Reduce Fuel Cost by Utilizing an Optimum Time-Cost-of-Money Coastdown Strategy - MTA-NF-001

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Administrative Items
Date	12/15/2020
Functional Area Where Benefits Will Be Realized	Nuclear Fuel Operations
Reference Implementation Guidance	2015 NEI TIP Awards – Submittal 47 (ID: 8214030)
Industry SME	EPRI Fuel Reliability Program Contact: NuclearPlantMod@epri.com
Previous Implementation	Please contact EPRI for implementation examples and contacts.
Implementation Enablers	N/A
Applicability	LWRs All geographic regions
Keywords	Fuel; cost; coastdown; burn-up
Business Case Analysis Cross-Reference	N/A

Description

A period of gradual power reduction (power coastdown) from full power at the end of a fuel operating cycle may be employed to increase fuel utilization, thereby reducing fuel costs. The optimal coastdown duration is determined by evaluating fuel costs and generation revenue. Utilities have developed a strategy to optimize the duration of the power coastdown for maximum net cost savings by balancing the incremental fuel cost associated with maintaining full power against the generation cost associated with lost generation during the coastdown. For example, a plant may save $3 million in fuel costs during a 24‑day coastdown, while forgoing $1 million in revenue due to decreased generation, leading to net savings of $2 million. During the optimized coastdown, the power level decreases because the fuel is not able to sustain full power levels.

Typical optimized coastdowns are 2 to 3 times shorter for PWRs than BWRs since the PWR coastdown rate is steeper than the BWR coastdown rate. As an example, BWRs using this approach have demonstrated an optimized coastdown length of 24‑30 days. However, the exact length of the optimized coastdown depends on a number of plant‑specific parameters, including:

• Reactor type (BWR or PWR)
• Fuel type
• Expectations for operating cycle (e.g., capacity factor, possible forced outages)
• Replacement cost of power (i.e., projected monthly around‑the‑clock prices during coastdown)
• Use of cycle‑extending strategies (e.g., final feedwater temperature reduction, increased core flow)

Utilities have developed Digital Technology Software Quality Assurance‑controlled spreadsheets that allow plants to quickly determine the impact of changing parameters (such as forward power prices). The spreadsheet has been used at multiple plants and is applicable to BWRs and PWRs.

Benefits

Benefits Estimate

Level 2 – Net savings per year depend on plant‑specific parameters such as replacement cost of power, fuel cost, and cycle length, but are expected to be approximately $1 million per year.

Benefits Description

• Reduced fuel cost due to lower reactivity requirements during the coastdown. The reduced power coefficient of reactivity at lower power levels reduces reactivity requirements and enables savings of approximately 5% fewer new assemblies for cycles using an optimized coastdown. Reduced fuel costs may also be achieved by increasing burn‑up.
• Reduced dose to workers during outages due to reduced load before the outage and reduced moisture carry‑over (BWRs).
• Improved spent fuel logistics (i.e., lower disposal costs, more efficient spent fuel pool usage) due to increased burn‑up and reduction in required number of new fuel assemblies during refueling.
• Increased nuclear safety due to lower number of fuel moves during refueling (assuming full core discharge is not necessary).
• Reduced burden on reactor engineers and nuclear fuels personnel in the weeks before an outage because no control rod maneuvers are necessary during coastdown.

Costs and Schedule

Cost

Level 3 – The implementation cost is minimal and is estimated to consist of three person‑months of effort to develop the methodology in a spreadsheet and to update guidance and procedures.

Schedule

One to three years – The changes to fuel procurement associated with optimized coastdowns typically have a lead‑time of approximately one year. Calculation of the optimized coastdown length is quick (on the order of seconds to minutes) once the spreadsheet is developed.

Scope Context

Per unit

Risks

The optimal coastdown length is determined when procuring fuel for the next operating cycle. The inputs required for the calculations are based on assumptions about future plant operation and market conditions (e.g., capacity factor, future power prices). When actual conditions differ from the assumptions, maximum net savings may not be achieved. For example:

• Lower burn‑up due to lower than expected capacity factors may lead to sub‑optimal fuel use.
• Unanticipated changes to power prices during the coastdown can adversely affect the financial benefits (i.e., increased opportunity cost and cost of replacement power).

SWEEP Score

Category	Level	Description
Cost	3	The cost to implement the strategy is less than $1 million.
Savings	2	Savings are expected to be approximately $1 million per year.
Payback	3	Payback is achieved during the first coastdown.
Licensing Readiness	3	No licensing changes are required as long as fuel burn‑up is maintained within established limits.
Technology Readiness	3	Optimized power coastdown is used at multiple plants.
Implementation Proficiency	3	No specialized digital knowledge is required to implement this strategy.