Reactor plant safety

Enhanced safety of the reactor plant is ensured by realization of basic safety principles 

The inherent safety of the reactor plant relies upon the following features  

1) radioactive discharges in normal operation at least one order of magnitude lower than the specified limits, and 

2) equivalent radiation doses to an individual at the boundary of the safety restricted zone and beyond it do not exceed the following values 0.02 mSv per year in normal operation and violations of normal operation conditions 10 mSv in design accidents and 50 mSv per year in beyond-design accidents. 

The elimination or at least minimization of the positive coolant density component of the temperature reactivity effect is a favourable factor in limitating the consequences of ULOF and UTOP. The negative reactivity feedback caused by a thermal expansion of the control rod drive lines also plays an important role. Analysis of a ULOF accident shows that sodium boiling and fuel melt are excluded because the core outlet temperature does not exceed 800 C. Nevertheless a refractory sodium-cooled tray beneath the core is provided to prevent release of corium beyond the reactor vessel boundary and formation of a critical mass. Preliminary safety analysis for the BN-1600M reactor plant shows that  

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The reactor plant safety is ensured without power supply or personnel intervention for not less than 72 hours following all possible disturbances and accidents (positive reactivity insertion, loss of heat removal, primary circuit depressurization) by means of the reactor inherent safety features and by using the complex of interconnected passive safety systems and devices. 

The transition to natural coolant circulation in the primary circuit and the reliability and efficiency of the emergency heat removal system have been confirmed by experiment and calculations. A large scale rig (1 200 for power, 1 1 for height) is being set up for the complex verification of the reactor plant safety. 

KAMANIN, YU.L., et al., BN-600 reactor plant safety insuring. Considering its operating experience, paper presented in the Int. Fast Reactor Safety Meeting, 12-16 August 1990, Snowbird, Utah, USA. 

Audits by INPO and the U.S. NRC aie a culmination of a high degree of self-auditing by the plant operators and the utihties themselves, often assisted by special third-party safety review boards set up to help carry out safety assessments (21). Self-auditing and self-criticism are essential to the process. These reflect the fundamental reactor safety principle that the owner-operator of the plant has the ultimate responsibiUty for plant safety. 

Rinard dedicated his research to a detailed analysis of methodological aspects of a micro-reactor plant concept which he also termed mini-plant production [85] (see also [4, 9, 10] for a commented, short description). Important criteria in this concept are JIT (Just-in-time) production, zero holdup, inherent safety, modularity and the KISS (keep it simple, stupid) principle. Based on this conceptual definition, Rinard describes different phases in plant development. Essential for his entire work is the pragmatic way of finding process solutions, truly of hybrid character ]149] (miniaturization only where really needed). Recent investigations are concerned with the scalability of hybrid micro-reactor plants and the limits thereof ]149], Expliddy he recommends jointly using micro- and meso-scale components. 

In this context, Benson and Ponton declare that while the chemical industry has made considerable achievements in reactor performance, safety and control, comparable to those in the microelectronics business, this success is by no means evident to the public, in deep contrast to the latter [139], It is said that this is mainly and in a way simply due to the visual recognition of chemical production plants. From a distance and for somebody outside the field, the chemical plants of the late 1940s and the early 1990s look virtually similar, whereas one is able immediately to see the big differences in, e.g., television sets and automobiles. Hence it is not evident that notable improvements were made over the decades. 

Chemiefabrik in der Grojie eines Chips, Handdsblatt, May 1996 Vision of shoe box-sized micro reactors plant cells as model for micro-reactor development cost, performance, and safety advantages LIGA process numbering-up safety processing of hazardous substances [237]. 

The fine chemicals business is characterized by a small volume of products manufactured. Therefore, batch production predominates and small-scale reactors are used. The need to implement fine chemistry processes into existing multiproduct plants often forces the choice of batch reactors. However, safety considerations may lead to the choice of continuous processing in spite of the small scale of operation. The inventory of hazardous materials must be kept low and this is achieved only in smaller continuous reactors. Thermal mnaways are less probable in continuous equipment as proven by statistics of accidents in the chemical industries. For short reaction times, continuous or semicontinuous operation is preferred. 

Guide for the Identification and Control of Exothermic Chemical Reactions" (TAA-GS-05 1994). A document in German by the Technischer Ausschuss fur Anlagensicherheit (Technical Committee for Plant Safety) of the Federal Ministry of the Environment, Nature Conservation and Reactor Safety. Addresses safety assessment of reactions during both normal operations and excursions, as well as selection and extent of measures to be adopted. An English translation of this document is provided on the CD-ROM included with this publication. 

Figure 4.35 Example of a micrestructured reactor plant based upon the modular fluidic backbone 1, heat exchanger 2, mixer 3, valve 4, safety valve 5, pump ...

A number of issues need to be resolved when dealing with batch reactors in industrial applications, ranging from design and planning of the plant to scheduling, optimization, and performance achievement of batch operations. Performance is usually specified in terms of productivity of the plant, safety of operations, and quality of final products. In order to meet such requirements, several problems need to be addressed ... 

The Hull site is a top-tier COMAH establishment and the individual plant safety reports were used as a base to identify the major hazard scenarios. While the Hull plants produce different final products, the key operational stages are the same, i.e., feed system, reactor section, initial separation and recycling, and final distillation train. The Risk Control Systems (RCS) were therefore fundamentally the same but each plant was reviewed in isolation. A total of eight different RCS were considered as part of the review and the process described in HSG 254 was used for each one. The Workbook produced during the review for one of the plants as part the process is attached in Appendix 1. ... 

In 1994 the German Secretary for Environmental Protection and Reactor Safety requested a guideline from his advisory coimcil on plant safety (TAA), which was to provide a flow-sheet type of assistance to the assessment of a process under normal operating conditions [8]. It is shown in Figure 2-3. 

Safety of the reactor plants is relied upon the reactors inherent self-protection features and application of successive protective barriers, redundant systems and equipment, efficient safety systems. 

High reliability and safety levels of the reactor plants are verified by their long operation experience. Projects of nuclear co-generation stations and power desahnation complex based on the propulsion-type reactor plants represent a certain commercial interest and can be attractive for domestic and foreign investors. 

Rules of Nuclear Safety for Nuclear Reactor Plants of NPPS" (PBYA RU AS-89). 

Small-scale reactors have more advantages than large-scale reactors in variety of energy utilization, construction, maintenance and adoption of innovative technologies, while the latter have scale merits in construction cost. The nuclear energy utilization of small-scale reactors are ship propulsion, electricity generation, heat supply, and sea water desalination, etc. Construction and maintenance for small-scale reactors can be made in factories exclusive use for them, but not at the site of the plant. In small-scale reactors, the safety can be enhanced sometimes by new technologies. 

BELIAEV, V. - KLT-40C Reactor Plant. Description and Safety Principles . Russian-Indonesian Seminar on Nuclear Technologies, 23-30 April 1998. 

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