Reduce Steam Generator Deposit Fouling Using Polymeric Dispersant - MTA-CY-001

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Administrative Items
Date	12/15/2020
Functional Area Where Benefits Will Be Realized	Chemistry & Environmental Maintenance Engineering
Reference Implementation Guidance	Dispersants for Pressurized Water Reactor Secondary Side Fouling Control: Sourcebook for Online and Offline Applications (EPRI 1025317) Dispersants for Pressurized Water Reactor Secondary Side Fouling Control: 2014 Field Evaluations (EPRI 3002005416) Technology and Process Improvement Readiness and Proposed Measurement Method for Nuclear Plant Modernization (EPRI 3002015802)
Industry SME	EPRI Chemistry and Radiation Safety Contact: NuclearPlantMod@epri.com
Previous Implementation	Please contact EPRI for implementation examples and contacts.
Implementation Enablers	N/A
Applicability	All PWRs All geographic regions
Keywords	Steam generator cleaning; equipment reliability; maintenance; deposit fouling; PWR; process chemistry; polymeric dispersants; thermal performance
Business Case Analysis Cross-Reference	Economic Evaluation of Long-Term Secondary-Side Online Dispersant Use at a Generic Plant with Thermally Treated Steam Generator Tubes. (EPRI 3002003366).

Description

Corrosion products on the secondary side of pressurized water reactor (PWR) steam generators (SGs) can deposit on the SG tubes or other SG internal surfaces. This deposit fouling causes heat -transfer losses, SG tube and internals corrosion, level instabilities, changes to internal flow fields, and reductions in generation. To address deposit fouling, utilities routinely perform mechanical and/or chemical cleaning on the SG. These efforts occur during outages and are often effective, but can be costly and carry risks of extended outages or incomplete cleaning.

Polymeric dispersant technology, specifically polyacrylic acid (PAA), reduces the rate of corrosion product deposition in SGs, supporting deferral of chemical cleaning and sludge lancing. The primary purpose of PAA is to maintain iron particles in suspended form rather than allowing them to deposit on SG surfaces. However, PAA has also been shown to promote removal of iron-based deposits from secondary plant components. PAA can be added to PWR secondary systems during full-power operation (online) and/or while the plant is offline (e.g., during wet layup or long-path recirculation cleanup evolutions). Online use has demonstrated substantial increases in the efficiency of SG blowdown iron removal, while offline use has demonstrated a reduction in the mass of iron- based deposits entering the SGs early in an operating cycle. A reduction of iron deposits from either online or offline use in turn leads to improved heat transfer efficiency in the SG and an increased reliability of the SG. This Modernization Technology Assessment (MTA) focuses on both online and offline applications of PAA to clean deposit fouling within PWR SGs and other secondary systems.

Benefits

Benefits Estimate

Level 2 – Savings are expected to be greater than $1 million but less than $5 million per year. Potential savings are related to eliminated or deferred chemical cleanings and sludge lancing. In addition, lesser fouling of heat transfer surfaces will improve power generation capability. Extent of savings are related to the condition of the SG before implementation of polymeric dispersant and are therefore plant-specific.

Benefits Description

• Improved SG heat-transfer efficiency due to decreases in fouling – Extent of benefits are unit-specific.
• Dispersant use may permit deferral (or potentially even avoidance) of other deposit removal activities (e.g., chemical cleaning).
• Reduced dose from potential deferral or avoidance of other deposit removal activities.
• Increased reliability in SGs through reduced risk of corrosion-related failures and structural failures associated with deposit fouling.

Costs and Schedule

Cost

Level 3 – Implementation costs should be less than $1 million, and are associated with sourcing the dispersant and any plant modifications needed for its injection into the secondary system.

Schedule

One to three years, which includes planning and implementation. If no modifications are needed to support injection of PAA, then procedure changes and other documentation could be completed within a year. If a modification is necessary, implementation may take longer.

Scope Context

Per unit

Risks

For online use, PAA secondary chemistry compatibility should be confirmed on a plant -specific basis. The EPRI Sourcebook (EPRI 1025317) contains information on compatibility testing, including a generic materials compatibility review and a section on steam generator vendor technical concurrence with online dispersant long-term use. Intended use is for relatively dilute solutions (in the range of 1-5 ppb PAA in the feedwater, and a limit of no more than 1 ppm in the SG blowdown with a recommended administrative limit of 100 ppb). Typical practice is to impose an administrative SG blowdown limit below 1 ppm and implement PAA monitoring to ensure the limit is not exceeded.

Some laboratory testing and some operating experience suggests that PAA may have an adverse effect on flow-accelerated corrosion (FAC). Research is currently being performed by EPRI to better understand this phenomenon.

SWEEP Score

Category	Level	Description
Cost	3	Implementation costs should be less than $1 million.
Savings	2	Savings are greater than $1 million per year but less than $5 million per year.
Payback	1	While investment costs are relatively small, payback is predicted to be realized after five years. This is because savings occur with eliminated chemical cleanings and reduced sludge lancings that occur on outage cycles.
Licensing Readiness	3	The safety (10 CFR 50.59) evaluations from pilot studies indicated that no changes were needed to the license of the site to implement the dispersant technology.
Technology Readiness	3	The technology has already been implemented at nuclear sites.
Implementation Proficiency	3	The implementation of polymeric dispersants does not require knowledge in implementing digital technologies.