Document: NRC Regulatory Guide
Document ID: 0b3f08e9-b342-468d-a869-a00f19278ecb
Document Type: regulatory_guide
Title: Normal Water Level and Discharge at Nuclear Power Plants
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740143.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.135
CFR Part: 
CFR Title: 

Content:
0.5 of occurrence at the time of interest. Some design basis events may actually consist of a series of events such as an earthluake followed by one or more aftershocks. This fact is important if the earthquake could affect the normal water level (or discharge) and result in a different water level (or dis charge) when the aftershocks occur. For example, the initial earthquake could affect an underdrain system to lower ground water levels at tjhe time of the aftershocks. Similarly, a dam failure caused by the in itial earthquake could substantially change the dis charge in a river at the time of the aftershocks. Under such conditions, the normal water level (or discharge) should be assumed only at the time of the initial event, and the water level (or discharge) during the aftershocks should be determined by analysis of the effect of the initial event. 1. Seasonal Occurrence of Design Basis Events Earthquakes, plane crashes, transportation acci dents, explosions, fires, and LOCAs may occur at any time. However, water levels (or discharges) may vary considerably during any year. Accordingly, when determining normal water levels (or discharges) for these events by the methods recommended in this guide, water levels (or discharges) for the entire year should be considered. On the other hand, floods, hurricanes, and tor nadoes are seasonal in most parts of the United States. In determining normal water levels (or dis charges) for these seasonal events, such seasonality should be taken into account. For example, tor nadoes do not generally occur during the winter months in the northern states. Therefore, the normal water level (or discharge) to be considered with tor nado effects should be derived only from data for those months in which tornadoes may be expected to occur. Similarly, in Florida hurricanes have been recorded in virtually every month, but they are more likely to occur during the late summer and early fall, which is coincidentally the period of the year in