Images de page
[ocr errors]

production, as were carlier liquid metal fast breeder: reactors. GE's reactor would not breed, and Rockwell's literature makes only a passing reference to a "brecding ratio slightly greater than unity to makc up for fuel cycle losses." Both reactors rely on the inherent safety features of liquid sodium as a coolant and use natural convection for decay heat removal.

GE's Power Reactor Inherently Safe Module (PRISM) would be a 1,395-MW (ncl) pool-type reactor plant consisting of threc, 465-MW power blocks. Each block would consist of three 155-MW modules, which include a nuclear steam supply system and a turbine, so largets could be changed in one module while the rest operated, providing the production flexibility so attractive in the MHTGR.

The reference commercial fuel is Argonne National Laboratory's (ANL) melallic suel, although oxide fuel could also be used. Like the MHTOR, the reactor would

be housed in an underground silo, and the reactor module would be factory-fabricated and shipped to the sile in one piece.

Rockwell's Sodium Advanced Fast Reactor (SAFR) would be a 1,800-MW pool-typo plant consisting of four, 450-MW modules. SAFR also would use metallic fuel, but could use oxide fuel as well. The reactor would be housed above grade, fabricated in a factory, and shipped 10 the site in one piece.

“DOE is our customer, and our customer requested that we make the presentation," said Robert Bergland, GE's manager of advanced nuclear technology. “But we're not interested."

“Both SAFR and PRISM are being proposed and advocated as super-sase advanced systems for electric power generation," said Richard Oldenkamp, director of power plant projects for Rockwell's Atomics International Rocketdync Division. DOE might want to use a LMR design

[ocr errors]



JULY 1988



This is an assessment of how the consideration of safety assurance should factor into the choice of technology for the New Production Reactor (NPR). It was prepared by two individuals experienced in the safety analysis and licensing of nuclear power plants, namely James F. Meyer and Roger J. Mattson. Their credentials are summarized in Appendix A.

The purpose in obtaining the regulatory perspective provided in this report is to put greater emphasis than has been given to date on an important factor in the choice of NPR technology, namely, the demonstration that the technology is safe enough. The Department of Energy has articulated its commitment to safety in stating that the new production reactor will provide a level of safety that is at least equivalent to that of the best of current commercial power plants. But there is more to the safety issue than just this overriding objective. That is, in implementing its safety commitment, DOE will find that the demonstration of safety is highly important because it can introduce controversy into the NPR program, potentially adding significantly to its costs and, more importantly, delaying the startup of the facility.

To illustrate how significant the safety controversy can be for the deployment of nuclear plants, it is useful to recall the effect of safety deliberations on the light water power reactors in the United States. Changes in safety regulation that were intended to increase the level of safety and the assurances of safety have been responsible for most of the cost escalation and delay of the light water nuclear power plants built in the U.S. since the accident at Three Mile Island. The delays have amounted to several years on most recent nuclear power plants. Such delays may be critical to the purpose underlying the choice of technology for and construction of the new production reactor--the critical need for goal quantities of tritium.

If this record of cost escalation and delay has occurred for a well established technology, and if the safety requirements for the commercial plants are to be copied for the NPR, which they most surely will be, then it is critical that those making the decisions about the choice of technology for the NPR give careful consideration to the technical basis that is or will become available to demonstrate the safety of that technology. This paper is an initial attempt to compare the present and future capabilities for the alternative technologies to demonstrate adequate safety


Summary of the Report

In the report that follows, five questions are addressed as follows.

1. What is adequate safety assurance for the new production reactor,

and how does that compare with licensed nuclear facilities?
2. What are the process options available to DOE to provide adequate

salety assurances for the NPR?

3. What is the expected safety assurance process, and what are the

desirable NPR technology attributes?

4. What has been the history of safety assurances for severe accidents?

5. What are the possible solutions to any problems expected in

providing adequate safety assurances for the NPR?

The principal conclusions of the report are as follows. When the alternative technologies available for the new production reactor are viewed from the perspective of these questions and from the perspective of providing the highest probability of demonstrating adequate safety in a timely and broadly acceptable fashion, certain conclusions can be drawn. The Heavy Water Reactor presents the highest risk because of the lack of regulatory background and the uncertainties surrounding severe accidents. The High Temperature Gas Cooled Reactor has significant advantages over the Light Water Reactor, the Liquid Metal Reactor, and the Heavy Water Reactor. It has a better technical basis for responding to determined intervention, it has a proven track record in the NRC licensing process, and it has lower severe accident risk.

Stepping back from the perspective of safety assurance of the NPR per se and considering some broader issues that affect safety of nuclear power in general in the United States, several further points are appropriate, all of which further support choosing the HTGR technology for the NPR.

[ocr errors]

The federal budget for nuclear technology, apart from the production
of nuclear defense materials, has been relatively constant for several
years, and all safety research has come out of that budget, whether it
is for commercial power or for DOE and military applications. If the
decision is made to go with the HWR, it will require large safety
expenditures for a technology unique to the NPR, thus diverting
needed funds from other important safety research programs. It could
detract from reactor safety research applicable to the commercial

[ocr errors]

Both the commercial and the military applications sectors could
benefit considerably from a shared safety technology. Safety
information developed for the commercial reactors could be of use by
the NPR and vice versa. The advantages of sharing safety
technology cannot be over estimated. This could not happen if the
HWR was chosen as the NPR.

It has been said that choosing a technology other than the HWR
would compromise the distinction between nuclear reactors for
weapons production and nuclear reactors for power production. This
argument may have some merit for one of the LWR candidates for the
NPR because that candidate is a pressurized water reactor that was
initially designed and built for commercial applications. However, it is
worth noting that the pressurized water reactor technology now used
around the world evolved from the U.S. Navy's nuclear propulsion

Finally, DOE, through its NPR program could make a significant
contribution to the future energy security of the United States by
choosing a reactor type that has potential to meet future energy needs
in a safe and environmentally acceptable way. In this way, the
Department also will serve to limit the number of nuclear reactor
designs in the United States. This is a problem of safety significance
that has plagued the country for a generation and that the Energy
Research Advisory Board has urged the Department to solve.

The bases for coming to the conclusion that the HTGR is the preferred technology when viewed from the safety assurance perspective are as follows:

There is a new era for demonstrating safety of nuclear plants in the United States and throughout the world. The four key elements of this

new era are:

A complex and exhaustive safety assurance process is embodied in the policy and practice of the U.S. Nuclear Regulatory Commission (NRC). Since the accident at Three Mile Island in 1979 and subsequent construction problems at several U. S. plants, there are new expectations of the level of safety to be achieved and of the degree of safety assurance to be provided for nuclear power plants. These increased expectations of safety have spread around the world, especially in the aftermath of the accident at Chernobyl in the Soviet Union in 1986. There is no presently acceptable alternative to the type of safety assurance process that has been set in place for commercial nuclear power plants. It is our view that DOE has no choice but to conform to the essential features of this process.

The public and Congress will have a major voice in the determination that the NPR is sate before it is built or operated. DOE facilities of this size and visibility are no longer insulated from public and congressional safety perceptions and scrutiny. Substantive response to Congressional and public concern for safety will be important to timely construction of the NPR.

Issues associated with severe accidents are more important now than they have been in the past. Protection of public health and safety requires that the probability and consequences of severe accidents be controlled. The public must also be assured, especially after the accidents at TMI and Chernobyl, that the severe accident risks are adequately addressed. In this regard, experience has shown that the actual risk of a new facility may not be as crucial to the acceptance of the facility as the uncertainties and unknowns regarding that risk. This is because a known risk can be properly factored into the design and siting decisions. It is much more difficult to reach consensus decisions when major uncertainties cloud the risk picture. In order to minimize schedule risks, and thereby national security risks, DOE must assure that severe accident issues are addressed clearly and in a forthright manner and that the technology chosen for the NPR minimizes these uncertainties.

Policy for new reactors world wide is emphasizing simplicity and inherent safety. The present light water reactors are too complicated and too dependent on active safety systems to be accepted in large numbers in the future. Virtually every advanced reactor design is striving for simplicity and safety that is not as dependent on operators or machinery as current designs. The choice of technology for the NPR should accommodate this new policy.

The choice of NPR technology from the available alternatives must address the four key elements comprising the new expectations in safety assurance. In addition, the potential for conflicts and delays associated with providing safety assurance can be reduced by selecting a technology for the NPR that has been tested and found acceptable by use of current safety assurance methods. Such a technology provides a more certain foundation for future success in the NPR program than does a technology for which there

is only a commitment to conform to current safety criteria and
no experience to show what it will cost or how long it will take to
achieve consensus that the design is acceptable. Thus, the attributes
of a NPR that would reduce the potential for future conflicts and
delays are as follows:

Regarding the safety assurance process, the most important
attributes would be: (a) experience with the current licensing
methods and criteria, (b) accommodation of lessons learned from
the licensing process, and (c) a base of technical knowledge and
experience, outside of the vendor and DOE, with the physics and
engineering, and performance of the design.

Regarding the public and Congress, the key attribute would be incontrovertible evidence that safety assurance will be provided. This requisite demonstration of safety may have little to do with a reasonable technical proof of safety. Rather, the safety perceptions of a concerned public must also be addressed, and what will convince the concerned public is not so much the low probability of severe accidents as the demonstrably low consequences of a severe accident, should one occur.

Regarding severe accident risks, the most important attributes
would be: (a) the risks have been assessed by the best available
technology and peer reviewed, (b) the risks are small, (c) the
uncertainties regarding the most important accident sequences
are small, and (d) there is experience with controlling the
contributors to severe accident risks in the construction and
operation of the technology.

Regarding simplicity and inherent safety, the most important
attributes would be: (a) a relatively long time available to make
decisions in the event of a serious incident, (b) the lack of safety
dependency on ac power or on active mechanical and electrical
systems, (c) the availability of passive reactivity control under all
conceivable conditions, and (d) low power density.



This is an assessment of how the consideration of safety assurance should factor into the choice of reactor technology for the New Production Reactor (NPR). It was prepared by two individuals experienced in safety analysis and licensing of nuclear power plants, James F. Meyer and Roger J. Mattson. Their credentials are summarized in Appendix A.

The purpose of obtaining the regulatory perspective provided in this report is to put greater emphasis than has been given to date on an important factor in the choice of NPR technology, namely, the demonstration that the technology is safe enough. The report shows that the demonstration of safety will have an important bearing on the implementation of the new production reactor. The report also establishes that there are differences among the alternative technologies in terms of uncertainties in demonstrating their safety. These uncertainties mean that there is varying potential among the alternative technologies for cost increases and schedule delays in bringing the NPR into operation. For this reason, the safety assurance questions deserve consideration in selecting the technology. The report is structured so as to answer five questions about the safety assurance process, as follows:

« PrécédentContinuer »