RADIATION MONITORING SYSTEM FOR CFVS STACKS


11th International Conference on CANDU® Maintenance and Nuclear Components - 2017 Oct. 01-04

Presented at:
11th International Conference on CANDU® Maintenance and Nuclear Components
2017 Oct. 01-04
Location:
Toronto, ON Canada
Session Title:
Post-Fukushima Strategies 2

Authors:
S. Hashemi (Tyne Engineering)
N. Reynolds (Tyne Engineering)
J. Robinson (Tyne Engineering)
  

Abstract

This paper describes Radiation Monitoring Systems (RMS) for a CANDU Plant Containment Filtered Vent Systems (CFVS). The RMS proposed by Tyne Engineering will provide reliable stack monitoring for 72 hours following a “Beyond Design Basis Event” (BDB) event. Two designs are proposed by Tyne. Design 1-particulate, and iodine is sampled and noble gas is measured, and Design 2- gross gamma is measured by an adjacent-to-stack monitor. Tyne will provide Design 1 in accordance with ANSI N13.1-1999 for “Sampling and Monitoring Releases of Airborne Radioactive Substances from the Stack and Ducts of Nuclear Facilities”. This will be achieved provided that velocity in the CFVS stack is within the range of stack velocity covered by ANSI code. Design 2 is based on an adjacent-to-stack gamma monitor providing overall gross gamma. As the noble gases are the major contributor to the stack discharge, they can be directly measured. Power is a significant issue as BDB accidents assume that no class IV or class III power is available. This option provides minimum power consumption as there is no need for a heater or a pump.
Monitoring is based on scintillation detector technology. The detector associated electronics are installed in a socketted module that attaches directly to the PMT. The compact configuration also allows for early analog to digital signal conversion and all signals being processed in a digital environment. Conventionally, a high-voltage power supply, a pre-amplifier, an amplifier, an analog to digital (A/D) converter and a Multi Channel Analyzer (MCA) are installed in a NIM (Nuclear Instrumentation Module) Rack which includes its own low voltage DC power supply to power the component boards installed inside. This configuration reduces the footprint and power consumption by eliminating the NIM rack.

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