Introduction
The WASH-1400 was a risk assessment tool compiled by a team of scientists led by Rasmussen, Norman; hence the reason why the tool is sometimes referred to as the Rasmussen report. This tool analyzed the probable events that would occur in case a serious accident occurred at a light water reactor. The WASH-1400 analyzed the radiological effects of such an accident, and the probability of its occurrence using an event tree approach. This methodology can also be referred to as the Probability Risk Assessment (Levenson & Rahn, 1). Rasmussen’s team concluded that the risks posed to the individual were small in comparison to other risks that were tolerable (Rasmussen, 1975). In order to understand the strong points and weaknesses of the WASH-1400 model it is necessary to compare it with other risk assessment models.
The WASH-1400 Model
This study was reviewed in 1977 by the ‘Lewis Committee’; the methodology was endorsed by the committee as the most efficient available method. The committee however warned that figures of risk given contained large uncertainty. The methodology used by the study was rather simple in comparison to today’s procedures and standards. After the Lewis Committee review, the report was reviewed by the American Physical Society. The society organized a team of scientists who identified several points to criticize in this risk assessment model. This team pointed out that the fatality estimates had only taken into consideration the deaths that would occur within the first 24 hours of such an accident occurring. This oversight by the WASH-1400 model occurred since the radioactive material released in case of such an accident would remain active in the atmosphere for decades (Kadak & Matsuo, 2007). The team of scientists organized by the society also noted that cancer, an illness resulting from exposure to radioactive materials, would only start occurring several years after the accident. The Rasmussen report was also criticized on the methodology used to predict the response of cooling systems during an emergency.
The findings by the team of scientists made the WASH-1400 model obsolete and it was replaced by the NUREG-1150; the latter is being replaced by an analysis of reactor consequence (SOARCA). The validity of the Rasmussen report was questioned by the team of scientists. The Probability Risk Assessment used by the WASH-1400 model is now used in nuclear power plants’ safety assessment. This report was however without a positive side; its publication initiated the process of creating a regulatory process that was risk informed. The approach used in the WASH-1400 showed the existence of the possibility of creating quantitative measures to be used in ensuring plant safety. The WASH-1400 is also significant in that it determined the existence of other accidents apart from those based on designs; though these accidents were smaller in terms of their consequence, their likelihood of occurring was much higher. One particular sequence that was identified as being dominant was the LOCA.
The WASH-1400 model had several weaknesses that were based on its Probability Risk Assessment approach. The major one that the Lewis Committee identified was the uncertainty of the risks mentioned by the model. However there were other weaknesses to the model and this include lack of experience in the industry due to the newness of the Probability Risk Assessment approach. Even the National Research Centre lacked the required expertise to apply this methodology.
The Preliminary Hazard Analysis Model
This model is based on the application of experience of a hazard, causative events for accidents, and analyzing the probability that an event will occur. The stages involved in the model are: one, identifying the possibility that a risk event will occur; two, a qualitative evaluation of the possible injuries and their extent; three, relatively ranking the hazard with the combination of likelihood of occurrence and severity; and four, identifying the possible measures to deal with the hazard (USDHHS, 2006). This model is useful during prioritizing hazards and analysis of systems that are existent where the surrounding circumstances cannot allow for the use of a more extensive technique. The most common application of this model involves identification of hazards based on the model and comparing the results to those from other risk assessment models.
The WASH-1400 is similar to the Preliminary Hazard Analysis Model in that both models analyzed the probability of an event occurring. The two models however differ on the basis that the Preliminary Hazard Analysis model does not only analyze the probability of an event occurring, unlike WASH-1400, but also the causative events and prior experience on the occurrence of an event. Probably due to the newness of risk assessment models, the WASH-1400 did not involve comparing its results to those of other models unlike the PHA. The PHA model is also commonly applied to places where more extensive techniques cannot be used unlike the WASH-1400 which is applicable in both circumstances.
HACCP Model of Risk Assessment
HACCP, a seven step procedure, is a risk assessment test that is normally used to check the hazards affecting food safety. It is based on the principle that those hazards can be eliminated or they can be reduced by preventing (Russell, 2004). This prevention can be carried out better during the production rather than when there is finished product. It aims at preventing the hazard as early as possible. Using this type of risk assessment has its strengths and its weaknesses. One of the advantages is that a company that adopts this system provides a greater confidence to their consumers about the safety of the food that they sell. One disadvantage is that the adoption of HACCP is that it requires the change in the attitudes of the staff and documentation of the results (Russell, 2004).
When compared to the WASH-1400 the HACCP method seems to be very complex. The WASH-1400 used the event tree approach which is a simple methodology. The WASH-1400 is a more holistic approach and operated on the possibility of the event occurring. The HACCP on the other hand is a step by step procedure and starts from identifying the risk at the early stages rather than identifying the outcome like in the WASH-1400. HACCP tries to prevent the events from happening but the WASH-1400 tries to see what would be done in the case of an event occurring. Due to the newness of WASH-1400 it was hard to implement; HACCP is hard to implement due to the difficulty in changing the attitudes of the staff and consistent documentation and recording.
Hazard and Operability Analysis
Hazard and operability analysis (HAZOP) is a structured method used for system examination and risk management. This system is normally used to identify possible hazards in a system and operable issues that are highly likely to lead to non- conformity in the product (MCT, 2011). The analogy process of this methodology is done in four phases; definition phase, this begins with the identification of the risk assessment team members, who identify the assessment scope to ensure a focus in effort. Preparation phase, this entails the identification of the supporting data and information, audience and users of the study outputs, project management preparations, template formats for recording outputs and the HAZOP guide words to be used in the study. Examination phase, at this stage, there is the identification of all the elements of the system. Documentation and follow up stage, in this phase, documentation of the analysis of the HAZOP occurs here. HAZOP is an important communication tool since it not only presents the results but it also gives an early buy-in on the approach.
The HAZOP method as compare to the WASH-1400 is more complex in that, the HAZOP has more methodology phases as compared to the latter. The HAZOP method gives a presentation of the results and continues to give an early buy-in on the approach, which is not the case in the WASH-1400. The HAZOP system gives an analysis of the current situation and communicates the results and finally gives an early buy-in on the approach while in the WASH-1400, the system analyses the probability of an event occurring.
REFERENCES
U. S. Department of Health and Human Services [USDHHS], (2006). Guidance for Industry: Quality Risk Management.
Russell, M. (2004). The HACCP Sea Food Program and Aquaculture. SRAC Publication No. 4900
UNCTAD, (2002). An Introduction to HACCP. New York; International Trade Centre.
Kadak, A. & Matsuo, T. (2007). The nuclear industry’s transition to risk-informed regulation and operation in the United States. Reliability Engineering and System Safety 92 (2007) 609- 618.
Rasmussen, N. (1975). Functions of Engineered Safety Features. Reactor Safety Study.Washington DC: NRC.
The WASH-1400 Report. Retrieved from http://teams.epri.com/PRA/Big%20List%20of%PRA%20Documents/WASH-1400/02-main%20Report.pdf
Levenson, M. & Rahn, F. Realistic Risk estimates. IAEA Bulletin, Vol 23, No. 4. California: EPRI
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