nuclear power

Patent number: 3052613
Filing date: Aug 29, 1945
Issue date: Sep 4, 1962

Patent number: 2743225
Filing date: Aug 27, 1946
Issue date: Apr 24, 1956

Patent number: 2770591
Filing date: Jul 3, 1946
Issue date: Nov 13, 1956

Critical size calculation for a sphere

Critical size calculation for a cylinder

Proposal for a Simplified Thorium Molten Salt Reactor

The dilution process can be implemented at low cost. It only requires a fluorination step and a larger amount of salt and Tho- rium. No additional fissile matter is needed since Uranium is not stocked in the tank. Although it leads to an increase of the fuel price, the dilution process seems to have major advantages.
We consider the single salt channel configuration studied in Section III.1. We assume that the bubbling system extracts FPs in a period of 1 month instead of 30 seconds. This less ambitious reprocessing is easier to implement than in the standard case. With no bubbling system, gaseous FPs are supposed to migrate towards surfaces, and noble metals to agglomerate on the walls. For these reasons, extraction of these FPs in 1 month with a low efficiency bubbling system makes sense.
One last important aspect is the thermal hydraulic constraint. The thermal power is evacuated by the fuel which thus has to circulate in the exchangers. Heat evacuation becomes more difficult as the specific power increases. Small sized or high power reactors are at a disadvantage in this respect, barring significant progress in heat exchanger technology. p5
Common structure materials cannot withstand such a
temperature increase. However, new promising solutions based
on carbon (carbon-carbon, carbon fiber, carbides) could help
solve this problem [9]. If this technology is not implemented,
then the HN proportion parameter cannot be modified in this
way and this solution must be ignored. p6

We have simulated several configurations operating at
1030 􀀀 C with 20 m3 of fuel salt. The proportion of (HN)F4
varies from 22 % to 2 %. At this temperature, the thermodynamic
efficiency is assumed to increase from 40 % to 60 %
and it has an incidence on the thermal power of the reactor:
1666 MWth instead of 2500 MWth are needed to produce
1000 MWe. Similarly, the salt density decreases from
4.3 to 3.89 because of the temperature related expansion effect.
Moreover, we suppose that the HN flow 5 in the reprocessing
unit must be kept constant, in order to keep the same reprocessing
difficulty. It leads to a reduction of the reprocessing time
for low proportions of HN.

There are numerous solutions to improve this reference configuration.
Very simple reactors may be designed by suppressing
the FP reprocessing. Even in this case, reactors can operate
some ten years before reaching excessive FP poisoning. The
reactor may also be strongly improved in terms of breeding capability
and chemical behavior by a dilution process. Other
paths of investigation are possible in order to reduce the fissile
inventory, such as increasing the specific power or modifying
the salt composition.

Our studies show that the MSR, and particularly a fast spectrum
configuration, is an interesting and sustainable concept
which can be used for Generation-IV deployment scenarios.

Introduction to the Physics of Molten Salt Reactors

As already stated, TMSRs are operated in the Thorium fuel cycle, using either 233U (233U-started TMSR) or Pu (transuranic-started TMSR or TRU-started TMSR) as initial fissile matter. The initial load of the non-moderated TMSR can thus be a mixture of thorium and, for its fissile material, the transuranic elements (Pu, Np, Am and Cm) produced in the water moderated reactors fed at present with natural or slightly enriched uranium. Actually, to be more realistic, these TMSRs are started with the mix of 87.5% of Pu (238Pu 2.7%, 239Pu 45.9% , 240Pu 21.5%, 241Pu 10.7%, and 242Pu 6.7%), 6.3% of Np, 5.3% of Am and 0.9% of Cm, corresponding to the transuranic elements of an UOX fuel after one use in a standard LWR and five years of storage (de Saint Jean et al. 2000).

For the typical TMSR configuration (with 17.5 mole% of HN in the salt), an amount of 7300 kg of fissile elements is needed initially, corresponding to 4.5 mole % of Plutonium.  (p8)
The interesting variable is thus the operating time necessary to produce one initial fissile (233U) inventory, called the reactor doubling time. We have studied the amount of excess 233U produced in each TMSR configuration. Transuranic-started TMSRs allow the extraction of significantly larger amounts of 233U during their first 20 years of operation, thanks to the burning of TRUs which saves a part of the 233U produced in the core. The higher deployment capabilities allowed by the use of TRUs in the transuranic-started TMSR are visible on the reactor doubling times, displayed in Fig. 3.5 (dashed line), where the configurations with HN proportions larger than 15% have the lower reactor doubling times, around 30-35 years,
The configuration with 17.5% of heavy nuclei in the salt appears particularly op-timal in terms of deployment capabiliities, especially with the faster reprocessing scheme and for the transuranic-started TMSRs. With these results, we have simu-lated the deployment of a fleet of such reactors at a worldwide and at a European scale and verified that large scale deployment is possible both with regard to the availability of fissile matter and to the control of fissile matter stockpiles and ra-dioactive wastes. (p10)
Beyond the safety aspects, using a liquid fuel allows the adjustment of fertile and fissile matter without unloading the core, doing away with the need for any initial reactivity reserve, contrary to the case of a LWR where this reactivity reserve amounts to 10 000 pcm. Some reactivity margins may be introduced in the core of the TMSR involuntary through three possible perturbations: a direct insertion of reactivity, the loss of salt circulation, and finally the loss of the fertile blanket surrounding the core. (p13)
If the salt circulation is stopped, all the delayed decays will occur in the reactor, since all the fission products will stay in core. This will represent an addition of 150 pcm to the multiplication coef-ficient in some ten seconds. (p14)
For insertion times greater or equal to one second, and a fortiori in a more realistic case of 100 seconds, the reactor feedback is fast enough to avoid the prompt reactivity regime. Thus the reactor succeeds in absorbing at least a 1000 pcm reactivity insertion in one second and behaves safely. (p17)


We then focussed on the configurations without any graphite moderator in the core, since they appear to be really promising. More precisely, the non-moderated TMSR configurations with high proportions of heavy nuclei, leading to a rather fast neutron spectrum, present particularly interesting characteristics regarding their safety performance and their ability to be first loaded with transuranic elements produced by today’s water cooled reactors. Finally, their rather large initial fissile inventory does not inhibit their capability for a fast deployment thanks to their very good 233U breeding ratio during the burning of transuranic elements.
Under these conditions the TMSR appears to be a very appealing concept; our calculations do not indicate any major reprocessing constraint, allowing batch mode reprocessing in the vicinity of the reactor. The main additional studies needed to demonstrate the scientific feasibility of the concept deal with the on-line control of the salt composition and of its chemical and physical properties. Such studies are in progress in the frame of the French concerted research program ‘Molten Salt Reactor’ (PCR-RSF). Finally we want to point out the hardiness and the flexibility of this TMSR concept, allowing it to be adjustable without loosing its advantages in the event of any technological stumbling block.