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Digital Technology for Fissile Materials Detection

#2978


Digital Technology for the Detection and Control of Fissile Materials in Devices with Pulsed Neutron Sources

Tech Area / Field

  • FIR-NSS/Nuclear Safety and Safeguarding/Fission Reactors
  • INS-DET/Detection Devices/Instrumentation

Status
8 Project completed

Registration date
21.01.2004

Completion date
07.04.2011

Senior Project Manager
Smirnova N V

Leading Institute
MIFI, Russia, Moscow

Supporting institutes

  • All-Russian Research Institute of Automatics, Russia, Moscow\nNIIIT (Pulse Techniques), Russia, Moscow

Collaborators

  • Oak Ridge National Laboratory / Nuclear Science and Technology Division, USA, TN, Oak Ridge\nBubble Technology Industries Inc., Canada, ON, Chalk River\nFraunhofer-INT, Germany, Euskirchen\nUniversita Degli Studi di Bari / Dipartimento Interateneo di Fisica, Italy, Bari

Project summary

The purpose of the Project is the development of physical methods and facilities for the detection and non-destructive control of fissile materials (FM) with use of pulsed neutron sources in combination with various neutron moderators. Response of FM is detected using digital processing of signals from scintillation systems. Creation of these devices is required due to problems of non-proliferation of nuclear weapons or their components, non-authorized transportation of uranium or plutonium across the state frontiers, assay of the nuclear waste composition, and also nuclear material control and account at the sites of its manufacture and storage.

It is known, that detection and control of uranium or plutonium can be performed using their natural neutron or photon radiation. However, not all nuclides have sufficiently high neutron yield, and their photon radiation has low energy and can be easily concealed even with thin layers of lead shields. Besides, the effect of radiation self-shielding by external layers of FM prevents analyzing the composition of “thick”, and especially non-uniform, samples with good accuracy. Thereof, the use of an external neutron source for the irradiation of an object under inspection can practically remove all specified problems of the FM analysis, as the penetrating capability of neutrons, especially prompt ones, is high, and their interaction with shields of heavy elements is sufficiently low. Known similar devices for the active FM control most often use radioisotope AmLi or 252Cf sources or neutrons of various nuclear reactions on accelerators and nuclear reactors. Application of these sources does not practically allow to change the neutron energy during the experiment, and in most cases they cannot be switched off, when the device is not in operation outage or when it is transported. The constancy of neutron energy of radioisotope sources considerably narrows the field of application of possible physical methods, and in case of act of terrorism, destruction of such sources causes severe contamination of the environment, and thus, essentially reduces their operational safety.

The existing devices use numerous electronic blocks of coincidence circuits, shift registers, peak and time analyzers, and also spectrometer devices of various types, which essentially worsens the conditions of their standardization and prevents decreasing the price of control devices on the whole. Helium counters currently used as detectors of neutron radiation, such as 3He counters, are applied for registering thermal neutrons, and efficiency of 4He counters used for registering fast neutrons is at a level of only 1%. Nevertheless, scintillation systems, having the efficiency of registering radiation approaching to 100% and fast operation, are rarely used as they detect neutrons and photons with approximately equal efficiency, and conventional spectrometry blocks for their discrimination have poor performance under high loads that are typical of express measurements.

The approach to the design of devices of FM detection and non-destructive control suggested in the Project practically eliminates all the listed drawbacks of existing devices. The basic idea of the Project consists in creation of active FM control devices with pulsed neutron sources and various combinations of moderators, in which the time dependencies of FM fission neutrons and photons can be separated with use of digital technology. In devices with various neutron moderators having different neutron slowing-down times it is feasible to design devices, in which various energy groups of neutrons exist some time later after a pulse of source neutrons.

However, this known property can be used in full only in combination with a neutron detector that has good spectrometric characteristics, and separates neutrons and photons under a high and variable load on the electronic channel. It can be achieved by rejecting many electronic blocks and proportional counters currently used, replacing them with circuits of digital analysis of scintillation pulses with subsequent digital recording of the amplitude-time distribution and the shape of FM response signals in the computer memory. FM response is detected practically with zero dead time, and high efficiency inherent in scintillation systems. The created database of digitized pulses allows to apply mathematical processing of the obtained time and amplitude sequences of pulses (probably consisting of separate independent electronic channels), and to obtain information on all possible functionals of the neutron and photon response of FM radiations in one experiment. With the help of software processing, it is possible to discriminate neutrons and photons, and also to study their coincidences of any multiplicity and in different energy groups. Thus, it is possible to create devices of active FM control of new generation, which will have the following advantages in comparison with those already existing:

1. Extended range of physical methods of FM control and detection, due to the use of various neutron energies and unique properties of detecting scintillation systems in one experiment.

2. Application of computer-integrated circuits of digital processing of FM response scintillation signals, which allows creating a universal system for the storage and processing of experimental information, and entails a considerable decrease in the number of various types of electronic blocks, thus reducing total expenses on the manufacture of the device.

3. Creation of a digitized database of FM scintillation responses. The database allows, by means of software processing and without any additional electronic blocks, to obtain practically all possible informative parameters of the FM composition or detection, for example, neutron and photon coincidences of any multiplicity, and separate time and amplitude distributions of neutrons and photons describing their spectral properties.

4. Capability to detect FM deliberately concealed with lead or cadmium shields.

5. Capability to discriminate neutrons and photons in conditions of high load on scintillation channels, and with practically zero dead time.

6. Possibility to design devices, which considerably reduce the self-shielding effect of FM of high 235U enrichment.

7. Capability to store the database of digitized pulses in the computer memory for the reprocessing of the experimental data.

8. Possibility to design FM control devices (using the DD reaction to obtain neutrons in neutron generators) that are environmentally safe even in case of their deliberate destruction (act of terrorism), and also safe during their operation outage or transportation.

The proposed Project is the continuation of the ISTC Project # 0596, in which the feasibility of digital processing of scintillation signals in the design of FM detection and control device models have been experimentally confirmed.

Implementation of the Project is supposed to solve a number of problems, including:

1. Development of digital technology for the processing of scintillation signals in FM control devices with pulsed neutron sources.

2. Design of a digital spectrometer of neutrons and photons for application in FM detection and control with high load on electronic channels working on-line.

3. Design of devices of FM detection and control by coincidences of neutrons and photons, based on digital technology and a pulsed DD neutron source.

4. Design of FM detection and control devices with pulsed neutron sources and various neutron moderators, in which it is impossible to conceal FM with the help of shields absorbing the interrogating radiation.

5. Design of devices for the control of the composition of highly enriched FM samples.

6. Verification of calculations of various concepts of non-destructive FM control devices with pulsed neutron sources and scintillation systems, with the code MCNP-4C2.

7. Modernization of pulsed neutron generators in order to enhance their reliability and adaptation to operating conditions at various points of FM control.

The scientific value of the suggested Project is that the digital processing of scintillation signals of a wide range of scintillators will allow to reveal the distinctive features of pulse forming for various charged particles. In particular, for the purposes of non-destructive FM control, the shape of pulses from recoil protons (neutrons) and electrons (photons) will be investigated in order to separate them with use of not only slow, but also fast components. Preliminary experiments have shown, that the fast component can be used to identify the type of particles, and this kind of signal analysis can be carried out under high loads on electronic channels.

The commercial value of the Project is that its full-scale implementation opens ways for the design of non-destructive FM control devices characterized by lower expenses on the manufacture, the universality of FM response detection systems admitting mass production, and environmentally safe in operation or even in case of their complete destruction. These devices can be used for FM detection in various customs control offices, and for the analysis of the composition of nuclear reactor fuel assemblies and highly enriched samples.

Implementation of the proposed Project will allow the scientists of the atomic industry working in the field of military subjects to proceed to the development of high technology in design and construction of devices preventing the proliferation of nuclear materials.


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