based model to estimate the base condition reliability costs. Any major rehabilitation strategy
changes at least some of the above listed values. The risk-based model can be rerun with the
revised values. Reductions in reliability costs resulting from the rehabilitation strategy represent
reliability benefits of the rehabilitation investment.
F-3. Description of Monte Carlo Simulation. The values shown in Tables F-1 and F-2 were
entered in a LOTUS macro written as a Monte Carlo simulation. In each year of the life-cycle,
the simulation generates a single random number for each unit. If a random number for a unit falls
between zero and the risk of Component 1 (between zero and .01360 for the turbine of Unit 1),
the unit performs unsatisfactorily due to mode or Component 1. If the random number falls
between the risk of Component 1 and the sum of the risks of Components 1 and 2 (between
.01360 and .01360+.01176), the unit performs unsatisfactorily due to mode or Component 2. If
the random number falls between the sum of the risk of Components 1 and 2 and one (between
.01360+.01176 and 1) the unit performs satisfactorily.
a. The initial risk, the degradation
rates, and the risk after unsatisfactorily
performance determine the risk of
Component 1 and 2 in each period. The risk
in any period depends on what happened to
each component in all the previous periods.
If a unit performs unsatisfactorily, the
present value of the repair costs is
calculated. A running total of this value for
each component of each unit is calculated
over the life-cycle. In addition, the total
number of units out simultaneously in a
period, regardless of cause, is used to
determine system energy losses using a
simple lookup table. A running total of the
present worth of this value is also calculated
Figure F-4: Running Average Lifecycle Costs
over the life-cycle. The length of the life-
cycle can be changed but is assumed to be
50 years in the macro.
1
In this example, the joint occurrence of both components performing unsatisfactorily is ignored.
F-4
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