Tell me about yourself.
Steve Unwin is currently a Nuclear Sector Manager at Pacific Northwest National Laboratories (PNNL). He was born in Manchester, in Northwest England. In that same year, in Northwest England, the first electron made its way from a nuclear power plant to an electric grid.
Steve Unwin’s homeland in Northwest England has a deep nuclear energy history. In the 18th century, John Dalton was the first person in the modern era to come up with the idea of atoms and how it might explain chemical behavior. In 1911, the University of Manchester discovered the nuclear nature of atoms by way of Rutherford’s famous gold foil experiment. This was the first discovery that atoms have a nuclear nature; most of it is empty space, with a kernel in the middle called a nucleus.
Steve Unwin studied physics at Imperial College in London, then returned to Manchester to complete a PhD in theoretical physics. He specialized in the field of quantum gravity, working to quantize the gravitational field. Steve completed research at the University of Manchester studying this topic. The UK Atomic Energy Authority (UKAEA) brought in people from specialized disciplines and taught them useful skills. Through this program, Steve learned probabilistic risk assessment (PRA).
What is the UKAEA? Is there a comparable institution in the US?
The UKAEA that Steve Unwin worked for at the time doesn’t exist anymore, as it has been supplanted by other organizations. It served both the regulator and the industry. A US National Lab is a somewhat parallel organization, as they serve industry, the Department of Energy (DOE), and the Nuclear Regulatory Commission (NRC).
Steve Unwin’s motivation for pursuing PRA was based on the state of current UK technology. All the reactors in the UK were gas reactors, carbon dioxide cooled and graphite moderated. Light water reactor (LWR) technology, created in the US, had become the dominant international technology. The UK wanted to benefit from all the insights coming research and development (R&D). UK built its first LWR pressurized water reactor in Eastern England at at site called Sizewell. In the late 1970’s, a new wave of PRA methods was developed called the WASH-1400, or the Reactor Safety Study. Steve learned about those new methods in order to apply them to Sizewell.
WASH-1400 was a true risk study that Steve Unwin implemented in his studies. Risk takes into account the consequences, but also the probability of it happening; this is the key ingredient to a PRA. The design-basis accidents that NRC had been using were a large break LOCA (Loss of Coolant Accident). After the risk study was done, the large break LOCA was not risk dominant due to the low probability of it happening. Other accidents were smaller in consequence, but larger in probability.
Steve Unwin’s research in PRA shows a large break LOCA at a commercial facility is viewed as highly unlikely. Small break LOCA’s were dominating the risk, as well as other risks such as loss of offsite power. Even though it wasn’t as severe from an impact perspective, it was more likely to happen. The PRA calculated what events could occur initially, how the plant would respond to it, how the safety systems would respond, and ultimately, if everything went wrong - with the incredibly low probability of that happening - what the consequences might be in the plant and beyond the fenceline. Steve was asked to become the Technical Attaché. The NRC funded a program in which they assigned persons from UKAEA and to a lab so they could share insights between UK and US. Steve was assigned to Sandia National Labs for a couple years to update the WASH-1400 study by adding more reactors.
WASH-1400 Impact on Risk
Did the WASH-1400 lower the risk from previous studies?
No risk assessment had been done on nuclear power plants before, so the WASH-1400 study formalized that process and allowed Steve Unwin to implement in his research across energy sectors. Risk perception and risk assessment are very different fields, but work hand-in-hand. Dread factor and knowledge of exposure are factors for risk perception. People do not understand nuclear energy and the technology associated with it, especially with the development of nuclear weapons.
Steve Unwin is looking at ways to make nuclear plants even safer via inherent safety. Conventional nuclear power plants have many safeguards, multiple redundancies. This creates low probability. Inherent safety relies less on engineered features, but take advantage of the laws of physics. This could change public perception.
The NUREG-1150 Paper
Were you at Sandia when you authored the NUREG-1150 paper?
Steve Unwin was part of the analysis team at Sandia, and then moved to Battelle Memorial Institute in Columbus, Ohio where he was involved in actually writing the document. It was published in 1990.
Steve Unwin had to analyze a large quantity of research between WASH 1400 and NUREG-1150. One insight was that some uncertainty bounds got a wider, but overall, concluded that risks were lower. The paper validated the conclusion that nuclear power is extraordinarily safe.
After working at Battelle, Steve Unwin worked for SAIC doing PRA, and diversified beyond nuclear into oil and gas. Steve then set up his own company based in Columbus doing risk assessment for the private sector. Steve got recruited by PNNL at this point.
Steve Unwin contributed to a large portfolio of projects at PNNL, and nuclear was a large portion of this work. Risk is about defining scenarios, probability of them happening, and consequences of that happening. Risk analysts want a bit of diversity, which was offered at PNNL.
Work at PNNL
What projects are you engaged in at PNNL?
Steve Unwin oversees all nuclear energy work as Nuclear Sector Manager at PNNL. He works with the DOE Office of Nuclear Energy, commercial organizations, and the Nuclear Regulatory Commission. Licensing and regulation is one of the biggest concerns in the industry. NRC is working to develop a different approach towards licensing for different reactor technologies. Steve’s group advises the NRC on these changes while also providing a technical understanding of materials and how they behave once exposed to harsh environments. This affects how facilities are licensed and regulated. The NRC is becoming increasingly focused on risk informed approach as opposed to deterministic approach.
Post Irradiation Examination
Can you explain the post irradiation examination you do?
Do other regulatory bodies use risk informed principles?
Steve Unwin’s international experience allows him to compare different principles of approaching risk in different countries. Steve helps NRC to review amendment requests utilizing the PRA. His group also advises the NRC on non-destructive examinations, especially in nuclear power plants as they age. PNNL has Category 2 nuclear facilities capable of doing post-irradiation testing.
Q: What is a Category 2 facility?
A: Facility category depends on what types of materials you can handle; Stephen Burn’s facilities can handle spent fuel and irradiated materials, and have a radiochemical processing lab.
Work at DOE
What DOE work are you involved in?
Steve Unwin completes work for the DOE across the entire fuel cycle. On the front end of the cycle, his group is currently examining the viability of extracting uranium from seawater, working in conjunction with Oak Ridge National Lab. PNNL has a Marine Sciences Lab that is used for this study. Steve’s group also works on reactor technology, radiochemistry, and material science on the back end of the fuel cycle.
Q: What was your relationship with the Hanford site?
A: Hanford was part of the Manhattan Project where plutonium was produced, and Steve Unwin was part of the technical authority to shut down some of the reactors and how to conduct clean up.
Spent Fuel Clean Up
What about the science behind clean up for spent fuel from commercial cells?
Steve Unwin’s group was involved in Yucca Mountain, and is looking to be involved in the future, due to their expertise in spent fuel. Risks analyzed include transportation and long-term storage. They are also working on how to instrument existing reactors. This merges PRA technology with materials technology. The US currently has a national policy against reprocessing spent fuel, due to proliferation. Modifying reprocessing methodologies to discourage proliferation could allowing the US to reprocess in the future.
Points of Pride
What are you most proud of? What’s next?
Steve Unwin is proud to be an important player with NRC getting design certification for the Vogtle plant. Working with the DOE and the Idaho labs were also beneficial to filling the niches that Steve group specialized in. Steve is confident that the golden age of nuclear energy is ahead of us and has untapped potential benefits.