A survey of load follow experience in US light water reactors

Load follow experience in U.S. LWRs is increasing and, while still not widespread, a number of units have accumulated significant experience. In this paper load follow experience in U.S. PWRs and BWRs is discussed, including both load follow demonstration tests and commercial load follow experience. Load follow demonstration tests have been performed at a number of units. The objectives and results of such tests are discussed, including: testing the ability of various computer codes to predict load follow behavior; testing the ability of the operating staff to perform load follow maneuvers within the vendor's power recovery guidelines; tests of remote dispatching systems; determining the margins to safety limits required for load follow flexibility. Commercial load follow operations have been performed not only because of grid load demands, but also for reasons such as the need to husband the reactor until a scheduled outage and to comply with environmental requirements on cooling water discharge temperatures. An unusual benefit of load follow occurred in one BWR which load followed during an end of cycle coastdown. In this case, an energy generation increase occurred because of a power overshoot on return to power. This overshoot was the result of xenon depletion during the period of low power operation. Load follow testing in the U.S. will be reviewed, and U.S. commercial daily load follow experience will be discussed for several PWRs and BWRs with the most extensive experience, including: number of load follow cycles; range of power changes; impact on fuel performance as indicated by primary coolant activity (PWRs) or off-gas activity (BWRs); impact on the performance of non-fuel core components; capacity factor losses due to restrictions on the rate of return to power. (author). 2 tabs