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CRITICALITY INCIDENT DETECTION GEOFF DRUCE

CRITICALITY INCIDENT DETECTION GEOFF DRUCE. CRITICALITY INCIDENT DETECTION. Aims & Objectives to provide the IRMF community with an overview of criticality incident detection & alarm systems

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CRITICALITY INCIDENT DETECTION GEOFF DRUCE

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  1. CRITICALITY INCIDENT DETECTION GEOFF DRUCE

  2. CRITICALITY INCIDENT DETECTION Aims & Objectives • to provide the IRMF community with an overview of criticality incident detection & alarm systems • to discuss the requirement to assign the system with a ‘safety status’ (Nuclear Site Licence Condition) • to describe the importance of criticality incident detection & alarm system testing to demonstrate that the demands of the safety status can be achieved • to gain IRMF community acceptance of the UK CIDS Service Providers produced Good Practice Guide into the NPL suite of documents

  3. CRITICALITY INCIDENT DETECTION What is criticality? • An unintentional or accidental occurrence of nuclear fission • When and where can it occur? • When all engineering controls and procedures fail • In an Aqueous process • In a Metal process What measures do we take should failure occur? • Rapid detection of the fission [criticality] • Personnel evacuation to a safe haven [primary function] • Warn of re-entry to the incident area • Option to make a process ‘safe’ • Remote assessment of radiological conditions • Emergency Planning

  4. CRITICALITY INCIDENT DETECTION Rapid detection of the criticality incident • From Delafield & Clifton (SRD R 309 1984) • Minimum credible event 1 E14 fissions • Tissue dose in free air @ 1 metre from an unshielded event/assembly • Hydrogen Moderated Event • 2 E-16 Gy/fission for Gamma • 1 E-16 Gy/fission for Neutron • Unmoderated Metal Event • 0.5 E-16 Gy/fission for Gamma • 3 E-16 Gy/fission for Neutron

  5. CRITICALITY INCIDENT DETECTION Detectors • Geiger Counters • Ion Chambers • Scintillation • Junction Diodes Trigger Methods • Dose Rate • Integrated Dose • Rate of Change

  6. CRITICALITY INCIDENT DETECTION Criticality Incident Detection & Alarm System • Detection System • Audible Alarm - Primary Alarm • Instantly recognised tone • Time to alarm criteria of 200 E-3 S • Human Factors • Visual warning in high ambient noise areas >80 dB • Visual Warnings - Secondary System • Remote outputs • Facility Control Room • Emergency Site Control Centre • Process Interface • Process Shutdown Systems

  7. CRITICALITY INCIDENT DETECTION Safety Status • Safety Assessment Principles for Nuclear Plant • Specific requirements for criticality • Availability & Reliability requirements • Failure to Alarm on Demand • Safety Integrity Levels • Consideration of post incident information • Assigning the Safety Status* • Detection & Alarm System • Detection & Alarm System with positive process action • The detection & alarm system will not prevent criticality

  8. CRITICALITY INCIDENT DETECTION Reliability & Testing • Dual Redundancy • Single point of failure criteria • Type Testing • To demonstrate fitness for purpose • Periodic Testing • To demonstrate the degree of certainty to function correctly Good Practice Guide for the UK • Why? • Agree common approach • Who was involved? • Part of the NPL portfolio

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