**RSICC CODE PACKAGE PSR-425**

**1. NAME AND TITLE**

DORIAN: Code System to Implement Bayes Method for Plant Aging Risk Analysis.

**2. CONTRIBUTORS**

EG&G Idaho, Inc, Idaho Falls, ID, through the Energy Science and Technology Software Center, Oak Ridge, Tennessee.

**3. CODING LANGUAGE AND COMPUTER**

Fortran 77 and C; IBM PC (P00425IBMPC00).

**4. NATURE OF PROBLEM SOLVED**

DORIAN is an integrated package for performing Bayesian aging analysis of reliability data; e.g. for identifying trends in component failure rates and/or outage durations as a function of time. The user must specify several alternatives hypothesized aging models (i.e. possible trends) along with prior probabilities indicating the subjective probability that each trend is actually the correct one. DORIAN then uses component failure and/or repair data over time to update these prior probabilities and develop a posterior probability for each aging model, representing the probability that each model is the correct one in light of the observed data rather than a priori. Mean, median, and 5th and 95th percentile trends are also compiled from the posterior probabilities.

**5. METHOD OF SOLUTION**

DORIAN carries out a Bayesian analysis of failure data and a prior distribution on a time-dependent failure rate to obtain a posterior distribution on the failure rate. The form of the time-dependent failure rate is arbitrary, because DORIAN approximates the form by a step function, constant within specified time intervals. Similarly, the parameters may have any prior distribution, because DORIAN uses a discrete distribution to approximate this. Likewise, the database file produced by DORIAN approximates the entire range of possible failure rates or outage durations developed by means of a discrete probability distribution containing no more than 20 distinct values with their probabilities.

**6. RESTRICTIONS OR LIMITATIONS**

Prior distribution is discrete with up to 25 values. Up to 60 times are accommodated in the discrete time history.

**7. TYPICAL RUNNING TIME**

No study has been done by RSICC of typical run times.

**8. COMPUTER HARDWARE REQUIREMENTS**

DORIAN requires an IBM PC or compatible computer with 640 Kbytes of memory, a fixed disk, one 3.5-inch, 720 Kbyte flexible disk drive, a color monitor (CGA, EGA, or VGA), and a math coprocessor.

**9. COMPUTER SOFTWARE REQUIREMENTS**

MS-DOS 3.3 or later. The included executable can be run in a DOS window of Windows95. No source files are included.

**10. REFERENCE**

V. M. Bier, D. C. Bley, D. H. Johnson, S. Kaplan, and J. E. Williamson, "Development and Demonstration of Methods for Nuclear Power Plant Aging Risk Analysis: Dorian Users Manual," EGG-SSRE-8991 (April 1990).

**11. CONTENTS OF CODE PACKAGE**

Included in the package are the referenced document and one DS/HD diskette containing a self-extracting compressed file which includes an executable and test case input.

**12. DATE OF ABSTRACT**

May 2001.

** KEYWORD:** RISK ASSESSMENT