Appendix CRF - Part 3 - Northamptonshire County Council

- The crater size can be estimated from theoretical models for estimated
impact parameters such as densities, impact velocity, impact angle,
missile dimensions and target density/type (Ref 21). Scoping calculations
indicate that crater sizes of 300 cum are conceivable. Actual crater sizes
from impacts due to Harrier jets (the type of aircraft currently based at
RAF Wittering) reveal a wide variation from virtually no displacement to
significant craters dependent on the nature of the event. A record (ref 23)
notes a Harrier jet impact forming a crater of approximately 300 cum. For
comparison, the Lockerbie B747 impact formed a crater of 560 cum (ref
24).
- The displaced waste contains the maximum concentration of a single
nuclide at 200 Bg/g. The chosen nuclide is Pu-239 which has a
conservative inhalation dose coefficient and yet is a credible nuclide to
occur at the concentration assumed.
- The density of the displaced waste is 1.5 t/cum. 300 cum or 450 tonnes
are displaced. Giving rise to displacement of 90,000 MBq.
- The distance to the nearest public is 200m and the event has 30 minute
release duration. This is on the basis that immediate evacuation of the
near zone would occur from such an extreme event and within the very
near zone immediate fatality due to impact would be likely.
- The effect of fire on dispersal is not included (refer Section 8.5)..
- The worker exposure is the same as the public exposure because
workers would evacuate quickly to the same distance.
- The atmospheric conditions are worst case still conditions and mixing is
not assumed to be enhanced by fire.
8.3.18 Dose from inhaling material discharged from displaced material:
Dose
inh,
bag
I RF1
RF2
C
B
D
DF
where I is the inventory of radionuclide Rn releasable (Bq)
RF1 is the release fraction (-)
RF2 is the respirable fraction (-)
C is the dispersion coefficient (s m -3 ).
B is the breathing rate (m 3 s -1 )
DF is the decontamination factor (-)
Dinh is the dose coefficient for inhalation of radionuclide,
Rn (Sv Bq -1 ).
Application for disposal of LLW including HV-VLLW under RSA 1993,
for the East Northants Resource Management Facility:
Supporting Information
Rn
inh
July 2009
66
WS010001/ENRMF/CONSAPPCRF 385