Isolation valves, leakage

USNRC RG 1.96 (June 1976) Design of main steam isolation valve leakage control systems for boiling water reactor nuclear power plants . USNRC RG 1.106 (March 1977) Thermal overload protection for electric motors on motor-operated valves . 

AR375 1.96 Design of main steam isolation valve leakage control systems for boiling water reactor nuclear... 

Main Steam Isolation Valve Leakage Control System (BWR)... 

D Radiological Consequences of a Design Basis Loss-of-Coolant Accident Leakage From Main Steam Isolation Valve Leakage Control System (BWR)... 

BWR MAIN STEAM ISOLATION VALVE LEAKAGE CONTROL SYSTEMS... 

Type C tests - tests to measure containment isolation valve leakage rates. 

Emergency isolation valves (EIV) should be located based one two principals (1) the amount of isolatable inventory that is desired and (2) protection of the EIV from the affects of external events. EIV valves are normally required to have a firesafe rating (i.e. minimal leakage and operability capability, Ref. Table 14). Valves and their actuating mechanisms should be afforded adequate protection when they are required to be located in an area that has potential to experience explosion and fire incidents. 

When the desired pressure is developed, isolate the system by closing the isolation valve and ensure no physical leakage takes place from all welding joints as well as bolted joints. If any leakage is identified, then release the pressure. After rectification... 

Thermal expansion on the isolation valve section (fire). Possible line fracture or flange leakage. g) Provide thermal expansion relief in the valved section. 

More Pressure 7. Isolation valve is closed in error whilst pump running. 8. Thermal expansion in the isolation valve section (fire). Lines subject to full delivery pressure. Possible line fracture or flange leakage. Covered by b). f) Perhaps worthwhile installing a pressure gauge upstream of the delivery pump. g) Provide thermal expansion relief in the valved section. 

More Pressure 8. All of 5, 6, and/or 7. 9. Thermal expansion in isolation valve section (fire). 10. PCV fails shut or isolation valve shut in error. As for 5, 6, and 7. Line fracture or flange leakage. As for 3. Covered by b) and c). f) Install thermal expansion relief in isolation valve section. Covered by b) and c). ... 

Isolation A means for pressure-isolating control valves, pumps, and other piping hardware for installation and maintenance is another common application for an on/off valve. In this application, the valve is required to have tight shutoff so that leakage is stopped when the piping system is under repair. As the need to cycle the valve in this application is far less than that of a throttling control valve, the wear characteristics of the valve are less important. Also, because many are required in a plant, the isolation valve needs to be reliable, simple in design, and simple in operation. 

In the systems with double containment with filtering of the effluents from the annulus between the two containments, a small pipe with a manually actuated valve can also be provided, which connects the space between the two isolation valves on a line with the leakage filtration system, if it is convenient to do so. 

Fortunately, this belief is not heard anymore, but, at one time, some people thought that the containment function was predominantly performed by the container shell and that, with an integer containment, a substantial separation of the internal atmosphere from the outside could be relied on. In reality, the containment is a machine which, in order to be able to perform its function, must pass from a state of multiple communication with the outside through the hundreds of mechanical penetrations usually present, to a state of isolation from the outside, by the closure of isolation valves and analogous devices. It must be remembered that the specified maximum design leakage of a containment is equivalent to the presence of a small hole, typically of about three millimetres diameter in the container shell. It is therefore vital that all the active isolation devices perfectly close in case of actuation of the containment isolation. 

B. The Main Steam Line Isolation Valves are designed to perform containment isolation functions for the main steam lines in the event of a design basis accident, as discussed in Section 6.2.4. In the event of a steam line break outside the containment, the isolation function serves to reduce the potential leakage of radioactivity to the environment. 

Turbo machine Leakages, Ruptures (prunary) Very high level of quality (R) Magnetic beanngs (S) Very high quality level for pressure vessel (burst proof) (S) Limitation of connectmg pipe diameters (L) Provision of isolation valves to be closed automatically (L)... 

Leakages/Ruptures (outside pmnaiy) Automatic closure of isolation valves (L)... 

This alarm warns the operator that leakage through the steam generator isolation valve and check valve is occurring. Therefore, these sensors provide indication to the operator of the potential of steam binding of the EFW pumps. 

A shutoff valve is used in each steam line outboard of the external containment isolation valve and fimctions as a backup to the isolation valve. The shutoff valve is part of leakage control system to prevent possible release of nuclear steam which could leak through the main steam containment isolation valves following a LOCA. Independent contairunent inboard and containment outboard divisions are used to establish a pressurized barrier between the containment barrier and the environs. Out leakage is effectively eliminated and in leakage is directed into the containment from the pressurized volume. Both divisions are powered from auxiliary and standby AC power. While either of the two divisions is sufficient to establish the necessary pressure barrier, both are initiated in the control... 

In order to cope with this issue, a practice of conducting ECT examination, and method to remove or replace it depending on the extent of wearing had been established. When leakage occurs, it can be stopped by closing the isolation valves. 

The assessment of the consequential effects of a pipe whip event has been addressed separately under internal flood, water spray, steam leakage, etc. Those systems designated essential for safe shutdown in the event of pipe rupture are the reactor coolant system, the steam generator system, the passive cooling system, the protection and safety monitoring system. Class 1 dc, the uninterruptible power supply, main control room and habitability system, contaimnent penetrations and isolation valves. 

The potential for release of activity from a break or leak in the chemical and volume control system is minimized by the location of the purification subsystem inside containment and the design and test of the isolation valves. Chemical and volume control system leakage inside containment is detectable by the reactor control leak detection function as potential reactor coolant pressure boundary leakage. 

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