Source Term Calculation

DOE-STD -3009-94

Appendix A

systems in the case of a spill.

(2) Take credit for passive safety features that are assessed to survive

accident conditions where that capability is necessary in order to define a

physically meaningful scenario. For example, in the case of a container

drop where the impact of the drop does not challenge container integrity,

it should not be assumed that the contents have dropped in an

uncontained manner. Similarly, if the presence of permanently installed

resilient flooring prevents an undesired consequence given a drop, an

assessment of the drop against some other non-resilient surface is not

meaningful. However, it is important to note that such defining

assumptions may warrant some level of safety SSC designation to assure

that the assumptions remain valid in the future. In the above examples,

the container and the flooring may warrant designation as SS or SC

design features.

(3) Take no credit for passive safety features producing a leakpath reduction

in source term, such as building filtration.

(4) Assume the availability of passive safety features that are not affected by

the accident scenario. For example, in the case of a process vessel

rupture, it should be assumed that other vessels not affected by the

accident are not ruptured or otherwise unavailable.

Defined as above, the unmitigated release calculation determines the need for

SC SSC designation, and provides the framework against which SC SSC

designation is made.

DESIGN BASIS ACCIDENT CALCULATION . Once a set of SC SSCs has

been identified, accident consequences can be estimated in a DBA calculation,

which represents the accident scenario progression where SC SSCs

successfully perform their intended safety function.

For each scenario in the DSA, sufficient documentation of both the

unmitigated and mitigated accident scenarios (DBAs) should be made such

that the thought process of determining the SC SSCs is well understood. In all

cases, the level of protection provided by the identified SC SSCs should be

evident. However, this does not require explicit reporting of unmitigated

consequences in the DSA, if it is evident that the unmitigated release

consequences are large, i.e., well above the EG.

A.3.2 Source Term Calculatio n

The radioactive airborne source term is typically estimated as the product of five

factors: (1) MAR, (2) damage ratio, (3) airborne release fraction, (4) respirable

fraction, and (5) leakpath factor. Detailed discussion of these parameters is

provided in DOE-HDBK-3010, "Airborne Release Fractions/Rates and Respirable

Fractions for Nonreactor Nuclear Facilities."

MATERIAL-AT-RISK (MAR). The MAR values used in hazard and

accident analysis must be consistent with the values noted in hazard

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