20. Letter From the Chairman of the Atomic Energy Commission (Seaborg) to President Johnson1

Dear Mr. President:

I met yesterday with Sir William Penney, Chairman of the UK Atomic Energy Authority, as a result of your exchange of correspondence with Prime Minister Home last week in which you agreed, in response to the request of the Prime Minister, to such a meeting of “experts.”2 Sir William had seen this correspondence exploring the possibility of concurrent announcements between the US, the UK and the Soviet Union concerning planned cutbacks in the rate of production of fissionable material. He wanted, in particular, to discuss for further clarification your response to the Prime Minister’s request that the US might immediately deliver all of the U-235, due normally for delivery to the UK between now and 1969, in return for the delivery to the US of plutonium from the UK according to the original schedule contemplated in the barter agreement entered into between the US and the UK in 1959.3

I explained to Sir William that your position is that such a speedup of delivery is not necessary at this time because what is contemplated is only a concurrent announcement on cutbacks of fissionable materials which had already largely been planned in the three countries. I said that it was the feeling of the US that the Prime Minister’s proposal, if appropriate at all, would presumably be better related at some future time to an agreement for the complete cutoff of the production of fissionable material. Sir William seemed to understand this and suggested that if such an event should come to pass, which seemed unlikely for a few years, the UK could again raise the question of immediate delivery of the remaining U-235 at that time; I said that the US would then have to decide at that time as to their response to any such request. Sir William said that, as he saw it, if such a cutoff agreement should be up for consideration at some future time, and if the US didn’t feel that they could, at [Page 44] that time, immediately deliver all of the U-235, the UK would have the option of either, (1) not signing the cutoff agreement and restarting their Capenhurst plant for the production of U-235 in order to meet their planned national goals in thermonuclear weapons, or, (2) signing the agreement and meeting their national requirements for thermonuclear weapons by producing some of them, less desirably, entirely from plutonium without the inclusion of any U-235.

Sir William went on to explain to me that they have set national goals for the production and acquisition of the fissionable materials, plutonium and U-235, through 1969, at which time their goals will be met. This requires the production of an additional [text deleted] weapons grade plutonium and the acquisition of all of the U-235 to be obtained from the US through the barter agreement by 1969. He said that with respect to the plutonium, he is recommending that their 8 production reactors, 4 at Chapel Cross and 4 at Windscale, now devoted in large part to the production of civilian power grade plutonium, be converted entirely to the production of weapons grade plutonium. Under this program the required additional [text deleted] weapons grade plutonium could be produced by 1966 since their reactors can each produce at the rate of about [text deleted] of weapons grade plutonium per year. Thus, if an agreement to cut off the production of fissionable material was signed by 1966, they would have all of their required plutonium but would still be short that portion of the U-235 to be delivered from the US from 1966 to 1969.

Sir William indicated that the maximum UK production rate of U-235 was about [text deleted] per year and that the total cost of their Capenhurst plant was less than some $80 million. This plant, of course, is now no longer producing weapons grade U-235 and is producing only a small amount of civilian power grade U-235. He expressed surprise that the French Pierrelatte plant would only produce, as he understood it, about [text deleted] of U-235 per year despite the billion dollar cost.

He also mentioned, interestingly, that he understood the French are having trouble in their plutonium production reactors with the leakage of plutonium through the cladding material which surrounds the uranium fuel elements. An ironic consequence of this is that they cannot run to the desired high exposure levels for the plutonium and, hence, are forced to make more low exposure level, weapons grade plutonium, than they might otherwise do.

Sir William also mentioned that it was his opinion that the French would conduct a test of a thermonuclear weapon in the Pacific by the end of next year, which, of course, would imply that it would have to be an all plutonium weapon. I regard this as an exceedingly interesting observation [Page 45] in view of my conversation with you on November 29, 1963, regarding this possibility.4


Glenn T. Seaborg 5
  1. Source: Seaborg, Journal, Vol. 8, pp. 171-173. The source text, originally classified, has been sanitized. All deletions are in the source text. Though the source text is undated, Seaborg’s Journal confirms that Seaborg wrote the letter on March 25. (Ibid., p. 169) The source text was sent under cover of a March 25 memorandum from Seaborg to McGeorge Bundy. (Ibid., p. 170) It is an account of his meeting with Penny on March 24, which Bundy asked Seaborg to write after hearing Seaborg’s oral report about it. (Ibid., pp. 162-163, 169)
  2. Home’s letter to President Johnson, March 17, is reproduced ibid., pp. 126-131. President Johnson’s letter to Home has not been further identified.
  3. Terms of this agreement are summarized in Senate Report No. 513, July 14, 1959, p. 6.
  4. An account of this conversation is in Seaborg, Journal, Vol. 7, p. 18.
  5. Printed from a copy that indicates Seaborg signed the original.