Probabilistic Risk Assessment (PRA), WASH-3, WASH-740, WASH-1400, &etc.

by Dan Hughes

The subjects of this post are well outside my areas of interests and experience. So, I’ll be working without a net. All corrections to incorrectos, and amplification of all aspects by providing additional information will be greatly appreciated.

Experiments and analysis of macro-scale water reactor safety T/H and micro-scale neutrons were not the only ground breaking activities underway at Camp NRTS back in the late 1960s and early 1970s. Probabilistic Risk Assessment (PRA) was also an active area of research. While perusing the results of the literature searches that are summarized here and here, I spotted Bill Vesely listed as an author. That citation helped clear out some Chronologically Mature Cobwebs and I went looking for some history.

Several landmark reports on water reactor safety have been issued over the decades. The major ones are summarized in the following short paragraphs.

The WASH-3 report:
United States Atomic Energy Commission Summary Report of Reactor Safeguards Committee, WASH-3, March, 1950, prepared and published by the US AEC seems to be among the first to consider the potential consequences of a major accident and failure of nuclear powered engineered equipment. The report was primarily developed relative to releases of radioactive materials, and associated issues, following a major failure of the early machines.

I have not found WASH-3 online, but here is an internal USNRC memo reporting an analysis of the equation that was the primary outcome of the work.

The WASH-740 report:
United States Atomic Energy Commission,
Theoretical Possibilities and Consequences of Major Accidents in Large Nuclear Power Plants. A Study of Possible Consequences if Certain Assumed Accidents, Theoretically Possible but Highly Improbable, were to Occur in Large Nuclear Power Plants, WASH-740, March 1957.

That is a barely readable copy of the report.

Next came WASH-1400:
United States Nuclear Regulatory Commission, Reactor Safety Study, An Assessment of Accident Risks In U.S. Commercial Nuclear Power Plants, WASH-1400 (NUREG-75/014), Washington, D.C., October 1975.

This online version starts with the Executive Summary that was determined in 1979 to be somewhat incomplete; defective it was labelled. The Lewis Report for the American Physical Society, the subject of this post, discussed some of the areas that needed improvemnt.

The report, while usually identified with Professor Norman Rassmussen at MIT and Saul Levine of the USNRC, was produced by a cast of hundreds. Bill Vesely was an important member of that cast.

A succession of reports have followed on after WASH-1400, including NUREG-1150:
United States Nuclear Regulatory Commission, Severe Accident Risks: An Assessment for Five U.S. Nuclear Power Plants, NUREG-1150, published December 1990.

The NRC, which initially conducted the NUREG-1150 study, has issued the following statement about NUREG-1150:
The U.S. Nuclear Regulatory Commission has devoted considerable research resources, both in the past and currently, to evaluating accidents and the possible public consequences of severe reactor accidents. The NRC’s most recent studies have confirmed that early research into the topic led to extremely conservative consequence analyses that generate invalid results for attempting to quantify the possible effects of very unlikely severe accidents. In particular, these previous studies did not reflect current plant design, operation, accident management strategies or security enhancements. They often used unnecessarily conservative estimates or assumptions concerning possible damage to the reactor core, the possible radioactive contamination that could be released, and possible failures of the reactor vessel and containment buildings. These previous studies also failed to realistically model the effect of emergency preparedness. The NRC staff is currently pursuing a new, state-of-the-art assessment of possible severe accidents and their consequences.

During my search for more information I ran across this good summary of WASH-1400 and PRA: its history, its role in reactor safety, the present status, and future direction:
WASH-1400. The Reactor Safety Study. The Introduction of Risk Assessment to the Regulation of Nuclear Reactors, August 2016, Prepared by: Reynold Bartel

A video of the lecture is reported to be available (Agencywide Documents Access and Management System (ADAMS) Accession No. ML15348A211), but I haven’t had any success in locating the video. I get stuck in a URL loop.

I did find this citation:
J. Samuel Walker and Thomas R. Wellock, A Short History of Nuclear Regulation, 1946–2009, Rev. 2, NUREG/BR-0175, October 31, 2010. ADAMS Accession No. ML102980443. Models, methods and software are not mentioned in that history.

The State-of-the-Art Reactor Consequence Analyses seems to be the most recent incarnation of PRA and its application to commercial power plants.

For more information on current PRA initiatives and recent history, see Probabilistic Risk Assessment and Regulatory Decisionmaking: Some Frequently Asked Questions, issued March 2016 (ADAMS Accession No. ML16061A559) and NRC Web page “History of the NRC’s Risk-Informed Regulatory Programs.”

Back to Bill Vesely
I have done a little literature searching and have found some info about what Bill has been up to following his departure from Camp NRTS.

Here’s a Google Scholar search for Bill’s publications. One hit of which, from 2013, is this special issue of the International Journal of Performability. Bill was the Guest Editor for the Issue and had two papers in the Issue.

The brief bio of Bill states:
William E. Vesely received his B.S. in Physics in 1964 from Case Institute of Technology and his M.S. and Ph.D. in Nuclear Engineering in 1966 and 1968, respectively, from the University of Illinois. Dr. Vesely has been in the risk assessment field for over 40 years. He was a principal author of the first major Probabilistic Risk Assessment (PRA) performed on nuclear plants, WASH-1400. He worked at the Nuclear Regulatory Commission as a risk specialist, and has been a PRA consultant for the Department of Defense, Department of Energy, various National Laboratories and various companies. Dr. Vesely has developed numerous approaches for risk and reliability evaluations, including techniques for data mining, pattern recognition, and risk trending.

Dr. Vesely has published over 100 papers and reports on PRA, statistical analysis, data analysis, and expert systems. He has been an adjunct professor for several universities.

Dr. Vesely has assurance responsibilities for risk assessments carried out by NASA. He also has responsibility for methods and tool developments for risk assessments and reliability assessments. He lectures at NASA’s Probabilistic Risk Assessment (PRA) Courses and teaches NASA Fault Tree Courses.

Bill is the principal author of the Fault Tree Handbook with Aerospace Applications published by NASA. He served as a technical coordinator for the Space Shuttle PRA.

Bill had significant roles in producing the Fault Tree Handbook and the Fault Tree Handbook with Aerospace Applications.

His position at the time of the special issue is given to be:

Manager, Risk Assessment
Office of Safety and Mission Assurance
NASA Headquarters
300 E Street SW Washington, DC 20546

I think Jerry Fussel worked with Bill at The Lab. And I have discovered that Steve Eide, who also worked at Camp NRTS and EI, presently occupies himself with related work. Pete Davis, who left Camp NRTS to work with George Brockett and Stan Johnson at Intermountain Technologies, inc. was (is?) active in the PRA arena for a very long time.

At one time EI had an office in the Seattle area that focused on PRA. I think Larry Conradi and Dan Reese worked out of that office. I also think that office eventually became a part of Larry Ybarrondo’s ScienTech.

We are Alumni of Camp NRTS. We are everywhere!

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