Long before the nuclear disaster in Japan began unfolding this week, scientists in the US had been trying to gain a better and more realistic picture of precisely what would happen if a similar accident occurred in that country.
For the past few years, researchers from the Nuclear Regulatory Commission (NRC) have been engaged in a project called State of the Art Reactor Consequence Assessment (SOARCA), to better understand how a nuclear reactor would behave in a severe accident, as well as what sort of radioactive release it would cause.
Similar research on hypothetical accidents at nuclear power plants have been conducted by the NRC and international nuclear safety groups for the past 25 years.
What's different with SOARCA, says the NRC, is that it uses modern computing resources and modelling software to generate more accurate and realistic accident simulations. It also examines extremely rare, "one in a million" accidents that could have a significant impact.
Such modelling and analyses of hypthetical accidents is designed to help stakeholders develop better protections and responses to nuclear accidents.
SOARCA models also take into account some of the new accident mitigation technologies and strategies that are deployed in nuclear power plants these days. The models factor in updated emergency preparedness measures and plant improvements that were put in place after the 9/11 terrorist attacks.
The studies are receiving renewed attention in light of engineers in Japan currently trying to avert a full scale meltdown of the country's Fukushima nuclear power plant.
The plant was damaged severely in last week's earthquake and subsequent tsunami. Concerns about the safety of the plant have been escalating sharply over the past few days. Those concerns were further heightened after a third explosion rocked the facility, causing radiation levels to increase to potentially dangerous levels.
The NRC said on Monday that it has sent several nuclear experts to Tokyo to provide assistance to officials there. Among other tasks, the team's mission is to better understand the potential impact of radioactive leaks on people and on the environment, the NRC said.
As part of SOARCA, the NRC has run computer modeling and simulation tools to study at least two operating nuclear power plants in the US over the last couple of years.
One of the plants that participated in the initial phase of the NRCs SOARCA project is the Peach Bottom Atomic Power Station in Pennsylvania. The plant features a boiling water reactor (BWR) similar to the most troubled reactors in Japan. The other plant is the Surry Power Station, a pressurised water reactor (PWR) in Virginia.
The commission did not respond to requests for comment on the status of its SOARCA project.
Understanding the consequences
Publicly available information on the project states that the project's goal is to develop an enhanced understanding of the consequences of a nuclear power plant accident involving the release of radioactive material into the environment. SOARCA will give the public and decision makers the "latest basis" for assessing the consequences of severe accidents at nuclear power plants, the information notes.
The study also is designed to examine the value and the extent to which existing defence-in-depth measures at nuclear power plants will mitigate potential fallout in an accident.
According to a FAQ on the NRC's website, SOARCA is a research effort that seeks to "realistically estimate" the outcomes of the leak of a nuclear power plant's radioactive material.
A core component of SOARCA's tests is a software tool from Sandia National Laboratories called MELCOR. The NRC describes MELCOR as software that can be used to model the "progression of severe accidents in light-water reactor nuclear power plants."
The NRC also uses a separate software tool called MACCS2 to study the potential health implications of an accident involving radiation leaks.
"MELCOR is designed specifically for the purpose of predicting the response of nuclear power plants to severe accidents that might be initiated by low frequency events involving multiple safety system failures," said Randall Gauntt, the manager of Sandia's severe accident and consequence assessment department.
One of the scenarios the software is designed to model is a so-called Station Blackout scenario initiated by seismic damage, similar to what is happening in Japan right now, he said.
"The MELCOR code analyses severe accidents in nuclear power plants, their progression through core melting, should inadequate cooling be available, and the release to the environment should containment systems fail," Gauntt said.
The potential public impact of radiation leaks are evaluated using the MACCS code, which was also developed at Sandia for the NRC, Gauntt said.
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