U.S. Nuclear Regulatory Commission (NRC) Chair Christopher Hanson told U.S. Rep. Tim Walberg (R-Tipton, Michigan) environmental reviews are going well. He said the agency is reviewing the regulatory filings submitted by Holtec International and expects to have a decision next May.

“I would hope from our side, at least on the regulatory issues we’ve got, that we’re going to be done in less than a year,” said Hanson.

The latest update came during a Congressional hearing this week.

Palisades, the 800 MW facility in Covert Township, Michigan, would be upgraded to produce baseload power until at least 2051.

Holtec acquired the plant in June 2022 just after it was shut down. In early 2023, the company for federal loan funding to repower Palisades, which it received in the form of a $1.5 billion loan.

In May Holtec announced several milestones, including re-establishing the plant’s workforce, revitalizing training programs, procurement of plant systems and components, regulatory developments and firming up of funding streams. Holtec said more than 360 employees were working at the plant, an increase of nearly 150 personnel since the re-start began. The recruitment includes both former plant employees and new hires.

In addition to the main 800 MW reactor, Holtec intends to use the Palisades site as the location for its first two small modular reactor units, which would potentially add an additional 800 MW of generation capacity at the site.

The proposed rule, to be published in the Federal Register in about six months, would create a new Part 53 section under the NRC’s regulations as an alternative to the existing, large light-water reactor licensing approaches under Parts 50 and 52.

“This proposed rule leverages significantly more risk insights than our existing regulatory framework in making safety determinations,” said NRC Chair Christopher Hanson. “Applicants can use our existing regulations today, but this proposed rule will provide future nuclear developers a clear, additional pathway for licensing.”

The rule, in meeting the requirements of the Nuclear Energy Innovation and Modernization Act, would give plant designers and plant operators flexibility in determining how their nuclear power plant will meet safety criteria, NRC said.

It would set out criteria in areas including reactor siting requirements; analyzing potential accidents; defining safety functions; categorizing structures, systems, and components; addressing construction and manufacturing requirements; providing defense in depth; and protecting the public and plant workers during normal operations.

The proposed rule also would modify agency regulations for operator licensing, employee fitness-for-duty, physical security and site access authorization.

NRC staff said it has conducted extensive public engagement on the proposed rule and plans to seek public feedback when the rule is issued later this year.

Unit 1 of the Palo Verde Nuclear Plant in Arizona automatically tripped offline April 8 due to a loss of power to reactor coolant pumps, according to a report filed with the U.S. Nuclear Regulatory Commission (NRC).

The notification to regulators from operator Arizona Public Service said prior to the reactor trip, the main turbine tripped due to a loss of hydraulic pressure. The main generator output breakers did not automatically open on the turbine trip as expected, so control room operators opened the breakers.

Once the breakers were opened, the two 13.8 kV electrical distribution buses failed to complete a fast bus transfer, which resulted in the loss of power to the reactor coolant pumps, initiating the reactor trip.

According to the NRC filing, control room operators manually actuated a main steam isolation signal per procedure, requiring use of the atmospheric dump valves. The unit had been operating at 100% power.

“Following the reactor trip, all control element assemblies inserted fully into the core,” reads the event narrative. “No automatic specified system actuation was required or occurred. No emergency plan classification was required per the Emergency Plan. Safety related buses remained powered from offsite power during the event and the offsite power grid is stable.”

The loss of hydraulic pressure, the main generator output breakers failing to automatically open and the fast bus transfer not actuating are being investigated.

“As soon as the plant (Unit 1) safely shut down, we started an investigation into what caused this to happen and why,” said an Arizona Public Service spokesperson in an email. “That investigation is still ongoing.”

The spokesperson was not able to comment further.

Palo Verde is the largest nuclear plant in the U.S., with a total net summer generating capacity of about 3,937 MW.

To help in that task, the Energy Department’s Sandia National Laboratories in New Mexico developed what they said is a standardized screening method to determine the most important radioactive isotopes that could leave an advanced reactor in the event of an accident. 

The Sandia team recently tested the method with a conceptual design for a heat pipe reactor.

A heat pipe reactor uses an inert gas or liquid metal to cool the core. This means the reactor could potentially require less water than conventional light-water reactors.

Fluid in the heat pipes also would need no moving parts–such as valves or pumps–to regulate the core’s temperature. This means they would not require electricity to ensure the reactor’s safety.

Isotope inventory

The Sandia team’s screening method started with an inventory of radioactive isotopes produced by a nuclear reactor and sorted them to determine which isotopes would pose the most risk to humans and the environment in the case of an accident.

Radioactive isotopes are unstable forms of elements. They release energy in various forms of potentially harmful radiation as part of the process of becoming more stable isotopes.

For example, naturally occurring radon-222 is a product of the decay of uranium and in turn decays into polonium-218, releasing alpha radiation. This decay process is harmful if it occurs in someone’s lungs, which is why homeowners often are urged to test for radon gas in their houses.

In the case of the heat pipe reactor, Sandia researchers started with a list of more than 1,200 radioactive isotopes, and threw out the isotopes that decay quickly.

For example, rhodium-106, a form of the element rhodium with 45 protons and 61 neutrons, has a half-life of 29.9 seconds. So, after 30 seconds, half of the initial amount of rhodium-106 will have become palladium-106, a stable metallic element with 46 protons and 60 neutrons. After 60 seconds, only a quarter of the initial amount of rhodium-106 will remain. Researchers said that even if an accident were to occur rapidly, scant rhodium-106 would remain to affect people or the environment.

The team next removed very rare isotopes, specifically those that made up less than 0.0001% of the inventory’s total radioactivity.

These first two screening methods were similar to those used in the 1970s and 1980s to determine radioactive isotopes of interest for light-water reactors. Using these two screenings, the team produced a narrower list of 110 radioactive isotopes for further study.

The team then took a set amount of each of the radioactive isotopes and determined the resulting radiation doses using values from the Environmental Protection Agency. The dose is a numerical representation of the health impacts of exposure from that radioactive isotope. 

The researchers used advanced computer codes like Maccs to calculate the transport of radioactive isotopes through the environment and also the hazard posed by the isotopes on bone marrow and the lungs. Those body parts offer a good picture of radiation exposure’s overall health impacts.

Calculating health impacts

Combining the dose values with the proportion of that isotope present in the heat pipe reactor inventory enabled the team to calculate both short-term and long-term health impacts of the studied radioactive isotopes. They next compared the dose values with equivalent doses of iodine-131 and cesium-137.

Iodine-131 is the radioactive isotope that scientists say poses the most short-term risk from an accident at conventional nuclear power reactors. That is why potassium iodide tablets — which block the body’s intake of radioactive iodine — are distributed near U.S. nuclear power plants. Cesium-137 is the isotope that represents the long-term risk from an accident at a conventional nuclear power reactor.

The Sandia researchers found more than a dozen radioactive isotopes present in the heat pipe reactor inventory that could pose short-term health risks on par with iodine-131. Four radioactive isotopes could pose long-term health risks on par with cesium-137.

The researchers said that while their work suggest that these isotopes may be important for future assessment of heat pipe reactors, more study is needed to refine the heat pipe reactor inventory and determine the proportions of isotopes that could be released during a possible accident.

Read the technical report here.

The unit is the first reactor to reach this stage under the NRC’s combined license process. The decision moves the 1,117 MW AP1000 generating unit out of NRC construction monitoring and into the regulatory body’s operating reactor oversight process.

On July 29, Southern Nuclear told the NRC that it had completed all inspections, tests, analyses and acceptance criteria needed to show Vogtle Unit 3 is ready for operation.

The milestone came with the receipt of the NRC’s so-called 103(g) finding, which signified that the new unit has been constructed and will be operated in conformance with the Combined License and NRC regulations.

In a statement, Southern Nuclear said that work would proceed over the next several weeks to load fuel, which is already on site, into the reactor. This step would be followed by several months of startup testing and operations.

The company said startup testing is designed to demonstrate the integrated operation of the primary coolant system and steam supply system at design temperature and pressure with fuel inside the reactor. It said that operators also would bring the plant from cold shutdown to initial criticality, synchronize the unit to the grid and systematically raise power to 100%.

The Vogtle Electric Generating Plant, located near Waynesboro in eastern Georgia near the South Carolina border, is jointly owned by Georgia Power (45.7%), Oglethorpe Power Corporation (30%), Municipal Electric Authority of Georgia (22.7%) and Dalton Utilities (1.6%).

Plant Vogtle units 3 and 4 are on track be the first new nuclear units built in the United States in the last three decades. But the two new units are years behind schedule and billions of dollars over their original budget.

In late June, a Georgia court was asked to decide whether two partners in the 2,200 MW nuclear power project can cap their exposure to rising construction costs and hand over at least a portion of their ownership stake in the venture.

The dispute pitted Oglethorpe Power Corp. and the Municipal Electric Authority of Georgia against Georgia Power, a unit of Atlanta-based Southern Company.

The two claimed that cost increases related to the new nuclear units triggered clauses in a 2018 ownership agreement. Those clauses allegedly would shift construction cost responsibility above a certain level to Georgia Power. They also claim the right to give up some of their ownership stake in the Alvin W. Vogtle Units 3 and 4 project.

The lawsuit was filed June 18 in the Superior Court of Fulton County, Georgia. In an email sent in June to Power Engineering, a Georgia Power spokesperson said that the utility and Oglethorpe “have a difference of opinion over the dollar amount” at which the tender option is triggered. “We continue to have a difference of opinion and Georgia Power does not believe OPC’s tender notice is valid,” the spokesperson said.

Cost overruns and construction problems have delayed the project, the first nuclear units to come online in the United States since 2016. Vogtle Unit 3 is currently expected to come online by the end of the first quarter of 2023, and Unit 4 is expected at the end of 2023.