Assessment of Fission Yields

DOE-HDBK-3010-94

6.0 Inadvertent Nuclear Criticality; Total Fission Yield

The model calculates the maximum fissions during a 5-sec burst, total fissions, and specific

fission rate (the duration is assumed to range from 10 min to 40 hours based upon historical

excursions). Only the volume of the tank (V, in liters) is required to calculate total fission

using the formula:

V x 1017 fissions

Total fissions =

(6-4)

For an excursion involving a large volume (1000 liters, 264 gallons), the estimate of total

fissions (1E+20) exceeds the estimate of total fission by Woodcock as cited in McLaughlin

(1991) by an order of magnitude. See Table 6-5 for a display of criticality accident fission

yields estimated by Woodcock (1966).

Olsen et al. (July 1974) also developed empirical models for solution excursions based upon

the CRAC experiments. Total fissions are the sum of Fb, fissions in initial burst, and Fp,

fissions during the plateau. The fissions during the initial burst are:

2.95(10)15(Vb)0.82

(6-5)

where:

Vb = volume solution at time of burst, liters.

The fission during the plateau are:

3.2 x 1018 (1-t-0.15)

(6-6)

where t = duration of the plateau, seconds. No method to determine the duration of the

plateau is identified. Currently, neither technique discussed in this subsection is commonly

used and both are considered very conservative.

6.2.3 A sses s men t of F ission Y ield s

Once it is determined that a postulated scenario may physically result in a excursion, it is

necessary to determine the potential fission yield for the purposed excursion. The total fission

yield is defined by the type of system and the fissile material involved. This section provides

reference fission yields that may be used for general SAR purposes. Care should be taken to

insure that, as the NRC has noted, potentially unique situations do not exist at a given

facility.

Table 6-5 provides a list of estimated criticality fission yields (Woodcock, 1966) that have

been discussed within both DOE and NRC literature. Many of these values are currently

considered excessively conservative in light of historic experience and current knowledge of

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