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Fact Sheet on Power Uprates for Nuclear Plants

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Introduction

When the NRC issues a license for a commercial nuclear power plant, the agency sets limits on the maximum heat output, or power level, for the reactor core. This power level plays an important role in many of the analyses that demonstrate plant safety, so the NRC's permission is required before a plant can change its maximum power level. A "power uprate" only occurs after the NRC approves a commercial nuclear power plant's request to increase its power.

Background

Utilities have used power uprates since the 1970s as a way to generate more electricity from their nuclear plants. As of January 2008, the NRC has approved 116 uprates, resulting in a gain of approximately 15,600 MWt (megawatts thermal) or 5,200 MWe (megawatts electric) at existing plants. These uprates are listed in Table 1 at the end of this document. Collectively, these uprates have added generating capacity at existing plants that is equivalent to more than five new reactors.

Discussion

To increase the power output of a reactor, typically a utility will refuel a reactor with either slightly more enriched uranium fuel or a higher percentage of new fuel. This enables the reactor to produce more thermal energy and therefore more steam, driving a turbine generator to produce electricity. In order to accomplish this, components such as pipes, valves, pumps, heat exchangers, electrical transformers and generators must be able to accommodate the conditions that would exist at the higher power level. For example, a higher power level usually involves higher steam and water flow through the systems used in converting the thermal power into electric power. These systems must be capable of accommodating the higher flows.

In some instances, licensees will modify and/or replace components in order to accommodate a higher power level. Depending on the desired increase in power level and original equipment design, this can involve major modifications to the plant such as the replacement of main turbines. All of these factors must be analyzed by the licensee as part of their request to amend their license for the uprate. The analyses must demonstrate that the proposed new configuration remains safe and that measures continue to be in place to protect the health and safety of the public. The NRC's technical and legal staffs review these analyses, which span many technical disciplines and may be complex, before approving a request for a power uprate.

Types of Power Uprates

The design of every U.S. commercial reactor has excess capacity needed to potentially allow for an uprate, which can fall into one of three categories: 1) measurement uncertainty recapture power uprates, 2) stretch power uprates and 3) extended power uprates.

1) Measurement uncertainty recapture power uprates are power increases less than 2 percent of the licensed power level, and are achieved by implementing enhanced techniques for calculating reactor power. This involves the use of state‑of‑the‑art devices to more precisely measure feedwater flow which is used to calculate reactor power. More precise measurements reduce the degree of uncertainty in the power level which is used by analysts to predict the ability of the reactor to be safely shut down under possible accident conditions.

2) Stretch power uprates are typically between 2 percent and 7 percent, with the actual increase in power depending on a plant design's specific operating margin. Stretch power uprates usually involve changes to instrumentation settings but do not involve major plant modifications.

3) Extended power uprates are greater than stretch power uprates and have been approved for increases as high as 20 percent. Extended power uprates usually require significant modifications to major pieces of non-nuclear equipment such as high-pressure turbines, condensate pumps and motors, main generators, and/or transformers.

Review Process

Since uprates affect a reactor's licensed power level, utilities apply for NRC permission to amend their operating license in order to implement a power uprate. The process for requesting and approving a change to a plant's power level is governed by 10 CFR 50.90-92. These regulations are available on the agency's Web site at: http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/. The applications and reviews are complex and involve many areas of expertise in the NRC's Offices of Nuclear Reactor Regulation and General Counsel. Some reviews may also involve the Office of Nuclear Regulatory Research and the Advisory Committee on Reactor Safeguards (ACRS). In evaluating a power uprate request, NRC reviews data and accident analyses submitted by a licensee to confirm that the plant can operate safely at the higher power level. Reviews of power uprate requests are a high priority.

The NRC uses a review standard for extended power uprates (RS-001, December 2003), that has been endorsed by the ACRS. The standard provides a comprehensive process and technical guidance for reviews by the NRC staff, and provides useful information to licensees considering applying for an extended uprate.

After a licensee submits an uprate application, the NRC places a notice in the Federal Register to notify the public that the agency is considering the application. The public has 30 days to comment on the licensee's request and 60 days to request a hearing where the application could be contested. The NRC thoroughly reviews the application and any public comments, while the Atomic Safety and Licensing Board (ASLB) considers any requests for hearings. NRC technical staff complete their review while considering and addressing any public comments, issuing a safety evaluation and another Federal Register notice to inform the public. If the ASLB determines a hearing is required, a separate legal process takes place, and NRC staff provides technical information, if needed. The safety evaluation and any hearing rulings form the basis for the NRC's final decision on the uprate request, although the staff can authorize an uprate while a hearing is underway. The NRC issues a press release for any approved uprate, and an updated list of approved uprates is available on the NRC's Web site at:
http://www.nrc.gov/reactors/operating/licensing/power-uprates/approved-applications.html.

The NRC usually has several applications for power uprates under review at any given time. The latest list of applications under review is on the NRC's Web site at:
http://www.nrc.gov/reactors/operating/licensing/power-uprates/pending-applications.html.

Expected Uprate Applications

Licensee responses to a September 2007 NRC survey indicate they plan to submit 24 power uprate applications in the next five years, including 17 extended uprates and 7 measurement uncertainty recapture uprates. If these applications are approved, the resulting uprates would add another 5,254 MWt (1,751 MWe) to the nation's generating capacity. Anticipated future applications can be found in Table 3 at the end of this fact sheet, and updates will be on the NRC's Web site at:
http://www.nrc.gov/reactors/operating/licensing/power-uprates/expected-applications.html.

Public Involvement

The NRC welcomes public involvement in our activities as part of our strong, fair oversight of the nuclear industry. The public's opportunities to participate in the power uprate arena include:

• Pre-application meetings, where licensees discuss their uprate plans with NRC staff (some portions of these meetings may be closed to the public to discuss proprietary information);
• Comments related to an application and requests for a hearing on the application.
• Briefings to the ACRS on the results of the staff's review of the applications (some portions of these meetings may be closed to the public to discuss proprietary information). ACRS meeting schedules are available on the NRC's Web site at this address: http://www.nrc.gov/reading-rm/doc-collections/acrs/agenda/.
• For each extended power uprate, the NRC staff typically issues a draft environmental assessment for a 30-day public comment period. The NRC staff considers and addresses all comments before finalizing the draft environmental assessment.

(TYPE -- S = Stretch; E = Extended; MU = Measurement Uncertainty Recapture)

Table 2 - Power Uprates Under Review, February 2008

(TYPE -- S = Stretch; E = Extended; MU = Measurement Uncertainty Recapture)

Table 3 - Expected Future Submittals for Power Uprates, December 2007

Additional Information

Additional information and guidance for power uprate license amendment request submittals can be found on the NRC's Power Uprate Web page at this address: http://www.nrc.gov/reactors/operating/licensing/power-uprates.html.

February 2008