Safety And Environmental Assessment Of Fusion Power Research Articles

The assessment of shutdown dose rate and radioactive waste of HCSB during its replacement in CFETR

Chinese Fusion Engineering Testing Reactor (CFETR) is a new test superconducting tokamak in China aimed to obtain the state-of-the-art technologies and bridge the gaps between ITER and DEMO. The helium cooled solid breeder blanket (HCSB) is one of three main blanket candidates for CFETR. During reactor operations, the highly radioactive nuclides will be produced by the blanket components which are located in the high-energy neutron radiation field. In order to protect the workers from too high radiation and ensure the normal operation of machinery, the Shutdown Dose Rate (SDR) of HCSB during its replacement is evaluated based on the rigorous two-step (R2S) method. Besides, according to the recommended standards provided by Safety and Environmental Assessment of Fusion Power (SEAFP) of the EU fusion program, the initial evaluation of the high level radioactive waste of the blanket is carried out as well. The results show that, based on current design of HCSB, the maximum SDR of the blanket is decreased to 4728 Sv/h after the reactor shutdown one day. And after 50 years of cooling, most of the structural materials can be recycled by simple remote operation.

Activation analysis and waste management of China ITER helium cooled solid breeder test blanket module

Activation characteristics have been assessed for the ITER China helium cooled solid breeder (CH-HCSB) 3 × 6 test blanket module (TBM). Taking a representative irradiation scenario, the activation calculations were performed by FISPACT code. Neutron fluxes distributions in the TBM were provided by a preceding MCNP calculation. These fluxes were passed to FISPACT for the activation calculation. The main activation parameters of the HCSB-TBM were calculated and discussed, such as activity, afterheat and contact dose rate. Meanwhile, the dominant radioactivity nuclides and reaction channel pathways have been identified. According to the Safety and Environmental Assessment of Fusion Power (SEAFP) waste management strategy, the activated materials can be re-used following the remote handling recycling options. The results will provide useful indications for further optimization design and waste management of the TBM.

Improved Consequence Modeling for Hypothetical Accidents in Fusion Power Plants

Refinements to consequence modelling for hypothetical accidents in Fusion Power Plants have been explored. This leads to improved accuracy and a reduction in some of the conservatism inherent in previous calculations. Assumptions made in previous analyses for the Safety and Environmental Assessment of Fusion Power (SEAFP) are examined, with particular emphasis given to aerosol modelling within the containment and dispersion and dose calculations. By employing a more realistic treatment of the time dependence in the aerosol model and introducing a procedure for accounting for the effects of wind meander, it is shown how to obtain results which may be used to adjust previously derived dose estimates. Further analysis assesses the possibility of aerosol particle removal by filtering in cracks in the containment barriers, as material leaks into the environment. The potential for mitigation by this mechanism has been neglected in previous calculations.

Materials optimisation for fusion power plants waste management from neutronics and activation assessment

The paper describes a study dedicated to the decommissioning and waste management issues of a commercial fusion power station. It is focused on the optimisation of structural materials for ex-vessel components of two safety and environmental assessment of fusion power (SEAFP) plant models (PM2 water-cooled and PM3 helium-cooled). The results of this study are: for PM2, the inboard and outboard coil case, the outboard vacuum vessel (VV), the outboard insulator and winding pack, the neutron and gamma shield and the concrete cryostat can be cleared; the same for PM3, excluding the outboard VV. Possible optimisations proposed are related to the outboard vessel both for PM2 and PM3. They deal with impurity level control and/or use OPTSTAB, a reduced-activation austenitic high-manganese steel.

Accidental and long-term safety assessment of fission and fusion power reactors

Fusion is seen as a much ‘cleaner’ energy than fission, and a resource for clean energy in the far future. However, being a form of nuclear energy, fusion shares with fission most of its safety problems. This study concerns the assessment of both the short term and the long term hazards associated with fusion, compared with the same figures for fission reactors. Fission data derive from well-known PWR safety assessments, and in particular from the Italian project Progetto Unificato Nucleare (PUN). Fusion data derive from the latest findings of the European Safety and Environmental Assessment of Fusion Power (SEAFP) programme. Concerning inadvertent intrusion in a radioactive waste disposal site and long-term degradation for fusion, this analysis was performed in the frame of the SEAFP studies, while for fission data are taken from typical European waste disposal sites. In all relevant cases, evaluation of associated risks is carried out, with a comparison of the obtained results.

The safety, environmental and economic implications of the use of silicon carbide in fusion power plant blankets

The potential safety, environmental and economic benefits of the use of silicon carbide as the first wall and blanket structure material in a fusion power plant have been assessed. The study has used a similar approach to that of the earlier European Safety and Environmental Assessment of Fusion Power (SEAFP), based on three new plant models using silicon carbide composites, allowing direct comparisons with the earlier study for vanadium alloy and ferritic–martensitic steel. Decay-heat driven temperature transients in postulated loss of cooling accidents and a number of waste management-related activation quantities have been analysed. Systems code studies have assessed the influence of silicon carbide use on economic factors.

Assessment of occupational radiation exposure for two fusion power plant designs

An assessment of the occupational radiation exposure issues of the fusion power stations has been performed focusing on the primary heat transport system (PHTS) of safety and environmental assessment of fusion power (SEAFP) reactor models. Fuel cycle systems have been considered for completeness, but not assessed. Fission reactor experience and fusion power reactor studies formed the basis of this assessment. Four assessments were performed. Two were based on SEAFP models 1 and 2, and the other two were based on improvements of these models suggested by an as low as reasonably achievable (ALARA) review. The following main conclusions are drawn from the assessments. The PHTS dose estimated for SEAFP model 1 (about 300 p-mSv/a) is below the current fission industry norm (about 500 p-mSv/a), but it is not ALARA. An ALARA value of 130 p-mSv/a is achievable and would be a reasonable target for the PHTS. The PHTS dose estimated for SEAFP model 2 (about 3000 p-mSv/a) is well above the current fission industry norm. Some design measures have been identified, that can reduce this dose to about 1200 p-mSv/a. While this is a substantial reduction, it is still well above the fission industry norm, therefore, additional effort is needed to obtain further reductions. The large difference in heat transport system doses between model 1 and model 2 is due to two main factors, the coolant and the coolant tubing material. The helium coolant eliminates the presence of corrosion products, and the vanadium alloy reduces the sputtering rate.

Analysis of Confinement Strategies for a Tokamak Fusion Reactor

The Safety and Environmental Assessment of Fusion Power (SEAFP) was performed in the framework of the European fusion program, whose results have already been published. The European Commission decided to continue this program for some identified issues that required development. One of these issues was the analysis and specification of the containment concepts that minimize accidental releases to the environment.To perform such an assessment, a methodology was followed to identify the most challenging accidental sequences in terms of containment integrity.The results of the accident selection and analysis that were performed during the extension of the SEAFP-2 program are given. Preliminary recommendations for the definition of a confinement strategy for tokamak fusion reactors are established.

Waste management for different fusion reactor designs

Safety and Environmental Assessment of Fusion Power (SEAFP) waste management studies performed up to 1998 concerned three power tokamak designs. In-vessel structural materials consist of V-alloys or low activation martensitic (LAM) steel; tritium-producing materials are Li 2O, Pb–17Li, Li 4SiO 4 with a Be-multiplier; coolants are helium or water. The strategy chosen reduces permanent radwaste by recycling the in-vessel materials and by clearance of the other structures. Limits of the contact dose rate and specific activity of the waste allowing such options are defined accordingly. SEAFP activities for 1999 enlarge the analysis to three additional reactors with in-vessel structures made with SiC/SiC composites. These materials cannot be recycled due to their form and, according to national regulations of E.C. countries, long-lived activation products hinder near-surface burial (NSB).

SEAFP and SEAL: safety and environmental aspects

The Safety and Environmental Assessment of Fusion Power (SEAFP) programme undertaken in the period 1992–1995 formed part of the ongoing effort in the European Fusion Programme to consider the safety and environmental aspects of fusion power. The assessment started with the development of a tokamak fusion power plant model of 3000 MW of fusion power. The analyses of safety included detailed consideration of effluents from normal operation, occupational doses, accidents (concentrating on the worst possible), and waste management. SEAFP was also the starting point for the Safety and Environmental Assessment of Fusion Power — Long Term Programme (SEAL) initiated within the European Fusion Programme in 1995. SEAL aims at broadening the scope and elaborating selected aspects in more detail. SEAFP and SEAL confirmed the favourable safety and environmental characteristics of fusion power. They also confirmed the need to support these characteristics by dedicated materials development and safety-related design decisions. Recently, a new study on fusion safety (SEAFP-2) has been launched, defined for the time period 1997–1998, using SEAFP and SEAL findings as starting points.

Application of SEAFP waste recycling and clearance strategies to ITER

The long-term action of safety and environmental assessment of fusion power (SEAFP) of the EU fusion program investigates fusion power reactor design. SEAFP strategy for the management of activated material is here applied to international thermonuclear experimental reactor (ITER). This strategy aims to reduce the amount of radioactive waste by conditional recycling (re-use of the activated material) in novel fusion plants and by clearance (declassification of the material with low activity level to non-active waste). Limits on the surface dose rates of the activated material after an interim storage of 50 years are proposed here to define the suitable recycling procedures. The possibility of clearance is assessed from limits on the specific activity of the material. These limits take into account the relative hazard of the various radionuclides contained in the material. It is shown that the amount of permanent radwaste arising from ITER may be substantially reduced to 0.

SEAFP-2 bounding accident analyses

Analyses have been performed of the potential consequences to the public of hypothetical loss-of-coolant accidents in conceptual fusion power plant designs. In order to establish upper bounds to the consequences of such events, a case has been studied in which total loss of all active cooling has been assumed, with no remedial intervention for the duration of the accident sequence. The analyses are based on three conceptual power plant designs, two of them similar to those assumed in the earlier safety and environmental assessment of fusion power (SEAFP) study (Raeder et al., 1995), with updating of assumed structural materials. The three models studied provide a broad range of design options. In all cases the decay-heat driven temperature transients are well below the level at which structural melting would begin. Based on conservative assumptions, mobilisation, release and dose calculations show that potential maximum doses to the public are very far below the levels at which evacuation might be considered.

Applications of the CATHARE and CONTAIN codes in parallel runs

Abstract The present work discussed the risks and consequences of multiple failure sequences for the Safety and Environmental Assessment of Fusion Power (SEAFP) tokamak concept. We analysed a double LOCA scenario within the divertor cooling loop; it starts with an ex-vessel LOCA, inducing an in-vessel LOCA. The induced in-vessel LOCA is due to a thermal crisis occuring in the plasma facing divertor structures, leading to suddenly enhanced thermo-mechanical stresses likely to cause a rupture. We wanted to calculate, as accurately as possible, the overpressure within the different compartments that are involved in the scenario, in order to verify that the design limits of these compartments are not exceeded. We calculated the transients with the help of the CATHARE code for the coolant loop analysis and the CONTAIN code for the containment analysis. A coupling was made, using the Parallel Virtual Machine (PVM) Sofware system on a Unix computers network; the results are compared to those of a manual coupling.

Reactor model for SEAFP

Objective of the Safety and Environmental Assessment of Fusion Power (SEAFP) [1]is to `assess the safety and environmental features of fusion on the basis of the conceptual studies of tokamak power reactors which incorporate safety and environmental features likely to ensure public acceptance and take into account the operating requirements of utilities'. The fusion reactors for commercial use are expected to enter in operation in several decades, therefore the assessment shall be as relevant as possible with respect to further development in physics and technology. The reactor has been conceived for monitored and filtered release of radioactivity to the environment during normal operation equivalent to a small fraction of the natural exposure; to avoid radioactivity release to the environment for all in-plant accidents and conceivable ex-plant accidents; to avoid disruption of community life outside the plant perimeter even in the case of rupture of confinement barriers, in particular by non-anticipated plant initiators. Consideration of possible fault conditions is an integrated part of the design of the main components and their associated support systems. the overall philosophy proposed is that all faults should be contained within an individual system regardless of the initiation fault or external action.

Overview of the SEAFP and SEAL Studies

The SEAFP (Safety and Environmental Assessment of Fusion Power) and SEAL (Safety and Environmental Assessment of fusion power, Long-term) programs form part of the ongoing effort in the European Fusion Programme to consider the safety and environmental aspects of fusion power. SEAFP was undertaken in the period 1992–1994. The assessment started with the development of two conceptual power plant designs, each of 3000 MW of fusion power, termed Model 1 and Model 2. Model 1 used vanadium alloy, helium cooling, and lithium oxide for tritium generation. Model 2 used a reduced-activation martensitic steel, water cooling, and a lithium–lead alloy for tritium generation. Both Models were designed for passive safety. The SEAFP analyses included detailed consideration of effluents, occupational doses, accidents (concentrating on the worst possible accidents), and waste management. The key results are summarized in this paper. SEAL was launched in 1995, with the aims of broadening the scope of SEAFP, and of elaborating selected aspects of SEAFP in more detail. The SEAL analyses include studies which extend the results of SEAFP to a wider class of blanket designs and material choices, improved assessments of the quantities of activated materials which may be exempted from regulatory control or recycled, improved modeling of occupational doses, and work in many areas to improve relevant data, modeling and analyses, or consider design improvements. Much of this work is ongoing, but key results from completed work are summarized in this paper.

SEAFP Modeling of Accident Sequences, Source Terms, and Public Doses

Within the European Safety and Environmental Assessment of Fusion Power (SEAFP), off-site public doses were assessed for representative hypothetical worst case fusion power station accident sequences driven by in-plant energies, without taking credit for any active safety measures. In this paper, in order to illustrate the calculations performed in SEAFP, the calculational sequence is described for one accident scenario. This is a major in-vessel LOCA. Several sources of active material are mobilized following the LOCA, and are transported across successive containment barriers as the accident evolves, with a small fraction of the source inventory eventually reaching the environment. Using conservative assumptions, modeling of thermo-fluid-mechanics, heat transfer, mobilization, transport, aerosol phenomena, and atmospheric dispersal and dilution, were used to determine several measures of public dose exposure. Calculations for other accident scenarios, performed within SEAFP, are not described in detail in this paper, but are commented on. The calculations indicate that maximum public doses would be well below levels at which emergency intervention would be required.

SEAL studies of variant blanket concepts and materials

Within the European SEAL (Safety and Environmental Assessment of fusion power, Long-term) program, safety and environmental assessments have been performed which extend the results of the earlier SEAFP (Safety and Environmental Assessment of Fusion Power) program to a wider range of blanket designs and material choices. The four blanket designs analysed were those which had been developed within the Blanket program of the European Fusion Programme. All four are based on martensitic steel as structural material, and otherwise may be summarized as: water-cooled lithium–lead; dual-cooled lithium–lead; helium-cooled lithium silicate (BOT geometry); helium-cooled lithium aluminate (or zirconate) (BIT geometry). The results reveal that all the blankets show the favorable S&E characteristics of fusion, though there are interesting and significant differences between them. The key results are described. Assessments have also been performed of a wider range of materials than was considered in SEAFP. These were: an alternative vanadium alloy, an alternative low-activation martensitic steel, titanium–aluminum intermetallic, and SiC composite. Assessed impurities were included in the compositions, and these had very important effects upon some of the results. Key results impacting upon accident characteristics, recycling, and waste management are described.

Occupational Exposure: The Role of Circuit Chemistry and Tube Coatings in Reducing the ORE of Advanced Water Cooled Fusion Plants and the Potential Effects of Magnetic Fields

On a conservative calculation for a nonoptimized design, the Safety and Environmental Assessment of Fusion Power (SEAFP) water cooled design (Model 2) was found to have an Occupational Radiological Exposure (ORE) which would be too high by today's standards. This paper describes the investigations which have been undertaken to reduce the expected ORE to acceptable levels. In addition, an investigation on allowable exposure to magnetic fields was carried out.

Occupational Dose for the Water Cooling System of the SEAFP Project

The Occupational Radiation Exposure (ORE) for the water primary cooling system (PCS) of the SEAFP (Safety and Environmental Assessment of Fusion Power) alternative plant model (APM) was assessed ta...

Low-activation properties of novel Cr-based materials for fusion reactors

Due to the low neutron-induced radioactivity of their main constituent, two novel Cr-based structural materials are examined, from the low-activation properties viewpoint, as candidate first-wall materials for fusion reactors. The two alloys are Cr 5Fe 1Y 2O 3, and Cr 44Fe 5Al 0.3Ti 0.5Y 2O 3. Their low-activation properties have been compared with those of some reference materials, in particular the austenitic steel AISI 316L, the Mn-based reduced-activation steel OPTSTAB, a V 5Ti alloy and a ceramic matrix composite (SiC/SiC). Impurities and tramp elements have been included in the calculations. Irradiation conditions envisaged for the SEAFP (Safety and Environmental Assessment of Fusion Power) study have been adopted. Advantages of the proposed materials with respect to steels, either reference alloys or reduced-activation ones, appear evident from the results of the activation analysis. Cr 5Fe 1Y 2O 3, in particular, show excellent low-activation characteristics. This material can be a good choice for further development and characterization of first-wall and blanket structural materials for fusion power reactors.