Vol.29,

A novel full-digital real time neutron flux monitor (NFM) has been developed for Thorium-based molten salt reactor (TMSR). The system is based on the high-speed, parallel, and pipeline processing of the field programmable gate array as well as the high-stability controller area network platform. A measurement range of 10⁸ counts per second is achieved with a single fission chamber by utilizing the normalization of the count and Campbell algorithms. With the advantages of using the measurement range, system integrity, and real time performance, digital NFM has been tested in the Xi’an Pulsed Reactor fission experiments and was found to exhibit superior experimental performance.

358

A magetoresistive random-access memory (MRAM) device was irradiated by ⁶⁰Co γ-rays and an electron beam. The synergistic effect of this on the MRAM was tested with an additional magnetic field during irradiation, from which the total ionizing dose (TID) and the synergistic damage mechanism of MRAM were analyzed. In addition, DC, AC, and functional parameters of the memory were tested under irradiation and annealing via a very large scale integrated (VLSI) circuit test system. The radiation-sensitive parameters were obtained through analyzing the data. Because of the magnetic field applied on the MRAM while testing the synergistic effects, shallow trench isolation (STI) leakage, and Frenkel–Poole emission due to synergistic effects were smaller than that of TID; and hence radiation damage of the synergistic effects was also lower.

341

In this paper, the design, construction, simulation, and performance of a position-sensitive plastic scintillator detector are presented. The readout of the detector uses wavelength-shifting fibers coupled with multi-anode photomultipliers (PMTs) for the x- and y-dimensions. After calibrating the multi-anode PMTs, a two-dimensional projection image of the square scintillator telescope hit by cosmic muons is demonstrated. By performing a cosmic test with the Micromegas telescope, the position resolution of the detector was determined to reach approximately 8.6 mm, which is close to the value obtained in physical simulation.

462

The response functions and pulse height spectrum (PHS) of a 2" × 2" BC501A detector were obtained through a general-purpose Monte-Carlo simulation toolkit, Geant4. A relatively simple but effective method was adopted to unfold the PHS. Recommendations regarding the response matrix were proposed to optimize the unfolding results. The results indicate that the accuracy of the unfolding can be greatly improved using many incident neutrons with a wide energy range, a proper energy interval, and an appropriate channel width of the response matrix. The above-mentioned method was verified by unfolding three different types of simulated spectrum, the results of which are in good accord with the simulated distribution.

353

A new development of indirect gating case in the differential decay curve method used for lifetime measurement has been introduced. The gate region was extended from partial shifted peak to both shifted and unshifted components. The statistics of flight and stop peaks in gating spectra was improved obviously. The reliability of this change has been tested by reanalysing the lifetime of 2⁺ state in ¹³⁴Ce. The result of 32.2(33) ps was fit well with the previous published values within the experimental uncertainty. The developed method was also used to analyse the lifetime of 21+ state in ¹³⁸Nd.

343

Studies on beam optics and the isocenter property in the gantry system for the SC200 (Superconducting Isochronous Cyclotron of 200 MeV in Hefei, China) are presented in this paper. The physical design of the isocentric gantry system is developed with the software TRANSPORT, which realizes a beam with a circular shape at the isocenter and a full width at half maximum (FWHM) of 4–10 mm. For stereotactic radiosurgery, the isocenter deviation of the gantry system should be less than 1 mm in diameter. In order to explore the property of the isocenter, an electromagnetic-structure coupling analysis has been conducted given the self-gravity and the electromagnetic (EM) force of the magnets on the gantry beam line. The correlation between the isocenter property and the EM force has also been carefully studied. This paper puts forward two methods to obtain the isocenter deviation based on the characteristics of the nozzle installation structure and the calculation of the optical path after the nozzle, respectively. The results show that the maximum isocenter deviation is less than 0.33 mm with a safety factor of 1.5, and the deviation caused by the EM force is 0.05 mm. The latter result indicates that the impact of the EM force is negligible. This paper puts forward one possible way to realize real-time acquisition of the isocenter deviation in practical application. The gantry of SC200 is under construction at ASIPP.

342

The production of J/ψ mesons in p+p and p+Pb collisions is studied in the framework of Color Glass Condensate together with a simple color evaporation model. Considering the nuclear effects with the Glauber-Gribov approach, we calculate the cross section and the nuclear modification factor of forward J/ψ production in p+Pb collisions at s=5.02 TeV. Then, the backward J/ψ production in p+Pb collisions at s=8.16 TeV is also analyzed. In our calculation, the phenomenology KLR-AdS/CFT model and the rcBK approach, which are valid at a small x, are used to calculate the three point function. It is shown that the theoretical results fit well with the experimental data from ALICE and LHCb.

513

Wax deposition in pipelines is a crucial problem in the oil industry. An approach that combines the gamma ray transmission method with scanning technology is proposed to detect the thickness of wax deposition. The performance of the method is validated through simulations with MCNP code. An experiment is also carried out with a 300 mCi ¹³⁷Cs source and a LaBr₃ detector. A good correspondence is observed between the simulation and experimental results. The results indicate that the approach is efficient for detecting the thickness of wax deposition in oil pipelines.

421

With respect to a liquid-fueled molten salt reactor (MSR), the temperature coefficient of reactivity mainly includes the moderator temperature coefficient (MTC) and the fuel salt temperature coefficient (FSTC). The FSTC is typically divided into the Doppler coefficient and the density coefficient. In order to compensate for the potentially positive MTC, the FSTC should be sufficiently negative, and this is mostly optimized in terms of the geometry aspect in pioneering studies. However, the properties of fuel salt also directly influence the FSTC. Thus, the effects of different fuel salt compositions including the ²³⁵U enrichment, heavy metal proportion in salt phase (HM proportion), and the ⁷Li enrichment on FSTC are investigated from the viewpoint of the essential six-factor formula. The analysis is based on an under-moderated MSR. With respect to the Doppler coefficient, the temperature coefficient of the fast fission factors (α_T(ε)) is positive and those of the resonance escape probability (α_T(p)), thermal reproduction factor (α_T(η)), thermal utilization factor (α_T(f)), and total non-leakage probability (α_T(Λ)) are negative. With respect to the density coefficient, α_T(p) and α_T(η) are positive while the others are negative. The results indicate that the effects of the ²³⁵U enrichment and HM on FSTC are mainly reflected in α_T(ε) and α_T(p), which are the dominant factors when the neutron spectrum is relatively hard. Furthermore, the ⁷Li enrichment influences FSTC by α_T(f) and α_T(Λ), which are the key factors in a relative soft spectrum. In order to obtain a more negative FSTC for an under-moderated MSR, the possible positive density coefficient, especially its α_T(p), should be suppressed. Thus, a lower ²³⁵U enrichment (albeit higher than a certain value, 5 wt% in this article) along with a lower HM proportion and/or a higher ⁷Li enrichment are recommended. The analyses provide an approach to achieve a more suitable fuel salt composition with a sufficiently negative FSTC.

433

The drift-flux model has a practical importance in two-phase flow analysis. In this study, a finite volume solution is developed for a transient four-equation drift-flux model through the staggered mesh, leading to the development of a fully implicit discretization method. The main advantage of the fully implicit method is its unconditional stability. Newton's scheme is a popular method of choice for the solution of a nonlinear system of equations arising from fully implicit discretization of field equations. However, the lack of convergence robustness and the construction of Jacobian matrix have created several difficulties for the researchers. In this paper, a fully implicit model is developed based on the SIMPLE algorithm for two-phase flow simulations. The drawbacks of Newton's method are avoided in the developed model. Different limiter functions are considered, and the stabilized method is developed under steady and transient conditions. The results obtained by the numerical modeling are in good agreement with the experimental data. As expected, the results prove that the developed model is not restricted by any stability limit.

519

To obtain a small-angle monoenergetic neutron source, a shielding collimator device is designed for the neutron source generated by a neutron tube. The device is divided into the collimator and the capture cave. The collimator is made of three layers of stainless steel, borated polyethylene, and lead to constrain neutrons in a small angle. The capture cave is used to increase the number of times neutron inelastic scattering occurs in the opposite direction of the radiation field, thereby reducing the proportion of scattered neutrons in the radiation field. Material thickness, aperture size, and the optimum structure of the capture cave were simulated using MCNP. The design features a neutron emission angle within a range of 3° and neutron fluxes in the radiation field, which are higher by two orders of magnitude than those outside the radiation field. This research has practical value for the generation of monoenergetic small-angle neutron sources and neutron applications.

636

The design of a bolted flat cover is extremely important for the structural integrity of pressure vessels. The present design codes provide the thickness calculation equations for a bolted flat cover with single metal gasket. However, the rules for a bolted flat cover with double metal sealing rings are not developed to date. In the study, a new thickness calculation equation for the bolted flat cover with double metal sealing rings is proposed. First, the theoretical stress solution for bolted flat cover with the double metal sealing rings is obtained, based on the theory of simply supported circular plate (SSCP) and then verified using the results from finite element analyses (FEAs). The results indicate that the influence of double metal sealing ring on the stress of the flat cover is more serious compared to single metal gasket. Second, a more accurate and reasonable equation is proposed to calculate the thickness of bolted flat cover with double metal sealing rings based on the derived theoretical equations of maximum stress. Finally, the influence of linear load and the spacing between rings on the thickness are discussed. Subsequently, a few suggestions are provided to design low-pressure or atmosphere pressure vessels. The study provides a theoretical foundation to develop design codes of pressure vessels in nuclear reactors.

384

Accelerator-driven systems based on molten salt fuel have several unique advantages and features for advanced nuclear fuel utilization. The aim of this work was to study the Th-U breeding capability in such systems, known as "accelerator-driven subcritical molten salt reactors" (ADS-MSRs). Breeding capacities including conversion ratio and net ²³³U production for various subcriticalities and different minor actinides (MA) loadings were analyzed for an ADS-MSR. The results show that the subcriticality of the core has a considerable effect on the Th-U breeding. A high subcriticality is favorable to improving the conversion ratio, increasing the net ²³³U production, and reducing the doubling time. Specifically, the doubling time for k_eff of 0.99 is larger than 80 years, while the counterpart for k_eff of 0.93 is only approximately 22 years. Nevertheless, in an ADS-MSR with a high initial MA loading, MA results in a non-negligible ²³³U depletion in the first two decades, while increasing the net ²³³U production compared to reactors without MA loading. During the 50 years of operation, for the subcritical reactor (k_eff=0.97) with MA fraction increasing from 1% to 14%, the net ²³³U production increases from 3.94 t to 8.24 t.

467

Beam signals captured from a button-type pickup contain multidimensional information including the bunch charge, transverse position, bunch length, and longitudinal phase. A bunch phase monitor, which retrieves longitudinal phase information from a pickup signal at a bunch-by-bunch rate, has been developed at the Shanghai Synchrotron Radiation Facility (SSRF). This paper introduces the basic principles, system setup, data processing method, and preliminary experimental results of this system. The systematic measurement error introduced by the limited system bandwidth, bunch length, and bunch charge variation was studied using simulation data. The random measurement uncertainty was evaluated using experimental beam data. The experimental result shows that the longitudinal phase resolution of this system is better than 1.0 ps. The first application, measuring the relationship between the longitudinal phase and bunch charge to determine the energy loss factor, was implemented, and the preliminary result is also discussed.

360

An X-ray pinhole camera has been used to determine the transverse beam size and emittance on the diagnostic beam line of the storage ring at SSRF since 2009. The performance of the beam size measurement is determined by the width of the point spread function of the X-ray pinhole camera. Beam-based calibration was carried in 2012 out by varying the beam size at the source point and measuring the image size. However, this calibration method requires special beam conditions. In order to overcome this limitation, the pinhole camera was upgraded and an X-ray quasi-monochromator was installed. A novel experimental method was introduced by combining the pinhole camera with the monochromator to calibrate the point spread function. The point spread function can be accurately resolved by adjusting the angle of the monochromator and measuring the image size. The X-ray spectrum can also be obtained. In this work, the X-ray quasi-monochromator and the novel beam-based calibration method will be presented in detail.

471