Transmutation Capability Research Articles

Non-destructive analysis of materials by neutron resonance transmission

In this paper a non-destructive technique Neutron Resonance Transmission Analysis (NRTA) is presented and demonstrated. The technique has been applied at the Time-Of-Flight facility GELINA of the Institute for Reference Materials and Measurements at Geel in Belgium to characterize a radioactive PbI 2 sample, which was used to study the transmutation capabilities of 129I. A transmission experiment divided into three measuring sequences allowed the identification and quantification of light ( 16O, 23Na and 32S) and heavy nuclei ( 127I, 206Pb, 207Pb and 208Pb) with an accuracy better than 7%. In addition, an upper limit of the hydrogen content was deduced from the attenuation of the neutron beam by the non-resonant scattering contribution.

A new LFR design concept for effective TRU transmutation

One of the lead-alloy cooled fast reactors, PEACER (Proliferation-resistant, Environment-friendly, Accident-tolerant, Continuable-energy, and Economical Reactor), has been designed by a university research team in Korea. This reactor is a medium-size modular fast reactor of 850 MWt (300 MWe) rated power with lead–bismuth coolant loop. A square lattice fuel assembly with large pitch size might be favorable to ensure sufficient mass flow rate not only in normal operation but also in natural cooling under accidents. A metal fuel of (U,TRU)10%Zr is chosen in this study for the advantage of high thermal conductivity. Multinational energy complex with a closed fuel cycle facilities should provide proliferation resistance with an institutional barrier. Under the material control safeguards, all fuel isotopes and radioactive material should be confined in a complex but as low-level radioactive waste. In order to achieve this goal, efficient transmutation of long-lived minor actinides (LLMAs) and long-lived fission products (LLFPs) should be completed in an LFR core. An energy complex, PEACER-Park, consists of four PEACERs and two collocated pyro-processing plants. Only low-level waste from spent fuel reprocessing plant is designed to be transported out of PEACER-Park. Recovery factors in reprocessing plant, therefore, should be high enough to make low-level tail satisfy US NRC class C classification. However, an interim storage should be collocated in PEACER-Park for storing radioactive fission products having short half-life such as Cs-135 and Sr-90. Parametric studies have been done for a core design to maximize its transmutation capability within safety criteria. ■ When a pitch to diameter ratio ( P/ D ratio) was increased, the transmutation capability of each LLMA isotope changed in different ways. ■ When neutron leakage was increased by making core shape flat, the transmutation enhanced. ■ It was confirmed that longer cycle length was favorable to transmutation. ■ In the case of feed fuel composition and coolant operation temperature, there were no significant effects on transmutation performance. The final optimized core was designed as follows: a flat core shape with 50 cm of active core height and 5 m core diameter, pitch to diameter ratio of 2.2 which could be compromised between different transmutation tendencies of Np-237 and Am-241 and three different enrichment zones with 1-year cycle length. This design could achieve a sufficient transmutation capability with a support ratio of 2.085. Maximum pin power peaking was less than 1.5. Large negative radial expansion feedback coefficient and a sufficient shutdown margin could also be guaranteed.

ICONE15-10515 TRANSMUTATION PERFORMANCE OF MOLTEN SALT VERSUS SOLID FUEL REACTORS

This study investigates the transmutation properties of a critical Molten Salt Reactor (MSR) and compares them against those of three types of solid fuel reactors - Lead cooled Fast Reactor (LFR), Sodium cooled Fast Reactor (SFR) and a PWR. A consistent comparison was made of the effect of the different reactor spectra. It was found that the fast reactors spectrum gives the best transmutation performance followed by the MSR and PWR spectra. A comparison of the fractional transmutations (FT) for an infinitive recycling of actinides (Ac) in the different reactors with a 0.1% loss fraction during reprocessing shows that the MSR has the highest FT due to its high specific power, followed by the SFR and the LFR. Taking into account FT and spectra differences the MSR has preferred transmutation capability.

Fuel design study and optimization for PEACER development

In order to increase the transmutation capability for the Pb-Bi cooled burner, PEACER, metallic fuel rods (60U–30TRU–10Zr with Pb-bond in HT-9 clad) having a short (50 cm) active length with a large gas plenum have been designed with a peak design TRU burnup of 15%. A 17 × 17 square-lattice with relatively high pitch-to-diameter ratio was employed to reduce the actinide production and pumping load associated with the high-density coolant. Fuel rod failure modes are identified and fuel design criteria are established. A fuel rod design model, named as RODSIS, has been obtained by incorporating Pb properties and a cladding oxidation rate equation. A thermal analysis has been conducted for a fuel rod having peak-power based on a predicted power distribution and history during an equilibrium cycle. Taking into account the high coolant density, all fuel rods are fastened in the assembly using a stiff middle grid structure and softer end grids made of HT-9. Based on fuel rod thermal analysis results, a finite element analysis (FEA) has been conducted for both thermal and mechanical analyses of the middle grid structure. Furthermore, a fuel assembly static analysis has been conducted to determine the consequences of the axial loading caused by buoyancy and flow. The PEACER fuel system design was visualized by using a three-dimensional design and visualization software.

Long-Lived Fission Product Transmutation Studies

A systematic study on long-lived fission products (LLFPs) transmutation has been performed with the aim of devising an optimal strategy for their transmutation in critical or subcritical reactor systems and evaluating impacts on the geologic repository. First, 99Tc and 129I were confirmed to have highest transmutation priorities in terms of transmutability and long-term radiological risk reduction. Then, the transmutation potentials of thermal and fast systems for 99Tc and 129I were evaluated by considering a typical pressurized water reactor (PWR) core and a sodium-cooled accelerator transmutation of waste system. To determine the best transmutation capabilities, various target design and loading optimization studies were performed. It was found that both 99Tc and 129I can be stabilized (i.e., zero net production) in the same PWR core under current design constraints by mixing 99Tc with fuel and by loading CaI2 target pins mixed with ZrH2 in guide tubes, but the PWR option appears to have a limited applicability as a burner of legacy LLFP. In fast systems, loading of moderated LLFP target assemblies in the core periphery (reflector region) was found to be preferable from the viewpoint of neutron economy and safety. By a simultaneous loading of 99Tc and 129I target assemblies in the reflector region, the self-generated 99Tc and 129I as well as the amount produced by several PWR cores could be consumed at a cost of ˜10% increased fuel inventory. Discharge burnups of ˜29 and ˜37% are achieved for 99Tc and 129I target assemblies with an ˜5-yr irradiation period.Based on these results, the impacts of 99Tc and 129I transmutation on the Yucca mountain repository were assessed in terms of the dose rate. The current Yucca Mountain release evaluations do not indicate a compelling need to transmute 99Tc and 129I because the resulting dose rates fall well below current regulatory limits. However, elimination of the LLFP inventory could allow significant relaxation of the waste form and container performance criteria, with associated economic benefits. Therefore, some development of either specialized waste form or transmutation target for the LLFP is prudent, especially considering the potential accumulation of large LLFP inventory with sustained use of nuclear energy into the future.

Transmutation of transuranic actinides in a spherical torus tokamak fusion reactor

In this paper, a concept for a fusion-driven waste transmutation reactor (FDTR) based on a spherical torus (ST) is put forward. A set of plasma parameters suitable for the transmutation blanket was chosen. The two-dimensional neutron transport code TWODANT, the three-dimensional Monte Carlo code MCNP/4B, the one-dimensional neutron transport and burn-up calculation code BISON3.0 and their associated data libraries were used to calculate the transmutation rate, the energy multiplication factor and the tritium-breeding ratio of the transmutation blanket. The calculation results for the system parameters and the actinide series isotopes for different operation times are presented. The engineering feasibility of the centre-post of FDTR has been investigated and the results provided. A preliminary neutronics calculation based on an ST transmutation blanket shows that the proposed system has a high transmutation capability for minor actinide wastes.

A preliminary design study for the HYPER system

In order to transmute the long-lived radioactive nuclides such as transuranics (TRU), Tc-99, and I-129 in LWR spent fuel, a preliminary conceptual design study has been performed for an accelerator driven subcritical reactor system, called HYPER (HYbrid Power Extraction Reactor). The core has a hybrid neutron energy spectrum which includes fast and thermal neutrons for the transmutation of TRU and fission products, respectively. TRU are loaded into the HYPER core in a TRU–Zr metal form because a metal type fuel has very good compatibility with the pyro-chemical process which retains the self-protection of transuranics at all times. On the other hand, Tc-99 and I-129 are loaded as pure technetium metal and sodium iodide, respectively. Pb–Bi is chosen as a primary coolant because Pb–Bi can provide a good spallation target and produce a very hard neutron energy spectrum. As results, the HYPER system does not need any independent spallation target system. 9Cr–2WVTa is used as a window material because this advanced ferritic/martensitic steel is known to have a good performance in the highly corrosive and radiative environment. The support ratios of the HYPER system are about 4–5 for TRU, Tc-99, and I-129. Therefore, a radiologically clean nuclear power, i.e. zero net production of TRU, Tc-99 and I-129 can be achieved by combining 4–5 LWRs with one HYPER system. In addition, the HYPER system, having good proliferation resistance and high nuclear waste transmutation capability, is believed to provide a breakthrough to the spent fuel problems the nuclear industry is facing with.

Transmutation of minor actinides in a spherical torus tokamak fusion reactor, FDTR

In this paper, a concept of transmutation minor actinide (MA) nuclear waste based on the spherical torus (ST) tokamak reactor, FDTR, was put forward. A set of plasma parameter was decided suitable for the ST transmutation nuclear waste blanket. Using the 2-D neutron transport code TWODANT, the 3-D Monte Carlo code MCNP-4B and the 1-D burn-up calculation code BISON3.0 and their associated data libraries to calculate the transmutation rate, the energy multiplication factor and the tritium breeding ratio of the transmutation blanket. The calculation results of the system parameters and the actinide series isotopes for different operation times were also given. The engineering feasibility of the center-post of FDTR has been investigated. Relevant results were also given. A preliminary neutronics calculation based on ST transmutation blanket shows that the proposed system has a high transmutation capability for MA wastes.

The implication of high-flux fusion neutron source for the self-consistency in multi-component nuclear energy system

Among fission products (FP) discharged from a fission reactor, long-lived fission products are considered as of primary concern. Their transmutation has been of high priority to reduce the long-term consequences of nuclear energy generation. A self-consistent nuclear energy system (SCNES) in which we center fast breeder reactor may not have enough degree of excess neutron sources to transmute the fission products that potentially would poses environmental hazards in long-term period if they are buried in geologic disposal. Here we propose a so-called multi-component SCNES in which fission reactor systems can be combined with fusion reactor systems mainly for compensating the loss of enough capability for the transmutation. Amongst long-lived fission products, major concern has been paid for iodine and technetium and little attention was given to radioactive 93Zr, although its hazard appears to be rather substantial. The importance of 93Zr transmutation is emphasized and the transmutation capability was examined with fusion neutron sources by incorporating adequate moderation structures. As a result, we have demonstrated that the fusion neutron sources with high-flux blanket can be applied to transmute 93Zr sufficiently and resolve the problem of its accumulation within the time period of several decades.

Parametric Studies on Plutonium Transmutation Using Uranium-Free Fuels in Light Water Reactors

To compare the once-through use of U-free fuels for plutonium burnup in light water reactors (LWRs), plutonium transmutation, minor actinide (MA) and long-life fission product (LLFP) buildup and radiotoxicity hazards were compared for PuO2 + ZrO2 (rock-like oxide: ROX) and PuO2 + ThO2 (thorium oxide: TOX) fuels, loaded in a soft-to-hard neutron spectrum LWR core (a moderator-to-fuel volume ratio Vm/Vf is from 0.5 to 3.0). For better understanding and proper improvement of the reactivity coefficient problem of ROX, the fuel temperature coefficient, the void coefficient, and the delayed neutron fraction were also studied. A mixed-oxide (MOX)-fueled LWR was considered for reference purposes.From the result of the cell burnup calculation, ROX fuel transmutes 90% of net initially loaded weapons-grade Pu, and 2.5% of initially loaded Pu is converted to MAs when Vm/Vf is 2.0 and discharge burnup in effective full-power days is equivalent to that of 33 GWd/t in MOX fuel. Reactor-grade Pu-based ROX fuel transmutes 80% of net initially loaded Pu, and 6.7% of initially loaded Pu converts to MAs with the same condition as the weapons-grade Pu ROX fuel. TOX fuel also has a good Pu transmutation capability, but the 233U production amount is approximately a half of the fissile Pu transmutation amount. The MA production amount in TOX fuel is lower than that in MOX and ROX fuels. The LLFP production amount in ROX fuel is lower than that in MOX and TOX fuels. The radiotoxicity hazard of ROX spent fuel is lower compared to that in TOX and MOX spent fuels.The thermal neutron energy region is important in ROX fuel for fuel temperature coefficient and void coefficient problems. From these calculations, 15 to 20% 232Th-added ROX fuel seems the best to use as a once-through Pu-burning fuel compared to TOX and MOX fuels in conventional LWRs, because of its higher Pu transmutation, lower radiotoxicity hazard.

A pan-shape transuranic burner core with a low sodium void worth

A 1575 MWt transuranic (TRU) burner reactor core with a low sodium void worth has been developed by devising a pan-shaped active core design. The core consists of two types of fule subassemblies that differ in the height of the fueled regions. This strategy has allowed an extreme "pancaking" of the inner core region while the radial dimension increase is limited by placing longer fuels in the outer core region. The fuel cycle analysis has been performed in the equilibrium cycle consisting of external feed fuel with reprocessed typical PWR spent fuel and fissile makeup with recycled TRU elements. The neutronic performance characteristics obtained from the equilibrium cycle analysis show that it would work safely as well as economically as measured in terms of burnup reactivity swing peak power density Doppler coefficient TRU burning and sodium void worth. The core has relatively low double power peaks in both the inner and outer cores without enrichment zoning and this enables to make an active core volume smaller. The developed TRU burner core has been subjected to an extensive parametric study on the reprocessing schemes. Investigations are given for sodium void worth transmutation capability burnup reactivity swing and minor actinide (MA) contents. Through this series of study a variant of the TRU burner core that is aimed at preferentially burning MA has been determined. This MA burner core uses U-235 as well as the homogeneously recycled TRU elements. This MA burner core consumes 140 kg of MA per year without penalizing the sodium void reactivity observed in the TRU burner core. Finally the combined introduction of developed TRU and MA burner cores shows the functional effectiveness of reducing PWR discharged TRU inventory.

The concept of proliferation-resistant, environment-friendly, accident-tolerant, continual and economical reactor (PEACER)

In an effort to ameliorate generic concerns with current power reactors such as the risk of proliferation, radiological hazard of the spent fuel, and the vulnerability to core-melt accidents, the concept of a revolutionary reactor, named PEACER, has been developed as a proliferation-resistant waste transmutation reactor based on the unique combination of technologies of a proven fast reactor and the heavy liquid metal coolant. In this paper, results of the PEACER conceptual design are presented by focusing on the estimated performance of the PEACER system. The proliferation resistance of PEACER is based upon both institutional and technical issues. The latter includes denaturing of fissile materials, Pu in particular, as well as the intense radiation field associated with the pyrochemical partitioning method. When the fuel volume fraction and the core aspect ratio( L D ) are optimized, the transmutation capability of PEACER for long-lived wastes from LWR spent fuels is found to exceed the production rate of two LWR's with the same electric rating. In contrast with current power reactor design principles, the lower power density and the higher neutron leakage rate lead to higher performance with respect to proliferation-resistance, transmutation capability and the accident-tolerance. Results of the present conceptual design show promising characteristics in all the five targets proposed by its name PEACER, which warrants more detailed study.