Protection from High-Pressure Events

1 Relief Rupture Disks for Processes Operating at Low Rates 

Rupture disks must be installed properly and inspected periodically to maintain safe operations. Two common mistakes for the installation of these devices are shown in Fig. 10.6. In Fig. 10.6(a), the flow path in the stem downstream from the 

2 Protection from Overpressurization for Processes Operating at High Rates 

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Possible remedies for PTS events are automatic overpressure protection which disable systems that can pressurize the RPV, adnodnistrative measures to isolate high pressure systems from the primary circuit, and dedicated outage safety valves. It is also possible to mitigate PTS by recovering the material properties of the RPV through thermal annealing. 

The primary cooling ciicuit in a PWR is a high-integrity, pressure-resistant system that will contain any fission products released from the fuel in an accident until the internal pressure exceeds the values that would actuate the pressure relief devices. A simple, conqiact primary system will be easier to qualify and inspect and to protect from seismic events and external hazards. The RPV penetrations should be as few as possible and of small diameter. All primary system openings would be kept sealed for die duration of autonomous operation. 

The outlet air temperature and pressure from the compressors gives a good indication of the state of downstream process plant, where additional pressure drop may be experienced due to the entrainment of dust in the drying bed, breakdown of the catalyst or malfunction of the control valves. The gas discharge pressure and preferably also the temperature should be recorded. In addition, for safety reasons and to protect the compressor, a high-pressure switch/alarm combination should be used to stop the compressor in the event of overpressure. The sulphur pumping system must be interlocked with compressor operation, to stop the pump when no process air is available. 

The operators calmly witnessed this sequence of events with a sense of normalcy. As expected, the reactor protection system automatically inserted the control rods to shut down the reactor and the Power Operated Relief Valves (PORVs) at the top of the Pressurizer opened briefly to relieve the high pressure within the RCS. Within 10 s of opening, the PORVs received a signal to close. Unfortunately, the PORV signal in the control room only indicated what directional signal (open/ close) had been sent to the PORVs, but did not display their actual position (Kemeny, 1979). So the operators assumed that the pressurizer valves were closed, thus preventing any further loss of coolant from the RCS. In fact, one PORV failed to shut, remained open and coolant continued flow out of the RCS. 

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