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With the mathematical models developed, the optimum arrangement of i n l e t and e x i t and plenum-chamber s i z e s and c o n f i g u r a t i o n s could be s e l e c t e d f o r various degrees of shock-wave a t t e n u a t i o n . The l a c k of prime-mover s e n s i t i v i t y to shock waves, as i n d i c a t e d by subsequent t h e o r e t i c a l a n a l y s i s and t e s t i n g of prime movers and the costs a s s o c i a t e d with an appreciable percentage of a t t e n u a t i o n , d i c t a t e d that the power system accept the a t t e n u a t i o n provided from the normal power-plant s t r u c t u r a l f e a t u r e s . DUST AND AIR-TEMPERATURE STUDIES Dust and air-temperature s t u d i e s were conducted to determine what adverse e f f e c t s n u c l e a r weapons would have on l a r g e power i n s t a l l a t i o n s . Power p l a n t s operating a t power l e v e l s of 20-75 megawatts r e q u i r e an enormous continuous a i r supply. The prime movers, e s p e c i a l l y gas t u r b i n e s , are s e n s i t i v e to dust and a i r temperature. Also, an economic h e a t - r e j e c t i o n system, employing above-ground cooling towers and underground heat s i n k s , i s q u i t e s e n s i t i v e to a n t i c i p a t e d dust c o n c e n t r a t i o n s . I n the absence of a u s e f u l body of data on n u c l e a r - weapons e f f e c t s and with a p o s i t i v e need f o r p r e d i c t i n g the poten- t i a l hazard f o r previous hardened systems, i t was necessary to conduct an i n v e s t i g a t i o n of a l l aspects of the problem. Since there i s a l i m i t to what can be accomplished on a t h e o r e t i c a l b a s i s , development of the theory had to be accompanied by f i e l d and laboratory t e s t s . The s t u d i e s c o n s i s t e d of: -30-
1. Development of theory and a computer program to p r e d i c t dust and a i r temperatures. 2. S m a l l - s c a l e l a b o r a t o r y experiments to determine the major e m p i r i c a l c o e f f i c i e n t s upon which the theory must depend: the s o i l - e r o s i o n co- e f f i c i e n t , the d u s t - t r a n s p o r t a n d - d i f f u s i o n c o e f f i c i e n t , and the dust p a r t i c l e - t o - a i r h e a t - t r a n s f e r c o e f f i c i e n t . 3. P a r t i c i p a t i o n i n a l a r g e - s c a l e h igh-explosive f i e l d t e s t (OPERATION DISTANT PLAIN 6) to measure dust. 4. Simulation of p o t e n t i a l s i t e l o c a t i o n s and b a t t l e environments and computation of the expected weapons e f f e c t s environment. E v a l u a t i o n of the r e s u l t s of such analyses were fed back to provide d i r e c t i o n f o r necessary a d d i t i o n a l t h e o r e t i c a l and experimental work. A compli- c a t i n g problem has been t h a t , u n l i k e most weapons e f f e c t s that are evaluated a t some point l o c a t i o n versus time, the e n t i r e dust cloud must be evaluated versus time. An e f f e c t i v e operating computer program was a v a i l a b l e f o r use i n May 1968. The program has been used s u c c e s s f u l l y and 23 i t s f i n a l v e r s i o n was a v a i l a b l e i n l a t e 1969. The l i m i t of f e a s i b l e t h e o r e t i c a l development has been reached. Unfortunately, much of the theory i s j u s t t h a t . Pre- v i o u s l y , f o r l a c k of proper instrumentation, dust was never adequately measured. Using radar meteorology techniques, t h i s problem can be overcome. The v e r i f i c a t i o n of the temperature theory can be accomplished only by p a r t i c i p a t i o n i n an atmospheric -31-
n u c l e a r t e s t of the type now p r o h i b i t e d by the Limited Nuclear Tes t Ban Treaty. The s u r f a c e winds induced by an a i r b l a s t wave pick up or erode the s u r f a c e s o i l p a r t i c l e s . These s o i l p a r t i c l e s are transported v e r t i c a l l y by the turbulent a c t i v i t y of the a i r . G r a v i t y f o r c e s cause the more massive p a r t i c l e s to s e t t l e out of the cloud q u i c k l y . The cloud height grows r a p i d l y during the p o s i t i v e phase duration of the b l a s t wave and reaches heights of many hundreds of f e e t f o r the weapons range s i z e s and overpres- sures of i n t e r e s t . The a i r flows past the power-plant s i t e , comes momentarily to r e s t a t the end of the p o s i t i v e phase d u r a t i o n , and then r e v e r s e s i t s e l f . L a t e r , the ambient wind slowly t r a n s p o r t s the dust cloud over the l o c a l t e r r a i n . The quantity of dust t h a t i s r a i s e d depends, i n p a r t , on s o i l and su r f a c e p r o p e r t i e s such as p a r t i c l e s i z e and d i s t r i b u t i o n , bulk and p a r t i c l e d e n s i t i e s , cohesive s t r e n g t h , and land usage. The dust density-time v a r i a t i o n a t the in t a k e and exhaust ports of the power p l a n t i s s e n s i t i v e to the s u r f a c e p r o p e r t i e s i n the general v i c i n i t y of the power p l a n t and e x h i b i t s s i g n i f i c a n t f l u c t u a t i o n s wherever the s u r f a c e p r o p e r t i e s or land usage vary appreciably. The maximum occurs very q u i c k l y and decays very s l o w l y . An examination of the s p e c t r a l d i s t r i b u t i o n of p a r t i c l e s i z e s a t a l a r g e number of p o t e n t i a l s i t e s i n d i c a t e s t h a t the d i s t r i b u t i o n s are not too d i s s i m i l a r and the weight f r a c t i o n s are â¢32-
largest f o r the smaller sizes. Thus, the particle-size d i s t r i b u - t i o n does not have a s i g n i f i c a n t influence on the peak dust densities i n the cloud. Land usage, however, i s the most s i g n i f i - cant variable. In some instances near water surfaces or large concreted areas, the dust densities are extremely small. After several minutes, the dust density may change d r a s t i c a l l y as the influence of a good or bad surface reaches the power-plant size. Local topography of the s i t e area does not influence the dust cloud s i g n i f i c a n t l y because the sites are generally located on r e l a t i v e l y f l a t t e r r a i n and because of the character- i s t i c manner of transport of dust by a i r . Ambient a i r conditions are not s i g n i f i c a n t either. The ambient temperature may vary appreciably at a given s i t e , but i t s influence i s extremely small. The ambient pressure i s a moderately i n f l u e n t i a l variable and, f o r a given s i t e and elevation, i t s value i s known. The weapon-attack conditions of interest can be quite varied and do have a s i g n i f i c a n t effect on the dust cloud. Weapon yi e l d i s not an important variable affecting i n i t i a l peak concen- trations. However, weapons y i e l d i s a major factor i n determining the t o t a l ingestion of the dust inasmuch as y i e l d and height of burst determine the size of the dust cloud. The height of burst (detonation height) i s important when i t i s above the optimum height of burst. The i n i t i a l dust density f a l l s o f f rapidly as the height i s increased, and i s zero f o r an overhead burst. The -33-
peak s i t e shock overpressure i s a s i g n i f i c a n t variable affecting i n i t i a l dust concentration; i t has l i t t l e e f f e c t on t o t a l dust ingested. A multiple-burst attack of r e l a t i v e l y similar weapon sizes does not increase the dust-cloud density s i g n i f i c a n t l y ; i n pa r t i c u l a r , each succeeding blast becomes correspondingly less e f f e c t i v e . The dust density predictions made f o r each specific s i t e or those made f o r the standard s i t e are needed f o r the evaluation of the response of the power plant ( i . e . , prime mover system) to the dust environment induced by the nuclear detonation attack. The dust density-time v a r i a t i o n i s also required to adequately size f i l t r a t i o n equipment and to evaluate i t s response to the predicted dust loading. A p r i n c i p a l conclusion drawn from the air-temperature studies i s that the dust cloud exhibits shielding effects. As the dust cloud grows i n height, above the intake and exhaust ports, i t acts as a shield f o r any fur t h e r f i r e b a l l radiation both from the f i r s t burst and from any ensuing nuclear detonations. The worst attack condition (from an air-temperature viewpoint) that could be imagined i s a series of multiple bursts occurring before the dust cloud at the s i t e location has risen to the elevation of the intake and exhaust ports. The generation of dust by the passage of a blast wave over the ground adjacent to the missile-site radar power-plant building, can cause excessive dust inputs to the diesel engines -34-
i n the power-plant building. This conclusion i s based upon the semi-empirical model of wind erosion of top s o i l and the sub- sequent transport of the eroded dust through the a i r by blast- induced winds, as proposed by the I I T Research I n s t i t u t e . The semi-empirical model has thus f a r used data from small TNT explosives experiments over a bed of top s o i l . However, the model has not yet been v e r i f i e d i n a large-scale f i e l d t e s t . I t remains neces- sary to check whether large-scale tests w i l l amplify or reduce the deleterious effects on power-plant performance. Diesel engines are not sensitive to short durations of increased combustion a i r temperature. Compression temperature w i l l increase; however, this has l i t t l e e f f e ct because the f u e l i s not injected u n t i l combustion i s desired and increased tempera- ture only accelerates the combustion by one or two engine degrees. The quantity of a i r f o r combustion i s greatly i n excess of the requirements f o r complete combustion. Added heat t o the pistons and cylinder bores requires consideration when the duration of higher combustion a i r temperature approaches 15 minutes or longer. Fortunately, the state-of-the-art of cooling combustion a i r permits specification of equipment that w i l l peimit r e l i a b l e extended operation at the maximum specified temperature of 150°F i n l e t a i r . Extensive dust-extraction devices are i n s t a l l e d i n the a i r intake. -35-
