United States Nuclear Regulatory Commission - Protecting People and the Environment

Operating Experience Assessment — Effects of Grid Events on Nuclear Power Plant Performance (NUREG-1784)

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Publication Information

Manuscript Completed: December 2003
Date Published:
December 2003

Prepared by:
W.S. Raughley, G.F. Lanik

Division of Systems Analysis and Regulatory Effectiveness
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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Deregulation of the electrical industry has resulted in major changes to the structure of the industry over the past few years. Whereas before, electric utilities produced the electricity and operated the transmission and distribution system, that is no longer the case. In many states, the electric utilities have split into separate generating companies, and transmission and distribution companies. Most nuclear power plant (NPP) operators no longer have control of the transmission and distribution system operations. NPPs rely on outside entities to maintain adequate reactive and voltage support for NPP operation. An assessment was completed by the Office of Nuclear Regulatory Research (RES) to identify changes to grid performance relative to NPPs which could impact safety. The assessment also provides some numerical measures to characterize grid performance before and after deregulation — in particular, those related to loss of offsite power (LOOP).

The information gathered1 provides a baseline of grid performance to gauge the impact of deregulation and changes in grid operation. The period 1985—1996 was considered "before deregulation" and 1997—2001 "after deregulation." The assessment found that major changes related to LOOPs after deregulation compared to before include the following: (1) the frequency of LOOP events at NPPs has decreased; (2) the average duration of LOOP events has increased; (3) where before LOOPs occurred more or less randomly throughout the year, for 1997—2001, most LOOP events occurred during the summer; and (4) the probability of a LOOP as a consequence of a reactor trip has increased.

The assessment re-enforces the need for NPP licensees and NRC to understand the condition of the grid throughout the year to assure that the risk due to potential grid conditions remains acceptable.

1 This work was completed prior to the August 14, 2003, blackout that affected several states and Canada.

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