Room 1 Safety Valve

On the boiler that exploded the manual individual burner valves were not closed when the boiler shut down. After the purge period, fuel gas was admitted to the header from remote manual controls in the control room and into the firebox. Low fuel gas pressure tripped the master safety valve after each attempt to pressure the fuel header. Three attempts were made to purge the boiler and on each of these occasions fuel gas was dumped into the furnace through the open manual burner gas valves. On the third attempt a severe explosion occurred. 

Most supercritical fluid equipment use CO2 non toxic, non flammable, it is particularly safe. However, CO2 build-up in closed rooms could lead to people asphyxia. It is the reason why all possible CO2 emissions (exit valves, safety valves, rupture disks,...) must be collected in a "over-dimensioned" vent line ensuring a good dispersion of the gas in the outside atmosphere. Moreover, it is highly recommended to install CO2 detectors in the equipment room but also in any connex room, for action on high power fans and operators information. Anyway, it is preferable not to operate an equipment in rooms located over other rooms, especially underground cellars, where CO2 that is heavier than air may accumulate. 

A reactor is located in a relatively large laboratory with a volume of 1100 m at 22°C and 1 atm. The reactor can emit as much as 0.75 gmol of hydrocarbon (HC) into the room if a safety valve ruptures. A hydrocarbon mole fraction in the air greater than 425 parts per billion (ppb) constitutes a health and safety hazard. 

Waste Heat Boilers, Steam Drum, and Superheater safety valves, level indicators, vents, fittings, non-retum valves, water gauge glass (should be visible from control room) position of blowdown vessel ... 

Similar improvements can be performed in specific compartments inside the reactor building. The installation of fire detector chains with 2-4 fire detectors in compartments for the pre-heaters, an installation stairwell, a room with a control board for the safety valves, and other process rooms will significantly reduce the compartment specific CDF. 

Indication of safety valve leakage is provided by the Acoustic Leak Monitoring System (ALMS). The signal from the accelerometer sensor is monitored continuously, along with the RMS value of the signal computed. These signals are compared to a pre-established baseline value and alarmed in the main control room via the Nuplex 80+ Data Processing System (DPS) and Discrete Indication and Alarm System (DIAS) displays (See Section 7.7). 

The containment is provided with a system that prevents it from being damaged in the event of a primaiy drcuh loss-of-integrity accident. The system consists of a 70 m bubbler tank with 12 m gas volume and bypass channels with a safety valve communicating with different containment rooms. 

Pressure suppression / rad mitigation system (PSRMS) X System of leak-tight rooms adjacent to containment eqmpped with bubbler and filters, mterccmnected by ducts with safety valves and membranes... 

Generic Safety Issue (GSI) II.D.3 in NUREG-0933 (Reference l), addresses the guidance identified in NUREG-0737 (Reference 2) for the provision of a positive indication in the control room of relief and/or safety valve position or a reliable indication of flow in the associated discharge piping. 

After the Three Mile Island Unit 2 (TNI) accident, the NRC determined that there was a need for direct indication of relief and safety valve position in the control room. This determination was made because the TMI accident demonstrated that, during an accident, these valves may not operate as expected and that the safety and relief valve instrumentation may fail to provide the operator with sufficient information concerning the status of these valves. Therefore, the NRC established new guidance in NUREG-0737 which addresses the installation of improved safety and relief valve indication in the control room to enhance the operator s ability to diagnose a safety and relief valve failure and/or incorrect position. 

First, positive indication of safety valve position is supplied in the control room by the Acoustic Leakage Monitoring System (ALMS). 

Third, safety valve leakage is indirectly monitored from the safety grade pressurizer pressure and level instrumentation system also located in the control room. 

The ALMS is part of the NSSS Integrity Monitoring System and is described in CESSAR-DC, Sections 7.7.1.6.1 and 7.7.1.6.2. The function of the ALMS is to detect a leak at specific locations or within specific components in the primary system including the primary safety valves. The ALMS provides the control room operator with a direct and unambiguous method of determining the position (open or closed) of the pressurizer safety valves as required by NUREG-0737. 

The ALMS is composed of sensors (accelerometers) which are installed on the pressurizer safety valve discharge lines (one per safety valve). Signals from the sensor area are routed to the in-containment amplifiers. The amplifier output is subsequently directed to the control room. Within the alarm instrumentation, the signal is compared to a threshold value obtained during startup testing. 

At Zaporozhe NPP, protection of the primary circuit against overpressure during incidents is provided by three safety valves on the pressurizer For Units 1 to 4, only one valve can be opened intentionally by actuating pilots from the control room and the emergency control room The other two safety valves are acting as passive pilot operated safety valves For Units 5 and 6, they have a new design of valves All the pilots of the safety valves can be actuated from the control rooms The pilots can be isolated by an additional pilot in case of impulse pipe failure The qualification of safety valves for water flow is not confirmed... 

The steam generator safety valves are pilot operated by the steam pressure The opening of the safety vaKe can be manually operated from the main control room by means of two electromagnets installed on the pilots These electromagnets are also automatically de-actuated by a high pressure signal Only one impulse line common to the two pilots is going to the safety valve The two safety valves are "safe close position" type, in the event that the impulse line fails, the valve will be kept closed and non-operable... 

A frequent argument is that vented batteries require special battery rooms, but valve-regulated batteries do not. Valve-regulated batteries can be accommodated as one likes but in this sense it is not correct. DIN VDE 0510 does not require separate battery rooms. This is a requirement of the owner/user who wants to have specific protection of the supply system, e.g. in case of fire or unauthorized access. This is to ensure system functionality even in cases of crisis (see DIN VDE 0108 Safety Power Supply Systems for Public Premises , Regulations for Electrotechnical Installations in Buildings.)... 

In the reaction flask, lithium aluminum hydride (14.4 g, 38 mmol) and benzyltriethylammonium chloride (2.9 g, 13 mmol) are dispersed in tetralin (450 mL) with stirring imder nitrogen. The product of Step 4 (63 mmol of (BrSiH2)4C and toluene) is added dropwise with stirring. The mixture is stirred for 70 h at room temperature, followed by 5 h at 60°C. Toluene and tetra(silyl)methane are then condensed out of the reaction mixture kept at 60°C in a vacuum and collected in a trap held at 10°C. (Small amounts of silane are trapped in a small final trap at -196°C. From there it is allowed to escape through a safety valve to burn upon careful warming of the trap.) The liquid is subjected to fractional distillation and the product collected at 89.5°C, 4.3 g yield (50%). It solidifies in the receiver as colorless cubic crystals, mp 38°C. NMR (benzene-de) 3.84 (s, SiHs) -39.0 (t dez), J(SiC) 31.3, J(CSiH) 5.5) Si -47.8 (q dez), J(SiH) 205.7, J(SiCSiH) 4.6). MS 137-124 (CSi4HJ. 

Isolation or emergency shutdown (ESD) valves should be installed to stop fuel flow and the process feed flow into the heater in the event of heater tube rupture. These valves can be automatically actuated by controls or safety interlocks or can be manually operated remotely. Remote actuation can be from a control room console or in the field field actuation stations should be located at least 50 ft (15 m) from the heater. It is also common to provide a manual block valve, located at least 50 ft (15 m) from the heater, on each of the fuel and process feed lines. These should be accessible to operators in the event of an incident involving the heater. 

Figure 3.14. The lower ends of fractionators, (a) Kettle reboiler. The heat source may be on TC of either of the two locations shown or on flow control, or on difference of pressure between key locations in the tower. Because of the built-in weir, no LC is needed. Less head room is needed than with the thermosiphon reboiler, (b) Thermosiphon reboiler. Compared with the kettle, the heat transfer coefficient is greater, the shorter residence time may prevent overheating of thermally sensitive materials, surface fouling will be less, and the smaller holdup of hot liquid is a safety precaution, (c) Forced circulation reboiler. High rate of heat transfer and a short residence time which is desirable with thermally sensitive materials are achieved, (d) Rate of supply of heat transfer medium is controlled by the difference in pressure between two key locations in the tower, (e) With the control valve in the condensate line, the rate of heat transfer is controlled by the amount of unflooded heat transfer surface present at any time, (f) Withdrawal on TC ensures that the product has the correct boiling point and presumably the correct composition. The LC on the steam supply ensures that the specified heat input is being maintained, (g) Cascade control The set point of the FC on the steam supply is adjusted by the TC to ensure constant temperature in the column, (h) Steam flow rate is controlled to ensure specified composition of the PF effluent. The composition may be measured directly or indirectly by measurement of some physical property such as vapor pressure, (i) The three-way valve in the hot oil heating supply prevents buildup of excessive pressure in case the flow to the reboiier is throttled substantially, (j) The three-way valve of case (i) is replaced by a two-way valve and a differential pressure controller. This method is more expensive but avoids use of the possibly troublesome three-way valve.

A 4-inch (10 cm) air-operated plug valve isolates the reactor. An actuator on the 4-inch (10 cm) plug valve could be opened from the control room. For added safety during the line cleaning operation, the procedures required the mechanics to remove the valve actuator so that it is not accidentally opened during cleaning. [12]... 

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