Nuclear Reactors Safety Norms Revisited

On the backdrop of the nuclear disaster in Japan and the fear spree that followed amongst the countries across the world, the safety norms across the nuclear power industry has got extremely stringent.

Fact file on Canada-Nuclear power plants have been existence in Canada since 1960s, a total of five plants are house to 22 nuclear power reactors.15 % of energy requirements are met through this nuclear power plants.

Nuclear reactors that are used in steam generation have some innumerable periphery of tubes that are used in constant flow of water to the turbines that create a pressurized environment facilitating power generation.

When it comes to safety norms, Canada has been a pioneer in leading other countries in safety norm regulation. Nuclear reactors across Canada use CANDU design to produce electricity through the process of fission, where atoms of natural uranium are split inside the reactor releasing radiation and heat.  The whole process leads to the chain reaction of multiplication of atoms.

Some of the standard measures that are incorporated across nuclear reactors in Canada-

1. Pressurised Water Reactors are subject to several types of degradation .Degradation here might refer to several aspects which might include denting , wasting, pitting, Inter-granual attack, Inter-granual stress corrosion cracking , erosion-corrosion ,fretting and wear. Degradation could initiate from either the inner surface or the outer surface of the tube. After such degradation is reported, corrective action must be taken when it breaches 40% or greater of the tube wall thickness. Corrective actions here include two major reinstallation processes that are famously known as plugging and sleeving.
2. Tube Plugging-is a corrective measure of removing the tube from the service by plugging that is replacing the tube with a plug, there has been an uptrend in this process since the outbreak of degradation of the tubes in the recent past.

Tube Sleeving–

It was an improvement over the conventional plugging method that made the degraded tube functional by implanting a sleeve that are resistant to corrosion not only from outside but also through the inside of the tube. Initially stainless steel was used in the process of sleeving the tube which was gradually upgraded to the usage of alloys that were far more resistive to the corrosive chemicals.

Containment Layers–

Nuclear reactors are built with multiple layers to contain radiation, at the core of the reactor there are pellets which forms the first layer of containment. These pellets are enclosed in rods which form the second layer of containment .These rods are then loaded in to pressurized tubes which are part of the heat transport system, which acts as third layer of containment.

Ventilators–

During its normal functioning nuclear power plants release very few amount of radiation into air and water. Airborne releases are contained through precisely engineered ventilators that regulate the airborne diseases. These filters reduce about 99 % of the radiation that are released in to the atmosphere.

Nuclear pools- Uranium that goes in generating power are removed from the reactor and are stored separately in a pool of water, water which acts as a coolant shields against radiation. Most of Canada’s fuel pools are built in ground in separate buildings to withstand earthquake

Shutdown Systems–

Shutdown systems are important in pulling down the reactor when any unprecedented activity jeopardizes the safety of the nuclear plant. Basically every reactor will have two shut down systems, the first one consists of rods that drop in and automatically stop the chain reaction if something irregular is detected. The second method is used by injecting some acid or poison in the reactor that stops the reactor. The biggest advantage of their design is that they can be operated even without having power or intervention of operators.

Regulatory norms that enforce the safety norms are robust across Canada, however much needs to be learned from the lesson what failure of Japanese reactors have put forth.