U.S. NRC Blog

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Throwback Thursday — Kennedy’s Nuclear Visit

hpDr_Alvin_Sen_KennedyBefore John F. Kennedy became president, he was elected to the U.S. House of Representatives and the U.S. Senate. During his time on Capitol Hill, he visited the Oak Ridge National Laboratory in Tennessee. Here, he’s photographed with ORNL Director Alvin Weinberg. Can you guess the year this photo was taken and who accompanied the then-Senator Kennedy? Extra points if you know what nuclear technology Weinberg is credited with spearheading. (Photo taken by Ed Westcott/DOE)

 

Tracing How Radioactive Materials Are Used in Research

Betsy Ullrich
Sr. Health Physicist
Region I
 

scientistScientists have been using radioactive materials in research nearly as long as they’ve known there were radioactive materials.

Most radioactive materials are used in research as “tracers.” A radioactive element is attached to a compound in order to see what happens to the compound. In other words, the radioactive material is used to “trace” what happens to the compound. Making the compound with the radiotracer is referred to as “labeling” or “tagging” the compound.

Let’s suppose a scientist is developing a new pesticide for treating crops. In order to understand what happens to that pesticide, the scientist uses tritium to label the compound. The atom of tritium will replace one of the normal hydrogen atoms on that compound. Then the pesticide labeled with the tritium tracer will be applied to a plant in a greenhouse. Samples of the leaves, roots and soil will be collected periodically and tested to see whether there is tritium in the samples.

Then the scientist will know whether the pesticide stays on the leaves, is absorbed into the plant, or gets into the soil from the plant roots or from being washed off the leaves during watering (in a laboratory setting).  

By far, the most frequently used radionuclides for research are carbon‑14 (C14), tritium (H3), iodine‑125 (I125), phosphorus‑32 (P32) and sulfur‑35 (S35), which have low enough energies to be easily shielded with thin plastic. I125 emits low-energy gamma radiation which also is easily shielded by plastic or glass.

Only very small quantities of these radionuclides are used, usually measured in microcuries or nanocuries. Because it’s gotten more expensive to use and dispose of radioactive materials, scientists have developed alternate testing methods for many studies. However, some research still requires radioactive materials because they’re the best way to label and trace a compound.

The use of radioactive materials in research requires a license from the NRC or an Agreement State, and scientists who use radioactive materials are trained in radiation safety and their research methods.

Failed Bolts Bedevil a Nuclear Plant

Neil Sheehan
Public Affairs Officer
Region I

 

Truly novel issues are, generally speaking, few and far between at U.S. nuclear power plants. Whether it’s a specific type of pipe that springs a leak or an electrical relay that goes on the fritz, chances are good that the problem has been experienced before somewhere across the nation’s fleet of commercial power reactors during the many decades they have been in operation.

An issue that has drawn attention at the Salem Unit 2 nuclear power plant, a pressurized-water reactor in southern New Jersey, has to do with the failure of small bolts contained in four reactor coolant pumps. The bolts, measuring 1 inch in diameter and 4 inches in length, are used to secure a turning vane inside the pumps.

These pumps stand about 30 feet tall and provide forced flow of coolant, or water, through the reactor to transport heat from the fuel to the steam generators. The steam generators, in turn, make use of that heat by converting it to steam. The steam is then piped to the turbine to spin it and generate electricity.

Salem Bolt imageAs can be seen in the graphic, water is drawn upward through the suction nozzle at the bottom of the pump via an impeller. The turning vane directly above the impeller then redirects the water toward an opening on the side, from which it flows into the reactor vessel.

When a refueling and maintenance outage began at the plant this spring and evaluation and maintenance work got under way, a number of turning vane boltheads were found in piping associated with one of the reactor coolant pumps and in the reactor vessel. (Similar discovery of these boltheads, albeit just a handful of them, had been observed in two prior outages.) Subsequent reviews, which have now included the examination of all of the pumps, have identified dozens of failed or sheared turning vane bolts in all of them.

Each pump has 20 such bolts. (The arrow shows the approximate location of the bolts.) A majority of the failed boltheads, though separated from the bolt shanks, remained in place thanks to mechanical restraints or tack welds.

While this is not a significant safety concern in terms of potentially causing a reactor core damage accident, there are several related operational issues. For one, the boltheads are considered foreign material that could have an adverse impact on reactor coolant system performance if they were to impact key components inside the system. For another, the turning vane could conceivably drop down and come into contact with the impeller and impede or halt its functioning.

The cause of the bolts’ failure remains under review, but one possibility is stress-corrosion cracking. Indeed, the NRC issued Information Notices to the industry in the 1990s regarding this phenomenon.

A 1994 Information Notice put out by the agency was designed to make the industry aware of stress-corrosion cracking that caused turning vane cap screws to fail at the Millstone Unit 3 nuclear power plant. Also, a 1990 Information Notice discussed the failure of turning vane bolts at a foreign reactor.

In a 1995 Information Notice, the NRC made plant owners aware of the loss of integrity for bolt-locking devices in the turning vanes of reactor coolant pumps at the Seabrook nuclear power plant but for a different reason: flow-induced vibrations.

PSEG, the owner and operator of the Salem and Hope Creek plants, will have to not only repair the Salem Unit 2 pumps but evaluate what went wrong. For now, the plant remains out of service while this work is taking place. NRC inspectors and specialists will closely follow these activities.

One area for consideration will be whether the problem could have been avoided based on previously available information.

The NRC Makes a Determination After Last Year’s Crane Collapse

Victor Dricks
Senior Public Affairs Officer
Region IV

 

Last year, the Arkansas Nuclear One facility experienced a tragic incident when a crane collapsed. One person was killed, eight were injured and important plant equipment was damaged. The NRC has now issued two “yellow” inspection findings as a result. The “yellow” means we found substantial safety significance related to the incident.

arkansasWorkers were moving a massive component out of the plant’s turbine building when the incident occurred. Unit 1 was in a refueling outage at the time, with all of the fuel still in the reactor vessel. At the time, Entergy Operations declared a Notice of Unusual Event, the lowest of four emergency classifications used by the NRC, because the crane collapse caused a small explosion inside electrical cabinets. The damaged equipment caused a loss of off-site power. The NRC’s senior resident inspector had driven to the plant to personally survey the damage and monitor the licensee’s response from the plant’s control room.

Here’s why NRC decided the incident had substantial safety significance even though both plants were safely shut down and there was no radiological release or danger to the public: Emergency diesel generators were relied upon for six days to supply power to heat removal systems.

The falling turbine component damaged electrical cables needed to route power from an alternate AC power source to key plant systems at both units. This condition increased risk to the plant because alternate means of providing electrical power to key safety-related systems was not available using installed plant equipment in the event the diesels failed.

Unit 2, which was operating at full power, automatically shut down when a reactor coolant pump tripped due to vibrations caused when the heavy component fell and hit the turbine building floor. Unit 2 never completely lost offsite power, and there was a way to provide it with emergency power using the diesel generators.

The NRC conducted an Augmented Team Inspection. We prepared a detailed chronology of the event, evaluated the licensee actions in response, and assessed what may have contributed to the incident. (Worker safety issues are the responsibility of the Occupational Safety and Health Administration, which conducted an independent inspection of the incident.)

The NRC determined that the lifting assembly collapse was a result of the licensee’s failure to adequately review the assembly design and to do an appropriate load test.

We held a public meeting in Russellville, Ark., on May 9, 2013, to discuss the team’s initial findings. From its follow-up inspections, the NRC issued a preliminary red finding to Unit 1 and a preliminary yellow finding to Unit 2. These are documented in a March 24 inspection report.

NRC held a regulatory conference with Entergy officials on May 1, and after considering information provided by the licensee determined that “yellow” findings were appropriate to characterize the risk significance of the event for both Unit 1 and 2. The NRC will determine the right level of agency oversight for the facility and notify Entergy officials of the decision in a separate letter.

River Levels on the Rise – The NRC At The Ready

Lara Uselding
Public Affairs Officer
Region IV
 

NEW UPDATE: Currently, river levels are at 1000 feet 6 inches with levels not expected to increase more than a few inches over the next 24 hours. OPPD is returning the plant to full power. NRC inspectors provided around the clock coverage through last weekend and the agency will continue closely monitoring plant operations and river conditions.

UPDATE: Fort Calhoun began decreasing power at midnight, and is currently holding at a reduced power level. The river level is now predicted to crest at 1,002.4 feet on Saturday, which is lower than previously predicted. For comparison, the 2011 flood peaked at about 1,007 feet. Three people from Region IV will begin around the clock coverage today in support of the resident inspectors.

Three years ago this month marks the anniversary of the record Missouri river floods. Now, due to heavy rains, the NRC is once again watching rising Missouri River levels impacting Nebraska’s Fort Calhoun nuclear power plant,  north of Omaha.

Cooper Nuclear Station in Brownville is not anticipating a major impact this weekend.

Fort Calhoun’s procedure requires them to declare a Notice of Unusual Event and be shut down by the time river levels at the site reach 1,004 feet mean sea level. Thursday afternoon, river levels were at 998 and rising. Normally, river levels at the site range from 980 to 990 feet mean sea level.

Over the past week, NRC’s Region IV in Arlington, Texas, has been engaged in routine calls with the United States Army Corps of Engineers, National Weather Service, Federal Emergency Management Agency, National Oceanic and Atmospheric Administration, states, and local response organizations to understand changes in the predicted river levels and assess potential impacts on the plants. 

Simultaneously, the NRC has been overseeing actions that Omaha Public Power District (Fort Calhoun) and Nebraska Public Power District (Cooper) are taking to protect the plant against impending flood waters. At this time, river levels at Cooper are not projected to be high enough to require a plant shutdown.

OPPD’s actions involve the use of sand bags, flood doors, and readying mobile pumps as river levels are projected to rise. They have also ordered equipment to protect certain buildings on site. NRC resident inspectors, who live in the area and work at the plant, have been monitoring the flood preparations.

The NRC is sending more staff to the plant to support the resident inspectors and provide around the clock coverage. During the 2011 flood, river levels at Fort Calhoun reached about 1007 feet and the plant remained in a safe shutdown condition. The plant restarted late last year only after extensive flooding improvements and other safety upgrades mandated by the NRC. Fort Calhoun remains under increased NRC regulatory oversight.

Region IV will continue monitoring the situation for both plants over the weekend.

 

 

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