Document: NUREG-0800
Document ID: 80fe9eee-2d6e-4a7e-b7dd-ec23aab2d39f
Document Type: srp
Title: STRATEGIES AND GUIDANCE TO ADDRESS LOSS OF LARGE AREAS OF
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1211/ML121110138.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.4
CFR Part: 
CFR Title: 

Content:
ruary 25, 2005. 14 Paragraph 3.2.1 in NEI 06-12, Revision 3 describes the basic assumptions for developing the extensive damage mitigation guidelines (EDMG). One assumption is that all ac and dc power required for operation of plant systems (i.e., both Class 1E and Non-class 1E sources) is lost. This is similar to the definition for loss of internal power distribution for most PWR and BWR strategies, which require implementation without any offsite or onsite ac or dc power. Another assumption is that other onsite control rooms and personnel in separated buildings are unaffected by the damage. At one licensed power reactor site, the Unit 1 and Unit 2 control rooms are in widely separated control buildings (much greater than 100 yards). For this site, the licensee assumed that if one control room survived, it would also be reasonable to assume that the Class 1E power located in that same control 19.4-24 Revision 0 – May 2013 building could also be expected to survive. The licensee also assumed that the damaged control unit would be expected to lose all onsite electrical power and both units would lose all offsite power. NEI 06-12 does not specifically address this possibility. At this particular site, the control buildings are very widely separated, and therefore, the NRC inspectors concluded that the licensees approach was reasonable for this site. Staff Position For purposes of developing EDMGs, the developer may assume that buildings containing the control room and Class 1E vital electrical equipment (batteries, diesels, switchgear, etc.) at least 100 yards apart have adequate spatial separation. This 100 yard separation is measured from the outer wall or perimeter of the buildings (not the centerline of the building). When developing EDMGs for multi-unit sites that have control rooms and vital Class 1E electric power equipment in control buildings that have adequate spatial separation, the developer may assume that one control building will survive and the vital