Reac. Memos
Notebook

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

September 10, 1950

Clifford Beck
Arthur Menius
Raymond Murray

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.

• 1. The prevailing wind - i.e. 14% of the time - is from the southwest.
•  
• 2. The only long-lived gaseous fission products which will escape from the
  reactor are Kr85, Rb87, Cs137.
•  
• 3. Assume that the reactor operates steadily (24 hrs/day) at 10 KW level for ten
  years The activity of the 3 listed elements at the end of ten years due to
  the cumulative total of each element produced is:

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

• 4. Assume that all of the Kr85 and 10% of the Cs137 (because of boiling point
  and low reactor temperature) escapes into the atmosphere. Rb87 may he neglected
  in comparison with Cs137 because of its long half-life.
•  
• 5. Assume that a building 60 feet high is 200 feet northeast of the reactor,
  directly in the path of the prevailing wind. No building will be closer
  than this, and none would be exposed to the stack exhaust more than this
  14% of the time.
•  
• 6. Assume that the stack gases are released at sufficiently low level (30 or 40
  feet) that the expanding cone-of-exposure at the building in question is at
  maximum; i.e. the area exposed to the cone of stack gases is 1/7 (200') 28' in
  diameter, = 5 x 105 cm² area.
•  
• 7. Assume that 0.05% of the radioactive gases in the cone of gases from the stack
  actually deposits on the building walls and is not subsequently weathered off.

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

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.

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

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:

80	2 Mev	[beta]'s/cm² sec.
270	2 Mev	n's/cm² sec.
3300	2 Mev	[gamma]'s/cm² sec.
46,500	1/40 ev	n'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