ASME NTB-5 pdf download

ASME NTB-5 pdf download Guidance for Determination of Risk-Informed Safety Classification for Light Water Reactor Nuclear Facility Pressure Retaining Components
1 SCOPE
This document provides a process for determining the Risk-Informed Safety Classification (RISC) of light water reactor nuclear facility Class 1, 2 and 3 pressure-retaining components and their welded attachments and supports. Pressure retaining components may include passive components (e.g., piping, vessels, tanks, etc.) and the pressure-retaining portion of active components (e.g., valve bodies, pump casings, etc.) and their welded attachments and supports.
2 APPLICABILITY
Guidance in this document is intended to be used by the Owner 2 , or his designee, to conduct risk classification for the purpose of specifying appropriate Codes and requirements for the construction of an LWR system or component. Having used this guidance, the Owner then specifies the Risk-informed Safety Classification, applicable Codes and all appropriate requirements for construction in the Design Specification as required by Section III of the ASME Boiler and Pressure Vessel Code, Paragraph NCA- 3250.
3 RISK-INFORMED SAFETY CLASSIFICATIONS
(a) The RISC process is described in Appendix I of this document. Pressure-retaining items should be classified high-safety significant (HSS) or low-safety significant (LSS), except as noted in 3(b) below.
(b) (1) Class 1 portions of the reactor coolant pressure boundary (RCPB) that do not meet (i) or (ii) below:
(i) in the event of postulated failure of the component during normal reactor operation, the reactor can be shut down and cooled down in an orderly manner, assuming makeup is provided by the reactor coolant makeup system.
(ii) the component is or can be isolated from the reactor coolant system by two valves in series (both closed, both open, or one closed and the other open). Each open valve must be capable of automatic actuation and, assuming the other valve is open, its closure time must be such that, in the event of postulated failure of the component during normal reactor operation, each valve remains operable and the reactor can be shut down and cooled down in an orderly manner, assuming makeup is provided by the reactor coolant makeup system only.
(2) ASME Boiler and Pressure Vessel Code, Section III, Class 1 items, that portion of the Class 2 feedwater system [> NPS 4 (DN 100)] of Pressurized Water Reactors (PWRs) from the steam generator to the outer containment isolation valve, and
(3) items that are within a break exclusion region 3 [> NPS 4 (DN 100)] for high-energy piping systems and their associated supports (NB, NC and NF) should be classified high-safety significant (HSS).