DETAILED ACTION
Notice of Pre-AIA or AIA Status
1. The present application, filed on or after March 16, 2013, is being examined under the first inventor to file provisions of the AIA .
Claim Status
2. Claims 1-2, 4-5, and 10-11 are pending. Claims 1-2, 4-5, and 10-11 are examined herein.
Prosecution Status
3. In view of the Appeal Brief filed on 11/03/25, PROSECUTION IS HEREBY REOPENED. A new ground of rejection is set forth below.
To avoid abandonment of the application, appellant must exercise one of the following two options:
(1) file a reply under 37 CFR 1.111 (if this Office action is non-final) or a reply under 37 CFR 1.113 (if this Office action is final); or,
(2) initiate a new appeal by filing a notice of appeal under 37 CFR 41.31 followed by an appeal brief under 37 CFR 41.37. The previously paid notice of appeal fee and appeal brief fee can be applied to the new appeal. If, however, the appeal fees set forth in 37 CFR 41.20 have been increased since they were previously paid, then appellant must pay the difference between the increased fees and the amount previously paid.
A Supervisory Patent Examiner (SPE) has approved of reopening prosecution by signing below:
/JACK W KEITH/Supervisory Patent Examiner, Art Unit 3646
Response to Arguments
4. Applicant’s arguments dated 11/03/25 are partially persuasive.
5. The arguments with respect to the rejection of claim 11 under 35 U.S.C. 112(a) are persuasive. 6. The prior art “Huke NPL” in combination with the instant disclosure establishes how a dual fluid reactor is “configured to transition the binary eutectic [fuel] into a pentary mixture…” To summarize, iron can be leached into the fuel through corrosion of reactor elements and thorium is present due to impurities or from the presence of a blanket. Additionally, fuel processing can add additional nuclei to the fuel mixture during operation.
7. The arguments with respect to the rejection of claim 1 under 35 U.S.C. 103 are not persuasive.
8. As an initial matter the examiner wishes to make clear that the term “dual fluid reactor” is a term coined by the inventors of this application.1 It is not a term that enjoys widespread use in the art. However, reactors utilizing two metallic fluids—a liquid metal fuel and a liquid metal coolant—have been known since the 1950s, as evidenced by, Poppendiek, Percival, Abraham, Tietel cited on the attached PTO-892.
9. Applicant argues that Huke’s suggestion applied by the examiner as the motivation for combining the fuel mixtures taught by Spedding must be narrowly construed to mean that only the “metal additives” lead and bismuth are suitable additions to metallic actinides. The examiner disagrees.
As a reminder, Huke discloses a dual fluid reactor employing a liquid fuel that is an actinide salt. The rejection under 35 U.S.C. 103 states (Final Office action, 06/05/25, at paragraph 18):
“Huke further suggests that its reactor could be fueled with “a liquid metal alloy” which would provide the advantages of “higher heat transfer capability and lower corrosion capability compared to a liquid salt,” which results in increased “power density [and] operating temperature,” thereby providing “maximum economic efficiency” ([0089]) … Spedding teaches a “molten-metal-fuel” nuclear reactor (Fig. 1) comprising a liquid fuel comprising a liquid metal fissionable mixture … One of ordinary skill in the art at the time of the invention/filing would have found it obvious to apply the molten metal fuel of Spedding to the reactor of Huke because Huke explicitly suggests such a modification and predicts the advantages that result from the substitution ([0089]).”
10. The assertion that a person of ordinary skill in the art would be unable to determine which metals possesses “sufficient neutronic properties” to be suitable for use in nuclear fuel is unreasonable in view of the prior art. Both Spedding and Buzzard are concerned with the use of binary metal fuels in nuclear fission reactors, suggesting that the fuel compositions described therein possess “sufficient neutronic properties” to be suitable for use in a nuclear fission reactor. Moreover, the neutron absorption cross sections of the elements are well-known to a skilled artisan2 and the nuclear reactor art is replete with statements pertaining to low neutron absorption properties of iron, chromium, and manganese.3 Thus, Applicant’s conclusion that a skilled artisan would regard the fuels taught by Spedding as falling outside the scope of Huke’s suggested modification is groundless.
11. There is nothing in Huke (nor in “Huke NPL”) that establishes that a dual fluid reactor must operate at the “desired operating temperature” of 1000 °C ([0065]). In fact, Huke appears to select its operating temperature based on the temperature of the lead coolant (see [0045]) and selects a fuel salt that is liquid at that temperature ([0046]). However, lead is liquid at temperatures above about 330 °C, meaning that suitable fuels for Huke’s reactor should also be liquid at such temperatures. Accordingly, the binary metal fuels taught by Spedding would be suitable for use in the reactor of Huke because they are liquid at the same temperatures that the coolant is liquid, as evidenced by both Buzzard and Spedding. Not only could the proposed combination of Spedding’s fuels with Huke’s reactor operate at the “desired temperature” of 1000 °C, it could also operate at lower temperatures. Thus, there is a reasonable expectation of success (MPEP 2143.02).
12. Additionally, the examiner can find no evidence in any of the cited prior art that the use of the binary metals taught by Spedding in the reactor of Huke would render Huke unsatisfactory for conducting nuclear fission reactors or would change the principle of operation of Huke (MPEP 2143.01(V) and (VI)). The fact that Huke suggests that liquid metal alloys of actinides with lead, bismuth, and tin could be used in its dual fluid reactor does not preclude the use of other liquid metal alloy mixtures in the reactor (MPEP 2143.01(I).
13. The examiner disagrees with the arguments that Spedding is non-analogous art. Spedding meets both analogous art criteria.
14. With respect to the arguments alleging that Spedding is not in the same field of endeavor as the present invention, the examiner submits that Applicant is unreasonably constricting the field of endeavor to a term that was created by the inventors themselves. The field of endeavor of both the invention and Spedding is a nuclear fission reactor using liquid metal fuels. Huke states “The present invention describes a nuclear reactor with a loop for liquid nuclear fuel” and that has “an additional coolant loop” (Abstract). Huke further states “the main task is to create a reactor design using liquid nuclear fuel” ([0023]). Spedding is concerned with “The Molten-metal-fuel Reactor” (Title) and illustrates “a molten-metal enriched fast reactor” (Fig. 1) fueled by “molten eutectics of enriched uranium with iron, chromium, or similar elements, such as nickel, cobalt of manganese (p.4). The examples of “Analogy in the Mechanical Arts” (MPEP 2141.01(a)(IV)) support the examiner’s broader interpretation of the field of endeavor rather than Applicant’s extremely narrow interpretation.
15. Spedding is also “reasonably pertinent to the problem faced by the inventor.” The present disclosure states “the task of the invention is to provide a liquid metal fissionable material…which is characterized by high thermal conductivity, high actinide nuclide density, high power density and a high working temperature, allows continuous discharge” (see [0011] of the published application). Spedding mentions all of these factors as “advantages of a molten fuel in a reactor” (p. 1): heat conduction (p. 2 “Eleventh, the heat-transfer problems become simpler because, in addition to conduction, advantage can be taken of the molten metal in transferring heat.”); high actinide nuclide density (p. 2 “If enriched materials are to be used, it can be made quite small. Second, the drastic limitations on materials which arise from nuclear properties are not nearly so serious if enriched materials are used.”); power output (p. 2: “offers excellent possibilities for producing very cheap power when operated as a breeder”); working temperature (p. 2: “the steam generation in connection with the reactor has a very large ΔT (temperature) though which to operate in order to give high hemodynamic efficiency”); and continuous discharge (p. 2: “the fission products and plutonium can be removed from the reactor by constant bleeding”).
16. Claim 11 is newly rejected under 35 U.S.C. 103.
Subject Matter Summary
17. The claimed invention is an apparatus, “a dual fluid reactor.” The disclosure is directed to various fuel compositions (referred to as “preferred variants”) usable in such a reactor. As explained in paragraphs 2-3 of the office action dated 08/22/23, Applicant elected the species of claim 10, which corresponds to Species I, the binary eutectic fuel mixture “preferred variant.” The disclosure provides details of this fuel composition at [0022-0027], [0032], [0046].
18. It is important to note that a binary eutectic as disclosed and as dictated by the definition of the term “binary” must contain two and only two elements, e.g., uranium and chromium. Note also the use of the terminology “consisting of” in the description of the preferred fuel variants at [0032-0040] and in the originally filed claims. Accordingly, the binary eutectics of the elected embodiment that are disclosed in the specification as filed are:
U/Cr
U/Mn
Th/Fe
19. The disclosure describes various “initial,” i.e., fresh, fuel mixtures. It is well-known in the art that as nuclear reactor fuel fissions, additional elements are created. This process as it applies to the binary fuel compositions of the elected embodiment is described at [0032]. Specifically, the U-235 isotope of the uranium component of the binary fuel produces Pu-239 as well as fission produces. The Th-232 produces U-233. Transmutation also occurs in the chromium, manganese, or iron atoms of the binary fuel.
Claim Rejections - 35 USC § 103
20. In the event the determination of the status of the application as subject to AIA 35 U.S.C. 102 and 103 (or as subject to pre-AIA 35 U.S.C. 102 and 103) is incorrect, any correction of the statutory basis (i.e., changing from AIA to pre-AIA ) for the rejection will not be considered a new ground of rejection if the prior art relied upon, and the rationale supporting the rejection, would be the same under either status.
21. For applicant's benefit, the portions of the reference(s) relied upon in the below rejections have been cited to aid in the review of the rejections. While every attempt has been made to be thorough and consistent within the rejection, it is noted that prior art must be considered in its entirety, including disclosures that teach away from the claims. See MPEP 2141.02 VI.
22. The following is a quotation of 35 U.S.C. 103 which forms the basis for all obviousness rejections set forth in this Office action:
A patent for a claimed invention may not be obtained, notwithstanding that the claimed invention is not identically disclosed as set forth in section 102, if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains. Patentability shall not be negated by the manner in which the invention was made.
23. Claims 1, 2, 4, and 5 are rejected under 35 U.S.C. 103 as being unpatentable over Huke et al., US 2014/0348287 in view of Spedding “The molten-metal-fuel reactor,” published in 1953, as evidenced by Buzzard "The Binary Alloys of Uranium," published in 1948.
24. Regarding claims 1, 2, 4, and 5 Huke discloses a DFR (Fig. 1, [0025]) consisting essentially of:
a first conduit (7) for continuously feeding and discharging a liquid fuel into a core volume in a reactor core vessel (4) of the DFR, said first conduit entering the reactor core vessel of the DFR via a first inlet (8), being guided through the core volume into a fission zone and leaving the reactor core vessel of the DFR via a first outlet (9) ([0046]),
wherein a chain reaction can proceed either critically or subcritically in the fission zone ([0025]), and
a second conduit (3) for a liquid coolant, arranged such that the coolant from the second conduit enters said reactor core vessel of the DFR via a second inlet (2), runs around the first conduit in the fission zone and leaves the reactor core vessel of the DFR again through a second outlet (5) ([0045]) ,
wherein a substantially complete heat transfer occurs between the first conduit and the second conduit in the fission zone ([0049]).
Huke further suggests that its reactor could be fueled with “a liquid metal alloy” which would provide the advantages of “higher heat transfer capability and lower corrosion capability compared to a liquid salt,” which results in increased “power density [and] operating temperature,” thereby providing “maximum economic efficiency” ([0089]).
Spedding teaches a “molten-metal-fuel” nuclear reactor (Fig. 1) comprising a liquid fuel comprising a liquid metal fissionable mixture, wherein the liquid metal fissionable mixture contains:
a predominant actinide content and additional non-actinide metals selected from chromium (Cr), manganese (Mn) and iron (Fe), wherein the liquid metal fissionable mixture, as fresh inventory in a reactor core, consists essentially of a binary eutectic of uranium and chromium; uranium and manganese; or thorium and iron (see Fig. 1 Legend: “U-Cr eutectic or perhaps U-Mn”).
Although Spedding does not explicitly state that the liquid metal fissionable mixture has a predominant actinide component of at least 69 at% and that the U:Cr or U:Mn molar ratio is 4:1, Spedding clearly states that the liquid metal fissionable mixture is a eutectic. Buzzard establishes that U-Cr has a eutectic point at 80% uranium (see Fig. 5), U-Mn has a eutectic point at 80% uranium (Fig. 11). Accordingly, the U-Cr and U-Mn fuel eutectics disclosed by Spedding have a predominant actinide content of at least 69 at% and a molar ratio of 4:1.
One of ordinary skill in the art at the time of the invention/filing would have found it obvious to apply the molten metal fuel of Spedding to the reactor of Huke because Huke explicitly suggests such a modification and predicts the advantages that result from the substitution ([0089]).
19. Regarding claim 5, the modification of Huke with the fuel of Spedding makes claim 1 obvious. Spedding further teaches a liquid metal fuel wherein the liquid metal fissionable mixture contains a uranium/chromium binary eutectic having 80 atom % U and 20 atom % Cr or a uranium/manganese binary eutectic possessing 80 atom % U and 20 atom % Mn (see rejections above).
Claim 5 further recites an “optional” limitation. It is noted that “[l]anguage that suggests or makes a feature or step optional but does not require that feature or step does not limit the scope of a claim under the broadest reasonable claim interpretation (MPEP 2143.03).
25. Claims 10 and 11 are rejected under 35 U.S.C. 103 as being unpatentable over Huke et al., US 2014/0348287 in view of Spedding “The molten-metal-fuel reactor,” published in 1953 as applied to claim 1, further in view of Huke, Armin, et al. "The Dual Fluid Reactor–A novel concept for a fast nuclear reactor of high efficiency." Annals of Nuclear Energy 80 (2015): 225-235 (hereinafter referred to as Huke-NPL).4
26. Regarding claim 10, the modification of Huke with the fuel of Spedding makes claim 1 obvious. Spedding further teaches that its fuel is “molten eutectics of enriched uranium” (p. 4, first paragraph) but is silent as to the absolute value of enrichment. However, Huke-NPL teaches for a DFR, “the initial load of enriched U depends on the size of the reactor core because of neutron losses through the surface” (p. 230, last paragraph of right column)
Accordingly, one of ordinary skill in the art at the time of invention/filing would have found it obvious to optimize the U-235 enrichment of the U-Cr or U-Mn fuel of Spedding in the reactor of Huke. Such an optimization would be based on “the size of the reactor core and neutron losses” as well as the desired fission rate in the reactor. A skilled artisan would be motivated to employ uranium enriched in U-235 to 7-12% as recited in claim 10 to achieve a desired power output in a smaller reactor design as compared to using LEU enriched to up to 5% U-235. Additionally, using HEU enriched to >20% poses proliferation concerns, making it less desirable for use in commercial reactors.
"[W]here the general conditions of a claim are disclosed in the prior art, it is not inventive to discover the optimum or workable ranges by routine experimentation" (MPEP 2144.05(II)(A)).
27. Regarding claim 11, the modification of Huke with the fuel of Spedding makes claim 1 obvious. Huke further discloses a dual fluid reactor that is configured to transition the binary eutectic into a quaternary mixture of either a U/Pu/Th/Cr or a U/Pu/Th/Mn mixture ([0082-3]: the binary U/Cr would transition to U/Pu/Th/Cr through transmutation of U-238 into Pu-239 under neutron irradiation from fission and thorium can be added to the fuel; the binary U/Mn would undergo the same transition).
Additionally, Huke-NPL establishes that “those of ordinary skill in the art familiar with dual fluid reactor designs and operation would have inherently known that the pentary mixtures of claim 11 can form from the corrosion of reactor elements during operation” and that “dual fluid reactors are also known to contain stainless-steel components that are in contact with the liquid fuel mixtures. Because the operation of a dual fluid reactor involves heating the fuel to high temperatures, chemical reactions can occur between the liquid fuel and the stainless-steel components. These chemical reactions leach iron and chromium into the liquid fuel.” (Huke-NPL at p. 232, Section 7. Materials and fabrications; Arguments 11/03/25 pp.6-7; and Huke at [0028], [0086], [0089]). Huke-NPL additionally teaches fuel treatment for “mixing in thorium or inert materials to even out the neutron surplus” (see p. 231, Section 6. Neutron economy) Thus, Huke-NPL establishes how the dual-fluid reactor is configured to form a pentary fuel mixture.
Huke and Huke-NPL are silent as to the atomic composition of the pentary mixtures. However, based on Huke-NPL’s discussion of “neutron economy” (see previous citation), one of ordinary skill in the art at the time of invention/filing would have found it obvious to operate the dual fluid reactor of Huke as modified by Spedding to obtain a term transition of the pentary mixtures to either a uranium/thorium/iron/chromium quaternary mixture or a uranium/thorium/iron/manganese quaternary mixture consisting of 7-12 atom-% U-233, 1-4 atom-% of either chromium or manganese, 59-64 atom-% thorium and 25-29 atom-% iron. Such an optimization would result in the predictable advantage of “even[ing] out the neutron surplus ( Huke-NPL, p. 231).
"[W]here the general conditions of a claim are disclosed in the prior art, it is not inventive to discover the optimum or workable ranges by routine experimentation" (MPEP 2144.05(II)(A)).
Claim 11 further recites an “optional” limitation. It is noted that “[l]anguage that suggests or makes a feature or step optional but does not require that feature or step does not limit the scope of a claim under the broadest reasonable claim interpretation (MPEP 2143.03).
Conclusion
THIS ACTION IS MADE FINAL. Applicant is reminded of the extension of time policy as set forth in 37 CFR 1.136(a).
A shortened statutory period for reply to this final action is set to expire THREE MONTHS from the mailing date of this action. In the event a first reply is filed within TWO MONTHS of the mailing date of this final action and the advisory action is not mailed until after the end of the THREE-MONTH shortened statutory period, then the shortened statutory period will expire on the date the advisory action is mailed, and any nonprovisional extension fee (37 CFR 1.17(a)) pursuant to 37 CFR 1.136(a) will be calculated from the mailing date of the advisory action. In no event, however, will the statutory period for reply expire later than SIX MONTHS from the mailing date of this final action.
Any inquiry concerning this communication or earlier communications from the examiner should be directed to SHARON M DAVIS whose telephone number is (571)272-6882. The examiner can normally be reached Monday - Thursday, 7:00 - 5:00 pm ET.
Examiner interviews are available via telephone, in-person, and video conferencing using a USPTO supplied web-based collaboration tool. To schedule an interview, applicant is encouraged to use the USPTO Automated Interview Request (AIR) at http://www.uspto.gov/interviewpractice.
If attempts to reach the examiner by telephone are unsuccessful, the examiner’s supervisor, Jack Keith can be reached on 571-272-6878. The fax phone number for the organization where this application or proceeding is assigned is 571-273-8300.
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/SHARON M DAVIS/Primary Examiner, Art Unit 3646
1 See attached Wikipedia article entitled “Dual fluid reactor.” See also the instant specification at [0002] and Huke at [0025].
2 See, for example, the references at periodictable.com (https://periodictable.com/Properties/A/NeutronCrossSection.an.log.html) and environmental chemistry.com (https://environmentalchemistry.com/yogi/periodic/crosssection.html). The second reference is attached hereto.
3 Patents to Barrett, Schonfeld cited on attached PTO-892 are representative.
4 The examiner notes that Huke-NPL clearly pertains to the same DFR as Huke US 2014/0348287