ML20234D634
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-t R. S. Boyd, Chief,'Research and Power October 5, 1964 Reactor Safety Branch, DRL J. F. Newell, Chief, Site-Environmental Branch, DRL SUPPLEMEffrAL CALCULATIONS OF MCA FOR BODEGA j
.h c FS At the request of Mr. Knuth of your branch the subject calculations were performed by Mr. Waterfield of this branch to study additional f acets of the MCA for this reactor. The general nature of the events during the accident were given in the request, while a, i
number of specific assumptions tabulated below were initiated in the process of making the calculations.
-I Case 1 and Case 2 deal with a situation following the standard TID 14844 meltdown in which the emergency ventilation system f ails, leading to an unfiltered, ground-level release.. It is also assumed l
I that all the released material passes freely into the refueling building, although it is not clear to the writer just how this.can happen. In Case 1, it is assumed that the -driving force for leakage from the refueling building is a rapid decrease in barometric pressure.
In Case 2, the leakage is caused by high winds which produce exfiltration from the building in the manner and rates postulated by Niagara Mohawk. Case 3 deals with a failtre of the recirculating cooling system some twelve hours after the standard I
TID meltdown, so that activity is displaced from the primary contain-ment by the incoming emergency cooling water, and is discharged through the emergency ventilation system, filters, and out the stack.
I More specific assumptions dealing with each case will be described below along with the resulting doses for each case.
For Case 1, experience with calculations for the NBS reactor was used to assume that the maximum probable rate of barometer change is 57. per day, accompanied by neutral diffusion conditions (Pasquil Type D), and wind velocity of three meters /sec. Values of uX/Q were obtained directly from ORO 545 for the distances of interest, and appropriate average values of the source strength for periods of two hours and thirty days were obtained from graphs used in all our l
hazards calculations. The final results are given below for these i
fracticas of the entire core inventory present in the refueling j
building: 1007. noble gases and 257. iodines.
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.2-Distance Vhole Body Doses Thyroid Dosen l
Miles 2 hrs.
30 days 2 hrs. 30 days 0.6 6.4 120 1100 38,000 1.5 1.8 35 310 11,000 3.0 0.5 10 90 3.200 5.0 0.2 4
29 1,300' 4
in preparing for Case 2, the calculations of the dependence of exfiltration rate on wind velocity presented by. Niagara Mohawk in the recent supplement to their Preliminary Hazards Summary I
Report were studied carefully.
It was found that the exfiltration rates they calculated are directly proportional to the velocity head for the wind, and that the magnitude is approximately that which would be 'obtained if 1/4 of the total area of the building were subjected to this pressure difference. It was found that for a period of two hours, while radioactive decay is relatively un-important, the off-site dose increases as the wind velocity increases. However, for longer periods of time extending until all the material has decayed, there is a critical wind velocity which produces the largest dose (40 mph in this case). This dose does not vary rapidly with wind velocity near this maximum value, however, so that for the case studied if the velocity is half l
that which gives the maximum dose, the dose is reduced to only approximately 78% of the maximum. It was also found that the maximum dose is associated with the wind velocity which produces an exfiltration rate which is equal numerier11y to the radioactive decay rate. Also, the value of the maximum dose is inversely proportional to the wind velocity necessary to produce it.
Therefore, while more rapid decay rates require larger wind velocities to produce the maximum dose, the value of this dose is less because l
of the higher wind velocities required.
The results tabulated below are-for a wind speed of 20 mph under inversion conditions, which seemed to be as high as is credible at dais site. Higher velocities occur under less stable conditions but the added diffusion more than compensates for the increased exfiltration which results, so that these doses are definitely maximum.
Distance Whole Body Doses Thyroid Doses Miles 2 hrs.
2 days 2 hrs.
2 days 0.6 36 335 6,200 85,000 omcE >
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Case 3 assumes the standard TID 14844 meltdown and release has occurred.. and that all the activity is contained within the dry u
well and suppression chamber.. After a period of twelve hours.
.1 the. recirculating cooling system for this containment fails, and' it is necessary to start adding emergency cooling water from an
'i external source, which displaces the airborne activity. - This j
activity is then vented at the displacement rate through ' filters <
which remove 95% of.the iodine,'and up the stack. The total' air space.in the containment initially is 195,000 cubic feet, and.the.
cooling water is added at the. rate of 300 gym. This displaces air at. the rate 'of 40 cfm, or 2400 cubts feet. per hour, or 30%
of-the contents per. day.- At this. rate, all the material'is dispisced approximately four days after initiation of the
'j accident. Decay during this period was accounted for over i
short-time intervals for greater. accuracy of calculation. The
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table below gives the. resulting doses during the first two d
I hours after the beginning of venting, and for theLentire period (infinite).
Distance Whole Body Doses Thyroid Doses i
Miles 2 hrs.
Infinite 2 hrs. Infinite i
0.6 0.7 11 193 5800 6.0 1.0 16 2851 8500 i
The dose at 0.6 miles 'is the maximum that occurs at any distance under Pasquil Type D (neutral) conditions with a wind speed of-j three meters /sec., and.is the maximura that can occur at the -
site boundary for any diffusion conditions with an elevated-release. The dose at 6.0 miles is'the maximum that occurs at any distance with the standard TID 14844 inversion conditions.
Without going to the same detail in the' calculation as originally done, it appears that if.the addition of water is begun at 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />, the whole body dose for the first two hours will be reduced to 40%
of the values above, while the other doses will be approximately -
70% of these values.
i ces D. Knuth, R&PRSB i\\
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