Development of water leak detection method in fusion reactors using water-soluble gas

A water leak detection method using krypton (Kr) as a water-soluble tracer has been proposed for fusion reactors with fully circulating the in-vessel cooling water. This method was targeted for applying to the International Thermonuclear Experimental Reactor (ITER), and the 10⁻³ Pa m³/s order of water leak valves were fabricated and connected to the water loop circuit. The water leaks were effused into the vacuum vessel evacuated by a cryopump and the water dissolved Kr was detected by a quadrupole mass spectrometer (QMS). When two leak valves with 1 m distance were attached to the test pipe with 30 °C heating, two distinct, the mass to charge number ratio (m/e) of 84 peak current rises caused by the water leak were successfully detected with the time interval of 39 s. On the other hand, the water accession length as a function of the traveling time was calculated by considering a natural convection flow caused by the 30 °C heating, where the traveling time was 44.6 s for the 1 m length. This means that the observed positional accuracy is 12.6%, based on the calculation. To enhance the positional accuracy, the detailed flow simulation is indispensable. This method can be applied to the ITER condition.     

低温吸附法分离氦气流中氢同位素的实验研究

采用穿透曲线法研究了液氮温度下活性炭、碳分子筛和碳纳米纤维对氢同位素的吸附等温线和同位素效应。结果表明：活性炭和碳分子筛都是良好的吸附剂，碳纳米纤维对氢同位素的吸附量太低而不具备工程应用的可能性。实验还对吸附剂进行了改性处理，考察了改性吸附剂对氢同位素的吸附性能。     

Pulsed extraction of ionization from helium buffer gas

The migration of intense ionization created in helium buffer gas under the influence of applied electric fields is considered. First the chemical evolution of the ionization created by fast heavy-ion beams is described. Straight forward estimates of the lifetimes for charge exchange indicate a clear suppression of charge exchange during ion migration in low pressure helium. Then self-consistent calculations of the migration of the ions in the electric field of a gas-filled cell at the National Superconducting Cyclotron Laboratory (NSCL) using a particle-in-cell computer code are presented. The results of the calculations are compared to measurements of the extracted ion current caused by beam pulses injected into the NSCL gas cell.     

A mass spectrometry method for quantitative and kinetic analysis of gas release from nuclear materials and its application to helium desorption from UO2 and fission gas release from irradiated fuel

A new system has been developed to determine absolute quantities of gas (mainly noble gases) released during thermal desorption in the range from 10^?12 to 10^?5 mol with a precision of few percent. The system is actually designed for simultaneous measurement of gaseous elements like He, Xe, Kr, thermally released from nuclear fuel samples and also allows the determination of the release kinetics as a function of time. This system, called Quantitative GAs MEasurement System (Q-GAMES), is based on the principle of collecting, purifying and spiking the sample gas in a “high-pressure” chamber, and continuous sampling of the gas for mass spectrometric analysis without sample depletion during the experiment. It is equipped with its own spike generator and with different gas purification systems. It is shown that this system fulfills the requirement to work with two existing very high-temperature gas desorption facilities for nuclear materials. This paper describes the Q-GAMES principle, the spiking system, its calibration, its operative mode, the different quantification techniques, as well as its technical data, in combination with some examples of typical application.     

Project of the GT-MHR high-temperature helium reactor with gas turbine

In February 1995, MINATOM of Russia and General Atomics (USA) signed the Agreement for the development and design of the GT-MHR facility with a modular helium reactor and a gas turbine intended to be constructed in Russia. This Agreement was subsequently expanded by the participation of Framatom and Fuji Electric. The GT-MHR facility is designed for burning weapons-grade plutonium and utilization of the heat produced in the direct gas-turbine cycle with electricity production efficiency of about 50%. In future such facilities with uranium fuel will be proposed for use as commercial NPPs. A GT-MHR prototype and fuel production facility are intended to be constructed at the Siberian Chemical Combine in Seversk (Tomsk-7). In accordance with the Agreement, a conceptual design of the GT-MHR should be developed in September 1997. As a part of the conceptual design, a reactor module with a power conversion system is being designed and plutonium fuel is being developed.     

A method of removing helium ash and impurities from fusion reactors

By injecting streams of small pellets through the edge of a reactor plasma, helium ash and other impurities can be captured and removed from the reactor. Calculations show that sufficient pumping capacity is available to remove 10²¹ He/s and that the equilibrium density of pellet material in the plasma is probably tolerable. If successful, this method of ash removal and impurity control simplifies reactor design considerably.     

Thermal mixing characteristics of helium gas in high-temperature gas-cooled reactor, (I) thermal mixing behavior of helium gas in HTTR

The future high-temperature gas-cooled reactor (HTGR) is now designed in Japan Atomic Energy Agency. The reactor has many merging points of helium gas with different temperatures. It is needed to clear the thermal mixing characteristics of helium gas at the pipe in the HTGR from the viewpoint of structure integrity and temperature control. Previously, the reactor inlet coolant temperature was controlled lower than specific one in the high-temperature engineering test reactor (HTTR) due to lack of mixing of helium gas in the primary cooling system. Now, the control system is improved to use the calculated bulk temperature of reactor inlet helium gas. In this paper, thermal–hydraulic analysis on the primary cooling system of the HTTR was conducted to clarify the thermal mixing behavior of helium gas. As a result, it was confirmed that the thermal mixing behavior is mainly affected by the aspect ratio of annular flow path, and it is needed to consider the mixing characteristics of helium gas at the piping design of the HTGR.     

Development of an acoustic leak monitoring system

The purpose, structure, and basic characteristics of an acoustic system for monitoring coolant leaks in the first loop of a VVER reactor are presented. The principle of operation of the diagnostics algorithm is described. The system has been checked on a special stand. The system satisfies all sensitivity and temporal requirements. In 2005, SAKT was put into experimental operation in the No. 3 unit of the Kalinin nuclear power plant. __________ Translated from Atomnaya énergiya, Vol. 103, No. 6, pp. 342–347, December, 2007.     

Acoustic method of leak detection using high-temperature microphones

A leak-detection method based on the use of high-temperature microphones was initially developed for ATR. The next-generation system was developed for RBMK entry and exit piping. Even though there are structural differences between them, RBMK and ATR have the same type of loop cooling. This has made it possible to develop a general approach to coolant leak detection. The microphone system of leak detection has been installed and successfully operating at the Leningrad nuclear power plant. The system detects leaks with sensitivity 0.23 m³/h, and it determines the site of a leak and estimates its size. The experience gained at the Leningrad nuclear power plant has subsequently been used at the Fugen nuclear power plant, where 0.046 m³/h was chosen as the target sensitivity for detecting leaks in the ATR entry piping. The possibility of detecting and determining the site of a small leak by the method proposed has been demonstrated in the present work.__________Translated from Atomnaya Énergiya, Vol. 98, No. 2, pp. 98–105, February, 2005.     

Evaluation method of corrosion lifetime of conventional stainless steel canister under oceanic air environment

Natural exposure and accelerated corrosion tests of conventional stainless steels for canisters of Types 304, 304L, and 316(LN) for concrete casks were conducted using several test specimens and 1/5 scale canister models. The welding residual stress of a full-scale model canister was also measured and the lifetime of sealability of canisters against corrosion evaluated. The maximum pitting rate and crevice corrosion rate of Type 304 were approximately 20 and 30 μm/year. Many SCC in the 4 Point Bending (4PB) test specimens were found to initiate from the bottom of the corrosion area by pitting or crevice corrosion. The SCC propagation rates in Types 304 and 304L under natural conditions were around 1.2E−12 to 1.8E−11 m/s in the K (Stress Intensity Factor) range of 0.6–9.0 MPa m^1/2, and that of the accelerated test (60 °C, 95% RHS, filled with NaCl mist) around 1.0E−10 to 3.5E−9 m/s in the K range of 0.5–30 MPa m^1/2. The SCC propagation rates under both natural and accelerated conditions were independent of K. The lifetime of sealability estimated from 1/5 scale models was longer than that from the small bending test specimens and has a safety margin as a structure.     

主动法探测贫化铀的实验研究

用有源（主动）的方法研究了贫化铀及其组合系统的中子诱发裂变缓发中子的探测技术。在不同质量和不同屏蔽体条件下测量和比较了贫化铀系统的裂变缓发中子随时间的分布,进一步分析了有源探测的入侵性和可核查性。探讨了采用缓发中子区分核与非核、贫化铀和浓缩铀系统的方法。     

Development of microphone leak detection technology on Fugen NPP

A method of leak detection, based on high-temperature resistant microphones, was originally developed in JNC to detect leakages with flow rates from 1 m³/h to 500m³/h. The development performed on Fugen is focused on detection of a small leakage at an early stage. Specifically, for the inlet feeder pipes the leak rate of 0.2gpm (0.046m³/h) has been chosen as a target detection capability. Evaluation of detection sensitivity was carried out in order to check the capability of the method to satisfy this requirement. The possibility of detecting and locating a small leakage has been demonstrated through the research.     

Effects of helium massive gas injection level on disruption mitigation on EAST

In this study, NIMROD simulations are performed to investigate the effects of massive helium gas injection level on the induced disruption on EAST tokamak. It is demonstrated in simulations that two different scenarios of plasma cooling(complete cooling and partial cooling) take place for different amounts of injected impurities. For the impurity injection above a critical level, a single MHD activity is able to induce a complete core temperature collapse. For impurity injection below the critical level, a series of multiple minor disruptions occur before the complete thermal quench.     

Performance of the gas turbine-modular helium reactor fuelled with different types of fertile TRISO particles

Preliminary studies have been performed on operation of the gas turbine-modular helium reactor (GT-MHR) with a thorium based fuel. The major options for a thorium fuel are a mixture with light water reactors spent fuel, mixture with military plutonium or with with fissile isotopes of uranium. Consequently, we assumed three models of the fuel containing a mixture of thorium with ²³⁹Pu, ²³³U or ²³⁵U in TRISO particles with a different kernel radius keeping constant the packing fraction at the level of 37.5%, which corresponds to the current compacting process limit. In order to allow thorium to act as a breeder of fissile uranium and ensure conditions for a self-sustaining fission chain, the fresh fuel must contain a certain quantity of fissile isotope at beginning of life; we refer to the initial fissile nuclide as triggering isotope. The small capture cross-section of ²³²Th in the thermal neutron energy range, compared to the fission one of the common fissile isotopes (²³⁹Pu, ²³³U and ²³⁵U), requires a quantity of thorium 25–30 times greater than that one of the triggering isotope in order to equilibrate the reaction rates. At the same time, the amount of the triggering isotope must be enough to set the criticality condition of the reactor. These two conditions must be simultaneously satisfied. The necessity of a large mass of fuel forces to utilize TRISO particles with a large radius of the kernel, 300 μm. Moreover, in order to improve the neutron economics, a fuel cycle based on thorium requires a low capture to fission ratio of the triggering isotope. Amid the common fissile isotopes, ²³³U, ²³⁵U and ²³⁹Pu, we have found that only the uranium nuclides have shown to have the suitable neutronic features to enable the GT-MHR to work on a fuel based on thorium.     

Thermal desorption of helium from reactor steel

Thermal desorption was used to study the behavioral particulars of the ion-implanted at 20 and 650°C helium in reactor ferrite-martensite EP-450, Eurofer-97, dispersion-hardened EP-450, Eurofer-97, and EK-164 austenitic steel. It is established that compared with the thermal desorption spectrum of EP-450 and Euroffer-97 steel the temperature interval for helium release from dispersion-hardened EP-450 and Eurofer 97 steels is wider for helium implantation at room temperature and especially at 650°C. In steel hardened by disperse oxides Y₂O₃, a substantial amount of helium is released at high temperatures after the main maximum in the thermal desorption spectrum as a result of the formation at the incoherent particle–matrix boundary of bubbles with high bonding energy with particles. In contrast to the ferrite-martensite steel irradiated in the temper state, the thermal desorption spectrum of EK-164 austenitic steel is more complex because of the multiple stage helium release due to the structural defects introduced by cold deformation.     

Development of mathematical model for optimization of sodium leak collection tray

Sodium leaks and resultant fire containment play an important role in the safe operation of a fast breeder reactor. Leak collection tray (LCT) is a passive device which is used to collect the highly reactive liquid sodium in the case of an accidental leakage. The consequences of sodium fire are mitigated by oxygen starvation in the vessel which collects the liquid sodium after leakage. The current paper deals with the optimization of the LCT geometry based on the hydrodynamic characteristics of the leaked liquid sodium. Isothermal numerical simulations have been performed to understand the interfacial dynamics of the hot liquid sodium flow in the top tray part and the variation of sodium draining rate into the holdup vessel for various drainpipe diameters and leak rates. Since the numerical simulations involve very high computational effort, an equivalent semi-analytical sloshing/draining model has also been developed which emulates the flow process in the LCT. The predictions of transient mass distributions in the top part and in the holdup vessel for the semi-analytical model are in close match with the results obtained from the detailed numerical study. The results reveal critical geometric parameters at which the un-burnt sodium collected in the LCT will be maximum.     

Thermal desorption of helium from defects in nickel

Helium atoms, introduced into materials by helium plasma or generated by the (n, α) nuclear reaction, have a strong tendency to accumulate at trapping sites such as vacancy clusters and dislocations. In this paper, the effects of dislocations, single vacancies and vacancy clusters on the retention and desorption of helium atoms in nickel were studied. Low energy (0.1-0.15 keV) helium atoms were implanted in nickel with vacancies or dislocations without causing any displacement damage. He atoms, interstitial-type dislocation loops, and vacancy clusters were also introduced with irradiation damage by 5.0 keV helium ions. Helium thermal desorption peaks from dislocations, helium-vacancy clusters and helium bubbles were obtained by thermal desorption spectroscopy at 940 K, in the range from 900 to 1370 K, and at 1500 K, respectively. In addition, a thermally quasi-stable state was found for helium-vacancy clusters.