Development of prototype induced-fission-based Pu accountancy instrument for safeguards applications
Introduction
One of the promising components of future spent-fuel management schemes in Korea is an advanced PWR fuel process that recovers U and U/TRU via electrochemical separation. One of the main design-based objectives of the process is to minimize, for safeguards and safety reasons, the amounts of TRU elements in the U product and wastes. On the other hand, the U/TRU product is produced with almost all the TRU elements in the spent fuel. Accordingly, nuclear material accountancy (NMA) for the U/TRU product is of great interest in terms of safeguards; however, there are some technical challenges in the nondestructive assay (NDA) of U/TRU products, including high neutron emission yields from spontaneous fission of 244Cm, neutron multiplication by induced fission from fissile materials (235U, 239Pu, and 241Pu), and the complex compositions of U and TRU elements as well as rare earth elements. Because the NDA technique is essential for near-real time accountancy (NRTA) (Pillay, 1989, Burr et al., 2015, Johnson and Ehinger, 2010), a very significant collaborative effort in developing an NDA technique suitable for NMA of the U/TRU product has been made by the Korea Atomic Energy Research Institute in partnership with the Los Alamos National Laboratory. The preferred characteristics of the NDA technique for NMA of the U/TRU product is (1) a passive method due to the limited availability of the active interrogating source with the higher neutron emission yield than that of the U/TRU product itself and (2) a direct measurement method independent of the Cm ratio technique (Miura and Menlove, 1994) due to the chance of an inconsistent Cm ratio between the input and output materials and the difficulties in measuring the Cm ratio by the NDA technique due to the complex isotopic composition. There are some existing passive-neutron measurement techniques based on coincidence and multiplicity counting (Reilly et al., 1991); however, their applicability is questionable in that the high neutron emission yield and high neutron multiplication might require dead-time and multiplication corrections, which usually are error prone when both (i.e., neutron emission yield and multiplication) are considerably high.
In the present study, a prototype induced-fission-based Pu accountancy instrument was developed, the performance of which was evaluated for various detector parameters including a high-voltage plateau, efficiency profiles, dead time, and stability. Its capability to measure the change in the average neutron energy, which is to say the FNEM signature, also was evaluated using AmLi, PuBe, 252Cf, as well as four Pu-oxide sources each with a different impurity (Al, F, Mg, and B) and producing (α,n) neutrons with different average energies.
Section snippets
Structure of prototype FNEM×PNAR system
The prototype is a hybrid-type neutron measurement system based on the fast neutron energy multiplication (FNEM) and passive neutron albedo reactivity (PNAR) methods (Menlove and Beddingfield, 1997). The physical basis of the FNEM method is that the average neutron energy is increased as the induced fission rate by the fast neutron increases, which is proportional to the amount of fissile materials, especially Pu, in the sample to be measured. Accordingly, the Pu mass can be calibrated as a
Signal processing circuit
A simple signal processing circuit for an OR logic and LED driver was developed (instead of using the OR logic capability of the PDT 110A), for summing of the signals from each detector ring and for external visual monitoring of the individual detector status by LED lights. The signal processing circuit diagram for one ring is shown in Fig. 3. The TTL logic signal produced in each PDT 110A module was fed into the buffer (SN74LS07). The buffer output was then split into the multi-vibrator
Summary
In the present study, a prototype safeguards instrument for NMA of U/TRU products that could be produced in an advanced PWR fuel processing facility was developed and characterized for various detector parameters (i.e., high-voltage plateau, efficiency profiles, dead time, stability, and die-away time) and compared with simulation results. In general, the measured data showed good agreement with the simulated data, which results confirmed the accuracy of the MCNP model for the prototype system.
Acknowledgments
This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (No. 2012M2A8A5025950).
References (15)
- et al.
Revisiting the form of dead time corrections for neutron coincidence counting
Radiat. Meas.
(2012) - et al.
Characterization and performance evaluation of a new passive neutron albedo reactivity counter for safeguards measurements
Rad. Meas.
(2014) - et al.
Optimization of hybrid-type instrumentation for Pu accountancy of U/TRU ingot in pyroprocessing
Appl. Radiat. Isot.
(2016) - ...
- ...
- et al.
Hybrid statistical testing for nuclear material accounting data and/or process monitoring data in nuclear safeguards
Energies
(2015) - Ensslin, N., Harker, W.C., Krick, M.S., Langner, D.G., Pickrell, M.M., Stewart, J.E., 1998. Application Guide to...
Cited by (3)
Conceptual design of neutron measurement system for input accountancy in pyroprocessing
2020, Nuclear Engineering and TechnologyCitation Excerpt :For example, because nuclear materials emit useful neutron signatures that penetrate bulk samples and container walls, passive neutrons have the potential to measure large and high-density samples with less concern for sample homogeneity. In two of our previous studies [9,10], a new, total-neutron-measurement-based hybrid concept for NMA of the final product in pyroprocessing (i.e., U/TRU ingots) was proposed and tested. NMA of input material should be considered to be as important as that of output materials.
Self-calibration Method for Dead Time Losses in Neutron Counting Systems
2017, ESARDA BulletinMonte Carlo simulations of safeguards neutron counter for oxide reduction process feed material
2016, Journal of the Korean Physical Society