Assessing Industrial Nuclear Reactor Risk using Incident Reporting Risk Matrix Method

This novel study assessed industrial nuclear reactor risk using incident reporting risk matrix. It has also investigated the dangers, causes leading to dangers and their effects and it has identified the occurrence possibilities and intensity of consequences. Moreover, risk levels have been obtained. It was found that 17%, 61%, and 22% of the risks were unlikely, weak, and possible, respectively. The same are 26%, 39% and 35% of the hazards with moderate, major and severe consequences, respectively. Also, according to the risk matrix, 4%, 26% and 70% of the risks have low, medium and high levels of risk, respectively. Those risks having the risk level of high, were in need of control and preventive actions. Due to this reason, control and preventive actions suitable with consequences and risk effects were proposed and presented. These control and preventive actions were generally placed in the design phase including thermal design, hydraulic design as well as process control.


Methodology
To assess the risks, incident reporting risk matrix method has been utilized. Remembrance 1: Risk assessing should be conducted by two perspectives of the possibility of risk occurrence in the future according to the guidance Table 1 as well as its consequences on the purposes as stated in the guidance Table 2.
Guidance Table 1: The possibility of risk occurrence in the future

Possibility percentage
Occurrence possibility Less than 1% Rare 1%-20% Unlikely 21%-50% Possible 51%-90% Likely More than 90% Almost certain Guidance Explaining the consequence of risk occurrence The intensity of the consequence It has an insignificant effect on the purpose of nuclear reactor*. Insignificant It has a minor effect on the purpose of nuclear reactor.
Minor It has a moderate effect on the purpose of nuclear reactor. Moderate It has a major effect on the purpose of nuclear reactor.
Major It has a severe effect on the purpose of nuclear reactor. Severe *In industrial measurements, the purpose of nuclear reactor is producing energy (electricity energy).
Guidance  Informing related individuals about the existing risk and applying more observance Acceptable Low

Results and discussions
The table of identifying and assessing as well as controlling risks have been specified and presented below.      According to Table 5, based on incident reporting risk matrix method, 23 important dangers with dangerous factors and consequences as well as related effects were identified. It was revealed that 17%, 61% and 22% of dangers had the occurrence possibility of rare, unlikely and possible, respectively (Table 6, Figure 1); this means that most of the risks had the occurrence possibility of unlikely and possible (83%). Accordingly, 26%, 39% and 35% of dangers had the consequence intensity of moderate, major and severe (Table 7, Figure 2); this means that most of the risks had the consequence intensity of major and severe (74%), which is due to the nature of the reactor (nuclear reactor) and its related consequences. Considering risk matrixes, 4%, 26% and 70% of the dangers had a risk levels equivalent to low, medium and high (Table 8, Figure 3). 8 risks had the occurrence possibility, consequence intensity and risk level equal to unlikely/rare (6 of them were unlikely and 2 of them were rare), severe and high. These were more severe than others. These types of risks were related to the risks and consequences of these effects, including radioactive radiation and the emission of hazardous radiation to the environment and the highly hazardous (human and environmental) damage caused by them and the same explosion in the reactor due to damage to the internal wall caused by the explosion of the nuclear reactor. 16 group of risks needed control and preventive actions. Risks having risk levels of high, needed control and preventive actions. Therefore, control and preventive actions suitable with consequences and risk effects were suggested and presented (Table 5). These control and preventive actions generally included designing and using appropriate material in fuel elements, using appropriate neutron controllers, accurate thermal designing according to heat transfer principles, exact designing of the fuel retention time and appropriate design of the fuel sheath (in terms of material, structure and geometrical form). Moreover, control actions` discussion includes reactor control systems in accident conditions, controlling reactor temperature, controlling cooling water`s level as well as appropriate and intelligent designing in the cooling system of the reactor.

Discussion
This study was conducted with the aim of analyzing industrial nuclear reactor`s risk. It was revealed that control and preventive actions are of utmost importance in the designing phase. The first and dangerous responsibility of nuclear reactor`s design of the heart is taken by nuclear engineer. Various aspects of designing such as thermal-hydraulic design, structural and geometrical design are important. It includes designing indexes, applicable discussions, reliability, security and etc. As it was indicated in the risk assessing table, in case errors take place in nuclear reactor`s design and process, various dangers and consequences resulting from that as well as irreparable effects would happen in nuclear reactor process. Risk assessing is a powerful and capable instrument for avoiding and preventing such dangers and their consequences.