Overpressure protection system

Dispersion, Flaring, Scrubbing, and Containment An example of an overpressure protection system designed to reduce emissions to the atmosphere and at the same time provide adequate protection to the equipment has been described [234]. The equipment indicated is used for the manufacture of ethylene-vinyl acetate-vinyl chloride polymer emulsions. The design pressures are up to 100 bar. 

The simple error of installing a rupture disc upside down is easy to do in a minute or two and can jeopardize the integrity of the overpressure protection system. Rupture disk manufacturer s representatives are available to discuss proper rupture disk handling with engineers and craftsman. Such training can be very helpful. 

Appendix 5A presents the design bases for sizing the overpressurization protection system. The loss of load transient which is used to size the primary safety valves is not intended to be used as a design transient for any other NSSS equipment. 

Section 15.2 of Chapter 15 provides the functional design evaluation of the overpressurization protection system. In this analysis, the adequacy of the overpressure protection system to maintain secondary and primary operating pressures within 110% of design is clearly demonstrated for the loss of load analysis. 

The applicable codes and classifications for the overpressurization protection system are contained in Table 3,2-1. The applicable codes and classification for the secondary safety valves are identified in Section 10.3.2. 

An LTOP enable temperature is defined in Branch Technical Position RSB 5-2, "Overpressurization Protection of Pressurized Water Reactors While Operating at Low Temperatures," to Standard Review Plan Section 5.2.2, "Overpressure Protection," issued November 1988 as Revision 2. The definition is based on measuring the degree of protection provided by the low temperature overpressure protection system (LTOP System) against violations of the P-T Limits in terms of the of the reactor vessel beltline material at either the l/4t or 3/it location,... 

The containment design of BWR 90 incorporates, as depicted in Figure 5 1 2 also some features that aim at protection of the public and the environment against major releases of radioactive material even in severe accident situations involving core degradation and core damages To this end the containment has been provided with an overpressure protection system... 

Specifically, the acceptance criteria for the overpressure protection system are based on meeting the intent of the relevant guidance identified in SRP Section 5.2.2 Rev. 2 (Reference 5). 

There have been numerous reported incidents of pressure transients in PWRs where Technical Specification pressure and temperature limits of the RCS have been exceeded. The majority of these events occurred while the reactor was in startup or shutdown conditions and at low reactor vessel temperatures. The issue is the reliability of the cold overpressure protection system and especially the safety and relief valves situated either on the pressurizer or RHR systems. The protection systems in US plants used to mitigate and reduce the potential for these events are termed low temperature overpressure protection (LTOP) systems. 

The unavailability of overpressure protection system may result in a beyond design condition of the reactor coolant system including connected systems. 

The relief capacities of the pressuriser safety valve is determined from the postulated overpressure transient conditions in conjunction with the action of the reactor protection system. An overpressure protection report is prepared according to Article NB-7300 of Section III of the ASME code. Reference 6.2 describes the analytical model used in the analysis ofthe overpressure protection system and the basis for its validity. 

Figure 1-2 shows the simplified schematic diagram of the SMART nuclear steam supply system (NSSS) and exhibits the safety systems and the primary system as well as auxiliary systems. The engineered safety systems designed to function passively on demand consist of a reactor shutdown system, passive residual heat removal system, emergency core cooling system, safeguard vessel and reactor overpressure protection system. 

Overpressure protection system and depressurization system 4 - Emergency core cooling system... 

An overpressure protection system for air space in the reactor pool. 

The safety system (Fig. 20.21) of SMART includes a shutdown cooling system, residual heat removal system, safety injection system, reactor overpressure protection system, and emergency boron injection tank. Each of the four independent passive residual heat removal systems with 50% capacity can remove the core decay heat through natural circulation at any design basis events. This feature can keep the core undamaged for 72 h without any corrective action by operators in a design basis accident (Kim et ah, 2014). 

The European standard EN 12186 (formerly the DIN G491) and more specific the EN 14382 (formerly DIN 3381) has been used for the past decades in (mechanically) instrumented overpressure protection systems. These standards prescribe the requirements for the overpressure protection systems, and their components, in gas plants. Not only the response time and accuracy of the loop but also safety factors for oversizing of the actuator of the final element are dictated by these standards. Independent design verification and testing to prove compliance to the EN 14382 standard is mandatory. Therefore, the users often refer to this standard for HIPPS design. 

OperabUity of the overpressure protection system should be maintained in the event of a loss of off-site power. The system should be operable with a power supply backed up by a battery or completely independently of any electrical power supply. 

In the design of the overpressure protection system and its components, it should be ensured that no unacceptable consequences could result from the possible spurious operation of relief valves in the overpressure protection system (e.g. by incorporating a system for monitoring valve positions in the main control room). 

Loads and load combinations resulting from operation of the overpressure protection system should be taken into consideration in the design of the components that are affected by such operation of the pressurizer... 

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