Preface 

This is the fourth edition of CSA N285.8, Technical requirements for in-service evaluation of zirconium alloy pressure tubes in CANDU reactors. It supersedes the previous editions, published in 2010, 2005, and 2015. This Standard specifies mandatory technical requirements and non-mandatory evaluation procedures for fitness-for-service assessments. Pressure tubes in Canadian CANDU nuclear power plants are inspected in accordance with CSA N285.4, Periodic inspection of CANDU nuclear power plant components. When a detected flaw indication does not satisfy the criteria of acceptance by examination, or when pressure tube to calandria tube contact is detected or predicted, Clause 12 of CSA N285.4 permits a fitness-for-service assessment to determine acceptability. Also, Clause 12 of CSA N285.4 requires evaluation of the results of specified material property surveillance measurements. Note: CANDU (CANada Deuterium Uranium) is a registered trademark of Atomic Energy of Canada Limited. The major changes to this edition include the following: 

a) removed provision in Clause 5.4.3.2 c) that exempts a Level A overload evaluation; 

b) updated Annex C to be consistent with current methods used in the industry for probabilistic core assessments and probabilistic leak before break (Clauses C.3 and C.4); 

c) revised Clause D.8 to support use of equation for fracture initiation toughness for higher Heq concentrations; 

d) added new Clause 6.5 for evaluation of pressure tube to calandria tube (PT-CT) contact to improve clarity of requirements, and to address observed spacer movement;

e) updated the definition of fitness for service (FFS) evaluation to use in a degraded condition that was not considered in the design to avoid using the terminology beyond design basis; 

f) evaluated use of the term structural integrity and revised the Standard as appropriate; 

g) included the recently published pC statistical equation into Annex D;

h) included the recently published FNR for non-ratcheting flaw assessments; and 

i) updated the maximum allowable operating interval (tmax) for operation of tubes left in contact (Clause 6.3) accounting for improved knowledge of deuterium ingress rates. 

This Standard is one of a series of CSA N285 Standards that provide consistent rules for the design, fabrication, installation, inspection, and assessment of pressure-retaining systems and components in CANDU nuclear power plants. The series outlines requirements that are particularly applicable to nuclear power plants in Canada and references the appropriate requirements of the ASME Boiler and Pressure Vessel Code. Users of this Standard are reminded that the site selection, design, manufacture, construction, installation, commissioning, operation, and decommissioning of nuclear facilities in Canada are subject to the Nuclear Safety and Control Act and its Regulations. The Canadian Nuclear Safety Commission might impose additional requirements to those specified in this Standard. The CSA N-Series of Standards provides an interlinked set of requirements for the management of nuclear facilities and activities. CSA N286 provides overall direction to management to develop and implement sound management practices and controls, while the other CSA Group nuclear Standards provide technical requirements and guidance that support the management system. This Standard works in harmony with CSA N286 and does not duplicate the generic requirements of CSA N286; however, it might provide more specific direction for those requirements. This Standard is based in part on fitness-for-service guidelines developed by a Technical Task Team formed by the CANDU Owners Group (COG). In order to facilitate adoption by the authority having jurisdiction, this Standard includes some regulatory provisions. 

Scope 

1.1 This Standard specifies the technical requirements for the owner/operator to evaluate cold-worked Zr-2.5 wt Nb alloy pressure tubes in operating CANDU reactors for continued operation. Clause 13 of CSA N285.0/N285.6 Series requires that when in-service inspection results or material surveillance results do not satisfy the requirements of the original inspection program, a fitness-for-service evaluation must be performed in accordance with CSA N285.4 to demonstrate acceptance. The requirements of this Standard address the specific fitness-for-service evaluation requirements of CSA N285.4, Clause 12. 

1.2 This Standard applies only to cold-worked Zr-2.5 wt Nb alloy pressure tubes in operating CANDU reactors and to evaluation of the volumetric inspection results, pressure tube to calandria tube contact, and material surveillance measurements listed herein. The definition of pressure tube material types is provided in CSA N285.0/N285.6 Series. 

1.3 This Standard does not apply to evaluation of pressure tube dimensional changes (other than pressure tube to calandria tube contact), material property surveillance measurements beyond those defined in CSA N285.4, or to other reactor types. This Standard does not apply to pressure tube materials other than cold-worked Zr-2.5 wt Nb. 

1.4 In this Standard, shall is used to express a requirement, i.e., a provision that the user is obliged to satisfy in order to comply with the Standard; should is used to express a recommendation or that which is advised but not required; and may is used to express an option or that which is permissible within the limits of the Standard. Notes accompanying clauses do not include requirements or alternative requirements; the purpose of a note accompanying a clause is to separate from the text explanatory or informative material. Notes to tables and figures are considered part of the table or figure and may be written as requirements. Annexes are designated normative (mandatory) or informative (non-mandatory) to define their application.