ML20196K620

Informs That During 460th Meeting ACRS on 990310-13, Committee Reviewed Status of NRC Confirmatory Research Program on High Burnup Fuel

ML20196K620
Person / Time
Issue date:	03/24/1999
From:	Powers D Advisory Committee on Reactor Safeguards
To:	Travers W NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO)
References
ACRS-R-1813, NUDOCS 9904020224
Download: ML20196K620 (3)

Text

9 / o UNITED STATES ACRSR-1813

,' 8 g U t NUCLEAR REGULATORY COMMISSION PDR ADVISORY COMMITTEE ON REACTOR SAFEZUARDS WASHINGTON, D. C. 20655

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March 24,1999 l

l Dr. William D. Travers Executive Director for Operations U.S. Nuclear Regulatory Commission WasbMa'on, D.C. 20555-0001

SUBJECT:

HIGH BURNUP FUEL PHENOMENA IDENTIFICATION AND RANKING During the 460* meeting of the Advisory Committee on Reactor Safeguards, March 10-13, '

1999, we reviewed the status of the NRC confirmatory research program on high bumup fuel.

During this review, we had the benefit of discussions with representatives of the Offices of Nuclear Regulatory Research (RES) and Nuclear Reactor Regulation (NRR), the industry, and of the documents referenced.

CONCLUSIONS AND RECOMMENDATIONS Conducting an expert opinion elicitation to identify and rank important phenomena that affect high bumup fuel will provide a sound technical basis for refining the NRC's confirmatory research program. It would provide a technical basis for establishing the data and analyses needed to support applications for extending fuel bumup beyond current regulatory limits.

e We urge NRR to participate in the proposed elicitation.

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RES should develop the formalism for conducting and documenting the expert opinion elicitation. Consideration should be given to adapting for the high bumup fuel effort one [

of the several expert elicitation formalisms developed by NRC in other efforts. '

RES should augment the expert opinion elicitation to include accident source term issues for high bumup fuels.

DISCUSSION in our report dated June 15,1998, we discussed the NRC research to confirm the regulatory decision to limit the extent of fuel bumup. In that report, we suggested that the staff develop an understanding of what data and analyses would be required oflicensees to support applications for extending fuel burnup beyond the current limit of 62 GWd/t. Development of such an 9904020224 990324 PDR ACRS 1 R-1813 PDR 1 / f1 - Q

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2 l understanding is a challenge since data on high bumup fuel behavior under accident conditions are sparse and scattered.

The RES staff will undertake an expert opinion elicitation to identify the physical and chemical phenomena that will affect fuel behavior, establish the state-of-knowledge concoming these phenomena, and rank them in terms of their importance to safety. The phenomena identification and ranking elicitation is to be done for accident scenarios found by RES to be risk important.

These are loss-of-coolant accidents for both pressurized water reactorr (PWRs) and boiling water reactors (BWRs). control rod ejection accidents for PWRs, and anticipated transients without scram (ATWS) for BWRs. RES plans to use this expert opinion elicitation to refine its own confirmatory research program, and is in the process of identifying and soliciting the participation of industry experts so that the phenomena identification and ranking can be extended to fuel bumup beyond current regulatory limits.

We are enthusiastic about the use of a disciplined, scrutable expert opinion elicitation to plan and refine the NRC research. We believe the elicitation to be an essential addition to the planning for extended fuel bumup being done by the Nuclear Energy Institute (NEI) and NRR staff. We encourage that both NEl and NRR participate in the effort being undertaken by RES.

Much remains to be done to complete the planni.1g for the phenomena identification and ranking. RES will need to develop the formalism for conducting and documenting the expert opinion elicitation. RES can adapt one of several formalisms developed by the NRC in other efforts.

RES should expand the original scope of its phenome.1a identification and ranking elicitation to include the issues of accident source term. The revised accident source term (NUREG-1465) approved by the Commission was developed from analyses of fuel taken to bumups that are moderate in comparison to bumups being achieved in current plants. We are concemed that the accident source term will have to be modified to account for the effects of extended fuel bumup. Chemical forms and volatilities of radionuclides may be affected by bumup because of higher oxygen potentiale in the fuel and the fuel-cladding gap. Releases of radionuclides from the fuel may be increased because of higher concentrations of interstitial oxygen, more extensive connection of . 3 yannular porosity, and smaller grain sizes in the so-called

• rim" regior RES has not established a 1ochnically defensible position on modifications of the accident source term to account for(uel bumup. Adequate data have not been marshaled. Analytical tools used to date do not 7.ppear to include adequate descriptions of pertinent phenomena and processes. Superior anraytical tools may be available in the U.S. and in other countries.

Additional data may be available from research done abroad. RES will gain substantial benefit for developing a position on modifying the ucident source term by including elicitation of expert opinion on the effects of bumup on radionuclide behavior in fuel.

In October 1998, we met with representatives of France, Germany, and Japan to discuss technicalissues of mutualinterest and as a result formed a Quadripartite Working Group on High Bumup Fuel. We believe this group could contribute to the planned expert opinion elicitation for phenomena identification and ranking.

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Dr. William J. Shack did not participate in the Committee's deliberations regarding this matter.

Sincerely, X

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Dana A. Powers

. Chairman

References:

1. Report dated June 15,1998, from R. L Seale, Chairman, ACRS, to Shiriey Ann Jackson..

Chairman, NRC,

Subject:

NRC Reactor Fuels Research Program.

2. U. S. Nue!aar Regulatory Commission, NUREG-1465, " Accident Source Term for Light- .

l Water Nucl ear Power Plant,' February 1995.

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