Document: NUREG-0800
Document ID: 9697248b-d015-42be-8808-2202db24977a
Document Type: srp
Title: STANDBY LIQUID CONTROL SYSTEM (BWR)
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0706/ML070680186.pdf
Revision Date: 2023-06
Chapter: 9
Section ID: 9.3.5
CFR Part: 
CFR Title: 

Content:
ent design principles be provided, with the reactivity control systems having a combined capability of reliably controlling reactivity changes under design-basis accident conditions. The primary means for fine and coarse control of reactivity in a BWR are the control rods and their drive system, with the SLCS serving as a backup system. As such, the SLCS is a reliable means and for newer designs is an automatic means of making the reactor subcritical following an anticipated transient with a failure of the shutdown rods to insert. Acting in conjunction with other features to mitigate an ATWS, the SLCS provides additional protection and safety for all barriers to the release of fission products by reducing the potential for exceeding fuel, reactor coolant pressure boundary, and containment integrity limits. 6. Compliance with 10 CFR 50.62(c)(4) invokes explicit requirements regarding the performance of the SLCS. In essence, 10 CFR 50.62(c)(4) states that each BWR must have an SLCS with a minimum flow capacity and boron content providing equivalent reactivity control to 326 Lpm (86 gpm) of 13 weight percent sodium pentaborate solution. As discussed in NRC Generic Letter (GL) 85-03 (Ref. 9), the “equivalent in control capacity” wording was chosen to allow flexibility in the implementation of the requirement (e.g., the equivalence can be obtained by appropriately adjusting flow rate, boron concentration, or boron enrichment). GL 85-03 also states that the 326 Lpm (86 gpm) and 13 weight percent sodium pentaborate were values used in the General Electric Company Licensing Topical Report, NEDE-24222, for BWR/4, BWR/5 and BWR/6 plants with a 638-cm (251-in.) vessel inside diameter (Ref. 10). NEDE-24222 recognized that different values would be equivalent for smaller plants. The important parameters to consider in establishing equivalence are the vessel boron concentration required to achieve shutdown and the time required to achieve that vessel boron concentration. The