Search Options | ||||
Index | Site Map | FAQ | Facility Info | Reading Rm | New | Help | Glossary | Contact Us |
October 17, 2001 The Honorable Richard A. Meserve
Dear Chairman Meserve: During the 486th meeting of the Advisory Committee on Reactor Safeguards, October 4-6, 2001, we met with representatives of the NRC staff and the Nuclear Management Company to review the license amendment request for an increase in core thermal power for the Duane Arnold Energy Center (DAEC), pursuant to the General Electric Nuclear Energy Extended Power Uprate Program. Our subcommittee on Thermal-Hydraulic Phenomena also reviewed this matter during meetings held on June 12 and September 26-27, 2001. During our review, we had the benefit of the documents referenced. CONCLUSIONS AND RECOMMENDATION
DISCUSSION The Nuclear Management Company has requested an amendment to the DAEC operating license for a 15.3% increase over the plant's current operating power limit. Previously, the staff had approved a smaller power uprate. Consequently, the current application is for a power uprate of 20% over the originally licensed power. This is the largest power uprate ever considered for boiling water reactors (BWRs) in the United States. It is anticipated that many other licensees will request similarly large increases in the operating powers of BWRs. Consequently, we anticipate that staff review of the DAEC power uprate will be a template for future reviews and will set the expectations for many future power uprate applications. A generic methodology for evaluating and justifying power uprates of up to 20% for BWRs has been developed by General Electric. This generic methodology has been approved by the staff. The DAEC application has adopted this methodology and, in fact, the NRC staff has used the methodology to guide its review of this power uprate application. The power increase at DAEC will be achieved by increasing steam production, while holding liquid flow in the core, dome pressure and temperatures quite near current values. The increased steam production is achieved by "flattening" the core power profile, which involves increasing power generation in the outer regions of the core. There is an increase in feedwater flow to match the increased production of steam. Balance-of-plant modifications are required and will cause the DAEC power increase to be performed in two steps. Many technical issues must be addressed in an application for power uprate. Of these, we consider five to be especially significant:
Our examinations of the staff's SER and Requests for Additional Information submitted by the staff to the applicant persuaded us that the staff had raised numerous, pertinent issues concerning the conformance of the power uprate to approved methodologies. Though we persuaded ourselves eventually that the DAEC power uprate could be accomplished safely, we found it difficult to obtain information on the technical resolution of the issues either in the staff's SER or in our meetings with the staff. An exception to this common difficulty was the resolution of issues concerning containment response to design-basis accident events. In this case, the staff provided us a report on comparisons of applicant analyses with analyses done using an independent computational tool. We found it far more difficult to assure ourselves that the DAEC core is susceptible only to global power oscillations and does not need to consider local power oscillations. It was similarly difficult to assure that ATWS recovery methods were applicable to cores with flattened power profiles, that critical human actions had been identified with adequate independence by the staff, and that material degradation sensitivities had been adequately assessed. Many of the challenges that we encountered in our review of the DAEC power uprate application could have been eased if the staff had improved guidance on the detail to be provided in SERs and developed criteria for when independent assessments should complement reviews of applicant submittals. ACRS Members Mario Bonaca and F. Peter Ford did not participate in the Committee's review of this matter.
References
|