Document: NUREG-0800
Document ID: b694ca5b-4dcc-4098-be04-431e0137a936
Document Type: srp
Title: - 15.5.2
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0708/ML070820081.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15.5.1
CFR Part: 
CFR Title: 

Content:
tory and (SRP Section 15.5.2), are more likely to challenge this criterion than other AOOs. The inadvertent operation of ECCS is a concern only in plants that are equipped with ECCS pumps (or charging pumps that are used in the ECCS mode) that can deliver flow to the RCS when the RCS is at nominal pressure. The inadvertent operation of an ECCS is postulated to occur as the result of spurious SI signal. The SI signal trips the reactor and actuates the ECCS. Therefore, since the reactor is shut down throughout the transient, violation of the DNBR safety limit is not likely to be a concern. The inadvertent operation of an ECCS, that actuates charging pumps in an SI mode, is assumed to operate the charging system at its peak performance level (i.e., no failures are assumed). The shutoff head of the charging system is necessarily greater than the nominal RCS pressure, and possibly high enough to lift the pressurizer safety valves; but not high enough to pressurize the RCS to 110 percent of its design pressure (e.g., 2750 psia). Therefore, overpressurization of the RCS is not likely to be a concern. Because the inadvertent operation of ECCS causes an immediate reactor trip, there is no power/steam flow mismatch. Consequently, there is little or no effect upon the main steam system. Overpressurization of the main steam system, therefore, is not likely to be a concern. If the inadvertent operation of the ECCS causes one or more pressurizer power-operated relief valves (PORVs) to open while the pressurizer is water-solid, then the PORV is generally assumed to fail open (i.e., PORVs are assumed to fail in the open position after having relieved water, if they are not (1) safety-related equipment and (2) qualified for water relief). The inadvertent operation of the ECCS, therefore, can lead to a LOCA, which may be considered the an AOO, a postulated accident, a Condition II event, or a Condition IV event, depending upon break size and the event categorization scheme in the