PROCESS SAFETY AND LOSS PREVENTION ASSIGNMENT INTRODUCTION TO HAZARD ANALYSIS AND RISK ASSESSMENT (CPE6001 Part 1) September 2011
1. Discuss the form in which risk predictions may be presented, including numerical values, and indicate the way in which these may be used by chemical plant managers and safety authorities to judge the acceptability of a particular chemical plant activity. Explain the philosophy underlying acceptability criteria, justifying any numerical values used, and discuss the issues which you would consider in applying acceptability criteria in developing and developed countries. (30 marks) 2. Figure 1 shows a schematic layout of the safety cooling system for the AP1000 pressurised water nuclear reactor.

Figure 1.

The reactor system is contained within a 'passive cooling' containment vessel (Figure 2) which is intended to provide natural and permanent cooling in the event of a loss of cooling event in the reactor loop.

Figure 2

Containment vessel for AP1000 cooling

A comprehensive description of the overall system is provided by Schulz (1) and is available on the University Mole system for CPE6001. A brief description of the safety cooling system would comprise the following : The safety system incorporates four sources of passive water management following a loss of coolant accident : - two accumulator vessels (ACC) provide high flow for several minutes - two core make-up tanks (CMT)provide moderately high flow for a longer period - an in-containment refuelling water storage tank (IRWST) provides lower flow for a much longer time - large scale recirculation containment for decay heat removal The ACC and CMT responses are activated by a significant drop in system pressure - activation devices are not dependant on AC power supplies, but on springs, stored pressure and batteries. Failure of heat removal from the reactor via the steam