RE: Gen. Atomics' GTMHR [was "British Energy plans nuclear power plants" ]

["Franta, Jaroslav" <frantaj@AECL.CA>]

On March 05, 2001 12:07  I asked the Question :  



Does anyone know why the US has to go S. Africa (PBMR) for its next

generation of reactors ?  What's up with Gen. Atomics' GTMHR ?

...personally, I think that on-line refueling (PBMR) makes for an

unnecessary complication for modular units -- its hardly going to make much

difference when you shut down one of your (dozen ?) 100MWe modules for

refueling.

Strange, isn't it ? 

<><><><><><><><><><>



......which has now been answered in the current, June 7, 2001 issue of

NUCLEONICS WEEK :



GENERAL ATOMICS ADAPTS WORK ON GAS-COOLED REACTOR FOR U.S.

General Atomics, drawing on its work on a gas-cooled

modular reactor being developed in Russia under a joint U.S.-Russian

Federation agreement, is considering commercializing

for the U.S. market a version that would substitute a low-enriched

uranium (LEU) core for the plutonium core.

The preliminary design for the gas turbine-modular helium

reactor (GT-MHR), which is jointly sponsored by the U.S.

DOE and the Russian Ministry of Atomic Energy and supported

by Japan and France, is expected to be completed early

next year, with startup of a prototype at Tomsk, Russia by

2009 (NW, 4 May ’00, 12). A four-module plant is scheduled

for completion in 2015.

General Atomics (GA) officials believe the schedule in

the U.S. could closely follow that timeframe, and the first

commercial GT-MHR module could be ready for service in

the U.S. a year later, by 2010. The company anticipates the

first module will take about four years to construct from

ground-breaking to startup but says construction time could

be shortened to three years for modules after that, with one

module coming on line every year through 2013.

A GA official said the commercial project, the GT-MHR,

would be jointly funded by GA and DOE. Four utilities have

agreed to sit on a Utility Advisory Board that will provide

"time and support" for the project, though not funding at this

point. The official declined to name the four utilities.

Laurence Parme, manager of safety and licensing in

GA’s power reactor division, told an NRC Advisory Committee

on Reactor Safeguards (ACRS) workshop on advanced

reactors June 4 that the GT-MHR is based on more than four

decades of work on high-temperature gas-cooled reactors (HTGRs).

There were several prototypes and demonstration plants

that used this technology, beginning with the Dragon plant in

the U.S. in the early 1960s, Parme said. HTGRs, like contemporary

LWRs, continued to be developed with scaled-up

cores through about 1980, after which the U.S. and the Federal

Republic of Germany turned their attention to smaller,

modular plants, he said. Philadelphia Electric Co. built a 40-MW HTGR, 

Peach Bottom-1, but it operated just seven years,

1967-74. The only other commercial HTGR in the U.S., the

330-MW Fort St. Vrain, started up in 1976 but encountered a

series of technical problems, particularly with intrusion of

moisture from water-cooled bearings, and was shut in 1989.

The biggest German HTGR, the THTR-300, had repeated

problems with fuel sphere deformation and operated only

1984 to 1989.

GA continued to develop the HTGR option, working with

DOE. Under the DOE modular HTGR (MHTGR) program,

the company submitted a design in the mid-1980s that underwent

a preapplication review by NRC and the ACRS.

Parme suggested picking up on the project where it left

off from nearly two decades ago to get design certification in

the U.S. GA officials said no new R&D would be needed

since most of the development and test work will be conducted

in Russia as part of the international program.

As envisioned, each GT-MHR module would be about

285 megawatts electric (600 MW thermal). Parme said the

GT-MHR improves upon the earlier gas-cooled technology.

He said the steam cycle was "replaced by a closed-loop gas

turbine Brayton cycle," so the heated gas is used directly to

spin the turbine. The modular reactor design "represents a

180-degree turnaround in design philosophy," he said. The

reactor has inherent features that "ensure that regardless of

cooling system operation or coolant boundary integrity, fuel

temperatures will never exceed the point at which fission

products would be released," Parme said.

He said the passive design features ensure fuel remains

below 1,600 degrees C. The reactor system is designed with

the reactor and shutdown cooling system in one vessel, the

gas turbine-based power conversion system in an adjacent

vessel, and the coaxial ducting of gas between the reactor and

power conversion system in a third, horizontal vessel. "The

entire nuclear unit is located in a below-grade [concrete] silo

with service areas above," Parme said. "The silo provides

containment and protection of the reactor but is not designed

to hold pressure. Naturally circulating air in panels around the

reactor vessel carry off heat radiated from the uninsulated

vessel and provide reactor cavity cooling."

GA says the ceramic-coated spherical fuel is the "key" to

both the reactor’s safety and economics. A kernel of uranium

oxycarbide is coated by a porous carbon buffer, then wrapped

in several layers of silicon carbide and pyrolytic carbon. The

coated fuel particles are then placed in fuel rods and loaded

into holes in graphite fuel elements.

Parme said the coated particles keep the fission products

from being released. He said the "worst case fuel temperature

(is) limited by design features" such as low-power density, the

low thermal rating per module, passive heat removal, and its

annular core. He said the core would shut down without rod

motion and would not melt.—Jenny Weil, Washington

 

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