The Institute of Nuclear Power Operations (INPO) manages the Significant Event and Information Network for its member utilities both within and outside the United States. In 1985 they issued an analysis of 180 significant event reports received in 1983- 84 (INPO 1985).
A total of 387 root causes were identified. These were assigned to five (5) main categories:
- human performance problems, 52%;
- design deficiencies, 33%;
- manufacturing deficiencies, 7%;
- external causes, 3%; and an
- “other unknown” category, 5%
The human performance problems were further broken down into the following subcategories:
- deficient procedures or documentation, 43%;
- lack of knowledge or training, 18%;
- failure to follow procedures, 16%;
- deficient planning or scheduling, 10%;
- miscommunication, 6%;
- deficient supervision, 3%;
- policy problems, 2%; and
- “other”, 2%
There are two important conclusions to be drawn from these data.
First, at least 92% of all root causes were man-made. Secondly, the operators initiated only a relatively small proportion of the root causes (approximately 8% of the total). The majority originated in either maintenance-related activities or fallible decisions taken within the organizational and managerial domains.
The major role played by maintenance-related errors in causing nuclear power plant events has also been established by two independent studies (Rasmussen 1980; NUMARC 1985). Of these, simple omissions (the failure to carry out necessary actions) formed the largest single category of identified human problems in nuclear power plant operations.
James Reason, The contribution of latent human failures to the breakdown of complex, 1990