[Federal Register Volume 59, Number 158 (Wednesday, August 17, 1994)] [Unknown Section] [Page 0] From the Federal Register Online via the Government Publishing Office [www.gpo.gov] [FR Doc No: 94-20135] [[Page Unknown]] [Federal Register: August 17, 1994] VOL. 59, NO. 158 Wednesday, August 17, 1994 NUCLEAR REGULATORY COMMISSION 10 CFR Part 50 [Docket No. PRM 50-53] Ohio Citizens for Responsible Energy, Inc., et al.; Denial of Petition for Rulemaking AGENCY: Nuclear Regulatory Commission. ACTION: Denial of petition for rulemaking. ----------------------------------------------------------------------- SUMMARY: The Nuclear Regulatory Commission (NRC) is denying a petition for rulemaking (PRM-50-53) from Ms. Susan L. Hiatt on behalf of the Ohio Citizens for Responsible Energy, Inc. (OCRE). The petition requested reopening of the rulemaking procedure that led to promulgation of 10 CFR 50.62, the ``Anticipated Transient Without Scram'' (ATWS) rule. The principal basis for the OCRE request was the possibility that the ATWS analyses that formed the underlying bases of the ATWS rule were invalid because they did not appropriately account for the effects of large power oscillations, such as those that occurred during the March 9, 1988, instability event at the LaSalle County Nuclear Station (Unit 2). The petition is being denied because the Commission has concluded, based on core stability analyses during hypothetical ATWS events, and based on recommended procedure changes at nuclear power plants, that large-amplitude power oscillations will not impact the core and containment response sufficiently to invalidate the assumptions and results of previous ATWS analyses that were the bases for the ATWS rule. The NRC has carefully considered the issues raised in the petition and has taken them into account in reaching its decision to deny the petition. ADDRESSES: Copies of the petition for rulemaking and the NRC's letter to the petitioner, including attachments (SECY-94-123), are available for public inspection or copying in the NRC Public Document Room, 2120 L Street, NW. (Lower Level), Washington, DC. FOR FURTHER INFORMATION CONTACT: Roy Woods, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, Washington, DC 20555, telephone (301) 415-6622. The Petition By letter dated July 22, 1988, Ms. Susan L. Hiatt, a representative of the Ohio Citizens for Responsible Energy, Inc., requested that the Director, Office of Nuclear Reactor Regulation (NRR), take immediate action with respect to boiling water reactors (BWRs) to relieve what she alleged to be undue risks to the public health and safety posed by the thermal-hydraulic instability of BWRs as revealed by an event at LaSalle County Station, Unit 2, on March 9, 1988. The petitioner requested that the NRC conduct a rulemaking procedure under 10 CFR 2.802 to address: 1. The possibility that the analyses used during the proceedings that promulgated 10 CFR 50.62 (the ``ATWS'' rule) were invalid because they did not appropriately account for the effect of large power oscillations (those analyses were the underlying basis for the design requirements established in 10 CFR 50.62 to reduce the risk from ATWS events); and 2. The appropriateness of the 10 CFR 50.62 requirement for automatic tripping of the recirculation pumps in response to designated ATWS signals. In light of the potential consequences of large power oscillations, since tripping the recirculation pumps moves reactor operation into a state with high power-to-flow ratio where oscillations are likely, the petitioner requested that the pump-tripping requirement be reconsidered. Staff Action on the Petition The staff has been reviewing generic concerns regarding the large power oscillations that were observed during the March 9, 1988, instability event at the LaSalle County Nuclear Station, Unit 2, since the event's occurrence. That part of the effort that has focused on developing a response to the OCRE petition has concentrated on developing an improved understanding of BWR stability phenomena. These staff [and associated Boiling Water Reactor Owner's Group (BWROG)] efforts have included analytical studies of ATWS scenarios, stability sensitivity studies, and the validation and verification of the analytical models and codes used for these studies. The primary objective was to determine if large-amplitude oscillations might impact the core and containment response sufficiently to invalidate the assumptions and results of previous ATWS analyses that were the bases for the ATWS rule. With respect to OCRE's contention that the automatic tripping of the recirculation pumps in response to designated ATWS signals, as required by the ATWS rule, is inappropriate in light of the potential consequences of large power oscillations, the staff reviewed the advantages (related to decreased heat load on the containment) and disadvantages (related to exacerbation of power oscillations) of the requirement that the recirculation pumps be tripped. Reasons for Denial The attachments to the NRC's letter to the petitioner (SECY-94-123) includes a detailed presentation of the bases for the denial of the petition. In summary, a substantial effort was necessary to develop computer codes to simulate the oscillation behavior of the modeled reactors and to validate and verify these codes to ensure that they give accurate predictions. On the basis of its review of TRACG code's qualifications for performing power oscillation analyses, the staff concluded that TRACG can serve as an adequate tool to estimate qualitatively the global behavior of operating reactors during transients that may result in large power oscillations. Although large power oscillations may increase the overheating and severity of fuel damage resulting from an ATWS event, the analyses indicate that core coolability and containment integrity can be acceptably maintained. Therefore, the staff concluded that the ATWS analyses that formed the bases of the ATWS rule remain valid. The staff's review of the advantages and disadvantages of the requirement that the recirculation pumps be tripped indicated that recirculation pump trip was appropriate and necessary to reduce heat load to the containment following an ATWS, and that the potentially adverse impact due to large power oscillations could be mitigated by revisions to the Emergency Procedure Guidelines (EPGs) that were recommended by the BWROG. Revisions to the EPGs are: prompt cessation of feedwater flow until water level is reduced to about one meter below the feedwater sparger, thus reducing core inlet subcooling which dampens power oscillations; and earlier injection of boron in the presence of power oscillations, thus reducing power level, which reduces the adverse consequences of any remaining power oscillations. The staff concluded that these revisions are sufficient for mitigating the consequences of a bounding ATWS event with large oscillations. On the bases of the above analyses and recommended procedure changes, the staff concludes that, although large power oscillations may increase the overheating and severity of fuel damage resulting from an ATWS event, core coolability and containment integrity can be acceptably maintained in a manner consistent with the assumptions and results of previous ATWS analyses that were the bases for the ATWS rule, and that, therefore, the requirements of the ATWS rule remain appropriate. Because each of the issues raised in the petition has been substantively resolved, the NRC has denied this petition. Dated at Rockville, Maryland, this 11th day of August 1994. For the Nuclear Regulatory Commission. John C. Hoyle, Acting Secretary. [FR Doc. 94-20135 Filed 8-16-94; 8:45 am] BILLING CODE 7590-01-P
