Fitz F. Carty1, Laura Comes1, Joel B. Forrester2, Harry S. Miley2, George (Bob) Shipman1, and Peter Van Davelaar1

General Dynamics-Advanced Information Systems1 and Pacific Northwest National Laboratory2

Sponsored by the Army Space and Missile Defense Command

Award Nos. W9113M-08-C-01731 and MIPROF089TGASF2

2011 Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies

Link to source pdf:


General Dynamics acts as the equipment provider and oversees the operations and maintenance (O&M)
responsibilities for the radionuclide monitoring systems of the International Monitoring System (IMS) which are
owned and/or maintained by the United States—specifically, 11 aerosol systems and 4 xenon systems. As such, we
are in a unique position to gather and evaluate performance data and assess the operational impact of both
equipment and O&M issues and anomalous events.

On 11 March 2011, a 9.0 magnitude earthquake and tsunami rocked the eastern coast of Japan, resulting in power
loss and cooling failures at the Daiichi nuclear power plant(s) in the Fukushima prefecture. Several institutions
reported on the early measurements of short-lived aerosol fission products and gaseous xenon isotopes detected
outside Japan following the release of radioactive material. We present a summary of the operational impacts of the
Fukushima incident on the U.S. network of aerosol monitoring stations.

We present a summary of the operational impacts of the Fukushima incident on the U.S. network of aerosol
monitoring stations.

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) specifies in Annex I to the Treaty Protocol, the locations of
all components of the IMS. These components are seismic, infrasound, hydroacoustic, and radionuclide monitoring
systems supported by radionuclide laboratories and the International Data Center. General Dynamics is the
designated Station Operator for the Untied Statess (U.S.) Radionuclide stations shown in Figure 1. These stations
house both Particulate and Noble Gas detection systems.

System Design:
The U.S. particulate system is the Radionuclide Aerosol Sampler/Analyzer (RASA), which employs an innovative
continuous feed system that automatically conducts sampling, decay, and acquisition in a secure housing with
infrequent on-site human support (Figure 2). The key to the RASA’s compact design is the division of the filter
sampling area into six individual sampling areas that are reassembled and encapsulated into an efficient geometry
for radionuclide measurement (Figure 3).

Noble Gas
The U.S. uses the Swedish Automatic Unit for Noble gas Acquisition (SAUNA) for xenon detection
(Ringbom, 2003). SAUNA consists of a rack containing sampling and processing units and two detectors
utilizing beta-gamma coincidence detectors (Figure 4).

SAUNA data is presented in the form of 3-D beta-gamma spectra (Figure 5, Berglund, 2009) which requires special
data reduction and analysis software.

Normal Operations:
During periods of normal operation, scheduled station operation and maintenance include daily, biweekly, and
semi-annual activities, some carried out by local operators on-site and some by senior operators on-site and at the
Sensor Operation Center located in Fairfax, Virginia. These activities are supplemented, as required, by unscheduled
maintenance when equipment failures occur.
Daily Activities
The key element in General Dynamics’ responsive Operation and Management Plan is the Daily Standup meeting.
Each morning during the work week, a brief Operations Meeting is held to review the status of all stations. This
meeting is led by the Hardware Team Leader and features details of the previous day’s system performance as well
as pending logistics issues. The system performance is measured against the requirements set by the Comprehensive
Nuclear-Test-Ban Treaty Organization (CTBTO) (CTBTO, 1999). Remotely-located team members and those on
travel are included by teleconference. During the meeting, actions to correct any station problems are discussed and

Bi-Weekly Activities
A bi-weekly on-site station visit is made by at least one of the two local operators to perform routine maintenance,
check on the station condition, and ensure that no problems are developing .
Semi-annual Preventative Maintenance visit
Twice each year, a General Dynamics engineer from the IMS Hardware Team visits each station and conducts a
detailed regimen of tests and procedures designed to detect or forestall potential problems. These tests provide an
early indication of required maintenance or replacement and provide detailed documentation of each station’s
condition. Scheduled upgrades, equipment replacements and Local Operator initial and refresher training are
provided at this time.

Fukushima-Daiichi Release Event
The first reported release of radiation (intentional, to reduce pressure in the reactor) occurred on 12 March 2011
(The Nuclear Energy Agency (NEA) of the Organisation for Economic Co-operation and Development (OECD),
The first major release of radionuclides from the Fukushima-Daiichi reactor site was reported on 19 March 2011
(NEA OECD, 2011). Prior to the release, a typical spectrum from USP70, the RASA particulate system in

Sacramento, California showed only normal background radiation due to uranium and thorium decay products and
other natural nuclides such as K-40 and Be-7 (Figure 6).

Figure 7. USP70 – During the Release
For the particulate systems, the highest levels of Cs-137 occurred for the 24-hr sample collections starting on 21 and
22 March 2011 (UTC) (Figure 8). The greatest concentration of Cs-137 was recorded in the Aleutian Islands at
RN71, Sand Point AK (9,808 µBq/m3).

For the Noble Gas systems, the highest levels of Xe-133 occurred for the 12-hr sample collections on 21 through 23
March 2011 (UTC) (Figure 9). The greatest concentration of Xe-133 was recorded in Ashland KS at RN74 (13,453

The Daiichi release was detected at all U.S.-operated IMS radionuclide stations except RN73 (Palmer Station,
As might be expected, the initial arrival of the release varied from station to station (Figure 10).

Event Impact on Operations
Immediately following news reports of the incidents at the Daiichi power plant, actions were taken to limit any
potential impact on the ability of the stations to perform their primary collection and detection mission in support of
the CTBT.
• All non-critical operations at the stations that would interfere with continuous collection were postponed to
avoid interruptions in data. This included the delay of scheduled “blank” measurements acquired routinely
on a periodic basis to detect potential contamination.

• The samples collected in March were held at each station instead of being sent to Vienna in the Quarterly
shipments of archival samples.

• Inlet plenums were not removed unless absolutely necessary. Normal internal cleaning of the inlet plenums
was postponed.

• Tests during semi-annual preventative maintenance visits to measure bypass flow were postponed as these
tests require shutting down the blower, removing the inlet plenum and blocking the airflow path through
the filters.

• Operations were modified to minimize stirring up contamination that may have settled in the station or
inside the inlet plenum of the system.

• Floors in the station were damp-mopped instead of swept to avoid spreading any potential contamination to
the detector region of the RASA system.

• Split samples were requested by the CTBTO from many of the stations in order to provide samples to two
different certified laboratories. Local operators had been previously trained to prepare these, and a step by
step procedure was emailed to the local operator with each split sample request

• Once anthropogenic nuclides were no longer being detected at a station, swipe samples were taken
following a carefully prepared procedure and counted under double-blind conditions to ensure unbiased
results. Acquisition and counting of these swipe samples is ongoing.

Network Performance and System Effects During the Month After the Release
All stations were fully mission capable during the entire first month of this incident.

The SAUNA Noble Gas monitoring systems are known to have memory effects caused by xenon adhering to the
walls of the beta cell. This effect is routinely seen during calibration as well as being seen during this event.
Following the detections in mid-March, the MDC for the Noble Gas systems was moderately elevated from 0.6
mBq/m3 before the release to about 7 mBq/m3 a week after the release. Measured xenon levels a week after the
peak of the release (13,452 mBq/m3 at RN74 on 23 March 2011) were still in the 1000 – 2000 mBq/m3 range.
Based on early swipe results, no U.S. stations appear to be contaminated due to the plume from the Daiichi nuclear
power plant.

General Dynamics AIS wishes to acknowledge our sponsor, Army Space and Missile Defense Command without
whose support our work would not be possible. We also wish to acknowledge Pacific Northwest National
Laboratory and the Comprehensive Nuclear-Test-Ban Treaty Organization whose help and data were instrumental in
developing this paper.

Berglund, H. (2009). SAUNA-II Detector Calibration. SAUNA-Detector Technical Training Program (p. Slide #13).
Uppsala, Sweden: GammaData.
Ringbom, A., T. Larson, A. Axelsson, K. Elmgren, and C. Johansson (2003). SAUNA—a system for automatic
sampling, processing, and analysis of radioactive xenon. Nucl. Instrum. Meth. Phy.s Res. A 508, 542–553.
The Nuclear Energy Agency (NEA) of the Organisation for Economic Co-operation and Development (OECD).
(2011, 6 20). OECD NEA – Timeline for the Fukushima Dai-ichi nuclear power plant accident. Retrieved 7
14, 2011, from Organisation for Economic Co-operation and Development (OECD): http://www.oecd-