Increasing Neutron Fluence Research Articles

Quantifying the effects of neutron fluence on proton signal retention in CR-39.

This paper reports on investigations on the impact of higher neutron fluences on the detection efficiency of protons with CR-39, a charged particle track detector. CR-39 is widely used as a diagnostic for inertial fusion applications and is an integral component of numerous particle diagnostics at the OMEGA laser facility and National Ignition Facility. As experiments continue to produce higher and higher yields, existing diagnostics are impacted by higher particle fluences than they were originally designed for. This paper presents data from experiments measuring proton signal on pieces of CR-39 with different levels of neutron fluence with two different etch times. The experiments show a decrease in signal recovery with increased neutron fluence, which is exacerbated at longer etch times. At 3h etch time, data suggest a 17% ± 7% signal loss at 1.3 × 105 neutron-induced tracks per cm2 and a 67% ± 21% loss at 6h etch time. Careful signal isolation techniques can recover most of the proton tracks even with moderate neutron fluence.

Frontier system-on-chip (SoC) technology for microwave diagnostics (invited).

The next generation of fusion reactors, exemplified by projects such as the Demonstration Power Plant following the International Thermonuclear Experimental Reactor, faces the monumental challenge of proving the viability of generating electricity through thermonuclear fusion. This pursuit introduces heightened complexities in diagnostic methodologies, particularly in microwave-based diagnostics. The increased neutron fluence necessitates significant reductions in vessel penetrations and the elimination of internal diagnostics, posing substantial challenges. SoC technology offers a promising solution by enabling the miniaturization, modularization, integration, and enhancing the reliability of microwave systems. After seven years of research, our team successfully pioneered the V- and W-band system-on-chip approach, leading to the development of active transmitters and passive receiver modules applied in practical settings, notably within the DIII-D tokamak project. Arrays of these modules have supported microwave imaging diagnostics. New physics measurement results from the Electron Cyclotron Emission Imaging system on DIII-D provide compelling evidence of improved diagnostics following the adoption of SoC technology. Furthermore, we achieved a breakthrough in developing an F-band SoC, advancing higher frequency capabilities for fusion devices. These achievements represent a significant leap forward in fusion diagnostic technology, marking substantial progress toward establishing reliable and efficient plasma diagnostics for future fusion reactors.

Особенности изменения мощности излучения светодиодов на основе соединений AlGaInP под воздействием быстрых нейтронов

The results of the study on the degradation of AlGaInP red (630 nm) light-emitting diode parameters under fast neutron irradiation are presented. The study showed that in the region of LEDs, an uneven drop in radiation power is characterized, for high currents, a smaller decrease in power and a constant angle of inclination of the curve are characteristic, while in the region of low currents, with an increase in neutron fluence, the angle of inclination of the curve describing this process increases. A feature of the studied LEDs for short-circuit and breakage modes is the restoration of radiation power at the first stage of irradiation, which is explained by the relaxation of mechanical stresses during partial annealing of structural defects under the influence of low fluences.

Enhanced backscatter and unsaturated blue wavelength shifts in F-doped fused silica optical fibers exposed to extreme neutron radiation damage

Amorphous fused silica (a-SiO2) optical fibers, with and without inscribed Bragg gratings, were interrogated using infrared (∼1550 nm) optical backscatter reflectometry during ∼25 days of intense neutron irradiation to a fast (energy > 0.1 MeV) neutron fluence of ∼1021 n/cm2, or ∼1.5 atomic displacements per atom. The reflected light amplitudes in Ge-doped core telecommunications fiber dropped below detection limits (>15 dB attenuation) within 3 days of irradiation (∼1020 fast n/cm2). Amplitudes from a pure silica core, F-doped silica cladding fiber reached equilibrium levels ∼1.5–2 dB higher than pre-irradiation values, whereas Bragg gratings inscribed in the same fiber using a femtosecond laser (point-by-point method) suffered > 45 dB attenuation. Blue wavelength shifts were initially consistent with previous radiation-induced compaction models but increased linearly with increasing neutron fluence (no evidence of saturation) beyond 1020 n/cm2 and exceeded 0.6%, which corresponds to >1,000 °C drift if used to measure temperature changes.

Fast Neutron Irradiation on GaN-Based Light-Emitting Diodes From Near-Ultraviolet to Green Spectral Ranges

Neutron irradiation effects were compared for GaN-based multi-quantum well (MQW) light emitting diodes (LEDs) with emission wavelength in the near-ultraviolet (NUV), blue and green spectral regions. Optical output power, current-voltage and peak wavelength were analyzed in detail before and after irradiation. Three colors of LEDs showed an increase and then a decrease in optical output power with the increase of neutron fluence ranging from 1.0×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> to 1.0×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . The enhanced light emission performance is attributed to the increase of carrier injection for neutron irradiated MQWs. In addition, the formation of tunneling conductivity channels in the p-doped AlGaN electron block layer (EBL) induced by neutrons is considered as the main factor that dominates the performance degradation. Among the three colors of LEDs, the order of severity for the optical and electrical properties influenced by this medium-fluence neutron irradiation is green, blue, and NUV LEDs, in turn becoming more serious. The NUV LEDs rely heavily on the EBL due to their poor carrier confinement in relatively shallow GaN/AlGaN MQWs, so an increase of carrier injection or leakage induced by neutrons has significant influence on device performance. As the green LEDs have deep quantum wells, the strong confinement of carriers leads to their being least sensitive to neutron irradiation. So we believe that design of LEDs with deep quantum wells to enhance the carrier confinement ability will be helpful to improve their radiation tolerance. The findings not only enrich the understanding of the influence mechanism of neutron irradiated GaN-based UV/visible LEDs, but are also helpful to radiation hardened design.

Fast neutron irradiation effects on Si- and GaN-based avalanche photodiodes

We report the behaviour of the dark current and gain characteristics of Si- and GaN-based avalanche photodiodes (APDs) irradiated by fast neutrons. For Si-based APDs, the dark current increases with the increase of neutron fluence, indicating that the avalanche property has been seriously affected. The gain values of Si-based APD slightly increase after irradiation by a low neutron fluence of 1.0 × 1012 cm−2, while the device exhibits gain degradation as the fluence increases to 1.0 × 1013 cm−2 or even above at high reverse bias voltage, unlike the previous studies where only degradation was observed. The steep increase of dark current and gain when approaching the breakdown voltage after neutron irradiation indicate that the avalanche property is almost unaffected for GaN-based APDs. Furthermore, we infer that the optical absorption between acceptor state and conduction band in the p-type layer plays an important role in influencing the change of dark current and gain at high reverse bias voltage. The findings not only enrich the understanding of neutron irradiation effect on Si- and GaN-based APDs, but also experimentally prove that GaN-based APDs hold better radiation resistance than Si-based devices.

Temelin Irradiated Cladding Project – TIRCLAD

It is widely known, that zirconium-based alloys have been used for nuclear fuel cladding fabrication for decades [1], [2]. Therefore, it is crucial for fuel vendors, utilities as well as safety authorities to understand their behaviour during reactor operation with strong fast neutron and gamma irradiation. To complement the information about material properties for current as well as prospective advanced zirconium-based alloys, a long term research project implemented by ALVEL has been carried out, in cooperation with its partners (ČEZ, Škoda Nuclear Machinery, UJV Rez, Research Centre Rez) [3], [4]. The project is implemented on the background of a large material research program sponsored by JSC TVEL and ČEZ (this program started in 2012 and it is planned to be finished in 2024). It is fully independently implemented in the Czech Republic.Irradiation of material samples started at Temelin NPP in 2014 and finished in spring 2020. The first three batches were already transported to UJV Rez and Research Centre Rez for post-irradiation evaluation. After finishing testing of reference non-irradiated samples testing in 2018 (determination of initial state, mechanical properties and as-received microstructure), six batches of irradiated material have been analysed sequentially with their increasing neutron fluence. The final irradiation damage of the last sixth batch corresponds approximately to fuel burnup of 80 MWd/kgU.This paper presents the developed methodologies and the expected experimental and other important outcome. Several material properties are being studied on different scales including high resolution microstructural and chemical analysis, creep and mechanical behaviour, nanoindentation, oxide layer morphology. The main objectives of the project include evaluation of materials’ microstructural and bulk properties and the derivation of dose- and temperature-dependent correlations that can be implemented into FEM models and fuel performance codes such as FRAPCON/FRAPTRAN [5], [6] or Transuranus [7]. These models can be then used to support licensing of new designs influenced by fuel cladding behaviour during long term dry storage, justification of dry storage for an extended period of time or justification of new safety criteria that can lead to enhanced operation of VVER reactors and spent nuclear fuel storage [8].

РАСПУХАНИЕ НЕЙТРОННОГО ПОГЛОТИТЕЛЯ НА ОСНОВЕ В4С ПРОМЫШЛЕННОГО И РЕФАБРИЦИРОВАННОГО КАЧЕСТВА ПОСЛЕ ДВУХЛЕТНЕГО ОБЛУЧЕНИЯ В СТЕРЖНЯХ АВАРИЙНОЙ ЗАЩИТЫ

The radiation swelling of hot-pressed B4C blocks of industrial and re-fabricated quality with the participation of absorber elements providing emergency protection, up to fast neutron fluence 7⋅1022 cm-2, was investigated. The reason of metal cladding machining deformation of neutron absorber during a two-year exposure period was swelling. The volumetric swelling and the porous parameters of the absorber are measured by hydrostatic weighing and digital analysis of electron microscopic fractograms of fresh splits. The pore allocation and destruction manner of B4C was studied by scanning electron microscopy. It was found that swelling for industrial and re-fabricated B4C, with maximum neutron fluence in the lower part of absorbing elements, culminates 12 and 18 % respectively. The drastic decrease in its swelling was caused by fluence reduction along of absorber rod. Volumetric changes are explained by growth of closed porosity. The maximum swelling of irradiated briquettes for industrial and re-manufactured B4C is 25 and 30 %, respectively, with the same initial values of about 19 and 23 %. The maximum value of closed porosity from industrial and re-manufactured B4C after irradiation is 14 and 21 %, respectively, against the initial values of 4 and 9 %. All detected pores settle at the grain border. The primary bulk of the pores is of technological origin. The size and concentration of pores correlate with an increase of neutron fluence and burnout during irradiation, as well as provoke to formation of microcracks between the crystals and grains of the boron carbide matrix. Nanoscale helium pores with a diameter of more than 100 nm were not detected in the grain body. The open porosity inside maximum swelling zone and mechanical interaction absorber with the cladding is reduced. The fracture nature of the swelling B4C changes from a mixture with a predominance of intragranular splitting to a purely intergranular type under increasing fluence.

Grain-boundary phosphorus segregation in highly neutron-irradiated reactor pressure vessel steels and its effect on irradiation embrittlement

Reactor pressure vessel (RPV) steels for pressurized water reactors (PWRs) with bulk P contents ranging from 0.007 to 0.012wt.% were subjected to neutron irradiation at fluences ranging from 0.3 to 1.2 × 1020 n/cm2 (E > 1 MeV) in PWRs or a materials testing reactor (MTR). Grain-boundary P segregation, which was analyzed using Auger electron spectroscopy (AES) on intergranular facets, increased with increasing neutron fluence. A rate theory model based on four diffusion-reaction equations for substitutional P atoms, octahedral interstitial P atoms, vacancies, and self-interstitial atoms was also used to simulate the increase in grain-boundary P segregation for RPV steels with a bulk P content up to 0.020wt.%, using parameters optimized by the present AES data. The increase in grain-boundary P segregation in RPV steel with a bulk P content of 0.015wt.%, which is the maximum P concentration in RPV steels used in Japanese nuclear power plants intended for restart, was estimated to be less than 0.1 in monolayer coverage at 1 × 1020 n/cm2 (E > 1 MeV). A comparison of the PWR data with the MTR data, including that from the literature, showed that neutron flux had no effect upon grain-boundary P segregation for A533B steels. The relationships of the ductile-brittle transition temperature (DBTT) shifts to grain-boundary P segregation and to yield strength were also discussed. A linear relationship between the yield strength and the DBTT shift with a slope of 0.63 was obtained for RPV steels with a bulk P content up to 0.026wt.%, which is higher than that of most U.S. A533B steels. It is concluded that the intergranular embrittlement is unlikely to occur for RPV steels irradiated in PWRs.

Complexes defects induced by neutron irradiation of Cz-silicon

The boron-doped Cz-Si was irradiated with 1 MeV neutrons delivered by the Es-Salam reactor at two different neutron fluence values, 1.98 × 1018 and 3.96 × 1018 n/cm2, respectively. Annealing processes were carried out under argon atmosphere, at 550 °C and 950 °C for 60 min, respectively. The effects of isochronal annealing on the neutron-irradiated silicon’s IR absorption spectrum are presented. The obtained results indicate two forms of the Near-Edge Absorption that increase with increasing neutron fluence. One centered at 1000–1500 nm (NEA-1) and second near 1600–1800 nm (NEA-2). After the annealing process at 550 °C, the IR absorption spectrum shows the change of the first Near-Edge Absorption band towards a shorter wavelength at 1000–1200 nm range as well as the disappearance of the (NEA-2) band near 1800 nm. The appearance of the lithium impurity associated with divacancy at 1700 nm that confirms the transmutation of boron into lithium of the samples. At 950 °C, the experimental data show that 1700 nm which is associated with Li divacancy persists for higher neutron fluence, but not for lower fluence.

МНОГОМЕРНЫЙ АНАЛИЗ ДАННЫХ НА ОСНОВЕ РЕЗУЛЬТАТОВ РАСЧЕТОВ ЯДЕРНОЙ ТРАНСМУТАЦИИ В ЦИРКОНИЕВЫХ СПЛАВАХ

The effects of nuclear transmutation in zirconium alloys are considered. The calculated scheme of transmutation of elements in alloys of the system [Zr + x% Nb + y% Mo] is determined. Numerical estimates of the molybdenum content in zirconium alloys of various compositions were carried out during irradiation in research (SM-3, BOR-60) and power (VVER-1000, PWR) reactors. The dynamics of the accumulation of molybdenum during irradiation in the SM reactor and the subsequent exposure of the samples for one year in standard zirconium alloys Zr + 1% Nb, Zr + 2.5% Nb and for the proposed initial compositions Zr + 1% Nb + 0.5% Mo were estimated Zr + 2.5% Nb + 0.5% Mo. Reactor irradiation leads to a significant accumulation of molybdenum in the Zr + 2.5% Nb alloy as a result of nuclear reactions: the molybdenum concentration increases to about 0.7 % with an increase in neutron fluence (E&gt; 0.1 MeV) to 1×1023 cm-2 at irradiation in a research reactor SM. The dynamics of the effects of nuclear transmutation of zirconium upon irradiation in the active zone of research (SM-3, BOR-60) and power (VVER-1000, PWR) reactors is estimated. The Zr element transmutes no more than 10 % in 100 years of exposure. The accumulation of molybdenum over the same time can be up to 104 ppm (appm). The results of the intellectual analysis of the calculations performed with multidimensional analysis based on OLAP of the multidimensional data space of the database provide knowledge in the form of classifications and confirm the need to develop zirconium alloys with additional doping with molybdenum, which can provide optimal physicomechanical properties, in particular, radiation growth characteristics, as well as acceptable level of nuclear-physical and corrosive properties.

Critical currents in REBaCuO superconducting tapes in response to neutron irradiation

Electromagnetic performance of superconducting REBaCuO tapes from several manufacturers was investigated in response to neutron irradiation. The aim was to test the feasibility of using these tapes for wiring high-Tc superconducting magnets for fusion reactors. Magnetic induction was employed to determine critical currents. In non-irradiated SuNAM, SuperOx, and SuperPower tapes without additional pinning centers, the normalized pinning force density as a function of the normalized magnetic field, h, exhibited the commonly observed single peak at about h = 0.2 in the whole temperature range 10 K–80 K. In the non-irradiated AP (advanced pinning) SuperPower tapes this dependence developed an extraordinary shape below 70 K. This feature changed with increasing neutron fluence. The effect of neutron irradiation on critical currents was found to be rather complex. In all samples, neutron irradiation by a total fluence of 8.03 × 1022 m−2 caused a critical current degradation at low magnetic fields in the temperature range 10 K–77 K. At high magnetic fields, the effect varied depending on the tape’s initial pinning structure, temperature, and neutron fluence. At 77 K, the current decreased and the irreversibility field was reduced in all the samples. At intermediate temperatures the critical current nearly did not change, while at temperatures below 30 K the critical current increased.

Structural, topological, electrical and luminescence properties of CZ-silicon (CZ-Si) irradiated by neutrons

In this paper, the changes in the XRD, Raman, AFM, the substrate resistivity and Photoluminescence of the p-type CZ-silicon samples are studied before and after the high fluences of 1 MeV equivalent neutrons. After irradiation, the samples are annealed at different temperatures in Ar atmosphere. It was found that the lattice parameter increases with increase of neutron fluence, related to the increment of the defect content. Also, the increasing of the crystallinity was caused by the fluence and the annealing temperature. It was found that the roughness increases with the increase of the neutron fluence and decreases with increasing of the annealing temperature and assigned to the degree of material smoothing. The electrical studies show that, with high annealing temperature, the lowest value of the resistivity was experimentally observed with the increase of the neutron irradiation. Therefore, the phosphorus and lithium atoms could be useful as a donor in CZ-Si. It was shown that increasing of the neutron fluence, the PL intensity decreases with decreasing of oxygen defects in SiOx.

Current–voltage characteristics of silicon PIN diodes irradiated in KAMINI nuclear reactor

The present study reports on the investigation of current–voltage (I–V) characteristics of commercial planar Si-PIN diodes, irradiated in a typical thermal nuclear reactor — KAMINI for neutron fluences ranging from 1×1014 to 1×1016 n/cm2. The I–V Characteristics of the virgin and neutron irradiated Si-PIN diodes are measured in ambient environment for the forward and reverse biased conditions. In the forward bias condition, one of the consequences of increasing the neutron irradiation fluence is the increase in knee voltage from ∼0.5 V for virgin diode to 37.4 V for neutron irradiated diode with fluence of 1×1016 n/cm2. Further analysis of forward characteristics, revealed increase in ideality factor from a typical value of ∼2 for virgin diode to an anomalous value of ∼496 for the highest irradiated diode specimen. This increase is attributed to the increasing neutron damage that the diodes undergo upon irradiation. Moreover, in the reverse biased condition, the reverse leakage current increased by four orders of magnitude from 10−9 to 10−5 ampere. A qualitative analysis of the forward and reverse I–V characteristics, showed that the diodes change from a rectifying to ohmic behaviour with increase in neutron fluence and this was inferred from the decrease in ‘gap’ between the forward and reverse currents in the low voltage regions. Quantitatively, the rectification ratio – ratio of the forward to reverse currents – was calculated to be 108 and 84 for the virgin and 1 × 1016 n/cm2 irradiated specimens, respectively. The damage constant evaluated from the reverse bias I–V measurements conditions was found to be 1.7683 × 10−18 A/cm.

Charge-collection properties of irradiated depleted CMOS pixel test structures

The edge transient-current technique (Edge-TCT) and charge-collection measurements with passive test structures made with the LFoundry 150-nm CMOS process on a p-type substrate with an initial resistivity of over 3 kΩcm are presented. The measurements were made before and after irradiation with reactor neutrons up to 2⋅1015 neq/cm2. Two sets of devices were investigated: unthinned (700 μm) with the substrate biased through the implant on top and thinned (200 μm) with a processed and metallised backplane.The depletion depth was estimated with the Edge-TCT and the collected charge was measured with a 90Sr source using an external amplifier having a 25-ns shaping time. The depletion depth for a given bias voltage decreased with the increasing neutron fluence, but it was still larger than 70 μm at 250 V after the highest fluence. After irradiation a much higher collected charge was measured for the thinned detectors with a processed backplane compared to the unthinned devices, although the same or an even larger depletion depth was measured in the unthinned devices. The most probable value of the collected charge of over 5000 electrons was measured with a thinned device also after irradiation to 2⋅1015 neq/cm2. This is sufficient to ensure the successful operation of these detectors at the outer layer of the pixel detector in the ATLAS experiment at the upgraded HL-LHC.

Annihilation behavior of irradiation defects in Li4SiO4 irradiated with high thermal neutron fluence

The annihilation behavior of irradiation defects in Li4SiO4 which were irradiated with thermal neutrons to a high fluence was studied by electron spin resonance (ESR). It was observed that the ratio of O-related centers to E'-centers increased with increasing annealing temperature. The total irradiation defects were annihilated through two processes, namely the fast (120–250 °C, 70%) and the slow ones (250–500 °C, 30%), and their activation energies were determined to be 0.63 ± 0.09 and 0.89 ± 0.14 eV, respectively. The observed annihilation behavior of irradiation defects in Li4SiO4 was found to be very different from that in a previous study, which could be attributed to the difference in concentration and types of irradiation defects generated by different neutron fluences. It was implied that the annihilation behavior of irradiation defects in ternary lithium oxides would become more complicated with increasing neutron fluence.

Penentuan Spektrum Neutron di LINAC Menggunakan Passive Single Sphere Spectrometer

Neutron spectra at Linear Acceleration (LINAC) facility was needed to protect neutron radiation. The purpose of determination of neutron spectra at LINAC using Passive Single Sphere Spectrometer is getting spectra and neutron fluence from LINAC and knowing the influence of input voltage at LINAC to its spectra and neutron fluence output. Single Sphere Spectrometer (SSS) with diameters 30 cm using seven gold foil detectors was set in position a half of diameter (0, 3, 6, 9, 11, 12, 13 cm) from center of the SSS. Measurement of neutron count rate was performed by placing SSS under gantry of LINAC with SSD 100 cm in distances. Next, neutron count rate was used as input data in UMG 3.3 program to get spectra. Based on measurement, total of neutron fluence at LINAC 10 MV and 15 MV is 5,78 ´ 10 4 n/cm 2 .s ± 0,01 ´ 10 4 and 9,44 ´ 10 5 n/cm 2 .s ± 0,22 ´ 10 5 , so increasing input voltage at LINAC was followed by increased neutron fluence.

Investigation of Changing Volt-Ampere Characteristics of AlGalnP Heterostructures with Multiple Quantum Wells under Ionizing Radiation

The results of research into degradation of volt-ampere characteristics of light emitting diodes produced on the base of AlGaInP heterostructures with multiple quantum wells are presented on the example of light emitting diodes (emission wavelengths 623 nm and 590 nm) under gamma quantum and fast neutron radiation in passive powering mode. The shifts of volt-ampere characteristics into the higher voltage range have been observed in conditions of increasing neutron fluence and radiation dose. The observed increase in the resistance of ohmic contacts is caused by the rising resistance of adjacent area, which in its turn results from the changing mobility of charge carriers. The latter varies with the growth of introduced defects under irradiation. Two different areas of current generation have been identified. A mechanism of current generation depends on injected charge carriers in the range of mid-level electron injection. Moreover, the range of high electron injection is distinguished by changing resistance of light emitting diode cores alongside with current generation conditioned by charge carrier injection.

Assessment of neutron-irradiated 3C-SiC implanted at 800 ℃

The favourable physical properties of SiC make it a potential material for use as containment layer in new generation nuclear reactors. The material will thus be exposed to high temperatures and fluences from fission products. The impact of increasing neutron fluence at constant irradiation temperature (800 ℃) on the properties of neutron-irradiated 3C-SiC was investigated, employing infrared reflectance spectroscopy and atomic force spectroscopy. A relation was found between the neutron fluence and the surface morphology of the irradiated 3C-SiC. The varying surface morphology also affected the dielectric parameters of the SiC.

Characterization and Simulation of Neutron Irradiated JBS Silicon Carbide Diode Structures

The effect of radiation damage produced by fast neutrons on characteristics of JBS diodes produced on 4HSiC epilayers was investigated. 1200V JBS diodes from Cree were irradiated in nuclear reactor by fast neutrons with fluences ranging from 1.3x1013 to 4x1014 cm-2 (1MeV NIEL equivalent in Si). Evolution of radiation damage was studied by deep level transient spectroscopy. New characterization method based on dynamic measurement of current to voltage characteristics in the kV range then allowed precise analysis of blocking characteristics and observation of free charge carrier removal with increasing neutron fluence. Results show that irradiation with fast neutrons introduces different point defect giving rise to acceptor like deep levels in SiC bandgap. These levels have a negligible effect on dynamic and blocking characteristics of irradiated JBS diodes, however, acceptor character of introduced deep levels accompanied by deactivation of donor dopants deteriorates diodes ON-state resistance already at low irradiation fluences. This degradation is then manifested by increasing values of the series resistance and the emission coefficient in the SPICE model of the JBS diode.