Underground nuclear power plant siting

This paper summarizes the results of investigations to define the design concepts and estimate cost penalties associated with the burial of large light-water reactor nuclear power plants in underground rock cavities. Several cavities are proposed to contain the major components of the power plant without requiring excessive spans. The cost penalty of the underground plant is estimated to be less than 10% above a similar surface plant in favorable geologic media. Preliminary analyses also indicate a potential improvement in containment of radioactive materials following a postulated accident.     

Small nuclear power plants based on ship-propulsion nuclear reactors

NIKIéT. Translated from Atomnaya énergiya, Vol. 77, No. 6, pp. 407–414, December, 1994.     

From conventional nuclear power reactors to accelerator-driven systems

Due to many factors, there is again increase in trend to use the nuclear power for energy production. But spent fuel from nuclear power plants has become one of the crucial problems of nuclear energy exploitation. Some problems attributed to the conventional nuclear power reactors along with their solutions and a historical transition from nuclear power reactors to accelerator-driven systems are briefly reviewed in the present work. It is argued that accelerator-driven systems (ADS), for transmutation of nuclear waste and energy production, are good alternatives to the conventional nuclear power plants. Important differences between the conventional nuclear reactors and the ADS along with the ADS physics are discussed. The ADS is considered to be relatively safe as compared to the other nuclear power reactors commonly in use.     

Supercritical-pressure, light-water-cooled reactors for economical nuclear power plants

Design studies of supercritical-pressure light-water-cooled reactors (SCLWRs) have been carried out to pursue drastic improvement of the economy of nuclear power generation. The core is cooled by supercritical water which is superheated without the phase change. The cooling system is a once-through type; the whole core flow is driven by the feedwater pumps and is directly led to the turbine. No recirculation line is necessary. Besides, steam separators and dryers are not needed. Water rods are used to enhance the moderation and to increase the flow velocity around the fuel rods. The radial peaking factor is satisfactorily reduced by controlling uranium enrichment and gadolinia concentration as well as water rods. Flattening of the radial power distribution is important to enhance the thermal efficiency. This can be achieved by the coolant density feedback and the out-in refueling pattern. Orificing is also effective to enhance the thermal efficiency. The thermal efficiency is above 40% with stainless steel cladding. Plant control system and safety system are also designed. The core flow should be directly maintained due to the once-through direct cycle. Plant behaviors of large break LOCAs and loss of offsite power are analyzed. Safety criteria are satisfied in both cases. The feasibility of SCLWR is shown.     

Underground nuclear power plants with surface turbine generators

This study has produced conceptual designs for light-water reactor underground nuclear power plants with portions of the plant at the surface. The investment cost penalty for underground excavation and cavity lining less interest during construction and escalation attributed to the underground portion of the plant at a favorable geologic site was estimated at between 3 and 4% above a comparable surface plant. The power plant turbine-generator was assumed to be at the surface and the reactor placed underground. Other equipment was located underground on the basis of a hazards analysis or by a functional relationship to the reactor. A guideline was adopted that the nuclear steam supply system and other principal subsystems should not require major redesign. Although some component relocation was allowable, it was permitted only if system performance and component operation were thought to be essentially unaffected. Plant size was stipulated as a single unit of 1000 MW(e) net which was not varied to determine an optimum size or number of units. Condenser cooling methods considered included natural convection wet cooling towers as well as once-through condenser cooling.In both the boiling-water (BWR) and pressurized-water (PWR) plant designs, four underground chambers are proposed to efficiently house the underground equipment. One of the four chambers is needed for the reactor and steam supply system. It is conceivable, if only reactor hazard protection is desired, that the equipment in two of the chambers (the nuclear auxiliaries and relay and switching) could be installed within a surface building. The location of the emergency core cooling system (ECCS) components as presently configured in surface plants relative to the nuclear steam supply system is critical to the satisfactory operation of the ECCS. In some situations the ECCS must draw water from the reactor area. The need for a positive head from this area to the appropriate pumps implies the pumps must be placed lower in elevation than the source of water. Consequently, it was appropriate to locate these ECCS components in a separate underground chamber near the reactor chamber.     

Design and safety optimization of ship-based small nuclear power reactors

Design and safety optimization of ship-based nuclear power reactors have been performed. The neutronic and thermo-hydraulic programs of the three-dimensional X–Y–Z geometry have been developed for the analysis of ship-based nuclear power plant. Quasi-static approach is adopted to treat seawater effect and quasi-static approach is also employed to treat neutronic aspect during safety analysis.

The reactors are loop type lead–bismuth-cooled fast reactors with nitride fuel and with relatively large coolant pipe above reactor core, the heat from primary coolant system is directly transferred to water–steam loop through steam generators. The power level is 100–200 MW th and excess reactivity is about 1$. Three types of core were investigated in the optimization process: balance, tall, and pancake with five values of Z–Y size ratio.

As the optimization results, the core outlet temperature distribution is changing with the elevation angle of the reactor system. The pancake core type has larger temperature distribution change as the elevation angle changes due to the sea wave. The natural circulation capability is good for safety. However, large driving head of natural circulation may cause large temperature fluctuation as the elevation angle changes.     

A neuro-fuzzy controller for axial power distribution an nuclear reactors

A neuro-fuzzy control algorithm is applied for the core power distribution in a pressurized water reactor. The inputs of the neural fuzzy system are composed of data from each region of the reactor core. Rule outputs consist of linear combinations of their inputs (first-order Sugeno-Takagi type). The consequent and antecedent parameters of the fuzzy rules are updated by the backpropagation method. The reactor model used for computer simulations is a two-point xenon oscillation model based on the nonlinear xenon and iodine balance equations and the one group, one-dimensional neutron diffusion equation having nonlinear power reactivity feedback. The reactor core is axially divided into two regions, and each region has one input and one output and is coupled with the other region. The interaction between the regions of the reactor core is treated by a decoupling scheme. This proposed control method exhibits very fast response to a step or a ramp change of target axial offset without any residual flux oscillations between the upper and lower halves of the reactor core.     

Efficiency of producing additional power in units of nuclear power stations containing water-cooled-water-moderated reactors

Conclusions There is a basic possibility to raise the maximum power of a unit containing the VVÉR-1000 reactor in the course of the fuel charge burn-up and with lowering the coefficient of the energy-release nonuniformity in the reactor core. It is more advantageous economically to obtain additional power in carrying the peak load. With the duration of such operating conditions for 1000–2000 h/yr savings can amounts to 1–4 million rubles per year per 100 MW of additional power when compared to peaking GTP.It is necessary to analyze in more detail the safety as well as technical and economic indexes of the VVÉR-1000 and of the entire power unit both under normal operating conditions and in emergency situation for the proposed elevated power mode.It is necessary to develop a procedure of experimental substantiation of a possible forcing level for the operating units of the NPS containing a VVÉR. The interested agencies should be involved in this development. Technical and economic advisability of making up a set of power-unit equipment suitable to carry short load peaks and prolonged elevation of the electric loads in the EPS should be determined on this basis and changes and additions should be introduced when developing new designs.Translated from Atomnaya Énergiya, Vol. 61, No. 6, pp. 397–401, December, 1986.