Tritium Safety of Russian Test Blanket Module

Transcription

1 Tritium Safety of Russian Test Blanket Module V.K. Kapyshev, V.G. Kovalenko, Y.S. Strebkov N.A. Dollezhal Research and Development Institute of Power Engineering, PO Box 788, Moscow , Russia Abstract The Russian Controlled Fusion Program involves development of the DEMO reactor for electrical power production, tritium breeding and demonstration of reactor safety operations. The DEMO solid breeder blanket contains a ceramic orthosilicate lithium breeder and beryllium multiplier. Test Breeding Modules (TBM) of the DEMO blanket are developed in the framework of the ITER reactor design program and are targeted for testing during the ITER operation. The main objectives of this program are tests of TBM elements and auxiliary systems, demonstration of attainment of the required coolant temperature and tritium breeding in the breeding zone. The paper presents the results of technology and design activities carried out on development of Ttitium Systems for TBM. Flow sheets of the systems and some estimation of tritium leakages under normal and abnormal situations are discussed. Introduction The main objective of the International Experimental Thermonuclear Reactor (ITER) development is to confirm the technical feasibility of an installation with the plasma parameters which provide the fusion reaction over a long period of time. ITER, when in operation, would demonstrate the possibilities to ignite and to confine for long time the large-in-volume plasma. At the same time, ITER will serve as a unique experimental basis for multifunctional tests of promising structural materials and approval of technical solutions for Demonstration Thermonuclear Reactor (DEMO) design. For this purpose, some special places were selected for testing of Experimental Breeding Modules (EBM) of the DEMO reactor. Principal tasks of TBM tests in ITER are: test of TBM`s parts and auxiliary systems; attainment of necessary coolant temperature; demonstration of tritium breeding in the breeding zone while providing tritium extraction, monitoring of its composition, transport and recovery. These tasks are the main activities to be undertaken under the TBM Test Program in ITER. The RF Team has designed the helium-cooled EBM with a ceramic breeder [1,2] and lithium cooled TBM. The RF proposals for TBM and auxiliary systems are based on the DEMO reactor concept developed in [3,4]. The design developed provides for adaptation of the EBM components to one of the ITER vacuum vessel ports and interfaces between the EBM system equipment and ITER installations and reactor buildings. Following the RF strategy of TBM tests and in view of an increasing number of ITER membercountries, the Russian Team has taken the decision to divide ceramic TBM of the DEMO blanket with helium coolant into two identical test breeder sub-modules (TBSM). These sub-modules are located on the support frame of the ITER horizontal port Such a decision will make it possible to promptly respond

2 to any changes in sharing the port space between the member-countries and, conceivably, to solve some technological problems. The paper presents the RF results of calculation and design of TBM for ITER ceramic blanket with helium coolant and auxiliary systems. 1. Ceramic Helium Cooled Experimental Breeder Module Special horizontal ports are envisaged to test DEMO experimental breeder blanket modules in ITER. TBM is installed in the horizontal port and attached to the support frame connected with the shielding plug (fig. 1) [3]. Fig. 1 Isometric view of the RF TBM in the support frame The frame sizes determine the overall sizes of TBSM, which, with consideration for 20 mm gaps, are 840 mm in height and 514 mm in width. This frame serves for fastening of the experimental modules. Tightening of the ITER vacuum vessel is provided by welding between the shielding plug and vacuum vessel. The flexible supports are used to fasten TBM to the support frame and the shear keys to take rotational moments. The auxiliary systems comprise a helium cooling system, tritium cycle system, control system and monitoring system. The horizontal port space behind the shielding plug and rooms in the ITER reactor building are provided for the equipment of these systems. The details of the Module have been published in [3,4] and some main TBM parameters of are presented in Table 1.

3 Coolant Table 1. Main parameters of RF TBM Helium Breeder Li 4 SiO 4 Coolant temperature, о С: - inlet outlet 500 Coolant temperature rise, о С 200 Coolant pressure, MPa 10 Coolant velocity (maximum), m/sec 13.6 Structural material Ferritic steel: Cr (8-10%), Mo (0,5-0,7%), V (0,2-0,35%) Maximum temperature of structural 600 materials, о С Neutron multiplier Be Maximum temperature of neutron multiplier, 650 о С Maximum temperature of breeder, о С 1000 The Tritium Cycle System (TCS) is included tritium extraction system, tritium breeder monitoring system (TBSM), coolant purification system. Conceptual diagram of the cycle is presented in fig tritium breeding zone (TBZ); 2-test blanket sub-module; 3-tritium extraction system; 4-purge-gas circuit; 5-monitoring system of tritium breeding in TBZ (TBSM); 6-coolant purification system; 7- helium coolant circuit. Fig. 2. Conceptual diagram of the TCS

4 To develop of TCS in details have to be given careful consideration all modes of tritium cycle operations. 2. Modes of Tritium Cycle System Operations The modes of TCS operations are shown in Table 2. Under international standard for nuclear installations and devices there are two modes: normal operations and abnormal situations. Modes of TCS operations Table Normal modes 1.1 Plasma pulses Operations of tritium cycle systems under plasma pulses 1.2 Ancillary operations Operations of tritium cycle systems during plasma pauses Maintenance Replacement of tritium absorbers, filters Module replacements Replacements of modules, tritium absorbers, filters Completion of Module Program Removing EBM, TCS and their transportation to RF 2. Abnormal situations 2.1 Incidents 1.Stoppage of analysis system activity 2.Break a modes of chemical purification absorber operations 3.Break of TBSM system 2.2 Accidents 1. Failure of vacuum pipe on TGS 2.Accidents of technology systems 2.3 Maximum design accident Break of coolant circuit in TBZ and enter of coolant to purge-gas system 2.4 Hypothetical accident Break of all barriers Operations of tritium cycle systems under plasma pulses (1.1), replacements of modules (1.2.2) for normal operations and maximum design accident (2.3), hypothetical accident (2.4) are discussed at present stage of RF TBM activity.

5 Review of TCS for p.p. 1.1, is necessary to develop a block-diagram of TCS and investigate operations with tritiated waste to develop Radiation Safety System (RSS). Maximum design and hypothetical accidents are selected for discussion because the consequences of ones are the most gravity for the reactor. 3. Tritium Cycle System of TBM Development of TCS for reactor/facilities is based on proposals [5,6] for RF DEMO. There are three interconnected parts: reactor tritium complex, tritium process system and radiation safety system (Fig. 3,[6]). Its comprise a subject of main technology operations and ancillary systems to meet of radiation safety requirements. The scheme may be applied for every controlled fusion facility or reactor. As for TBM Tritium Breeding Zone is discussed instead a reactor and RSS must be added to meet requirements of tritiated waste processes accordingly the list of the normal and abnormal modes. Result of flow sheet development for TBM is shown in fig tritium breeding zone (TBZ); 1-test blanket sub-module; 2- transporter; 3- T-plant; 4- T-laboratory; 5- tritium purification of purge-gas; 6 - tritium purification device in helium coolant circuit; 7- purge-gas circuit; 8- helium coolant circuit; 9- gas waste from purge-gas circuit; 10- gas waste from helium coolant circuit; 11- tritiated waste Fig. 3. Conception diagram of TCS location. The Tritium Gas System (TGS) provides the purge-gas circulation through TBZ, extraction of bred tritium, tritium processing to remove it from the TBSM systems, tritium transportation from the reactor and analytical monitoring of purge-gas chemical composition. TGS includes an analytical sub-system (ASS) and a tritium extraction system (TES). ASS provides monitoring of the tritium concentration in purge-gas and the relation between tritium gaseous and oxide forms. The monitoring of hydrogen and impurity content is carried out by sampling. Tritium concentration and relation between tritium forms are measured by two radiometric ionization chambers.

6 At initial stage of researches it was assumed that TBM and TCS have to operate independently from Tritium Building of ITER. TBM and with all systems contained tritium had to be removed to Hostess TBM. To meet the requirement technology based on intermetallic compounds was adopted. Processing of tritium-containing gaseous mixtures from the breeding zone and the ASS is based on using Zr-based hydride-generating intermetallic compounds. Two identical processes lines (fig. 4) each containing three units (1,2,3) and (4,5,6) operate in consecutive order to purify impurities and absorb tritium. Gas cleared from tritium for necessary radiation limits is directed to TBZ. It is possibly to exhaust in air through RSS. Measurement of tritium breeding rate (TBR) in TBZ will be provided by MTBS. The tritium balance operations and estimation of TBR can be carried out using ASS and MTBS. MTBS is a reactor assembly for TBM, which contains ampoules with lithium-6, lithium-7 isotopes and neutron detectors. The ampoules with lithium isotopes will be removed and replaced after a pulse during a pause Fig. 4 Tritium Extraction System for RF TBSM 1-6 absorbers (t=700 C); 7 filter; 8 flow metter; 9-11 vacuum pump; 12 receiver; 13 sampling; 14 pressure monitoring; 15 purge-gas circuit; 16 RSS; ;17 purge-gas; 18 air; 19 sampling Coolant purification system is at a by-pass line of helium coolant loop. Process of tritium purification is based on using two parallel technology lines for absorption and for segregation as well. The gas waste as a result of the operations is directed to RSS. However the most part of gas waste flow will be a result of module replacement and volume of gas waste to RSS can be considerable. Some details of a replacement technology have to discussed in order to evaluate the amount of the waste arisen as a result of the operations with the reactor devices.

7 A scheme of plasma facing component (PFC) removal from a vacuum vessel is shown in Fig. 5. The modes of the operations are associated with surface decontamination. There are four main stages of the operation and an each stage supplies cross contamination waste [7]. L in G in (a) (b) 2 10 L out G out Fig. 5 System of PFC/Module Transportation from Vacuum Vessel to Transport Cask 1 Vacuum Vessel (VV), 2 PFC/Module, 3 Vacuum Port of VV, 4 Technological Space (TS), 5 Technological Zone for Decontamination Device, 6 Transport Cask (TC), 7 and 8 Doors, 9 Exit Parts of Port and Cask, 10 Separable Protective Covers, L in and G in Inlet of Decontamination Liquid and Gas in TC, L out and G out Outlet of Liquid and Gas after Decontamination, (a)-(b) Transfer Way of PFC Some essential points of the technology and amounts of the waste are in Table 3. Dimensions of a technology zone (pos. 5, Fig. 5) have to comply with maximum sizes of the Module. In this case this is 3.6 m long, 2 m high, 1.6 m wide. The upper value of gas waste demonstrate necessary to treat of it using tritium systems of Tritium Building. Furthermore some part of gas waste from TGS may be processed there as well. Location of the TCS and their connections with tritium building is presented in fig. 4. Gaseous from purge-gas and coolant purification devices (5,6) are directed to tritium laboratory of tritium building for follow treatment in ITER` tritium cycle. Samples from measurement devises and tritium waste go to the laboratory too.

8 Table 3. Technology of PFC/Module replacement Operations 1. Hooking up Transport Cask to Vacuum Port of the Vacuum Interim tritiated waste Gas (m 3 ) Vessel, evacuation of Technological Zone, evacuation of Transport Cask, detritiation of PFC, opening of Vacuum Seals of VV and TC Disassemble and replacement of PFC, transportation of Auxiliary <0.01 Devices to Blanket, dewatering from Cooling System, decontamination of Inner Surface of Cooling System, cutting Pipelines, sealing of the Pipelines, transportation of the PFC from VV to TC 3. Transportation of new PFC in VV and assembly, transportation of <0.01 PFC from TC to VV, hooking up PFC to Reactor System, preparation of PFC for operation, sealing of VV and TC 4. Decontamination and transportation of PFC to RSS TOTAL Tritium leakage in accidents Conservative estimations of tritium leakage for maximum and hypothetical accidents are based on experimental data obtained as results of researches with nuclear reactor modules [6,8]. Tritium inventory for TBZ and TCS under normal reactor operation is in Table 4. Rows 3 and 4 demonstrate maximum tritium inventory for one-weak period gas sorption.

9 Table 4 - Tritium inventory for TBZ and TCS 1 TBZ (ceramic) inventory Ci 2 Purge-gas circuit 50 Ci 3 Tritium in analytical sub-system 2*10 3 Ci/weak 4 Tritium in extraction system 2*10 3 Ci/weak The most part of tritium volume is contained in TGS and maximum leakage in accident can be 5000 Ci. Total leakage can be decreased up to 1000 Ci if tritium extraction period will be reduced to 1 day and tritium inventory TBZ to 400 Ci using results of in- pile experiments in nuclear reactor [6]. Conclusion 1. Flow sheet of Tritium Cycle System demonstrates that the research programs under ITER operations can be carried out. 2. An international interface between TBM`s systems and T-plant is necessary under all modes of TBM operations. 3. Developed block-diagram of tritiated gas waste treatment may be a base for providing of radioactive waste in a DEMO to tritium LLW. 4. Tritium release for accidents can be decreased using new methods of tritium extraction from ceramic References 1. Y. A. Sokolov, et.al., Russian DEMO plant study, Fusion Eng. and Des. 41 (1998) G. Shatalov, et.al., Russian DEMO-5 reactor with continuos plasma burn, Fusion Eng. and Des (2000) V.Kovalenko et. al., RF test blanket sub-module with ceramic breeder and helium cooling test in ITER, Fusion Eng. and Des. 81(2006) Design Description Document for the Russian Federation Ceramic Helium Cooled (CHC) Test Blanket Module. Status V. K. Kapyshev, L. A. Rivkis, G. L. Saksagansky, D. V. Serebrennikov Vacuum-tritium complex of magnetic confinement fusion reactors I. Plasma Devices and Operations, 1 (1990) V. K. Kapyshev et.al., Lithium ceramic blankets for Russian fusion reactor and influence of breeding operation mode on parameters of reactor tritium systems, Fusion Science and Technology 1-806(2005) L. A. Ionesyan, V. K. Kapyshev, V. N. Tebus et.al., Fusion Initial tritium waste management criteria and assessment for ITER Fus. Eng. and Des. 42 (1998) V. K. Kapyshev, E. P. Starshin, V. N. Frolov Radiation of lithium aluminate, lithium ortho-and metasilicate tablets in thermonuclear reactor and study of their gas emission and strength properties I. Plasma Devices and Opeations, 3 (1994)