CSI Nuclear

March 24, 2015
Dave Lochbaum

Nuclear Energy Activist Toolkit #51

Cops responding to a reported disturbance sometimes find an individual holding a smoking gun standing over a dead body oozing blood from bullet holes. Such crime cases are easy to solve even without a confession from the person holding the gun or a declaration from the corpse on the floor.

More often, cops arrive and can only establish that something bad has happened. In these cases, Crime Scene Investigators (CSIs) are brought in to collect data and perform forensic analysis. In parallel, detectives interview people and investigate who had recent contact with the victims. Their goal is supplement the initial determination of what happened with solid insights as to how it happened and, more importantly, who did it.

CSI Nuclear involves a similar process. It’s generally apparent when something at a nuclear plant goes wrong, such as occurred in late January when the Pilgrim nuclear plant in Massachusetts automatically shut down after it was disconnected from the offsite electrical grid during winter storm Juno and workers encountered some equipment malfunctions. But CSI Nuclear takes time to collect data and analyze it so as to rule out potential suspects and zero in on the real culprits.

The National Transportation Safety Board (NTSB) illustrates the concept. The NTSB is called in to investigate aircraft accidents. Even before the NTSB’s investigators arrive onsite, victim’s families, media representatives, aircraft vendors and owners, airline travelers, and many others want to know why the plane crashed. Despite very strong desires for immediate answers, it is generally understood that the NTSB’s investigators must collect the black box, the cockpit voice recorder, and other data and then analyze this information. And NTSB’s investigators will review maintenance records, meteorological reports, and other information to understand the context leading to the aircraft’s final moments. Only after completing that necessary homework will the NTSB issue its conclusions as to why the aircraft crashed.

Nuclear plant owners and NRC inspectors report what happened fairly soon after it happens. But it takes CSI Nuclear time to gather and process the information needed to determine why it happened (or why expected responses didn’t happen).

Two nuclear events in Japan illustrate the consequences from not waiting for CSI Nuclear to be completed. On July 16, 2007, an earthquake of magnitude 6.6 on the Richter Scale occurred with an epicenter about 10 miles from the Kashiwazaki-Kariwa nuclear plant in Japan. Three reactors were operating at the time, three reactors were shut down, and the seventh was restarting from an outage. The earthquake caused shaking at the plant greater than it had been designed to withstand. All three operating reactors automatically shut down. The earthquake started a fire at the site, caused the unplanned releases of radioactively contaminated water to the sea and gases to the air, and damaged onsite buildings.

The plant’s owner and the Japanese government issued periodic news releases about conditions at the site. One of the early releases listed items damaged at the site by the earthquake. Two or three days later, another news release provided a significantly longer list of damaged items. Some people cited the short and long lists in questioning the veracity of the plant’s owner and accusing it of covering up the real conditions at the plant. But the length of the lists reflected the progress of CSI Nuclear rather than being a truthfulness gauge. Right after the earthquake, workers walked through the plant to compile a list of broken items. Later, workers supplemented their initial triage effort with more detailed examinations of structures and components. They added items that had been damaged, but not clearly broken, to the original list. The news releases reported what was known at the time with more becoming known with the passage of time.

An earthquake on March 11, 2011, also caused three operating reactors at the Fukushima Daiichi nuclear plant to automatically shut down. But the consequences became far more tragic when a tsunami spawned by the earthquake inundated the site, disabling virtually all the emergency core cooling systems. Three reactors cores suffered extensive overheating damage. The Unit 4 reactor at Fukushima was shut down at the time with its entire reactor core offloaded into the spent fuel pool. A few days into the accident, a violent explosion extensively damaged the Unit 4 reactor building. Circumstantial evidence convinced many people, including me, that the explosion meant that the water level in the spent fuel pool dropped low enough to uncover part or all of the irradiated fuel inside. The exposed fuel heated up, producing large amounts of hydrogen gas through a well-known chemical reaction process. Something detonated this hydrogen gas. That explanation certainly fit the data known at that time.

CSI Nuclear gathered additional data such as the amounts of radioactivity in the water of the Unit 4 spent fuel pool and the radiation levels in a ventilation system shared by the Unit 3 and Unit 4 reactors and revealed a different conclusion—hydrogen gas produced when the Unit 3 reactor core overheated flowed through the common ventilation piping into the Unit 4 reactor building and detonated. The fuel in the Unit 4 spent fuel pool had not been the source of the hydrogen.

Bottom Line

When something happens at a nuclear plant, my initial response is to explain what happened based on available information. When applicable, the response broadens to pose key questions that the ensuing CSI Nuclear should strive to answer.

For events at U.S. nuclear plants, it typically takes two months or longer for CSI Nuclear to be completed. Federal regulations allow plant owners to take up to 60 days to submit written reports to the NRC about event causes and corrective actions. And the NRC strives to issue reports 30 to 45 days after completing its inspections at plants.

CSI Nuclear plays an important role. Unfortunately, it’s not like CSI, CSI Miami, CSI New York, or even CSI New Orleans in that the case is never wrapped up in an hour. But like these television dramas, it’s better to wait for the final scene to reveal the real culprit than to guess at suspects during the opening act.


The UCS Nuclear Energy Activist Toolkit (NEAT) is a series of post intended to help citizens understand nuclear technology and the Nuclear Regulatory Commission’s processes for overseeing nuclear plant safety.