[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.

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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]
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