Tracking casks

RECENT MOVES TOWARDS SMALL MODULAR reactor (SMR) systems, due to their lower projected construction costs, mean the number of SMR units could increase rapidly in developing countries. In turn, nuclear materials inventories will also increase.

Nuclear materials may be vulnerable to terrorism, especially during transportation, so measures have to be taken for continuous monitoring of packages during transport, storage and disposal. Continuous surveillance can be achieved by integrating modern microcontrollers with sensors and wireless communication techniques. This can help enhance safety and security by informing first responders of the position, nature and severity of any incidents.

Monitoring systems

Continuous monitoring systems such as Argonne’s ARG-US RFID, ARG-US CommBox and RAMM systems technology can be used. However, these systems may be vulnerable to ‘lone wolf’ attacks. To overcome this, a new design approach for intelligent transportation systems (ITS) has been proposed based on the internet of things.

For most nuclear newcomer countries, without an ITS or private satellite communication, an alternative system can be used. In this system, a customised Global System for Mobile communication (GSM) module is designed for wireless radiation monitoring using the short messaging service (SMS).

The module is able to receive serial data from radiation monitoring devices such as a survey meter or area monitor and transmit the data as a text SMS to a host server. It provides two-way communication for data transmission, status queries, and configuration setup. Integrating this module with a radiation monitoring device will create a mobile and wireless radiation monitoring system capable of alerting users to high levels of radiation. This system has not been used to track nuclear materials. This article proposes a system using global satellite communication that can be attached to transportation casks for nuclear materials tracking.

Design

The proposed system (Figure 1) comprises a microcontroller with on board GPS and GSM modules, sensors, application software, a database server and web page. It monitors critical parameters, including the status of seals, movement of objects, and environmental conditions of the cask in real time. It provides an alarm (by SMS) when preset levels for the sensors are exceeded.

The information collected by the system is transmitted to a dedicated central database server that can be accessed by authorised users via a secure network. The system allows casks to be tracked and inspected through storage, transportation, and disposal. The software provides easy-to- use graphical interfaces that allow access to all vital information once the security and privilege requirements have been met.

Sensor modules

The prototype sensors include: safety sensors (for radiation and temperature), a security sensor (for monitoring the status of seals) and a driver violation detector (speed of the truck). In this paper, the EPR reactor spent fuel is selected as the nuclear material.

Safety sensors are used to indicate the radiation and temperature level states of the cask. The Origen computer code is used to calculate the thermal and radiation loads of the cask, which will be used to determine the sensor threshold level (Figure 2). The preparation details of the Origen input file based on EPR fuel are available in “Cooling period calculation of evolutionary power reactor spent fuel for dry management safety”, Nuclear and Radiation Safety Journal, Volume 2).

The radiation and temperature sensor threshold levels are determined as follows:
Radiation: when EPR spent fuel (5% enriched) is placed in a real cask system, the dose rate on the external surface of the cask will be lower than 1000mrem/hour. Therefore, the prototype will use PIN diodes to detect the increasing in gamma level, where 1000mrem/hour is sufficient to excite the PIN diodes. Any gamma detector PIN diode circuit consists of a low noise amplifier and comparator (Figure 3). The advantage of using a photodiode is its small sensitive area. This makes it suitable for the high dose rate of the cask, and it is not affected by the low background rate due to cosmic rays.  

Temperature: EPR spent fuel can be loaded to MPC-24 basket. In accordance with the equation in the paper referred to above, peak cladding temperature (PCT) is 307.12°C in normal condition operations when the decay heat is 1.050kW/assembly. For the 24 PWR assembly storage cask system with a burnup of 55GWd/MtU and 25.2kW decay heat load, the normal temperature for long-term events (e.g. onsite and offsite transportations, and storage) are 302°C for PCT, 64°C for the overpack outer surface and 67°C, for the air outlet. Therefore, for the EPR spent fuel, the normal temperatures are 307°C for the PCT, 69°C for the outer surface and 72°C for the air outlet. The normal temperature limits for the overpack outer surface and air outlet are 98°C and 72°C, respectively.

For the prototype, the circuit used two digital temperature sensors. Where their positions are in the overpack outer surface (near the top air outlet) and air outlet, the temperature alarm SMS will be delivered to the control unit (or to an emergency specified telephone number) if the temperature exceeds 98°C for overpack and 72°C for the outer surface.

Status of seals: The seal sensor can be located under one or two of the seal bolts of the cask overpack. It is a short-circuit wire warped around the bolt of the cask overpack. When the bolt is loosened, the microcontroller triggers an alarm; the alarm is broadcasted by SMS to the responsible bodies.

Online cask monitoring and tracking

The system is used to receive location data from satellites (via GPS module) and monitoring data (via sensors), and transmit it to the desired web servers using a GPRS connection (via GSM module).

GPS Module: The embedded system used the recommended minimum specific GPS/Transit data ($GPRMC) frame. This frame contains information about the locations of the cask and the cask speed over ground. The speed can be used as a driver violation if it exceeds a predefined value. It can also be used as a motion detector for the cask in storage if it is greater than zero km/hour.

GSM Module: GSM and GPRS international communications standards provide wireless communications capabilities. The GSM module sends the SMS messages while connection of the ES to the internet is through the mobile operators GSM/GPRS.

Web servers: There are two servers. The first is for confidential data, e.g. the cask monitoring data, while the second server is for tracking data.

Microcontroller

The microcontroller is a programmable system-on-chip cypress chip. The chip includes CPU core, configurable blocks of analogue and digital logic, and programmable interconnects. This architecture allows the user to create customised peripheral configurations for each application.

Proposed frame format

Data are sent to the main servers as frame format. All data are grouped in a frame with a defined format. Fields contain: cask identification number (ID), cask tracking location, seal status, and cask monitoring sensors data. The microcontroller takes the location data from the GPS module and put it in its field in the frame (Figure 4).

Operation

The operation methodology is shown above (Figure 5). The system reads the sensors and sends these data to monitoring and tracking servers by GPRS. If any one of the sensor values exceeds the limit, the ES send an instantaneous SMS to the predefined telephone number; the monitoring and tracking are instantaneous. For power saving, in normal operations, the system is programmable to wait a time between each reading process (e.g. in casks storage site, the waiting time will be about ten minutes).

Gamma source terms calculation

Radiation source terms of spent fuel are photons and neutrons. The photon source of the EPR spent fuel is calculated using the Origen code based on EPR parameters, where the photons are the source term of gamma. The EPR spent fuel photon source decay of the activation products, actinides and daughters, and fission products are calculated (Figure 6a). As shown, the main gamma source term is the fission products photons. The radioactive characteristics of the EPR fuel has previously been calculated, but for a burnup of 60GWd/MtU and enrichment of 4%. To make sure that our calculations of the gamma sources (5% enriched EPR fuel) correspond to that calculations, we compared our results with the reference results.

Beyond five years of cooling, the differences between the two curves are small – about 0.078393% at 20 years – providing that the values of the flux-to-dose conversion coefficients for photons given by ANSI/ANS-6.1.1-1977 are about 20% larger than the version 1991, and ICRP74 coefficients at the energies of interest. This means that, when EPR spent fuel (5% enriched) is placed in a real cask system, the dose rate on the external surface of the cask will be lower than 1000mrem/hour, which satisfies US Nuclear Regulatory Commission requirements.

Online cask monitoring

The online cask monitoring data are held by the responsible body. The cask monitoring data are: cask ID, seal status, location (north and east), radiation status, overpack outer surface temperature and air outlet temperature. In the prototype, the cask seal status is either ‘Ok’ or ’Opened’. Cask radiation and temperature statuses are ‘Ok’ or ‘Over Limit’.

Online cask tracking

The truck is followed either using Google maps web page or the Traccar system.

In Google maps, the authorised user will copy the longitude and latitude received in a cask monitoring server to Google maps web page. This method reduces the code complexity and cost of the ES.

The alternative method uses the free and open source system provided by Traccar, which supports more protocols and device models. The cask can be viewed in real-time with no delay, by the ES GPS module. Traccar have various mapping options, including road maps and satellite imagery. The cost is between $20.00 and $100.00 per month.

The Traccar system can send immediate SMS warnings about driving violations to a predefined telephone number, and alerts about danger states of the cask can be sent directly to predefined telephone numbers such as police or nuclear safety staff, to ensure rapid intervention.

Issues to be addressed

Some problems that may face the applications of the system include possible ionising radiation effects on the electronic components, loss of GSM network as well as data security.

In normal operations, the dose rate on the external surface of the package is below 1000mrem/hour, which will not
affect electronics. Research shows that the microcontroller does not fail until the total ionising dose exposure accumulates up to 11.3krad (Si), and it performs normally even when the neutron fluence is up to 3.0 x 1013n/cm2.

Electrical and the communication systems on the site must be maintained because physical protection of stored spent fuel and the geologic repository requires continuous surveillance and an active alarm system.

Spent fuel must be stored only within a protected area with adequate illumination. The alarm system is monitored in two independent, continually staffed stations, although the secondary station requires only summary indications. Personnel ID and controlled lock systems must be established and maintained. Redundant communications capability must be established between onsite security force members and designated response force.

The geologic repository area requires:

• Means to monitor and control radioactive contamination.
• Means to control access to high radiation level areas.
• Alerts in case of rising radiation levels.
• Uninterrupted power systems for instruments, operating systems important to safety, and service systems.
• Inspection, test, and maintenance.

Each storage installation must have accident detection systems. The store and the repository sites must have access to more than one communication network. That may include the Iridium satellite (e.g. RockBLOCK 9602) transceiver models. RockBLOCK 9602 can send and receive short messages from anywhere on earth with a clear view of the sky. It works far beyond the reach of Wi-Fi and GSM networks but at a relatively high cost.  

Acknowledgement

Authors wish to acknowledge the Professor Ezzat A. Eisawy for his strong support. They are thankful to Eng. Nagdy for his cooperation in the laboratory work. Also, they want to thank Eng. Emile Rushdie for his valuable discussion. 

Author information: M. I. Youssef, Faculty of Engineering, Al Azhar University, Cairo, Egypt; M. Elzorkany, National Telecommunication Institute; G. F. Sultan, Egyptian Nuclear and Radiological Regulatory Authority; Hassan F. Morsi, Egyptian Nuclear and Radiological Regulatory Authority