MTA-EN-014

Administrative Items
Date	12/14/2021
Functional Area Where Benefits Will Be Realized	Engineering Operations Maintenance
Reference Implementation Guidance	Digital Engineering Guide: Decision Making Using Systems Engineering (EPRI 3002011816)
Industry SME	EPRI – Kurt Crytzer Contact: NuclearPlantMod@epri.com
Previous Implementation	Please contact EPRI for implementation examples and contacts.
Implementation Enablers	N/A
SWEEP Score	Cost – Level 1 – Implementation cost is greater than $5 million. Savings – Level 2 – Savings are greater than $1 million per year but less than $5 million per year. Payback – Level 2 – Payback period depends on implementation time and credited benefits, but is expected to be between 1 year and 5 years. Technical Readiness – Level 3 – The technology is ready for wide operational deployment. Licensing Readiness – Level 3 – No change in regulations is required, but implementation may require a LAR for each upgrading unit. Implementation Proficiency – Level 2 – Implementation of this technology benefits from experience with digital control systems.
Applicability	All reactor types All geographic regions
Keywords	Digital upgrade; instrumentation & control; feedwater heater; reliability; modernization
Business Case Analysis Cross-Reference	N/A

Description

Implementing a digital feedwater heater level control system with an upgraded level sensor and valve positioner suite improves plant stability and incorporates added benefits of having sensors, actuators, and controllers compatible with online monitoring and having some level of self‑diagnostics. Single points of vulnerability can also be resolved by replacing hard‑wired level switches with software in the control system. Any heater drain tank level controls can be added to this system, gaining similar benefits.

Digital feedwater heater level controls help extend the life of the feedwater heaters through more precise control of water level in each feedwater heater, which compensates for the effects of shrink and swell transients during plant operation through all ranges of reactor power and plant conditions. This improvement extends service life and allows postponing replacement costs for new feedwater heaters. In addition, the incoming feedwater temperature is more consistent and will also serve to provide a more stable neutron flux through the core during transients.

Data from the digital control system should be maintained in a data historian, for long‑term trending and use in online monitoring and efficiency calculations. The pair of existing controllers, each with a single level transmitter and controlling a single valve, can be augmented to triple‑redundant measurements, allowing the control system to choose the best readings automatically and discard one of the three readings on sensing failures. The single level‑indicating controllers are replaced with individual controllers, each controlling a digital valve positioner with precision using the existing pneumatically actuated valve. Modern digital transmitters and valve positioners support self‑diagnostics, which can be used to support condition‑based maintenance practices, reducing the number and frequency of periodicity‑based maintenance requirements.

Combined with the rising costs and decreasing supply of replacement components, maintaining legacy analog I&C systems is growing more expensive year by year. Most of the existing feedwater heater level controls are pneumatic, which is more expensive to maintain. Though the complete replacement of a legacy feedwater heater level control system requires a substantial up‑front investment in planning and cost, the upgrade is projected to provide a sizeable return on investment over the life of the replacement system.

A similar modernization improvement for digital feedwater level control upgrade can be performed concurrently with this digital modernization effort for an implementation efficiency benefit. See MTA‑EN‑013 for more details.

Benefits

Benefits Estimate

Level 2 – Annualized benefits are expected to be greater than $1 million and less than $5 million per year.

Benefits Description

• Increased day‑to‑day reliability of the feedwater heater level control system through automation, enhancements in the control logic, and self‑diagnostics in the valve controls.
• Elimination of single points of vulnerability.
• Reduced time and cost for routine testing and maintenance.
• Reduction in the potential for reactivity control events and reactor trips from feedwater heater level control system failures.
• Reduced time and cost for system repairs with higher reliability equipment that is more readily available than analog control system components that are now obsolete.
• Extending life of heaters by maintaining water level constant and at required depth.
• More stable neutron flux through reactor core during transients.

Costs and Schedule

Cost

Level 1 – Greater than $5 million. This cost for upgrading to a digital feedwater heater level control system is for a single unit. This effort can be scaled for multi‑unit plants.

Schedule

More than three years. Detailed planning to include measurements and surveys are required prior to beginning the upgrade (1‑2 outages). Installation could take multiple outages to complete, although installation can be completed in a single outage with pre‑positioning of equipment and maximizing installation activities possible with the plant online.

Scope Context

One unit. The scope encompasses feedwater heater and drain tank level control components.

Risks

With substantial up‑front cost, one of the greatest risks is a reliable return on investment. A positive ROI for digital I&C upgrades is realized over the course of years and relies on the continued operation of the plant.

If the upgrade effort involves replacing transmitters inside containment, performing due diligence during the planning phase of verifying dimensions, fit‑up, accessibility, etc., will reduce the risk for outage delays resulting from the installation.

Modern digital systems will require the appropriate cybersecurity measures to be implemented and require IT and I&C resources to maintain and operate.