Truth (?) about the current nuclear weapon controversy

There has been continuous controversy about the yield of the Indian weapon
tests (Pokhran 1 in 1974; Pokhran 2 in 1998) for the last 35 years. Western
scientists in particular have challenged the yields of Pokhran 1 (P1) and that
of Pokhran 2 (P2). Government of India (GOI) has claimed the P1 fission bomb
yield to be 12 kilotons (kts) while western estimates have been of the order of 4-5 kts. P.K. Iyengar a retired Indian defence scientist has estimated the
P1 yield to be 8 kts. There has been even fiercer controversy about the yields
of the thermonuclear device (S1) of the P2 event. Now this controversy has
taken a new life by the revelations of Dr. Santhanam. Santhanam has rubbished
GOI claims about the Pokhran 2 S1 and the fission bomb (S2) yields. I will
discuss here my understanding of the emerging Indian nuclear weapon scene.

Santhanam has revealed that the actual yield of the Indian thermonuclear (TN)
device (S1) was only 60 % of the 45 kts claimed by Bhabha Atomic Research Center (BARC). The second stage of the S1 device did not work properly. He
also claimed that the fission bomb (S2) had a yield of 25 kts.

There are 4 inconsistencies even after the revealations of Santhanam:

(1) Total Yield

GOI claimed that the total yield of P2 was 60 kt (S1=45 kt; S2=15 kt).
Santhanam claims the total yield to be about 50 kt (S1=60 % of 45 kt=27 kt; S2=25 kt); Western seismologists claim the total yield to be 5-20 kt.

Even if we take the total yield to be 25 kt (larger than the largest number of
the western seismologists), Santhanam’s number is twice that number. Moreover
the Santhanum total yield would be more than 6 times Pokhran 1 8 kt yield (as
claimed by Iyengar) which contradicts the seismic observations. A comparison of the seismic disturbances observed during P1 and P2 shows that P2 disturbance was only a factor 3 larger than P1.

GOI claims that the destructive interference due to two explosions separated by 1 km is the cause of the apparently low seismic yield. I am skeptical about this since it is difficult to believe that any substantial effect of such interference would be visible thousands of kms from Pokharan.

(2) Crater Size

GOI claimed that the 15 kt S2 yielded a crater of 40 m diameter. That value has been accepted as a reasonable figure by the international seismological community. Now according to Santhanam the figure is 25 kt for S2 yield. Won’t that change the crater size? Also won’t a S1=27 kt explosion at more than 200m
below the surface (double the depth of S2) show larger effect than seen at the
S1 site? Won’t it at least damage the shaft?

(3) Tritium

It is being claimed that India is producing Tritium. Why should India need Tritium if all that it has are 25 kt fission weapons.

(4) Gen V P Malik

Gen Malik wanted the scientists to reassure the military about the yield of the thermonuclear device. Why should the military care about any TN device if all that it has is fission weapons?

Is there any scenario that explains all these inconsistencies?

I think there is a scenario that can explain all these inconsistencies. It
seems to me that neither GOI nor Santhanum are telling the complete truth. I think the S2 weapon was simply a debugged Pokhran 1 fission weapon of yield 12
kt. It worked fine. The S1 TN device had a boosted primary of 15 Kt and the second stage of 30 Kt. What happened was that only the boosted fission primary
of the S1 device worked as Santhanum is saying . Thus the true values of the total yield S1+S2 was about 15+12=27 kt which would then bring the total yield
in line with the international estimate. Also such an estimate would bring it in line with the seismic observation with the total yield of P2 being only a factor of 3 greater than the Pokhran 1 8 kt yield (as claimed by Iyengar).

One can understand why GOI is not telling the truth. Why is Santhanum obfuscating? I think he is not telling the true yield because of the official secrets act. Moreover the current standardized Indian military fission weapon is a 25 kt weapon. So it does not matter what the exact yield of S2 was.

This scenario also explains why there was no shaft damage in S1. The 15 kt boosted primary of the S1 device was not capable of damaging the shaft when placed at twice the depth of the S2 device. It would have taken the second stage to create a crater and damage the shaft as Santhanum is saying.

SOME FURTHER QUESTIONS

Why is India producing Tritium and why did Gen Malik want reassurance from scientists about the true yield of the TN device? This is strange since the TN
device has not been weaponized according to Santhanum. Why does Santhanum want
at least 2 more tests?

The answers to these questions are as follows.

When BARC first designed the TN device in 1995 they were flying blind. It was a theoretical model with no constraints. BARC did not know the accuracy of the
model. For example, BARC had no idea if the fusion stage would work at all or how much radioactivity would show. There was no constraint on the model.

After the 1998 S1 test the situation changed. BARC had answers to their questions. P K Iyengar suggested there was a < 10 % fusion yield from the second stage of the S1 device. The BARC weaponeers were able to compare their model predictions with the actual classified radiochemical data obtained by probing the explosion site. They tweaked their TN device model to match the observed radioactivity. They then used that TN device model as input to a seismic code originally developed for Pokhran 1 to match the observed seismic disturbance seen at S1. They then used that same seismic code to model the seismic disturbance of the American Bainbury explosion as suggested by Kakodkar.Thus the 1998 S1 explosion was used to constrain the original BARC TN device model.
The BARC seismic code was constrained by using 3 data points, Pokhran 1, the S1 and the Bainbury seismic data points.

There is some confidence that the BARC seismic code works since it has been checked thrice using Pokhran 1, S1 and the American Bainbury tests. The BARC TN device simulation code has been checked only once using the S1 explosion. This is the reason why Santhanum is asking for 2 tests since that would help
the BARC TN simulation code to be constrained using a minimum of 3 data points. That would greatly enhance confidence in the BARC TN device simulation
code.

It is true that the Indian military will not accept any unproven weapon and has accepted only the proven fission weapons. However, BARC has tweaked the unweaponised TN device using their improved TN simulation code. I have no doubt that in extreme emergency such a weapon will be used to deter say China if it is found that fission weapons are not able to deter that country. Also India must have also developed fusion boosted fission devices which need Tritium to boost yields. This is the reason for the Tritium production and for General Malik’s question.

ONE FURTHER QUESTION

There still remains the question about the usefulness of the Pokhran 2 explosions. Were they useful? I think yes. It has enabled the weaponisation of
the fission weapon. It has also greatly enhanced BARC’s understanding of how a
TN device works. It would be wonderful if BARC can test twice because then they can really trust their TN device simulation code.

 

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