Under the SAFE Port Act, DNDO is required, among other functions, to develop, in coordination with other federal agencies, an enhanced Global Nuclear Detection Architecture. DNDO serves as the primary entity in the United States to develop programs and initiatives related to the Global Nuclear Detection Architecture, identify any gaps in it, and improve radiological and nuclear detection capabilities. DNDO also assists DHS agencies with implementing the domestic portion of the Global Nuclear Detection Architecture, including deployment of radiation detection equipment at ports of entry along the U.S. border. Accordingly, DNDO acquires and deploys RPMs and provides for associated scientific and technical expertise, with assistance from the Department of Energy’s national laboratories, including PNNL and Los Alamos National Laboratory. CBP operates the RPMs and maintains them after their first year of deployment. As of August 2016, CBP operates approximately 1,300 RPMs, which can detect radiation but cannot identify the type of material causing an alarm, as well as almost 2,700 handheld radiation detectors, which can identify the sources of radiation. RPMs are the primary means by which CBP scans cargo and vehicles at U.S. ports of entry for nuclear and radiological material. Before leaving a port of entry, most cargo containers and vehicles first travel through an RPM. (See fig. 1.) If an alarm is triggered, the cargo container or vehicle is directed to a secondary inspection area for further inspection and clearance by a CBP officer using a handheld radiation detector that can identify the source of the radiation. (See fig. 2.) RPM alarms can result from naturally occurring radioactive materials (NORM), which are often emitted from certain consumer and trade goods, such as ceramics, fertilizers, and granite tile. RPM alarms from NORM are termed “nuisance” alarms by DHS and require CBP officers to spend time determining that the source of the alarm is NORM and not nuclear or radiological threat materials before the cargo container or vehicle can leave the port. Although fewer than 2 percent of cargo containers have historically set off an RPM alarm, according to DHS, with more than 20 million cargo containers and more than 100 million vehicles passing through the nation’s ports annually, nuisance alarms account for hundreds of thousands of alarms per year. To reduce nuisance alarms and decrease the need for secondary scanning by CBP officers, in 2014 and 2015, CBP developed and deployed a new set of RPM alarm threshold settings, with support from DNDO and scientists at PNNL. This upgrade, which is referred to as revised operational settings, is implemented during calibration. It optimizes RPM effectiveness by tuning the threshold settings of individual RPMs to account for local background radiation and common NORM passing through the RPMs. These new threshold settings result in a similar sensitivity to materials that pose a threat but significantly reduce nuisance alarms from NORM. According to CBP, as of the end of fiscal year 2015, DNDO and CBP had upgraded RPMs at 28 seaports and 15 land border crossings, which has reduced nuisance alarms by more than 75 percent, on average, at these sites. Before fiscal year 2015, DHS had acquired 1,706 RPMs, including 384 from Ludlum Measurements, Inc. (Ludlum) and 1,322 from Leidos Holdings, Inc. (Leidos). The Ludlum RPMs were the first to be acquired and were deployed beginning in fiscal year 2003, and the Leidos RPMs were first acquired and deployed in fiscal year 2004. (See table 1.) Ludlum and Leidos RPMs have comparable designs—both use specialized detection panels made of plastic as well as helium-filled tubes—and provide similar technical capacity to detect nuclear and radiological materials. However, because of limitations in the design of the plastic panels in the Ludlum RPMs that DHS acquired, these RPMs cannot be upgraded with the revised operational settings and thus do not have the threat discrimination capabilities equal to the upgraded Leidos RPMs. Threat discrimination refers to the ability of the RPM to distinguish between radiation emitted from NORM and radiation emitted from radioactive materials that could be used in a nuclear device or a dirty bomb. As of August 5, 2016, DHS had 1,386 RPMs deployed—including 277 Ludlum RPMs and 1,109 Leidos RPMs—with the remaining RPMs in storage. Of the deployed RPMs, 885 were at northern and southern border crossings; 320 were at seaports; and 181 were at airports, ferry terminals, or other facilities. (See table 2.) According to DHS officials, the actual number of deployed RPMs varies on a day-to-day basis in response to port reconfigurations and expansions and because DHS periodically decommissions RPMs that are infrequently used. As of August 2016, 100 percent of cargo containers and vehicles entering land border crossings and nearly 100 percent of cargo containers passing through seaports are scanned by RPMs, according to DNDO. However, as we found in 2012, significant technological and logistical challenges exist for scanning cargo at airports and international rail ports of entry, and as of August 2016, some cargo containers that enter through these pathways are not being scanned by RPMs. Scanning of air cargo is primarily carried out with handheld radiation detectors, and scanning of international rail cargo is mainly conducted with such detectors and radiographic imaging systems. Radiographic imaging systems use gamma rays or X-rays to produce an image of cargo to detect anomalies, such as high-density material or hidden cargo, but they do not detect radioactivity. DHS’s assessment of its RPM fleet shifted over time, and as a result DHS has changed the focus of its RPM replacement strategy. More specifically, in fiscal years 2014 and 2015, DHS began planning to replace the full fleet based on a conservatively estimated 13-year service life. However, recent DNDO studies indicate the fleet can remain operational until at least 2030, with proactive maintenance and sufficient availability of spare parts, so DHS has refocused its strategy on selective replacements to improve efficiency. Before the RPMs began to reach the end of their estimated service life, DNDO commissioned a field study assessing how well the RPM systems were aging and a separate study specifically assessing the aging of the RPM’s key component—the plastic detection panels. These studies were published in 2011 and both concluded that the original 10-year RPM service life estimate should be updated. One of the studies concluded that the plastic detection panels could last up to 20 years—with 13 years as a conservative estimate of the panels’ life spans. The other study concluded that the panels would last between 15 and 20 years and that the RPMs could be sustained for an extended period with routine inspections, maintenance, and repairs as needed. According to DNDO officials, after these studies were published, DNDO began using a 13- year service life estimate for RPM life-cycle planning and budgeting purposes. Echoing one of the studies, a DNDO management official told us that the 13-year RPM service life was considered a conservative estimate that resulted in an acceptable level of risk to the program. The official further stated that although the 13-year estimate contained a great deal of uncertainty, DHS was trying to ensure that the necessary steps would be taken to keep the fleet fully functional. DNDO used the 13-year service life estimate for its RPM program planning and budget justifications throughout fiscal years 2014 and 2015, including in the following cases: DNDO’s RPM Program Management Plan for fiscal years 2014 through 2019, published in January 2014, stated that more than 500 of the then-deployed RPMs would reach the end of their service lives by 2019 and would require either refurbishment or replacement. The plan outlined DNDO’s efforts to extend the service life of the RPMs while working on a strategy for RPM replacement. DHS’s budget justification for fiscal year 2015 referred to RPMs exceeding the end of their estimated service lives as part of a discussion of RPM program needs. DHS’s June 2014 Global Nuclear Detection Architecture Strategic Plan of Investments highlighted a need for significant funding increases to replace RPMs as they reached the end of their estimated service lives. The plan projected significant decreases in RPM scanning coverage—the percentage of vehicles or cargo containers scanned—beginning in fiscal year 2016 based on the service life estimate, anticipated port expansions and reconfigurations, and projected budget levels. Specifically, the plan projected that RPM scanning coverage at seaports would fall from 100 percent in fiscal year 2014 to 69 percent in fiscal year 2019. For land border crossings, it projected a decrease from 98 percent scanning coverage to 39 percent over the same period. In its February 2015 update to its RPM Program Management Plan, DHS again emphasized the need for RPM replacements because RPMs would begin reaching the end of their estimated 13-year service lives. In addition, the plan stated that projected budget levels through fiscal year 2019 were sufficient for the program to begin to replace the RPMs reaching the end of their service life. The plan also highlighted the importance of efforts to extend RPM service life to retain the ability to perform required scanning. DHS’s budget justification for fiscal year 2016 referred to the 13-year RPM service life as it called for increased funding for replacements based on service life concerns. The budget justification stated that funding increases would address sustainability of aging RPMs and ensure compliance with the SAFE Port Act as DHS formulates a long-term strategy for the replacement of RPMs at the end of their life cycle. Furthermore, in October 2015, a senior DNDO official told us that DNDO was using 13 years as a conservative estimate for RPM service life.