User:David MacQuigg/Sandbox/The protactinium problem

Uranium-233, the fissile material in thorium reactors, is produced from thorium-232.

Is thorium a proliferation risk? Will the worldwide deployment of nuclear reactors using thorium add additional risk, beyond what we already have with reactors using uranium? The problem with thorium as a nuclear fuel, sometimes called the protactinium problem {cite Uribe 2018} is that it is relatively easy to extract weapons-grade U-233 from the mix of isotopes produced in a thorium reactor (See Figure 1).

Unlike issues of safety, waste management, and cost, which can be easily understood by non-technical people, this one requires some basic understanding of nuclear physics. The purpose of this article is to provide that understanding with a minimum of technical detail, and to summarize the arguments for and against thorium.

Extraction of pure U-233 can be compared to the extraction of pure Pu-239 using big, expensive "purex" plants (see Figure 2).

Any source of neutrons, including all presently deployed reactors, has some risk of abuse as a source of weapons-grade fissile material. The question on proliferation should be - will deployment of a new technology make production of material for bombs simpler or more easily hidden than what is already available to any nation determined to acquire nuclear weapons?

Here is what happens when you irradiate thorium with neutrons:

• Irradiating thorium with neutrons produces a mix of thorium, protactinium, and uranium isotopes.
• After removal from the neutron flux, the neutron transmutations stop.
• Pa isotopes will decay in a few days, except for Pa-233, which has a half-life of 27 days.
• Uranium can be cleanly separated from everything else by fluorination, a simple chemical process.
• A second separation, after a few months aging in the wine cellar, will yield weapons-grade U-233.

Proponents of thorium argue: For many decades, proliferators have chosen uranium enrichment and plutonium breeding. If the thorium path had any advantages, it would have been done by now. U-232 will be always present, and will “denature” the mix. On-site processing of thorium fuel actually improves security, because we can monitor the chemical composition of the fuel.{cite: Kirk Sorensen} None of this matters. Security of ALL reactors must be assured by keeping all fuel processing in safe locations, and providing reactors only in sealed cans that will be very difficult to access on site.{cite: ThorCon}.

Opponents of thorium argue: If the HootinMuhnies topple the government of BhaZookastan, and take over their thorium reactors, they will have access to tons of U-233. U-232 is a poor choice to “denature” U-233. It decays slowly, and it takes decades for the radiation from its progeny to build up. These progeny can be chemically separated to maintain the U-233 stockpile at weapons grade. {cite: Ed Pheil} Chemical separation of uranium is simple, and can be done in an easily hidden location. Adding a second uranium extraction to an existing process loop, and removing a small amount U-233 will not stop normal operation of a thorium reactor. Supplies of thorium and equipment will be much more available if there are thousands of thorium reactors all over the world. Reactor designs will be all over the Internet. Proliferators may prefer this route, if secrecy is needed.{cite: Tom Ledbetter} Chemical monitors add little security to a system with video monitors. Let’s hold off on thorium for now. We have plenty of uranium, maybe enough to last until we (or our AI progeny) evolve to avoid war. The uranium fuel cycle (breeding plutonium) can be protected by “spiking” the fuel with isotopes that are extremely difficult to separate from Pu-239. Comments Why are molten salt nuclear reactors (the type being advocated for thorium reactors) such a huge proliferation danger? Why are people so determined to ignore or deny such a simple and clear danger? - Quora 2015 Answer from Tom Ledbetter’s "little lesson in nuclear proliferation prevention": …“a 1 GWe plant would generate the material for a bomb every week, although you could not use that; instead you could siphon off the material for a bomb every 16 weeks (with a BR of 1.06) and still maintain your reactor running tip-top.” … “If that doesn't scare you, you're insane. Literally.” Answer from Robert Steinhaus: “The key point for discussion of Thorium fuel cycle proliferation safety is that there is a well known identified method of starting with highly contaminated (220 - 400 ppm Pa232 content) reactor grade Protactinium and then economically producing weapons usable U233 with less than 50 PPM U232 (and even weapons grade U233 with some finishing chemistry to remove light elements like Lithium and Beryllium).” Bulletin of the Atomic Scientists Eva C. Uribe 2018 https://thebulletin.org/2018/08/thorium-power-has-a-protactinium-problem “There is little to be gained by calling thorium fuel cycles intrinsically proliferation-resistant. The best way to realize nuclear power from thorium fuel cycles is to acknowledge their unique proliferation vulnerabilities, and to adequately safeguard them against theft and misuse.” Useful Links Livechart - Table of Nuclides - Nuclear structure and decay data - for half-lives & decay modes ThorCon— the Do-able Molten Salt Reactor Safeguards and Security - for a thorough discussion of the three proliferation threats and how ThorCon counters them. Table 3, p.10 shows plutonium composition as a function of burnup. Pu-240 will build to 10% of the total Pu after 120 days, making the spent fuel useless for bombs. Best time for diversion is 60 days, when the Pu-239 has built to 7kg and the Pu-240 is only 5%. NONPROLIFERATION ASPECTS OF THE IFR Chapter 12 in Plentiful Energy, Till & Chang 2011. History of the use of fissile material for weapons IFR safeguards and proliferation resistant properties Myth #3: Thorium reactors cannot make bombs! Dr. Nick Touran’s debunking of several widespread myths.

Thorium Opera Physical security, verification, enforcement. Radioactive materials should be difficult for the bad guys to access, allowing plenty of time for response from law enforcement or the military. The reactor and surroundings should be under 24/7 video surveillance, with active control of the cameras, so the monitoring agency can’t be fooled with a simple replay of old footage. Enforcement is the hard part. If a reactor goes rogue, we need a quick IAEA resolution authorizing destruction of that reactor by any nation that feels threatened. How about a plug at the bottom of the reactor that would drain the fuel if there is not a continuous signal from the IAEA allowing normal operation. Reaction time would have to be less than the time it takes to remove the reactor from its silo and disable the receiver.

To understand the risks of proliferation, we need to think like the bad guys. Imagine you are trying to secretly produce fissile material for a bomb, using resources available in a world with thousands of nuclear reactors in almost all the countries. The easiest routes are currently centrifuges to make U-235, and breeder reactors to make Pu-239. Both of these require large plants that cannot be hidden. Here is the “Queen Mary”, a plutonium extraction plant at Hanford:

You will need three things: Fertile material. Uranium and thorium are the two possibilities, and both should be readily available in a world with thousands of nuclear power plants. Access to a reactor with surplus neutrons to convert the fertile material to fissile. You will need to get the fertile material inside the core of the reactor, or maybe around the outside, if there is sufficient leakage of neutrons. If you plan to steal neutrons from the core, the loss can be detected by the need for more fresh fuel to keep the reactor running. A means of extracting the fissile material with sufficient quantity and purity to make a bomb. The thorium fuel cycle seems to offer that possibility via uranium fluorination. Uranium hexafluoride is a gas, and can be easily separated from all other elements in the mix. Questions: Is there a fundamental difference between Uranium and Thorium with regard to proliferation risk? Is the breeding and chemical extraction of weapons-grade fissile material simpler or more easily concealed starting with Thorium? Is Tom Ledbetter right that a 1 GWe power plant could produce enough material for a bomb every 16 weeks? More from the Internet: Post in FB Forum Liquid Fluoride Thorium Reactor (LFTR) by Rober Steinhaus, 2 Nov /2019, A presentation on production of U233 from Thorium by Bob Olsen, TEAC 10. https://www.facebook.com/groups/229881329205/posts/10157976920104206/ Comments: Jon Schattke Total energy from the U232 decay chain is 36.35 MeV. With a decay constant of 3.2e-10, to get one watt you need 1.72e8 decays, and with the decay constant, that means 5.39e17 atoms. That means 200 mg/watt. 400 ppm is 400 milligrams per kilogram; or 2 W per kg, or about 18W in a critical bare sphere. The claim that U232 at produced rates self-protects from using the material in a bomb is false. Any one of you could have done this math in a few minutes yourself.

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Reply Share Ed Pheil Jon Schattke Typically, the CLAIM is the high gamma rad dose of >50ppm....after a few months. 4y Like

Reply Share Ed Pheil Jon Schattke I am not disputing your calc, or correction of the article, just stating what the ASSUMPTION for protection actually is. I am not even saying THAT assumption is correct, as I haven't looked at that either.

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Reply Share Lars Jorgensen As I've heard the claim it is that the presence of U232 (and its daughters) makes manual assembling a bomb impossible. It also sends out a very easily detected signal that is hard to shield so you can't smuggle such a weapon in. Frankly, I'm not confident in such claims and assume we will have to have more traditional safeguards.

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Reply Share Lars Jorgensen Look for a high energy gamma in the decay chain (not U232 decay but further down the chain). Try wiki https://en.wikipedia.org/wiki/Uranium-232 Ti-208 produces a 2.6MeV gamma.

EN.WIKIPEDIA.ORG Uranium-232 - Wikipedia Uranium-232 - Wikipedia

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Reply Share Lars Jorgensen I've gone about as far as I can with U232 - like I said earlier I'm not convinced that U232 is a viable way to implement safeguards. But U234 has 3,600 times as long a half-life so there will be much lower concentrations of daughter products and it includes 75,000 year half-life Th-230 so it will take more than a little while before you reach equilibrium.

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Reply Share Lars Jorgensen I think it will come down to computer studies and arguments with IAEA and the US. I don't expect that folks will succeed with the argument that the U232 provides the safeguards and reactors will have to have the normal seals, cameras, alarms, and inspections. Kirk Sorensen expected that HEU would be allowed in the core for weapons states. We chose to stick with LEU.

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Reply Share Albert Rogers The bit that sticks in my craw about all this alarmist stuff regarding part-used civilian fuel, is -- if I'm correct -- that even a villain like Trump's friend in North Korea has folk who know that it's easier to do it the way the Manhattan Project did. It's even known that you can get military grade "enrichment" of uranium more easily from a first class gas centrifuge, than from a diffusion apparatus. I'm still astonished and horrified that apparently tritium is not as strictly controlled as plutonium! FaceBook Discussions: Comments from Robert Laird