1 - Internship at Three Mile Island
Bret Kugelmass: How did you get into the nuclear space?
Dean Divittore: Dean Divittore grew up in Middletown, Pennsylvania, about three miles from Three Mile Island (TMI) Nuclear Power Plant. He got interested in nuclear power during high school and was selected as an intern for the team that owned Three Mile Island during the summer of 1983. Divittore was in 8th grade during the TMI 2 accident. When the accident happened, it was scary for the neighborhoods because they were not educated about nuclear power at the time. Following the accident, everyone was educated very well about nuclear power, the effects of radiation, and how the accident didn’t have that much effect on the environment. Divittore’s father worked in security at TMI at the time of the accident, but his family was more educated about nuclear than most families. During his internship, Divittore went through simple operations training to understand the plant and learn about each department in the plant. Three Mile Island Unit 1 was built first and TMI 2 was built after Unit 2 was already operating. They are both Babcock & Wilcox (B&W) pressurized water reactors (PWR’s). Divittore was offered a job at the plant right after graduating high school and went into radiation protection. He wanted to be involved in radiation protection to protect and educate people on-site and in the public.
2 - Radiation Protection
Bret Kugelmass: Would people who work inside a nuclear power plant receive less radiation than people who don’t work in a nuclear power plant?
Dean Divittore: In some cases, like in parts of the medical industry, people receive more radiation that workers at a nuclear power plant. Administrative limits at a nuclear power plant are set even lower than federal limits and workers don’t get much more than background radiation from other places, such as x-rays and cosmic radiation. Background radiation comes from naturally occurring things, such as uranium in the Earth and cosmic radiation from the sun. Radiation is an energy that affects cellular growth in the body, so the industry follows the LARA (low as reasonably achievable) principle so as to see no effects. Radiation cannot be seen, but can always be measured, similar to electricity. Radiation is measured using radiological instruments, such as the Geiger and ion chambers. Dean Divittore was a radiation protection technician for 14 years and a supervisor for four years. At Three Mile Island, he worked through the clean-up of Unit 2 and the outages for refueling the reactor. During an outage, a radiation protection tech supports the maintenance and operations and focuses on protecting people from radiation sources. Different areas of a plant have different levels of radiation, such as the auxiliary building which has all the supporting systems for the reactor core which has primary water going through them and therefore is radioactive. The turbine building has no reactivity in it. A pressurized water reactor (PWR) has a bioshield; concrete shields the reactor, steam generators, and recirc pumps so that the people working around those areas are shielded by the radiation sources. The radiation sources are the fuel, where it originates, steam generators, recirc pumps, and piping inside the containment building.
3 - How Water Shields Radioactivity
Bret Kugelmass: How do radioactive sources move through water and how is the water arranged to act as a shielding source?
Dean Divittore: Water is a neutron moderator. When the reactor is operating, the neutrons are absorbed in the water and the water also acts as a shield. The gamma radiation, high energy N16 gamma, is formed as part of the reaction between the neutron and water. It has a half-life in milliseconds, so when the reactor is shut down for a refueling outage, all the N16 gammas are gone within seconds. Other radioactive isotopes include cobalt-58, cobalt-60, cesium, and transuranic fuel, if there is a defect in the fuel. A fuel defect is when a fuel pin may have a defect in it that lets gases escape from the fuel pellet. This is found through chemistry sampling and gases rising in the reactor coolant system. Reactor engineers cannot determine which specific pin has a defect, but they can determine whether it is a first, second, or third burn assembly and whether it is on the outer or inner area of the core. The whole assembly may be removed from the core or the pin may be removed, reconstructed, an re-inserted.
4 - Radioactivity in the Containment Building
Bret Kugelmass: What’s a hot spot and how do they form within a controlled environment?
Dean Divittore: The most common hot spot forms in low flow areas where corrosion builds up, creating cobalt-58 or cobalt-60. The area will get signage to identify the hot spot location and it is mitigated through shielding and flushing. Shielding, such as with a lead blanket, could be used until it is able to be flushed. Hot spots are flushed with hydrolasers during shutdowns. When people need to go inside the containment building, they will get a briefing about the expected conditions. A radiation protection technician will accompany them into containment and they wear a protective suit for contamination. Contamination is when the radioactivity escapes the system, maybe from a small leak in a valve, becomes airborne, and settles on the floor. After being a radiation protection supervisor at Three Mile Island (TMI), Dean Divittore went into work management where he scheduled and planned work as the plant was online and through outages. Divittore also worked for nuclear oversight, went back into radiation protection as a radiological engineering, became the radiological engineering manager, and then the radiation protection manager. He was responsible for all the programs in radiation protection, including field operations, technical support, and radiological engineering. Some challenges of the job include how to do some portions of the work, including leak identification inside the containment unit during operation with the use of robots, cameras, and drones.
5 - Innovation’s Impact on Radiation Protection
Bret Kugelmass: Are there other radiation protection management techniques or mechanisms?
Dean Divittore: The fleet has an innovation team that came up with a new way to survey things in the plant. Live cameras all over the plant allow people to see what’s going on in other areas, such as the auxiliary building. The innovation team combined best practices from all the sites to create one program that all sites now use. Touch screens bring up a map of the plant and plots radiation across different areas. The plant also has a 360-degree scanned image of different areas, which are useful for planning work. Other smart procedures include a radiation protection technician taking out their procedure for an air sample on an iPad, input the sample readings, and the program will calculate the air activity. This process saves time and saves dose for the individual. The energy level of a gamma ray determines at what distance the ray drops off and the level of shielding required. The distance at which a person is safe is also dependent on the geometry of the ray source.
6 - Benefits of Nuclear Power
Bret Kugelmass: How did you end up at Calvert Cliffs?
Dean Divittore: Dean Divittore served as radiation protection manager (RPM) at Three Mile Island for eight years and was ready for something new, leading him to another site in Exelon’s fleet, Calvert Cliffs. Calvert Cliffs is more challenging because there are two units, compared to Three Mile Island’s single unit in operation. Three Mile Island Unit 1 is due to be shut down in October 2019, but they are looking at legislature that could help them stay open. Divitorre considers himself an advocate for nuclear power. Nuclear plants bring very stable power to the grid, compared to other energy sources that may fluctuate a lot. It’s important for people to have power and shutting down nuclear power plants could have impacts on your access to power.