Methods of reusing a cleaning solution
An aqueous cleaning solution that has been previously used to remove deposits from a nuclear steam generator (or other vessel) is reused after being transferred from the steam generator into an external vessel. The spent cleaning solution may be reconditioned and reused in a further cleaning of the same steam generator or a different steam generator. The different cleanings being accomplished by the cleaning solution may be of the same type or different types (e.g., iron oxide removal and/or copper removal).
1. A method of removing at least some deposits within one or more steam generators of one or more nuclear power plants, the method comprising:
disposing an aqueous cleaning solution in a first nuclear steam generator for a first treatment period to dislodge or dissolve first deposits from the first nuclear steam generator, the aqueous cleaning solution comprising a chelant or cleaning agent;
after said disposing of the aqueous cleaning solution in the first steam generator, transferring the aqueous cleaning solution and at least some of the dislodged or dissolved first deposits from the first nuclear steam generator to an external vessel;
transferring the aqueous cleaning solution from the external vessel into the first nuclear steam generator or a second nuclear steam generator and keeping the aqueous cleaning solution in the first or second nuclear steam generator for a second treatment period to dislodge or dissolve second deposits from the first or second nuclear steam generator; and
after said keeping of the aqueous cleaning solution in the first or second nuclear steam generator for the treatment period, removing the aqueous cleaning solution and at least some of the dislodged or dissolved second deposits from the first or second nuclear steam generator.
2. The method of claim 1 , further comprising, between (1) transferring the aqueous cleaning solution and at least some of the dislodged or dissolved first deposits from the first nuclear steam generator to the external vessel and (2) keeping the aqueous cleaning solution in said first or second nuclear steam generator for the second treatment period: introducing additional chelant or cleaning agent into the aqueous cleaning solution.
3. The method of claim 1 , wherein:
said dislodging or dissolving of the first deposits from the first nuclear steam generator comprises complexing the deposits with the chelant or cleaning agent; and
the method further comprises, between (1) transferring the aqueous cleaning solution and at least some of the dislodged or dissolved first deposits from the first nuclear steam generator to the external vessel and (2) keeping the aqueous cleaning solution in said first or second nuclear steam generator for the second treatment period: uncomplexing at least some of the complexed chelant or cleaning agent from the complexed deposits so as to regenerate a deposit-removal capacity of the chelant or cleaning agent by increasing a degree to which the chelant or cleaning agent is uncomplexed and therefore active.
4. The method of claim 1 , wherein transferring the aqueous cleaning solution from the external vessel into the first or second nuclear steam generator comprises transferring at least some of the dislodged or dissolved first deposits into the first or second nuclear steam generator.
5. The method of claim 1 , wherein:
disposing the aqueous cleaning solution in the first nuclear steam generator for the first treatment period comprises disposing the aqueous cleaning solution in the first nuclear steam generator in a reducing condition for the first treatment period to dislodge or dissolve iron oxide deposits;
the dislodged or dissolved first deposits comprise dislodged or dissolved iron oxide deposits;
keeping the aqueous cleaning solution in said first or second nuclear steam generator for the second treatment period comprises keeping the aqueous cleaning solution in said first or second nuclear steam generator in a reducing condition for the second treatment period to dislodge or dissolve iron oxide deposits; and
the dislodged or dissolved second deposits comprise dislodged or dissolved iron oxide deposits.
6. The method of claim 5 , further comprising, between (1) transferring the aqueous cleaning solution and at least some of the dislodged or dissolved first deposits from the first nuclear steam generator to the external vessel and (2) keeping the aqueous cleaning solution in said first or second nuclear steam generator for the second treatment period: deaerating the aqueous cleaning solution.
7. The method of claim 1 , wherein the first or second nuclear steam generator is the second nuclear steam generator such that transferring the aqueous cleaning solution from the external vessel into the first or second nuclear steam generator comprises transferring the aqueous cleaning solution into the second nuclear steam generator.
8. The method of claim 1 , wherein the first or second nuclear steam generator is the first nuclear steam generator such that:
transferring the aqueous cleaning solution from the external vessel into the first or second nuclear steam generator comprises transferring the aqueous cleaning solution back into the first nuclear steam generator; and
keeping the aqueous cleaning solution in said first or second nuclear steam generator for the second treatment period comprises keeping the aqueous cleaning solution in said first nuclear steam generator for the second treatment period.
9. The method of claim 8 , further comprising, between (1) transferring the aqueous cleaning solution from the first nuclear steam generator to an external vessel and (2) keeping the aqueous cleaning solution in said first nuclear steam generator for the second treatment period:
introducing additional chelant or cleaning agent into the aqueous cleaning solution.
10. The method of claim 8 , wherein:
disposing the aqueous cleaning solution in the first nuclear steam generator for the first treatment period comprises disposing the aqueous cleaning solution in the first nuclear steam generator in a reducing condition for the first treatment period to dislodge or dissolve iron oxide deposits;
the dislodged or dissolved first deposits comprise dislodged or dissolved iron oxide deposits;
the method further comprises, before said keeping the aqueous cleaning solution in said first nuclear steam generator for the second treatment period, converting the aqueous cleaning solution from a reducing condition to an oxidizing condition;
keeping the aqueous cleaning solution in said first nuclear steam generator for the second treatment period comprises keeping the aqueous cleaning solution in said first nuclear steam generator in an oxidizing condition for the second treatment period to dislodge or dissolve copper deposits; and
the dislodged or dissolved second deposits comprise dislodged or dissolved copper deposits.
11. The method of claim 10 , wherein the aqueous cleaning solution disposed in the first nuclear steam generator in the reducing condition for the first treatment period comprises a corrosion inhibitor.
12. The method of claim 10 , wherein:
the aqueous cleaning solution disposed in the first nuclear steam generator in a reducing condition for the first treatment period comprises a reducing agent, and
converting the aqueous cleaning solution from a reducing condition to an oxidizing condition comprises decreasing an amount of the reducing agent in the aqueous cleaning solution.
13. The method of claim 10 , wherein the converting of the aqueous cleaning solution from a reducing condition to an oxidizing condition occurs before the transferring of the aqueous cleaning solution back into the first nuclear steam generator.
14. The method of claim 8 , wherein:
disposing the aqueous cleaning solution in the first nuclear steam generator for the first treatment period comprises disposing the aqueous cleaning solution in the first nuclear steam generator in an oxidizing condition for the first treatment period to dislodge or dissolve copper deposits;
the dislodged or dissolved first deposits comprise dislodged or dissolved copper deposits;
the method further comprises, before said keeping of the aqueous cleaning solution in said first nuclear steam generator for the second treatment period, converting the aqueous cleaning solution from an oxidizing condition to a reducing condition;
keeping the aqueous cleaning solution in said first nuclear steam generator for the second treatment period comprises keeping the aqueous cleaning solution in said first nuclear steam generator in a reducing condition for the second treatment period to dislodge or dissolve iron oxide deposits; and
the dislodged or dissolved second deposits comprise dislodged or dissolved iron oxide deposits.
15. The method of claim 8 , further comprising:
before disposing an aqueous cleaning solution in the first nuclear steam generator for the first treatment period, taking the first nuclear steam generator out of service; and
between (1) transferring the aqueous cleaning solution from the first nuclear steam generator to an external vessel and (2) transferring the aqueous cleaning solution back into the first nuclear steam generator: returning the first nuclear steam generator to service, and thereafter taking the first nuclear steam generator out of service again before said transferring of the aqueous cleaning solution back into the first nuclear steam generator.