Further Notes on Characteristics of N. C. State Research Reactor
Typescript
6 pp.
Sep. 10, 1950
MurNBfurther091050



Reac. Memos
Notebook

FURTHER NOTES ON CHARACTERISTICS OF N. C. STATE RESEARCH REACTOR

September 10, 1950

Clifford Beck
Arthur Menius
Raymond Murray


[ 2]

DEPOSITION OF LONG-LIVED FISSION PRODUCTS FROM THE REACTOR

At upper limit may be calculated for the quantity of long-lived fission prod-
ucts
which could collect on the walls of buildings surrounding the reactor.

Element Boiling Point Half Life Fission Yield (f) Disintegrations/second from Total
Amt. Produced in 10 years (= 1.4 x
10-3) (3x1010) P(watts) f(1-e -.693t/[lambda])
Kr85 gas 10 y 0.24% 3.9 x 108
Rb87 700° 6.3x1010y 3. % Negativeligible
Csl37 670° 33 y 6. % 2. x 1010


[ 3]

The activity on the building wall at the end of ten years is then
Kr85: 3.9 x 108 x 0.05%= .2 x 106 disintegrations/sec.
Cs137: 2 x 1010 x 10% x 0.05% = 1 x 106
Total= 1.2 x 106 disintegrations/sec/5 x 105 cm²
= 1.2 x 106 = 2.4 disintegrations/sec/cm²
5 x 105


[ 4]

HEATING OF REACTOR AFTER SHUT-DOWN

If the reactor is "shut-down" and the cooling water is cut off simultaneously,
there is the possibility of a rise in temperature due to the activity of the fission
products. The power due to the activity of [beta] and [gamma] rays from the fission products is
given by (Way and Wigner)

where f is the previous rate of use of uranium, T is the previous operation time of the
reactor and t is the time after shut-down. At 10 KW f [~=] 1/100 gms/day. Assume that
T = 100 days and t = 0.001 (about 1 1/2 minutes). Then

E (T,t) = 225 watts.

Calculations on the conduction of heat through the graphite, assuming reactor
temperature, Tr 80°C and temperature at end of graphite reflector, Tt 20°C, indi-
cate
that about 1 KW can be thus dissipated.

The reactor temperature, therefore, will decrease after shut-down, whether the
cooling water continues to flow or not.


[ 5]

RADIATION EXPOSURE HAZARD RESULTING FROM EXPLOSIVE VAPORIZATION
OF 50% OF FISSION PRODUCTS IN THE REACTOR

If, due to sabotage, a non nuclear explosion should vaporize 50% of the fission
products accumulated in the reactor, an approximation may he made of the radiation
exposure hazard which could result.

The hazard is calculated for two possible cases: 1. The explosion causes
formation of a small cloud near ground level, which subsequently drifts away. The
cloud in assumed to spread laterally 1/7th the distance of downwind travel. 2. The
explosion causes formation in the reactor room of a cloud which is exhausted through
the building stack (150 feet high). The cloud subsequently drifts away from the top
of the stack, spreading as above.

Assumptions:

1. Reactor has operated steadily at 5 KW.
2. Wind velocity is 2 m/hr.
3. Range of [beta] = 5ft; of [gamma] = 1000 ft.
4. Exposure (Roentgens) = 2 x 1010

Case 1. Cloud is formed near ground-level and drifts toward a man 200 feet away. The
man's exposure is

Case 2. Cloud is dispersed from top of 150 foot stack and reaches ground level at 1050
feet. A man's exposure at 1050 feet, at the point the cloud reaches ground
level, is


[ 6]

TOLERANCE LEVELS

The daily tolerance level of permissable total body exposure to radiation is
0.1 r/8 hours. Each or the following fluxes will result in approximately 0.1 r/8 hrs:

802 Mev[beta]'s/cm² sec.
2702 Mevn's/cm² sec.
33002 Mev[gamma]'s/cm² sec.
46,5001/40 evn's/cm² sec.

Plutonium tolerance - 5 x 10-5 [mu] grams/cc in drinking water

Drinking water tolerance 10-6 curries/cu ft.

|<--40"-->|<--6'-->|

270 n/cm²/sec 0.1r in 8 hrs.
2x1018 n/sec

Father Joseph Lynch, Fordham
Earthquakes