In Re Jean-paul Millot and Guy Desfontaines, 950 F.2d 732 (Fed. Cir. 1991)

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U.S. Court of Appeals for the Federal Circuit - 950 F.2d 732 (Fed. Cir. 1991) Nov. 29, 1991

Before RICH, MICHEL and LOURIE, Circuit Judges.


LOURIE, Circuit Judge.

Jean-Paul Millot and Guy Desfontaines (Millot) appeal from the December 12, 1990, decision of the United States Patent and Trademark Office Board of Patent Appeals and Interferences, Appeal No. 89-3178. The Board majority sustained the rejection of claims 1-9, all the claims in the case, in application serial number 865,312, as unpatentable under 35 U.S.C. § 103. We affirm.


Millot's invention concerns a process for operating a nuclear reactor, wherein fertile material is placed in spectrum shift rods.1  The spectrum shift rods are inserted into the reactor core during a first phase of operation. Due to the selective absorption of low energy neutrons by the fertile material contained within the rods, and the displacement of the water moderator by the rods, the spectrum of the neutrons in the core is shifted toward the higher energy part of the spectrum. This shifting of the spectrum, known as "hardening," has several beneficial effects. First, the excess reactivity present at the initialization of a new fuel load is reduced. Second, this control of excess reactivity allows more of the uranium fuel to be utilized. Additionally, the absorption of low energy neutrons causes the fertile material in the rods to be converted to usable fissile material.

The Board sustained the examiner's rejection of all claims as obvious in view of Impink, U.S. Patent 4,432,930; MacRae, British Patent 798,466; Dodd, British Patent 963,791; and other references. The Board found that it would have been obvious to substitute the fertile material of MacRae or Dodd for the "gray" material in the spectrum shift rods of Impink to achieve the spectral shift function.

Millot first urges that no prima facie case of obviousness has been shown, arguing that the references merely suggest the use of fertile material in control rods, not spectrum shift rods. We agree with the Board that the references do suggest the use of fertile material in spectrum shift rods. Both Impink and MacRae specifically distinguish between control rods and what Impink calls "displacer" or "gray" rods and MacRae refers to as "absorber" rods. MacRae's "absorber" rods contain "material which under radiation produces fissile material" (i.e., fertile material) and are inserted into the reactor core to control the "distribution of neutron flux." MacRae even suggests the use of thorium, the same material suggested by Millot, as the fertile material. MacRae further notes that the thorium may be used to produce new reactor fuel as a result of its absorption of neutrons.

Similarly, Dodd expressly teaches that fertile material may be used to shift the neutron spectrum, thereby reducing the reactivity of the core. Finally, we note that Impink provides an express suggestion that neutron absorbing material may be placed in its "displacer" rods. Therefore, we find clear and abundant support for the Board's conclusion that it would have been obvious to one skilled in the art to substitute fertile material into Impink's "displacer" or "gray" rods, thereby arriving at Millot's spectrum shift process.

Additionally, Millot argues that his claimed process is segregated into two distinct phases and that this process is nonobvious in view of the cited references. We will not consider this argument since it was not considered by the Board.2 

Even if a prima facie case of obviousness has been shown, it has been rebutted, Millot argues, by a showing of unexpected results. We find the record clearly demonstrates that the results were not unexpected. Far from it, the references clearly show that the art recognized the beneficial effects of using fertile material to shift the neutron spectrum. Both Dodd and MacRae teach that fertile material used to shift the spectrum is converted into fissile material when irradiated by neutrons. Additionally, Dodd teaches that this spectrum shift is useful in reducing the excess reactivity of the core present at the initial loading of the fuel. The fact that spectrum shift rods need not be inserted in each fuel cell assembly would have been obvious to one skilled in the art as being a direct result of the neutron absorbing capacity of the fertile material. Additionally, we note that it does not appear that Millot raised this issue below.

Millot's other arguments have been considered, but are not considered persuasive.


We include claim 1 as illustrative of the invention. However, at appellant's urging, we have not considered claim 1 to be representative of all claims. Rather, we have considered the limitations of each claim separately

Claim 1


A process for operating a nuclear reactor having a core comprising a plurality of vertical fuel assemblies immersed in moderating and cooling light water, said fuel assemblies each having rods containing both fissile isotopes and fertile isotopes, which comprises, during a same operating cycle of said reactor with the same fuel assemblies:

(a) during a first phase of the cycle, operating the reactor with a plurality of spectrum shift rods distributed throughout said core and all inserted in said core, said rods each consisting of fertile material selected from depleted uranium and thorium in a sheath,

(b) at the end of said first phase, withdrawing said fertile rods from said core into equipment situated above the core in the course of operation, and

(c) during a second phase of the same cycle, operating the reactor with a neutron spectrum of lower energy substantially in the thermal range, corresponding to increased fission cross-section of the fissile material.


The Board refused to consider this argument, which it found to have been raised by Millot for the first time in its petition for reconsideration. Millot does not argue here that the issue was raised below