Piping is a primary component of nuclear power plant infrastructure, acting as the channels through which fluids necessary for the production and management of nuclear energy can be transferred. Some of these pipes are buried and require certain considerations to prevent the leakage of nuclear waste into the surrounding environment. Essential to the functioning of these pipes are valves and fittings, which control the flow of these liquids and gases and help prevent nuclear disasters.
The materials transported through pipes at nuclear power plants include cooling water and diesel, among others. Cooling water is generally taken from a nearby body of water and, after being used to lower the elevated temperature of nuclear fuel and generate steam to spin the primary electricity-generating turbines, leftover water is returned back to that original host water with harmless natural amounts of radiation.
|Nuclear Power Cooling Towers|
Diesel is circulated through the pipe system to be used as fuel for backup power in the case of an emergency, as a nuclear power plant can otherwise power itself. This potential for emergency and related disaster emphasizes the importance of properly functioning valves at nuclear power plants. The Three Mile Island Disaster, which in 1979 opened the world’s eyes to the potential dangers of mismanaged nuclear power, should have been prevented by a working pilot-operated relief valve (PORV) on the pressurizer. However, this valve remained open as it attempted to balance the pressure and remove heat and steam from the turbine, setting off the catastrophe.
This is an extreme example of what can happen, since Three Mile Island resulted from several other factors, but it should not diminish the importance of properly fabricated valves and fittings. Nuclear fuel, after being removed from a nuclear reactor, is very hot and requires storage in water pools for up to a period of ten years before it is disposed as nuclear waste. Because of this, there is water in the plant that carries levels of radiation too high for it to be released into the surrounding environment. This irradiated water flows through the pipes of the plant, so it is absolutely necessary that the valves and fittings securing and connecting those pipes properly manage pressure and do not leak.
Valve and fitting standards catered specifically to the nuclear industry include:
MSS SP-100-2015 - Qualification Requirements for Elastomer Diaphragms for Nuclear Service Diaphragm Valves
MSS SP-87-1991 (R 2006 - REINSTATED 2011) - Factory-Made Butt-Welding Fittings for Class 1 Nuclear Piping Applications
Specifications for valves and pipe fittings in the nuclear industry, like those in many other industries, are written by the Manufacturers Standardization Society (MSS) of the Valve and Fittings Industry.