PLANT SSC IDENTIFICATION,SCOPING AND SCREENING PROCESSES

I- SSC Identification and General Inventory:

A preliminary activity based on the associative groups established in order to identify the integral amount of passive and active SSC that are accomplishing or not and that are sustaining or not an associated function, that have a long or specified life duration , with or without moving parts, with or without changing their properties or configuration. An associative group contains SSC arranged in a rational manner according to their similarities (design, fabrication materials, ageing assessment methodologies, working environments).

Major Associative Groups:

    a - Buildings and Structures
    b - Reactor and Mechanical Systems
    c - Power supply and Instrumentation & Control Systems

Minor Associative Groups:

    a - Structural Supports of Nuclear Steam Plant Systems
    b - Special and Consumable Materials
    c - Cranes and Handling Devices
    d - Fastening, fixing, blocking assemblies and mechanical commodities

 Associated Function: a set of intrinsic characteristics and/or operational features which must be   satisfied in any  operating or accident conditions during plant design life, including the extended period, such that plant operability    status and its essential safety functions to be accomplished. The associated functions are made-up from the following groups of primary functions:

  a - Process Function = a function assigned to a SSC in order to sustain actively or  passively nuclear, thermal,mechanical, hydraulic, thermodynamic, chemical and electrical processes required by the specified operational status and its performance and operability requirements.

  b - Nuclear Safety Function = a function assigned to a SSC in order to sustain actively or passively its preventive and/or protective characteristics and whose effectiveness is required by the essential nuclear safety functions accomplishment, during operating regimes and postulated accident conditions.

  c - Passive Function = a function assigned to a passive SSC which act in support of safety and/or process functions.

II - SSC Scoping:

The identification process of those plant parts (SSC) which are the objective of nuclear facility licensing renewal and that are submitted to selection process. A structure, system or component is classified if at least one scoping criterion is fulfilled. The following are the scoping criteria established for CANDU-6 plant:

    1- Safety criterion derived from the nuclear safety functions classification and requiremets (SR, NSR)
    2 - Physical barrier criterion derived from SSC type SR functional characteristics (preventive or protective function)
    3 - Seismic criterion derived from seismic qualification requirements (DBE, SDE, NSQ)
    4 - Environmental conditions criterion derived from environmental qualification requirements (EQ, NEQ)
    5 - Design criterion derived from mechanical, electrical,…eso, design requirements (ASME, ANSI, IEEE,..)
    6 - Availability criterion associated to power supply systems, derived from users reliability and operational requirements (Clasă I, II, III sau IV)
    7 - Analytic criterion derived from the initiating events conservative assumptions and occurrence frequency (SSC credited and not credited in analyses of events class 1, 2, 3, 4 or 5)
    8 - Other criteria (technological derived from the nature, internal energy and function of process fluids, of reliability derived from the Grouping and Separation principle requirements)

III - SSC Screening:

The identification process of those plant parts (SSC) which are the objective of licensing renewal and that shall be evaluated in order to assess their ageing degradation or to identify the exceptions, if any. A structure, system or component is selected if at least one of the following criteria is met:

1 - SSC is Safety Related and it must be remain operational during and after a design basis event in order to  provide that  essential safety functions are met;

2 - SSC is Not Safety Related but its failure could impair at least one essential safety function completion   (missiles production, flooding, large weights or fuel handling errors, HE systems impairment);

3 - SSC is SR or NSR but which are credited in safety analyses or plant assessments complying with     specific associated function, during specified event classes (Fires, L-LOCA, Thermal shock,ATWS, LOCLIV).

    OR EQUIVALENT,
    a - SSC accomplishes an associated function without any moving parts, nor to change its configuration or properties,
    AND
      b - SSC are not subjected to replacement procedures based on a qualified life time or a specified time period.

IV - Selected CANDU-6 SSC categories:

1 - Limiting Critical SSC = those SSC for which:

  • it must be assured their integrity and functional capabilities during operating life and       while in shutdown states
  • there is no replacement possibility;
  • it’s estimated a total control over plant life;
  • it must be realized Life Assessment analyses, or a Life Cycle Management plan.
      • * Calandria vessel
      *  ESCS components
      *  Calandria tubes
      *  In-core Reactivity Mechanism Control components
      *  MMS pipe spools inside calandria vault
      *  Containment and essential internal structures

    2 - Critical SSC = those SSC for which:

  • it must be assured their integrity and functional capabilities during the operating life and while in shutdown states;
  • it is extremely difficult to replace them;
  • there are estimated high costs, long terms operation in shutdown state, radiation  exposure significant risk;
  • there must be realized Life Assessment analyses or Systematic Assessment of     Maintenance studies.
      • *  PHTS equipment and pipes
      *  Pressure Tubes
      *  Steam Generators
      *  PHTS pumps
      *  PHTS feeders
      * ECCS pipes and equipment
      * SDCS pipes and equipment
      * MMS pumps and heat exchangers
      * Special safety systems
      * Structures with essential or safety related functions
      * High capacity heat exchangers
      * Others SSC in a variable number (10 - 20)

    3 - Important SSC = those SSC for which:

  • there is the possibility of their replacement in an orderly manner;
  • the programs of preventive maintenance, in-service inspection and components  status/surveillance evaluation are applicable;
  • it must be realized Systematic Assessment of Maintenance (for structures and  components) and a Life Cycle Management program (for systems), both used in plant condition evaluation.
      • *  ESCS pipes and equipment
      *  Calandria vault cooling system components
      *  PHTS feed system pumps
      *  Turbine-Generator system
      *  Service water systems pipes and equipment
      *  BFWS pipes and equipment
      *  Medium and low capacity heat exchangers
      *  Diesel generators
      *  Power supply and distribution systems
      *  Battery cells system

    4 - Not important SSC = those SSC which:

  • could represent a residual risk for Ageing Management Review analyses;
  • have support functions for safety related SSC;
  • can be periodically replaced without difficulty;
  • are subjected to the preventive maintenance, in-service inspection and     assessment/surveillance programs prescriptions for components.
      • *  Compressors and compressed air system components
      *  Instrument air system
      *  D2O vapor recovery dryers
      *  Air exhaust system fans
      *  Transformers
      *  Power cables and I&C systems