238Pu Content Research Articles

High-Precision Measurement of the 238Pu/239Pu Isotope Ratio by TIMS.

With an aim to improve the precision of isotopic standards of special nuclear materials like uranium and plutonium, National Bureau of Standards (NBS) undertook the recertification of isotopic standards prepared between 1960 and 1970. In a recent initiative, Lawrence Livermore National Laboratory (LLNL) in collaboration with New Brunswick Laboratory Program Office (NBL PO) undertaken efforts to recertify SRM 946, SRM 947, and SRM 948. The primary goal of this drive is to lower the uncertainties associated with the isotopic compositions of plutonium standards. The drive is also aims to minimize the uncertainty associated with measurement of the 238Pu content from 2% to ∼0.3%. In this connection, our laboratory at the Fuel Chemistry Division, Bhabha Atomic Research Centre, proposes a novel indicator "minima in the (RMO254/(i+16))/(RM238/i) curve" (where i = m/z 233 or 235 amu), which is the ratio of the isotope ratio of metal oxides (238M16O/iM16O) to that of metal ions (238M/iM) of uranium in determining the accurate 238Pu content by thermal ionization mass spectrometry. Various enriched uranium spikes have been employed to study the efficacy of the minima in the (RMO(254)/(i+16))/(RM238/i) curve. With the combination of monitoring the minima in the (RMO(254)/(i+16))/(RM238/i) curve and the application of the 233U spike (with an isotope abundance of 238U ∼ 0.05%), an external precision of 0.2% has been achieved in the determination of the 238Pu/239Pu isotope ratio for isotopic standard SRM 947.

О ТРАНСМУТАЦИИ МИНОРНЫХ АКТИНОИДОВ В ЖИДКОСОЛЕВОМ РЕАКТОРЕ-СЖИГАТЕЛЕ

Reduction in the amount of accumulated minor actinides (Np, Am, and Cm isotopes), as well as, the long-lived fission products, to the extent possible, is a top-priority task for the nuclear power engineering. Transmutation of this waste in a special-purpose molten-salt burner reactor has been currently proposed as a possible solution for this problem. The objective of the present paper is to investigate basic regularities of Np, Am, and Cm transmutation in the molten salt burner reactor and to determine optimal operational conditions of the reactor. In the optimal equilibrium mode just fluorides of these elements are added into the fuel composition but the fission products are extracted from it. This mode are reached by maintaining a specified actinide concentration. In order to provide the reactor criticality with a lower than optimum actinide concentration, it is required to add plutonium in the feed fuel instead of a certain amount of minor actinides, thus impairing the transmutation efficiency. To keep the critical state in the equilibrium mode, in situations where the actinide concentration is higher than the optimum one, it is essential to extract a portion of fuel with high content of 238Pu. It has been shown that the reactor configuration is the primary factor responsible for optimum actinide concentration value and that this value varies little with the feed fuel composition, the type of salt dissolving agent, and the fuel reprocessing mode. Optimal concentration for the molten-salt burner reactor with the core volume ranging from 2 to 30 m3 is within 17…10 mole %.

Quantitative evaluation of the plutonium proliferation resistance

The mathematical model presented in (Kulikov et al. 2018) can be used for the quantitative evaluation of the plutonium proliferation resistance. This requires the warm-up process of an implosion nuclear explosive device (NED) with a different structure to be analyzed with respect to various heat removal conditions and the option to be identified in which the NED remains operational for the longest time possible. The fraction of the 238Pu isotope with which, even in this case, the NED will prove to be operational only for quite a short time can be regarded as sufficient for the plutonium with such composition to be considered a proliferation resistant material. The purpose of the paper is to evaluate in quantitative terms the content of 238Pu in plutonium for ensuring its proliferation resistance and to identify the factors which influence significantly this evaluation. The data, procedures and findings from earlier works on the topic, as well as the authors’ own estimates and calculations were used for the study. It has been shown that the important factors involved in the plutonium proliferation resistance evaluation are the NED technology level and the required NED lifetime. Depending on the required lifetime, tougher requirements can be introduced with respect to the 238Pu content both from the standpoint of low-technology and high-technology NEDs. With a lifetime of five hours taken as the guide-mark (a NED is unlikely to be finally assembled, transported and used for such a short time), it is only plutonium containing 55% of 238Pu that can be considered a proliferation resistant fissile material.

Time dependent heat transfer of proliferation resistant plutonium

Abstract Increasing proliferation resistance of plutonium by way of increased 238Pu content is of interest to the nuclear nonproliferation and international safeguards community. Considering the high alpha decay heat of 238Pu, increasing the isotopic fraction leads to a noticeably higher amount of heat generation within the plutonium. High heat generation is especially unattractive in the scenario of weaponization. Upon weaponization of the plutonium, the plutonium may generate enough heat to elevate the temperature in the high explosives to above its self-explosion temperature, rendering the weapon useless. In addition, elevated temperatures will cause thermal expansion in the components of a nuclear explosive device that may produce thermal stresses high enough to produce failure in the materials, reducing the effectiveness of the weapon. Understanding the technical limit of 238Pu required to reduce the possibility of weaponization is key to reducing the current limit on safeguarded plutonium (greater than 80 at. % 238Pu). The plutonium vector evaluated in this study was found by simulating public information on Lightbridge’s fuel design for pressurized water reactors. This study explores the temperature profile and maximum stress within a simple (first generation design) hypothetical nuclear explosive device of four unique scenarios over time. Analyzing the transient development of both the temperature profile and maximum stress not only establishes a technical limit on the 238Pu content, but also establishes a time limit for which each scenario would be useable.

Proliferation resistant plutonium: An updated analysis

Achieving a proliferation resistant, or possibly even proliferation proof, plutonium is a goal of the nuclear security and safeguards community. Considering that nearly all plutonium is under international safeguards, with the exception of plutonium with greater than 80 at.% 238Pu, reducing the necessity of these safeguards would be beneficial to both those in industry and in national and international security. Due to the 238Pu high decay heat, establishing a technical limit for 238Pu content in which rendering the plutonium useless for weapons purposes may be possible. Following the analysis done by Kessler, the authors analyzed two realistic models for hypothetical nuclear explosive devices seeking to establish this technical limit for 238Pu content. The given plutonium vector used for this analysis was obtained through simulations of the Lightbridge fuel design in a pressurized water reactor. Calculating the temperature profile within the two hypothetical nuclear explosive device models showed that this plutonium vector would render the two models useless by causing the high explosives to undergo self-explosion.

Determination of 241Pu by the method of disturbed radioactive equilibrium using 2πα-counting and precision gamma-spectrometry

A simple technique is proposed for the determination of the content of 241Pu, which is based on disturbance of radioactive equilibrium in the genetically related 237U←241Pu→241Am decay chain of radionuclides, with the subsequent use of 2πα-counting and precision gamma-spectroscopy for monitoring the process of restoration of that equilibrium.It has been shown that the data on dynamics of accumulation of the daughter 241Am, which were obtained from the results of measurements of α- and γ-spectra of the samples, correspond to the estimates calculated for the chain of two genetically related radionuclides, the differences in the estimates of 241Pu radioactivity not exceeding 2%.Combining the different methods of registration (2πα-counting, semiconductor alpha- and gamma-spectrometry) enables the proposed method to be efficiently applied both for calibration of 241Pu-sources (from several hundreds of kBq and higher) and for radioisotopic analysis of plutonium mixtures. In doing so, there is a deep purification of 241Pu from its daughter decay products required due to unavailability of commercial detectors that could make it possible, based only on analysis of alpha-spectra, to conduct quantitative analysis of the content of 238Pu and 241Am.

Study on FBR core concepts to increase proliferation resistance of plutonium in LWR–FBR transition period

The possibility to enhance proliferation resistance of discharged plutonium in fast breeder reactor (FBR) has been investigated in terms of reactor core-design aspects. The provisional target for proliferation resistance measures based on Saito's attractiveness (ATTR) is defined. It is found that a few percent of plutonium loading and/or Am/Cm loading, which come from various types of spent fuel, might satisfy the provisional target with a minimum impact on the core neutronic performances. On Am/Cm loading core, decay heat constraints for fuel-handling aspects are found to be important and should be considered in design. There is not significant change on the current developing scenarios for light water reactor–FBR transition period by applying the measures based on Saito's ATTR. It is found that applying Kimura's proposal, 15% 238Pu content requires about 7% MA loading fraction both in the core and the blanket, and it only can be applied at limited case. The period to consume minor actinides is shorter than to consume plutonium.

Synthesis of Self-glowing Crystals of Zircon and Zirconia Doped with Plutonium-238 and Terbium

ABSTRACTDurable crystalline actinide host phases of ceramic waste forms are considered as advanced materials which are prospective for safe use of Pu and minor actinides before their final disposal. Development of self-glowing actinide-doped materials with matrices that are chemically inert and resistant to radiation damage may significantly change the approaches to actinide immobilization. Single crystals of zircon doped with different amount of Tb and 238Pu were synthesized by the flux method. Different non-radioactive crystals of Tb-doped zircon were studied first by cathodoluminescence method in order to identify the optimal content of Tb3+ that provides the highest luminescence emission. Then self-glowing crystals of zircon were grown with the optimal Tb content and small admixture of 238Pu (less than 0.1 wt. %). It was proposed that the valence state of Tb incorporated into zircon crystals can be (3+) and (4+), but only trivalent Tb is responsible for intensive luminescence. It is demonstrated that a small addition of Zr-phosphate to the flux supports Tb incorporation into zircon lattice and stabilizes preferably Tb3+. At the same time the addition of Zr-phosphate caused the crystallization of zirconia as a minor phase. Zircon crystals with very intensive self-glowing were successfully synthesized. The 238Pu content was 0.02 wt.% and the Tb concentration varied between 0.2 and 0.3 wt.%. Zirconia crystals obtained from the same experiment are characterized by weak self-glowing, although the Tb content was only 0.02 wt.%, while the content of 238Pu was comparable to that of zircon, i.e. 0.03 wt. %.

Development of New Generation of Durable Radio-luminescence Emitters based on Actinide-doped Crystals

Development of actinide-doped materials with matrices that are chemically inert and resistant to radiation damage may significantly change the approaches to actinide immobilization. Durable crystalline actinide host phases would be considered as advanced materials which are prospective for safe use of actinides before their final disposal. One of prospective applications of such materials is fabrication of radio-luminescence emitters with extremely durable matrices based on self-glowing crystals. Single crystals of zircon, monazite and xenotime doped with different amount of luminescence ions such as Tb, Eu and actinides such as 239Pu, 238Pu, 241Am, 237Np have been grown using flux method. Non-radioactive crystals were studied first using cathodoluminescence method in order to identify optimal contents of Tb3+and Eu3+, which provide the highest intensity of luminescence emission. Then radioactive self-glowing crystals doped with the same content of luminescence ion and small admixture of actinide were grown. It was suggested that content of 238Pu and 241Am in self-glowing crystals should not exceed 0.1 wt. %. Intensively glowing crystals of zircon, xenotime and monazite were successfully obtained and studied. Principal features of these crystals are discussed.

Electron spin resonance study of Fe 3+ and Mn 2+ ions in 17-year-old nuclear-waste-glass simulants containing PuO 2 with different degrees of 238Pu substitution

In 1982, three samples of a model nuclear waste glass, DRG-P1, P2, and P3, were prepared at Pacific Northwest National Laboratory with identical chemical compositions but respectively batched with 0.0, 0.1, and 0.9 wt.% of 238PuO 2 (half life 87.8 years) partially replacing the 1.0 wt.% 239PuO 2 (half life 2410 years) present in DRG-P1. In 1999, sub-samples of these three glasses were sent to the Naval Research Laboratory, where electron spin resonance (ESR) was to be used to search for self-irradiation effects due to 238Pu α decay. However, no radiation-induced point defects associated with the aluminoborosilicate network were observed. Rather, profound α-decay-induced changes in the ESR spectra of the batched iron-group ions were found. The spectra recorded for DRG-P1 were shown by absolute spin counts to have ESR intensities equivalent to ~ 85% of the sum of the batched 8.28 mol% Fe 3+ and 2.79 mol% Mn 2+, assuming that all of those ions behave as paramagnetic S = 5/2 states at room temperature. (Only 1.7 mol% Ni 2+ was batched, and ion-for-ion this S = 1 specie is calculated to contribute only ~ 1/3 of the ESR intensity of an S = 5/2 ion.) Separate experiments and calculations ruled out the possibility of small-particle magnetite-like precipitates comprising even so much as 0.01% of the total iron. A relatively weak ESR spectral feature observed in all three of the DRG-P n samples at g = 4.3 is the known signature of dilute Fe 3+ in glasses. By far the strongest ESR signal was found to be a broad line characterized by a first-derivative zero crossing at g = 2.06 and a peak-to-peak derivative linewidth of ~ 150 mT, both of which are shown to be virtually insensitive to temperature variations in the range 4.2 to 500 K and α-decay doses in the range provided by the 17-year aging of the three samples with differing 238Pu contents. It was discovered that these broad line shapes could be accurately simulated as weighted sums of Lorentzian shape functions of differing widths but having the same g value. The absence of any measurable anisotropy in the broad line, coupled with the temperature invariance of its width, imply the existence of extremely strong exchange interactions within clusters of Fe 3+, Fe 2+, Mn 2+, and Ni 2+ ions. The result is a speromagnetic system (amorphous antiferromagnet) characterized by progressive freezing out of like-ion pairs as the temperature is lowered, as opposed to exhibiting a distinct Néel temperature. Calculations that confirm this inference hinge on use of an equation previously derived by one of the authors [D.L. Griscom, V. Beltrán-López, C.I. Merzbacher, and E. Bolden, J. Non-Cryst. Solids 253 (1999) 1–22] that expresses the ESR intensity of ions behaving as non-interacting paramagnets as a function of their spin S, the spectrometer frequency ν, and the temperature T. The most evident ESR effect of 17 years of 238Pu decay is the (irreversible) lowering of the intensity of the broad line in rough proportion to the amount of 238Pu in the sample, with associated increases in the amplitude of the narrow g = 4.3 feature. It was additionally observed that cooling these glasses gives rise to reversible lowering of the broad-line intensity and increasing of the strength of the g = 4.3 feature when compared with theoretical expectation for temperature dependence of non-interacting S = 5/2 paramagnets . The ESR integrated intensity of the broad line as a function of 238Pu α-decay dose proved to be accurately fitted by a simple saturating exponential function asymptotic to zero for infinite-time self irradiation. This result thus promises a precise means of extrapolating thousands of years into the future the process of “super vitrification” resulting from the creation and rapid quenching of “thermal spikes” due to α decay in glasses immobilizing 239Pu or other actinide elements. In addition, because the ESR spectra of several very different candidate high-level nuclear waste (HLW) glass compositions containing even higher amounts of Fe 2O 3 are also shown here to be decomposable into sums of pure Lorentzians, the analytical method we have devised should be applicable to these and many other HLW glasses containing both iron-group oxides and radionuclides.

Denaturing Generated Pu in Fast Breeder Reactor Blanket

Protected Pu production (P3) is a recently developed concept to enhance the proliferation resistance properties of Pu by increasing the fraction of even-mass-number Pu isotopes thus leading to the denaturing of Pu. The present paper deals with the possibility of denaturing Pu by consideration of Pu and minor actinides (MAs) multicycling in medium-size fast breeder reactors (FBRs). It was found that multicycling of Pu and MAs in FBRs enhances the proliferation resistance of Pu by increasing the fraction of evenmass-number Pu isotopes. The proliferation resistance of Pu in P3 recycling options satisfied criteria based on Kessler's proposal, i.e., 6% 238Pu content, and Pellaud's proposal, i.e., 30% 240Pu content. The normalized attractiveness of Pu in P3 recycling options satisfied both criteria in the core as well as in the blanket with the combination of even-mass-number Pu isotopes. At the initial introduction, two P3 FBRs (714 MWth class) with the addition of 5 wt% MA into the blanket can be operated using the annual discharged spent fuel in Japan.

Denaturing Generated Pu in Fast Breeder Reactor Blanket

Protected Pu production (P3) is a recently developed concept to enhance the proliferation resistance properties of Pu by increasing the fraction of even-mass-number Pu isotopes thus leading to the denaturing of Pu. The present paper deals with the possibility of denaturing Pu by consideration of Pu and minor actinides (MAs) multicycling in medium-size fast breeder reactors (FBRs). It was found that multicycling of Pu and MAs in FBRs enhances the proliferation resistance of Pu by increasing the fraction of evenmass-number Pu isotopes. The proliferation resistance of Pu in P3 recycling options satisfied criteria based on Kessler's proposal, i.e., 6% 238Pu content, and Pellaud's proposal, i.e., 30% 240Pu content. The normalized attractiveness of Pu in P3 recycling options satisfied both criteria in the core as well as in the blanket with the combination of even-mass-number Pu isotopes. At the initial introduction, two P3 FBRs (714 MWth class) with the addition of 5 wt% MA into the blanket can be operated usi...

Neptunium in the Fuel Cycle: Nonproliferation Benefits Versus Industrial Drawbacks

Introducing neptunium into the nuclear fuel cycle has been proposed in the past as a way to impede the diversion or the direct use of plutonium to fabricate a nuclear explosive device. This paper aims to technically analyze the industrial consequences should this proposal be implemented. Two scenarios are considered: (a) adding neptunium to fresh uranium oxide (UOX) fuel before irradiation in a light water reactor (LWR) and (b) separating neptunium together with plutonium from used UOX fuel and using this combined oxide to fabricate mixed oxide (MOX) fuel before subsequent irradiation in an LWR. In both cases, assembly calculations for a pressurized water reactor using fresh fuel doped with neptunium are presented for a wide range of neptunium proportions. The consequences on the core and fuel performance and the fuel cycle are analyzed. The analysis shows that while irradiating neptunium-doped UOX fuel can offer significant proliferation-resistance benefits because of the increased quantity of the plutonium isotope 238Pu in the discharged fuel, it entails heavy industrial penalties even at 1% Np content. The use of neptunium with MOX fuel is limited to 0.5% in order to maintain a negative void coefficient. At this proportion, it offers minimal increase in 238Pu content, and it is unlikely that detectability through gamma-ray emissions of the resulting plutonium-neptunium oxide mixture is increased. The fact that neptunium itself may pose a proliferation risk must be carefully weighed in any decision to use neptunium as a tool to increase proliferation resistance.

A spectrometric method for determining α emitters based on acid extraction of fuel particles

A method for determining the 238U, 234U, 242Pu, 241Pu, 240Pu + 239Pu, 238Pu, 243Am, 241Am, 244Cm, and 242Cm contents of fuel particles is proposed. The lower detection limit for these radionuclides is 0.001 Bq per particle.

Protected Plutonium Breeding by Transmutation of Minor Actinides in Fast Breeder Reactor

The improvement of proliferation resistance properties of Pu and the burnup characteristics of fast breeder reactor (FBR) had been studied by utilizing minor actinides (MAs) to produce more 238Pu from 237Np and 241Am through neutron capture reaction. The higher the 238Pu content in the fuel, the higher the proliferation resistance of the fuel would be owing to the natural characteristics of 238Pu with high decay heat and high neutron production. The present paper deals with the assessment of passive measure against nuclear material proliferation by focusing on improving the inherent proliferation barrier of discharged Pu from an FBR. Results showed that 5% MA doping to the blanket of an FBR gives as high as 17–19% 238Pu, which could be seen as a significant improvement of the proliferation properties of Pu. Moreover, additional 5% ZrH2, togather with 5% MA doping to the blanket, could enhance the 238Pu fraction much more (22–24%). With an assumption of protected Pu whose 238Pu isotopic fraction is more than 12%, the present paper revealed that protected Pu could be produced more than the Pu consumed (protected Pu breeding) through incineration in an FBR with doping of a minimum 3% MAs or (2% MAs + 5% ZrH2) to the blanket.

Protected Plutonium Breeding by Transmutation of Minor Actinides in Fast Breeder Reactor

The improvement of proliferation resistance properties of Pu and the burnup characteristics of fast breeder reactor (FBR) had been studied by utilizing minor actinides (MAs) to produce more 238Pu from 237Np and 241Am through neutron capture reaction. The higher the 238Pu content in the fuel, the higher the proliferation resistance of the fuel would be owing to the natural characteristics of 238Pu with high decay heat and high neutron production. The present paper deals with the assessment of passive measure against nuclear material proliferation by focusing on improving the inherent proliferation barrier of discharged Pu from an FBR. Results showed that 5% MA doping to the blanket of an FBR gives as high as 17–19% 238Pu, which could be seen as a significant improvement of the proliferation properties of Pu. Moreover, additional 5% ZrH2, togather with 5% MA doping to the blanket, could enhance the 238Pu fraction much more (22–24%). With an assumption of protected Pu whose 238Pu isotopic fraction is more than 12%, the present paper revealed that protected Pu could be produced more than the Pu consumed (protected Pu breeding) through incineration in an FBR with doping of a minimum 3% MAs or (2% MAs + 5% ZrH2) to the blanket.

Application of Fusion Neutron Source for Denaturing of Plutonium

Potential of DT fusion neutron source to enhance proliferation resistance properties of plutonium by means of its isotopic denaturing is addressed. The approach is exemplified by denaturing of pure 239Pu and plutonium of typical LWR spent fuel through transmutation of neptunium. The essential feature of a fusion driven system proposed in the study is a zero mass balance of plutonium: total plutonium inventory is constant during irradiation. The system is capable to convert pure 239Pu into plutonium composition with more than 20% fraction of key 238Pu isotope during 1,000 d of irradiation under initial neutron loading of 1 MW.m−2. Denaturing of LWR spent fuel plutonium under the same conditions would increase its 238Pu content up to 10-12%.

Determination of 238Pu in plutonium bearing fuels by thermal ionization mass spectrometry

Determination of 238Pu in plutonium bearing fuels is required as a part of the chemical quality assurance of nuclear fuels. In addition, the determination of 238Pu is required in nuclear technology for many other applications, e.g., for developing isotope correlations and while using 238Pu as a spike (tracer) in isotope dilution α-spectrometry (IDAS). This determination usually involves the use of α-spectrometry on purified Pu sample. In view of the random errors associated with the counting statistics and the systematic errors due to (1) in-growth of 241Am in purified Pu sample and (2) tail contribution correction methodology in α-spectrometry, the precision and accuracy obtainable by α-spectrometry are limited. Thermal ionization mass spectrometry (TIMS) is generally used for the determination of different Pu isotopes other than 238Pu. This is due to the ubiquitous isobaric interference from 238U at 238Pu in TIMS. Recently, we have carried out studies on the formation of atomic and oxide ions of U and Pu by TIMS and developed a novel approach using interfering element correction methodology to account for the isobaric interference of 238U at 238Pu in TIMS. This methodology is based on the addition of 235U (enrichment >90 atom%) to Pu sample followed by the determination of 238U/235U atom ratio using UO+ ion and determination of Pu isotope ratios using Pu+ ion, from the same filament loading. The TIMS methodology was used for the determination of 238Pu in different Pu samples in U based nuclear fuels from PHWRs with 238Pu content about 0.2 atom%. The 238Pu determination was also carried out using α-spectrometry. This paper reports the results obtained by the two methods and presents the ments and shortcomings of the two approaches.

The use of cathodoluminescence for the development of durable self-glowing crystals based on solid solutions YPO4-EuPO4

Local cathodoluminescence spectroscopy has been suggested for the development of durable self-glowing crystals based on crystalline solid solutions (Y, Eu)PO4. Nonradioactive ions of Eu3+ in these crystals cause strong luminescence in the visible range, initiated by small admixture (less than 1 wt %) of α-radioactive 238Pu. The intensity of self-glowing depends on the Y: Eu ratio and the 238Pu content. The optimal Y: Eu ratio responsible for the most intensive luminescence has been identified. The principal features of cathodoluminescence emission in (Y, Eu)PO4 crystals of various chemical compositions are being discussed.

On the transmutation of Am in a fast lead-cooled system

Characteristics of the equilibrium fuel cycle for the core or a blanket of ADS having the structure of the core of a fast lead-cooled reactor of type BREST (Russian abbreviation for ‘Bystryy Reaktor so Svintsovym Teplonositelem’) in a mode of americium transmutation are calculated. Americium loading was taken 5% of heavy atoms. Keeping the average multiplication factor the same as in a standard equilibrium cycle, reactivity swing over 1 year's microcycle is about 1%, that demands partial fuel reloading with a periodicity of about one month. For one year of operation, 61 kg of americium is destroyed, and due to increased 238Pu content, americium is mainly converted to fission products. Thus in a system of 1 GWt (thermal), 87 kg of americium can be transmuted yearly. The estimate of the reactivity void effect has shown that it increases to 0.6% almost linearly with the void fraction increasing up to 25% and reaches its maximum of 0.7% at a void fraction of about 50%. Application of similar strategy for ADS with a sub-criticality level ≈0.96−0.98 can essentially relax safety problems related to positive void effects.