Methodology - std1134990012

DOE-STD-1134-99

Key Review Issues

Ensure any referenced material in this section is available and valid.

4.0 Methodology

This section of the evaluation describes how the subcritical limits and controls for the process or

operation were obtained or derived. This section should contain a brief summary of the

method(s) relied upon to develop the subcritical limits on the process. The preferred method, as

stated in ANSI/ANS-8.1, is by reference to experiments or "accepted" published subcritical

limits. The alternative is to perform hand calculations or, more probably, computer calculations.

Detailed documentation of the verification and validation of computer codes need not be

included in this section. A reference to an existing validation document is sufficient. The

calculations themselves may reside in referenced documents so long as the documentation trail is

recorded.

Review of this section is very straightforward if single parameter subcritical limits are used from

ANSI/ANS-8.1. These will invariably be conservative and only the value from the standard need

be quoted and a brief (i.e., a sentence or two) reason for why the limit is applicable.

If other handbook data is cited, the reviewer needs to be aware of some potential pitfalls. In

general, subcritical limits may be taken from ARH-600, LA-10860, TID-7016, etc. The data in

ARH-600 are from calculations that did not have extensive peer review but are nevertheless very

helpful in understanding sensitivity of controlled parameters. Although some caution is prudent,

the reference is nevertheless helpful. The data in LA-10860 and TID-7016 are mostly taken

from critical experiments, however, calculational results appear in spots. The intent is to

establish subcritical limits using critical data by applying an appropriate safety margin. A typical

rule of thumb is that the maximum subcritical value will not exceed 90% of the critical value

after a contingency occurs. Note that the minimum subcritical value does not correspond to a keff

of 0.95, or any other particular value of keff. In practice, values taken from these industry

accepted-handbooks, with appropriate allowances for uncertainty, are roughly equivalent, with

regards to establishing safety margins, to the single parameter limits contained in ANSI/ANS-

8.1.

The trickiest analysis to review is one based on hand calculations. This is so because of the

many assumptions implicit in the method. Hand calculations are, in general, extrapolations from

known critical data to a specific application. The reviewer should be very familiar with the

hand-calculation method being used. The reviewer should be alert for mis-application and

incorrect mathematics. This section should include a reference to the publication or technical

data on which the hand calculation is based. If done properly within the area of applicability for

the method, hand calculations will yield conservative results. The reviewer should spot-check

the mathematics and review the reference against the model to assure compatibility.