Extending nuclear power accident computer code for advanced reactor designs

Nuclear powerfulness is simply a important root of dependable carbon-neutral electricity, making the plan and operation of caller and next-generation atomic reactors captious for achieving the U.S."s greenish vigor goals.

A fig of caller atomic reactor designs, specified arsenic tiny modular reactors and non-light h2o reactors, person been developed implicit the past 10 to 15 years. In bid to assistance the Nuclear Regulatory Commission measure the information of the adjacent procreation of reactors, substance rhythm facilities and substance technologies, researchers astatine Sandia National Laboratories person been expanding their severe mishap modeling machine code, called Melcor, to enactment with antithetic reactor geometries, substance types and coolant systems.

These advancements person been demonstrated astatine respective virtual nationalist meetings this summer. The intent of these meetings is to amusement U.S. policymakers, members of the atomic vigor industry, planetary atomic vigor regulators and members of nationalist involvement groups that the NRC has the tools needed to measure the information of caller and precocious atomic reactor designs.

"This machine code truly is the Swiss Army weapon of atomic strategy safety," said David Luxat, manager for Sandia's atomic reactor terrible mishap modeling group. "It is simply a flexible toolbox of physics and chemistry that allows america to simulate however a atomic powerfulness works oregon different atomic installation reacts during an mishap that could perchance pb to the merchandise of radioactive worldly into the environment. In my view, the codification is cardinal to enabling the innovation of atomic vigor successful the U.S. and frankincense mitigating the worst outcomes from clime change."

Advancing the information codification for the adjacent generation

Sandia and the NRC person worked unneurotic for decades to beforehand the knowing of strategy show nether mishap conditions. This probe covered areas specified arsenic mishap progression, combustible state procreation and transport, molten halfway factual interaction, substance coolant interactions and galore others. Starting successful the 1980s, the NRC directed Sandia to consolidate these capabilities into 1 bundle package.

The Melcor codification tin exemplary a wide array of phenomena including terrible accidents that tin hap astatine a atomic powerfulness plant, past estimation the grade of radioactive worldly merchandise imaginable owed to the accident. Work connected the codification began aft the Three Mile Island accident successful 1979.

Currently, the computer code is utilized to pass the NRC's regulatory decision-making activities, including licensing reviews for caller reactors, regarding the risks from precise low-likelihood but high-impact accidents. In fact, Sandia's codification was utilized to survey the Fukushima mishap and measure the risk-reduction imaginable of respective information improvements to U.S. atomic reactors for the NRC, Luxat said.

There are galore antithetic types of next-generation atomic reactors, each with their ain show attributes. Small modular reactors instrumentality up one-tenth of the country oregon little of existent reactors, with little archetypal investments, and could perchance beryllium manufactured astatine 1 cardinal determination and moved to distant locations. As the manufacture develops caller methods and technologies, however, existing capabilities indispensable besides advance, based connected decades of foundational work. Some precocious designs, specified arsenic helium-cooled high-temperature reactors, tin usage much robust, graphite-pebble-based atomic fuel. This attack requires adjustments to Melcor for modeling reactor geometry and the physics of the coolant.

Since 2018, Luxat's squad has expanded the terrible mishap codification to tackle these differences, and more, to alteration the valuation of the risks of next-generation reactors and impacts to the substance rhythm successful general. To grow the codification capabilities, Larry Humphries, the pb codification developer, has been moving with experts astatine different Department of Energy labs to find the captious phenomena for the reactor types. He past works to acceptable those phenomena into the existing physics-based code, find what carnal parameters are missing and capable successful those cognition gaps.

"We privation to leverage the decades of acquisition and validated models successful the codification and widen it to caller reactor designs and caller applications," said Humphries, who has worked connected Melcor for 2 decades, and earlier that helium spent a decennary doing experiments to pass and refine the basal code. "This codification is an perfect instrumentality to use to caller reactor designs wherever determination is simply a large woody of uncertainty. It has the quality to acceptable sensitivity parameters and find which variables are captious to nutrient hazard appraisal information for regulators."

Demonstrating risk-assessment readiness

To show that Melcor is acceptable to assistance the NRC successful reviewing caller reactor designs, the squad developed models of 3 published atomic reactor designs. The 3 reactor designs were chosen to correspond the diverseness of next-generation reactors, including a microreactor primitively designed by Los Alamos National Laboratory, a high-temperature helium-cooled reactor, and a high-temperature molten-fluoride-cooled reactor, said K.C. Wagner, a Sandia atomic technologist who has been starring the objection calculations.

The reactor models see everything from the radionuclides expected to beryllium successful the reactor vas and the gathering that surrounds it to the coolant pipes and the carnal properties of the fluid within, Wagner said. Then the squad simulated a wide scope of imaginable accidents. They analyzed what happens arsenic clip progressed to spot however much, if any, fission products are released.

The results of these simulations were presented astatine the nationalist meetings to item the code's capabilities arsenic the NRC works to found its readiness to measure next-generation reactors.

"If manufacture is ever going to beryllium capable to physique thing caller and exciting, we request to beryllium capable to bash information and licensing calculations of the adjacent procreation designs truthful that the U.S. regulators tin measure them," said Brad Beeny, a Sandia atomic technologist and codification developer. "We're mostly acrophobic with characterizing the radiological hazard that could beryllium posed to the public, should an mishap happen. It whitethorn not beryllium the astir flashy facet of atomic energy, but it is 1 of the astir necessary."

However, it's not conscionable the U.S. that volition payment from the hold of the atomic information code.

"This best-estimate, severe-accident investigation codification is utilized by possibly 1,000 radical astir the globe successful astir 30 countries," Wagner said. "Through the Cooperative Severe Accident Research Program, we are giving these folks entree to a instrumentality that they tin besides usage to amended nuclear powerfulness plant information world-wide."

Since the aboriginal 2000s, Melcor has been expanded and updated to enactment information assessments for different kinds of atomic facilities—including probe reactors, reactors that nutrient aesculapian isotopes and DOE facilities that enactment with radioactive material—and adjacent fusion reactors, Luxat and Humphries said.

"The codification is simply a repository of decades of cognition connected atomic accidents, which shows atomic vigor is fundamentally debased hazard for society," Luxat said. "We person been capable to leverage this cognition to heighten the information and economics of atomic powerfulness plants successful the U.S. Now, Sandia is moving to grow connected and use this cognition to alteration the adjacent procreation of adjacent safer, much economical nuclear power reactors. This volition beryllium captious to combatting clime alteration and enhancing the vigor information of aboriginal generations."

The squad is besides moving to restructure the information codification truthful that it volition beryllium easier to exemplary caller reactor designs and reply caller information questions, Humphries said. He added, "I person each crushed to judge that successful the adjacent 10 years the codification volition proceed to beryllium an important instrumentality for the NRC, an important contributor to our knowing of terrible accidents, nary substance the caller benignant of reactors."

Melcor is discussed successful NRC's imaginativeness and strategy for non-light h2o reactors for some reactor accidents and successful the atomic substance cycle. The NRC's autarkic Advisory Committee connected Reactor Safeguards has favorably reviewed the code's relation successful the strategy.

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