Low Power and Shutdown PSA

1
Low Power and Shutdown PSA
IAEA Training Course on Safety Assessment of
NPPs to Assist Decision Making
Lecturer Lesson IV 3_10

• Workshop Information

IAEA Workshop
City , CountryXX - XX Month, Year
2
Plant Operating States

• Low power and shutdown include many different
  plant conditions.

• Need to select those that pose the most
  significant risk.

• A Plant Operating State (POS) is a determined
  plant condition that can be unmistakably
  distinguished in respect of its characteristics
  as far as carrying out a PSA is concerned.

3
Plant Operating States Definition
Characteristics to define plant operating states
and to select those that represent a greater
potential risk of fuel damage

• Success criteria to assure safety functions.
• Similarity of initiating events within the same
  operating state.
• Level of existing residual heat.
• Water inventory.
• Reactor vessel head and vent status.

4
Selection of Initiating Events
5
Grouping of Initiating Events
Criteria for grouping Initiating Events

• The accident sequences they generate are the
  same.
• The consequences they generate are the same.
• The requirements and availability of systems are
  the same.
• The success criteria of the safety functions are
  similar.
• The responses of the operating groups are
  identical.
• The state of the containment is the same.

6
Scenario Definition
Scenario ? Group of initiating events that could
arise in a given POS.
Selection Criteria

• Availability of systems in each POS.
• Permanence time in each POS.
• Level of residual heat in each POS.
• Consequences which can be extrapolated from the
  full power PSA.

7
Accident Sequences and Success Criteria
8
System Modelling

• Consistent methodology with that used in the full
  power PSA.
• Use as much as possible models developed for the
  full power PSA.
• New models for systems not analysed in the full
  power PSA.
• Some systems could be operating with different
  alignment than in the full power PSA.

9
Data Analysis

• Permanence time in each Plant Operating State
  (POS)
• Use of component reliability data and common
  cause failure obtained in the full power PSA.
• Use of plant-specific data whenever available.
• Component unavailability data based on schedules
  established for plant shutdown.

10
Human Reliability Analysis (1/3)
Differences with respect to HRA in full power
operation

• Need to actuate equipment manually.
• Low availability of procedures.
• Lack of training or experience.
• Instrumentation and indications not available.

11
Human Reliability Analysis (2/3)
12
Human Reliability Analysis (3/3)
13
Area Initiating Events
Internal Fires
14
Area Initiating Events
Internal Flooding

• Activities involving the transfer of liquids.
• Greater number of maintenance activities.
• Possible opening of barriers delimiting flood
  zones.
• Possible activation of automatic fire
  extinguishing systems.