Document: NUREG-0800
Document ID: 48fb37ec-8e3e-4c2c-96c3-daa5e7da62f9
Document Type: srp
Title: of the applicant's SAR is reviewed to identify any missing data,
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052340557.pdf
Revision Date: 2023-06
Chapter: 2
Section ID: 2.4.12
CFR Part: 
CFR Title: 

Content:
ed situation or not to prevent structural failures and internal flooding under potentially frequent conditions, we have been very concerned with system reliability. Many applicants have indicated that their plants can withstand, or have been designed against, full hydrostatic loadings that would occur in the absence of the underdrain systems, but not if an earthquake were to occur. If the plant can withstand full hydrostatic loading, assuming degradation of the underdrain system, many of the staff's concerns may be eliminated from further consideration because of the time available for remedial action after detection of system degradation. III. Situations Identified During Previous Reviews Four general categories of situations have been identified during case reviews as follows: (a) Estimating and Confirming Permeability Values It is necessary to estimate the amount of water that will .be collected so that system components such as strip drains, blanket drains, collector pipes, and pumps are adequately designed and sized. One of the most important and most difficult parameters to evaluate is 2. 4.12-12 Rev. 2 - July 1981 the permeability of the soil and rock existing at a site. A permeabi- lity value could be affected significantly by conditions of concentrated flow along joints in fractured and weathered rocks, or within other aquifers affected by foundation excavation. In addition, geological and foundation conditions that were not detected in site explorations may affect flow conditions and cause the estimated permeability values and flow regimes to be substantially different from those assumed at the CP preliminary design stage. These conditions are often first detected during construction dewatering. Therefore, we have required a commitment to consider construction excavation and dewatering data in the final design of underdrain systems. (See situation (d) below.) (b) Operational Monitoring Requirements To guard against system malfunctions and to assure