 to 6.
Claim 15
Dependent Claim
34 words
A process as claimed in claim 1 or claim 2 wherein the molar concentration of the complexing agent is from 3 to 10 times the molar concentration of V II or Cr II .
Claim 16
Dependent Claim
39 words
A process as claimed in claim 1 or claim 2 wherein formate or acetate is present as a counterion at a molar concentration of from 5 to 20 times the molar concentration of V II or Cr II .
Claim 17
Dependent Claim
42 words
A process as claimed in claim 14 wherein formate is present as the counterion, in which process the low oxidation state V II of vanadium or the low oxidation state Cr II of chromium is regenerated by radiation during the decontamination process.
Claim 18
Dependent Claim
47 words
A process as claimed in claim 1 or claim 2 wherein after treatment of the cooling system, or a component associated with the cooling system or other contaminated plant items, the decontaminating reagent is subjected to treatment with an ion exchange resin to remove the radioactivity therefrom.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1990-11-09 | 1991-05-11 | 1991-11-10 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1994-11-09 | 1995-05-11 | 1995-11-10 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1998-11-09 | 1999-05-11 | 1999-11-10 | $7700.00 | Window Closed / Lapsed |