 Safety is important in any activity that we do, so we prepare by ensuring we have the proper equipment and the proper safety gear. If nuclear reactors were cyclists, they'd look something like this. In a nuclear reactor, the most important thing to consider is an oncoming traffic, but heat. Inside the nuclear reactor, nuclear fission processes take place inside fuel bundles, which release a large amount of energy into their surroundings. Surrounding the fuel bundles are pressurized pipes with water flowing inside, removing heat from the fuel bundles. The water in these pipes is called the coolant. The fuel bundles and coolant systems sit inside a larger pool of water, acting as a passive cooling system for the hot bundles. The Thermal Hydraulics Lab at Chalk River Laboratories looks at how water and heat flow through the reactor systems. Thermal means heat and hydraulic means moving liquids. My name is Ali Siddiqi. I'm a Thermal Hydraulic Analyst here in the Thermal Hydraulics Lab. So what that means is that I am running experiments, planning experiments, interpreting data. Here, the most extreme limits of the reactor are tested. To ensure that in the unlikely scenario of an accident, the reactor can continue to cool down the fuel bundles and shut down safely. In a reactor, you have very high pressures and fairly high temperatures as well. And under accident scenarios that we're interested in, like a loss of coolant accident, you'd have a break in a pipe somewhere. And that would lead to the system depressurizing. Temperature and pressure are two properties of fluids that are related to each other. For example, this pot of water boils at 100 degrees Celsius here at sea level. But if I move my pot of water up to the top of a mountain at about 6000 meters, the water would actually boil at a lower temperature, about 80 degrees Celsius. That's because the air pressure up here in the mountains is actually lower than at sea level. The boiling temperature of this water decreases when the air pressure decreases and it takes less heat to boil this water. The water coolant inside the pipes is a lot like the water in the pot, sitting at a comfortable 300 degrees Celsius, but still not boiling because it's at 100 times the normal atmospheric pressure at sea level. If a pipe breaks, however, the pressure will decrease and the water may start boiling. Steam would start forming and boiling. We're interested to see where does that air go? If you get certain channels that fill with air, that could be an issue because of course that would mean that there's less heat transferred from the fuel to the coolant. When the temperature increase of the bundle, the bundle itself will deform and inside you see the sub-channel will be closing up. The gap between the fuel element will close up, so it means that the coolant will not be able to pass through and remove the heat. This physical behavior of the fuel bundle is studied using special apparatus in Catherine's lab. Lasers will scan the bundle back and forth as it's heated up with superheated steam, coming out at a whopping 1150 degrees Celsius. Fuel bundles can survive some tough stuff, but the emergency shutdown systems will put an end to rising temperatures in these fuel bundles long before they can reach the temperatures in these tests. The results from all these safety tests are used to create computer models to ensure that there are no surprises in the behavior of a reactor and its components should an accident occur. Safety tests like these ones are top priority at Canadian Nuclear Laboratories, keeping nuclear energy safe for everyone. I'm definitely ready to hit the road.