Light-Water Reactor Patents: Who Leads, Where the Gaps Are 2026
- 34.1% of all 16,613 records sit with the top five assignees — dense concentration in reactor core and fuel assembly claims, but well short of a monopoly.
- Filings fell 35% from 2021 to 2024 (494 to 319), the last span with complete publication data — a real pullback, not a filing artefact.
- G21C alone covers 78.4% of records while alloys, steam generation and digital monitoring subclasses each stay under 4%, marking where claim density is thin.
Filing growth compares 2021 (494 records) with 2024 (319) — a three-year span. 2024 is the most recent year we treat as complete: publication lags filing by roughly 18 months, so 2025 onwards are still filling in and any growth rate that ends there would understate the field. Top-5 share is the combined record count of the five largest assignees divided by all 16,613 records in scope (CR5), not by the ranked leaders only.
What this landscape covers
This dataset pulls 16,613 published records matching light-water and pressurized-water reactor terms alongside core mechanical and safety concepts: reactor coolant, fuel assembly, reactor core, radiation field and safety barrier. It spans filings published from 2015 through the 2026-08-31 cut-off, with the assignee ranking built on the full set of patent families rather than raw document counts.
Because publication trails filing by roughly 18 months, the last one to two years in any trend understate real filing activity. The 2021-2024 window is the most recent stretch that can be read as complete, and it shows a genuine pullback in filing volume rather than a data artefact.
Filing trend and technology composition
Two views of the same 16,613 records: how filing volume has moved year over year, and how those records distribute across IPC subclasses. Class shares are computed against the full record count, and they sum past 100% because a single record can carry more than one class.
A decade of filing activity, with a clear post-2018 pullback
Filings peaked in 2018 at 567 and ran near 458 in 2017. By 2021 the annual count was 494; by 2024, the last complete year, it had fallen to 319 — a 35% decline over that three-year span. Years from 2025 onward are still filling in and should not be read as a continuation of the decline.
Reactor-level claims dominate; adjacent subclasses stay thin
G21C (nuclear reactors) covers 78.4% of the 16,613 records, an order of magnitude above the next subclass, G21D (nuclear power plants) at 13.9%. Radiation protection sits at 8.3%, and materials-adjacent classes — alloys, steam generation, digital data processing, material testing and nuclear conversion — each hold under 4% of records, the range where claim space is least crowded.
Shares are the percentage of the 16,613 records in scope. A patent can carry several IPC classes, so the shares add up to more than 100%.
Go deeper on Light-Water Reactors Patent Landscape with Eureka
This page is one run against one query. Ask Eureka your own question about light-water reactors patent landscape and every answer comes back with the patent numbers behind it.
Try EurekaRepresentative filing and most-cited prior art
Light water reactor fuel assembly, light water reactor core and MOX fuel assembly production method
Light water reactor fuel assemblies comprising fuel rods with enriched uranium arranged parallel to burnable-poison rods of lower enrichment, set out in a lattice pattern, with an initial enrichment value set to govern reactivity distribution across the assembly.Filed by Toshiba; illustrates how enrichment gradients and burnable-poison placement are claimed at the fuel-rod-arrangement level rather than at the material level.
| # | Publication no. | Patent title | Citations |
|---|---|---|---|
| 1 | US4790028A | Method and apparatus for generating variably scaled displays | 520 |
| 2 | JP1990032293A | Boiling water nuclear reactor | 486 |
| 3 | US20090189617A1 | Continuous subsurface heater temperature measurement | 258 |
| 4 | US4977529A | Training simulator for a nuclear power plant | 250 |
| 5 | US4541055A | Laser machining system | 224 |
| 6 | US20090194333A1 | Ranging methods for developing wellbores in subsurface formations | 208 |
| 7 | US20100258265A1 | Recovering energy from a subsurface formation | 202 |
| 8 | US5291190A | Operator interface for plant component control system | 194 |
| 9 | US20080123797A1 | Automated nuclear power reactor for long-term operation | 191 |
| 10 | US20100316181A1 | Integral helical coil pressurized water nuclear reactor | 186 |
Citation counts reflect influence within this searched corpus and skew toward older records; they are not a measure of current commercial relevance.
Each row carries its publication number; clicking a row searches Eureka by that number.
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Three patterns stand out once the ranking, the trend and the IPC composition are read together: filings are concentrated but not locked up, activity has genuinely cooled off its 2018 peak, and the claim space outside the core reactor subclass remains comparatively open.
A leading group, not a monopoly
The top five assignees combined hold 34.1% of all records in scope, and the top ten hold 45.5%. That leaves well over half the field spread across a long tail of single- and few-filing entrants, which is unusual for a technology this mature.
A real pullback, not a publication lag
Annual filings dropped from 494 in 2021 to 319 in 2024 — the most recent three-year span not distorted by publication delay. Several of the largest historical filers show near-zero or sharply negative year-on-year activity in the latest tracked year.
Reactor-level claims crowd one subclass
Nuclear reactors (G21C) accounts for 78.4% of records, dwarfing power-plant-level claims (G21D, 13.9%) and radiation protection (G21F, 8.3%). Materials, steam generation, digital monitoring and nuclear conversion subclasses each sit under 4%, suggesting thinner prior art there.
Eureka can read the same corpus for gaps instead of for coverage: under-claimed branches adjacent to light-water reactors patent landscape, with the prior art for and against each one.
| Assignee | Co-assignee | Shared families |
|---|---|---|
| Kabushiki Kaisha Toshiba (Toshiba Corporation) | Japan Nuclear Fuel Co., Ltd. | 84 |
| Framatome SA | COGEMA | 38 |
| NuScale Power LLC | Rock Creek Innovations LLC | 29 |
| Mitsubishi Heavy Industries, Ltd. | Shikoku Electric Power Co., Inc. | 27 |
| Mitsubishi Heavy Industries, Ltd. | Kyushu Electric Power Co., Inc. | 27 |
| Hitachi, Ltd. | Hitachi Engineering Co., Ltd. | 26 |
| Mitsubishi Heavy Industries, Ltd. | Japan Atomic Power Company | 25 |
| Mitsubishi Heavy Industries, Ltd. | Hokkaido Electric Power Co., Inc. | 25 |
Ten identified co-assignee pairs exist in this dataset, with the strongest joint-filing relationships appearing between reactor OEMs and their national fuel-cycle or engineering affiliates — a sign that core reactor claims are often filed jointly with a fuel-services or plant-engineering partner rather than solely by the reactor vendor.
Who holds the claim space
The ranked leaders span established reactor OEMs, national utilities and newer small-modular-reactor entrants. Recent-year momentum has cooled sharply even among the largest historical filers, which opens room to look for where the next wave of claims might land.
A single leader well ahead of the field
The top-ranked assignee holds 3,224 records, more than six times the fifth-place count of 470. That gap suggests one organisation has built a genuinely broad portfolio across multiple reactor subsystems rather than a narrow specialism.
A tighter cluster below the leader
From fifth to tenth place, counts run from 470 down to 296 — a much shallower drop-off than between first and fifth place. This is where reactor OEMs, fuel-assembly specialists and utility-affiliated filers compete on comparable footing.
Even top filers have slowed sharply
Several of the historically largest assignees show steep year-on-year declines or zero filings in the latest tracked year. Given the 18-month publication lag, this understates true recent activity, but the direction across multiple large filers is consistent enough to note.
| Assignee | Recent year | YoY |
|---|---|---|
| Westinghouse Electric Corp | 2 | -85% |
| NuScale Power LLC | 1 | -80% |
| Mitsubishi Heavy Industries, Ltd. | 0 | — |
| Kabushiki Kaisha Toshiba (Toshiba Corporation) | 0 | — |
| Hitachi, Ltd. | 0 | — |
| Westinghouse Electric Sweden AB | 0 | -100% |
| Framatome SA | 0 | -100% |
| General Electric Company | 0 | — |
Where to take this research
The dataset points to where claim density is heaviest and where it thins out. Turning that into a filing or licensing decision means going deeper on the specific subclass, assignee or family that matters to the work at hand.
Check freedom-to-operate in thin subclasses
Alloys, steam generation and digital monitoring each hold under 4% of records. Before drafting claims in these areas, run a targeted search against the specific assignees active there rather than the whole field.
Explore in Patsnap EurekaTrack momentum, not just historical volume
The largest historical filers show sharply reduced recent-year activity. A portfolio review should weight recent filing behaviour alongside cumulative counts before assuming a leader's position is stable.
Explore in Patsnap EurekaLook at co-filing structures around core claims
Ten identified co-assignee pairs suggest joint filing between OEMs and affiliated fuel or engineering entities. Mapping these relationships can reveal licensing paths that a single-assignee search would miss.
Explore in Patsnap EurekaCommon questions on light-water reactor patents
The assignee ranking in this dataset covers 100 companies drawn from 16,613 records, and the leading assignee alone holds 3,224 of them, well ahead of the fifth-ranked company at 470. The top five combined account for 34.1% of all records in scope, and the top ten account for 45.5%. That leaves a substantial long tail of smaller filers, so the field is concentrated at the top but far from a closed market.
Annual filings ran near 458 in 2017, peaked at 567 in 2018, and had fallen to 319 by 2024, the most recent year with complete publication data. That represents a 35% decline from 2021's 494 filings to 2024's 319. Because publication lags filing by roughly 18 months, 2025 and 2026 figures are still incomplete and should not be read as confirming a continued slowdown, but the 2021-2024 window is a genuine and measurable pullback.
Nuclear reactors as a subclass (G21C) covers 78.4% of the 16,613 records, far ahead of nuclear power plants (G21D) at 13.9% and radiation protection and shielding (G21F) at 8.3%. Materials-adjacent areas — alloys, steam generation, digital data processing, material testing and nuclear conversion — each account for under 4% of records. That gap suggests claim density around the core reactor itself is heavy, while surrounding materials and monitoring technologies are comparatively open.
This Toshiba filing describes light-water reactor fuel assemblies combining enriched-uranium fuel rods with burnable-poison-containing rods of lower enrichment, arranged in a defined lattice pattern with a set initial enrichment value governing reactivity. It matters because it claims at the level of fuel-rod arrangement and enrichment gradient rather than at the material or chemistry level, which is a narrower and more specific claim style than many surrounding filings. Anyone designing a MOX or mixed-enrichment fuel assembly for a light-water reactor should check this family before finalising a rod-lattice layout.
The clearest gaps sit outside the dominant G21C reactor-core subclass: alloys used in cladding, steam generator tube-bundle design, digital core-monitoring algorithms, radiation-field sensor placement, post-irradiation material testing and coolant-loop integration for modular reactors all hold under 4% of the 16,613 records. Combined with several of the largest historical assignees showing sharply reduced recent-year filing, this suggests both technical and competitive room to file well-drafted claims in these adjacent areas rather than contesting the crowded reactor-core subclass directly.
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Disclaimer. This page is generated from Patsnap Eureka data drawn from a limited snapshot of global patent and scientific-literature records, and is provided for general information and reference only.
Patent data carries inherent limitations: recent filings (typically the most recent 18–24 months) are under-counted due to standard publication lag; counts may be reported at either a patent-family or a patent-record basis and are not always directly comparable; classification, applicant-name, and citation data may contain errors, duplicates, or omissions; and the underlying search query defines and constrains the scope shown. As a result, the analysis may be incomplete or inaccurate and may not reflect the full technology landscape.
Nothing on this page constitutes an exhaustive prior-art, novelty, freedom-to-operate, or validity search, nor does it constitute legal, financial, investment, or professional advice, and it should not be relied upon as such. Any patent, commercial, or strategic decision should be verified independently and reviewed with qualified patent, legal, and domain professionals. Patsnap makes no warranties, express or implied, as to the accuracy, completeness, or fitness for any particular purpose of the information presented.
Machine translation. Assignee and organisation names originally recorded in Chinese, Japanese or Korean have been rendered into English by an AI translation step so that the tables stay readable. These renderings are best-effort and may not match a company’s registered English name; the original name is what the underlying patent record carries, and it is what any Eureka query launched from this page uses.