closure project manager - Document Request - U.S. Department of ...

As stated earlier, inherent preventive and mitigative features required to be in place in
order to maintain those Risk Class111 and IV accident scenarios identified in the hazard
evaluation tables as low-risk scenarios were carried forward with corresponding bounding
accident scenarios. Postulated accident scenarios identified in the hazard evaluation tables as
Risk Class I or I1 scenarios were evaluated fiuther to determine if any preventive or mitigative
features exist, which if implemented, could reduce the scenario risk to a Risk Class 111 or IV
category. The collection of the credited preventive and mitigative features associated with initial
and bounding scenario evaluations were then carried forward into the development of the control
set in Appendix A, Building 99 I Complex Technical Safety Requirements.
For those postulated accident scenarios that were evaluated to be Risk Class1 or I1
scenarios and for which no preventive or mitigative features were identified to reduce the
scenario risk class, discussions related to the acceptability of the high-risk scenarios was
provided in the Control Set AdequacyNulnerability discussion of each accident scenario to
ensure that the DOE is cognizant of facility risks.
The application of Table 4-1 requires frequency bin and consequence bin assignments.
Frequency bin assignments are in accordance with DOE-STD-3011-94; i.e., events more
frequent than 10-2peryear are classified as anticipted, those with frequencies between
10"' per year and 10" per year are classified as unlike&, and those less frequent than
10"' per year are classified as extremely unlikely. These frequency bin terms and assignments are
consistent with DOE-STD-3009-94 qualitative likelihood classifications. Low-likelihood
high-risk scenarios were identified and discussed in those instances where the risk potential of
the postulated accident scenario was judged to be significant relative to other credible scenarios.
Estimates of scenario frequency are generally qualitative but may be quantitatively defmed, in
some cases, with the use of event trees. In cases where sufficient qualitative arguments for
lower, accident scenario frequencies cannot be made, the scenario is classified as anticiwed.
4.3.2.1 Radiological Risk
Radiological dose consequence evaluations were performed using the following equation:
Dose== * DR * ARRF * LPF * x/Q * BR * DCF /PDC
where MAR is the radioactive material-at-risk (in grams, varies with scenario);
DR is the MAR damage ratio (varies with scenario);
ARRJ? is the airborne respirable release fraction (varies with form of radioactive
material and scenario);
LPF is the facility leakpath factor (initially set to 1.0, varies with scenario);
x/Q is the atmospheric dispersion factor (in s/m3, varies with receptor and scenario);
BR is the receptor breathing rate (in m3/s, set for heavy activity);
DCF is the radiological material dose conversion factor (in redgram, varies with
material type); and
Revision 1
September 1999
4-5
Building 991 Complex FSAR
I