[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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