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Answer 4
(continued):

I reiterate my point that the HTGR is about ten years behind

the ALWR because of the need for an approximately ten-year

Tong HTGR demonstration project to precede NRC design

certification. Such a demonstration project is not required

for the ALWR.

COMMITTEE ON ENERGY AND NATURAL RESOURCES

Question 5

Following up on the discussion at the hearing on the
possibility of a meltdown of HTGR technology, could you
please explain the Department's views on this question?
Also, I have been told that, with the HTGR, there would be a
potential for release of radiation in the event that the
graphite moderator caught on fire. Could you please
elaborate on this risk? What would potentially cause the
graphite to catch on fire? Under those circumstances,
wouldn't it be appropriate to have a containment structure
over the reactor to prevent any release of radiation to the
accessible environment?

Answer:

Your concerns about meltdown, graphite fires, and a

containment structure have been considered for many years by

the gas-cooled reactor community including the Nuclear Regulatory Commission (NRC) and overseas high temperature gas-cooled reactor (HTGR) developers. First, it should be

said that meltdown is not an approp

ate description for the

HTGR concept, as HTGR fuel is fully ceramic and its failure,

which is at temperatures in excess of 1600 degrees C is

characterized by fission product diffusion through barriers

that maintain their geometry. The rearrangement of

fissionable material in the core or disruption of the core

itself does not occur. Of course, HTGR fuel failure

potentials and consequences are major concerns.

These are

being addressed in the modular high temperature gas reactor

(MHTGR) by the passive decay heat removal configuration, use

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Answer 5
(continued):

of high temperature fuel, and the control of pathways for fission product transport to the environs.

The graphite fire potential was evaluated by the NRC (with assistance from Brookhaven National Laboratory) during the Fort St. Vrain licensing process, following the Chernobyl accident and in the course of its preapplication review for the MHTGR. The NRC states that it believes that air availability pathways, including flow channels in the core, would not support a sustained or damaging graphite fire even if a containment structure was not provided. The NRC states

that confirmatory experiments might be desirable but has not

yet stated this as a requirement. The Department is renewing

interactions with the NRC and the subject of graphite fires will be included in these forthcoming discussions.

QUESTIONS FROM SENATOR WALLOP

ALMR

Question 6(a):

Would you agree that the long-term promise of nuclear energy is essentially unlimited through the development of advanced liquid metal reactor technologies?

Answer:

It was recognized early in the development of nuclear power

that if nuclear fission energy is to make a large
contribution to the world's energy supply for the long term,
that is, beyond a number of decades, a reactor type is needed

which can utilize essentially all the fissionable material

available in nature from uranium ore, as opposed to the

current light water, heavy water, and graphite moderated

reactor systems which utilize only about one percent of the
energy available in uranium. The advanced nuclear reactor
development work carried out worldwide over the past several
decades suggest that the liquid metal (sodium) cooled reactor
could be suitable for this purpose, and that once deployed,
it could supply much of the world's energy needs for

centuries.

QUESTIONS FROM SENATOR WALLOP

DOE Program

Question 6(b):

In your judgment should DOE's program be more aggressive in this regard?

Answer:

Within the available budgets, the DOE program is well focused on the highest priority needs for the development of advanced

liquid metal reactor technologies.

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