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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
Page A-5


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