Mikihide Nakamaru

Study on two-phase flow dynamics in steam injectors. II. High-pressure tests using scale-models

Analytical and experimental studies have been conducted on large-scale steam injectors for a next-generation reactor. The steam injectors are simple, compact, passive steam jet pumps for a steam-injector-driven passive core injection system (SI-PCIS) or steam-injector-driven primary loop recirculation system (SI-PLR). In order to check the feasibility of such large-scale steam injectors we developed the separate-two-phase flow models installed in the PHOENICS Code, and scale-model tests were conducted for both SI-PCIS and SI-PLR. A 1/2 scale SI-PCIS model achieved a discharge pressure of almost 8 MPa with 7 MPa steam and 0.4 MPa water, and a 1/5 scale SI-PLR model attained a discharge pressure of 12.5 MPa with 3 MPa steam and 7 MPa water. Both results are in good agreement with the analysis, confirming the feasibility of both systems. The systems will help to simplify the next generation of BWRs.

Safety System Design Concept and Performance Evaluation for a Long Operating Cycle Simplified Boiling Water Reactor

Abstract The long operating cycle simplified boiling water reactor is a reactor concept that pursues both safety and the economy by employing a natural circulation reactor core without a refueling, a passive decay heat removal, and an integrated building for the reactor and turbine. Throughout the entire spectrum of the design basis accident, the reactor core is kept covered by the passive emergency core cooling system. The decay heat is removed by the conventional active low-pressure residual heat removal system. As for a postulated severe accident, the suppression pool water floods the lower part of the reactor pressure vessel (RPV) in the case when core damage occurs, and the in-vessel retention that keeps the melt inside the RPV is achieved by supplying the coolant. The containment adopts a parallel–double-steel-plate structure similar to a hull structure, which contains coolant between the inner and outer walls to absorb the heat transferred from the inside of the containment. Consequently, the containment structure functions as a passive containment cooling system (PCCS) to remove the decay heat in case of an accident. This paper describes the PCCS performance evaluation by using TRAC code to show one of the characteristic plant features. The core damage frequency for internal events was also evaluated to examine the safety level of the plant and to show the adequacy of the safety system design.

The Development of the Evolutionary BWR (AB1600)

Considering the delay of the first breeding reactor (FBR), it is expected that the light water reactor will still play the main role of the electric power generation in the 2030’s. Accordingly, Toshiba has been developing a new conceptual ABWR as the near-term BWR. We tentatively call it AB1600. The AB1600 has introduced the hybrid active/passive safety system in order to have independent countermeasure for severe accidents and better probability of core damage frequency (CDF) considered external events such as earthquake. On the other hand, we have another goal of the AB1600, which is to retain the safety performance superior or equivalent to the current ABWR without deterioration of economy. In order to achieve both economy and safety performance, we have optimized the safety system configuration of the AB1600 by partly introducing passive safety system to design basis event (DBEs). At the same time, we have adopted the simplification of the overall plant systems in order to improve economy. In order to reduce capital cost, to shorten refueling period and to reduce maintenance effort, the AB1600 introduces the large fuel bundle size. The bundle size is 1.2 times as large as that of the ABWR and the fuel rod array is 12 by 12. And then by progressing the core design, we can reduce the number of reactor internal pumps (RIPs) to eight from the current ABWR of ten. The core power density, the number of fuel bundles, and the core diameter of AB1600 are decided in order to achieve 24 months fuel cycle length on the condition with below 5wt% enrichment of fuel and with eight RIPs.Copyright

Development of Simplified Compact Containment BWR Plant

In Japan, increase of nuclear plant unit capacity has been promoted to take advantage of economies of scale while further enhancing safety and reliability. As a result, more than 50 units of nuclear power plants are playing important role in electric power generation. However, the factors, such as stagnant growth in the recent electricity demand, limitation in electricity grid capacity and limited in initial investment avoiding risk, will not be in favor of large plant outputs. The reactor concept considered in this paper has a small power output, a compact containment and a simplified BWR configuration with comprehensive safety features. The Compact Containment Boiling Water Reactor (CCR), which is being developed with matured BWR technologies together with innovative systems/components, will provide attractiveness for the energy market in the world due to its flexibility in energy demands as well as in site conditions, its high potential in reducing investment risk and its safety feature facilitating public acceptance. The flexibility is achieved by CCR’s small power output of 300 MWe class and capability of long operating cycle (refueling intervals). The high investment potential is expected from CCR’s simplification/innovation in design such as natural circulation core cooling with the bottom located short core, internal upper entry control rod drives (CRDs) with ring-type dryers and simplified ECCS system with high pressure containment concept. The natural circulation core eliminates recirculation pumps as well as needs for maintenance of such pumps. The internal upper entry CRDs shorten the height of the reactor vessel (RPV) and consequently shorten the primary containment vessel (PCV). The safety feature mainly consists of large water inventory above the core without large penetration below the top of the core, passive cooling system by isolation condenser (IC), passive auto catalytic recombiner and in-vessel retention (IVR) capability. The large inventory increases the system response time in case of design base accidents including loss of coolant accidents. The IC suppresses PCV pressure by steam condensation without any AC power. The recombiner decreases hydrogen concentration in the PCV in case of a severe accident. Cooling the molten core inside the RPV if the core should be damaged by loss of core coolability could attain the IVR. The Compact Containment Boiling Water Reactor (CCR) has possibilities of attaining both economical and safe small reactor by simplified system and compact PCV technologies.Copyright