Improving Reliability Through Digital Feedwater Level Control - MTA-EN-013
| 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 – Matt Gibson
Contact: NuclearPlantMod@epri.com |
| Previous Implementation | Please contact EPRI for implementation examples and contacts. |
| Implementation Enablers | N/A |
| SWEEP Score |
|
| Applicability | All reactor types
All geographic regions |
| Keywords | Digital upgrade; instrumentation & control; feedwater; reliability; modernization |
| Business Case Analysis Cross-Reference | N/A |
Description
Implementing a digital feedwater level control system and upgrading the sensor and actuator suite improves plant stability and incorporates added benefits of having sensors, actuators, and controllers providing data for storage in a data historian and for use by online monitoring.
Digital feedwater level control improves the performance of an existing plant through more precise control of water level in the reactor or steam generator using a flexible control system that can control water level through all ranges of reactor power and plant conditions. An effective feedwater level control system minimizes the impact of shrink and swell transients during steam demand transients, startup, and shutdown. Digital control systems have demonstrated their ability to effectively fulfill the need for precise control and provide rapid response to transients. By reducing the severity of shrink and swell events and maintaining water levels within acceptable limits, the potential for safety system actuations is decreased.
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. Any existing single or dual level transmitters can be augmented to triple redundancy, allowing the control system to choose the best readings automatically and discard one of the three readings on a sensor failure. The control logic could automatically select an appropriate value from the three readings (e.g., average, median) for control. The existing valve positioning can be updated with digital positioning. 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 each year, requiring plant resources that could best be used on other functions. Though the complete replacement of a legacy feedwater 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 a digital feedwater heater level control upgrade can be implemented concurrently with this digital modernization effort for an implementation efficiency benefit. See MTA‑EN‑014 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 through automation of the feedwater control system, enhancements in the control logic, and self‑diagnostics in the valve control.
- Reduced time and cost for routine testing and maintenance.
- Reduced time and cost for system repairs with higher reliability equipment.
- Reduction or elimination of operator actions to control feedwater levels.
- Reduction in the potential for reactor trips from feedwater system failures.
- Potential for improved plant thermal efficiency through more precise control of feedwater systems.
Costs and Schedule
Cost
Level 1 – Greater than $5 million. This cost for upgrading to a digital feedwater 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 limited installation activities possible without the plant being in outage.
Scope Context
One unit. The scope encompasses the feedwater level control system, water level instrumentation, and valve positioners. The scope does not include control of steam‑driven feed pumps, which could be included in the control system.
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 equipment inside containment, performing the 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.