Information Notice 2013-03, Recent Issue with the Definition of Core Quadrant
| ML12272A003 | |
| Person / Time | |
|---|---|
| Issue date: | 03/05/2013 |
| From: | Laura Dudes, Kokajko L Division of Construction Inspection and Operational Programs, Division of Policy and Rulemaking |
| To: | |
| Panicker M | |
| References | |
| IN-13-003 | |
| Download: ML12272A003 (5) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
OFFICE OF NEW REACTORS
WASHINGTON, DC 20555-0001 March 5, 2013 NRC INFORMATION NOTICE 2013-03: RECENT ISSUE WITH THE DEFINITION OF
CORE QUADRANT
ADDRESSEES
All holders of an operating license or construction permit for a nuclear power reactor under
Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of
Production and Utilization Facilities, except those who have permanently ceased operations
and have certified that fuel has been permanently removed from the reactor vessel.
All holders of or applicants for an early site permit, standard design certification, standard
design approval, manufacturing license, or combined license under 10 CFR Part 52, Licenses, Certifications, and Approvals for Nuclear Power Plants.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees of a recent issue regarding the definition of core quadrants as it applies to source
range monitors (SRMs) in the context of fuel movement and core alterations. The NRC expects
recipients to review the information within this IN for applicability to their facilities and consider
actions, as appropriate. However, suggestions contained in this IN are not NRC requirements;
therefore, no specific action or written response is required.
BACKGROUND
SRMs monitor the neutron level at very low flux levels in the core during refueling and startup.
As such, the SRM indication is used to monitor the approach to criticality and to determine when
criticality is achieved. The SRMs are maintained fully inserted until the count rate is greater
than a minimum allowed count rate (a control rod block is set at this condition). After
SRM-to-intermediate range monitor overlap is demonstrated during startup, the SRMs are
normally fully withdrawn from the core. During refueling operations, SRM operability is
important to monitoring the state of the core. Revision 4.0 of Standard Technical Specifications
(STS) Bases state, The SRMs provide monitoring of reactivity changes during fuel and control
rod movement and give control room operators early indication of unexpected subcritical
multiplication that could be indicative of an approach to criticality.
DESCRIPTION OF CIRCUMSTANCES
During an NRC inspection at the James A. FitzPatrick Nuclear Power Plant (FitzPatrick) located
in Scriba, New York, NRC inspectors reviewed the control and monitoring of core alterations
during refueling activities. The FitzPatrick plant is a boiling-water reactor design facility. The
reactor core contains four installed SRMs to monitor reactivity changes during fuel or control rod
movement. During the refueling operations, the NRC inspectors observed that one of the four
installed SRMs was inoperable. When the inspectors inquired with the FitzPatrick staff on how
ML12272A003 the fuel movement was being controlled such that no movements would be performed in the
core quadrant that contained the inoperable SRM, the plant staff responded that, in accordance
with their plant procedure, refueling operations could proceed in any of the core locations with
any single SRM out of service based on a definition of core quadrant that was developed and
adopted by the plant staff in 2004. The inspectors reviewed the issue of SRM operability
requirements during refueling operations to determine whether the FitzPatrick definition of a
core quadrant, was consistent with the plants technical specification (TS) requirements.
The FitzPatrick reactor core consists of 560 fuel assemblies arranged symmetrically in an
octagonal configuration. Due to this symmetry, the core can be divided into four equal
quadrants, using two perpendicular axes (000o-180° and 090°-270°) that cross at the geometric
center of the core. The reactor core also contains four installed SRMs, with one in each of the
quadrants, as described above. This definition of core quadrant is consistent with that
described in the Task Interface Agreement (TIA) 2012-01, James A. Fitzpatrick Nuclear Power
Plant Definition of Core Quadrant, dated November 8, 2012 (Agencywide Documents Access
and Management System (ADAMS) Accession No. ML12290A287). The NRC staff believes
this definition ensures quadrants are symmetric and that installed SRMs will be capable of
effectively monitor reactivity changes throughout the core.
During core alterations (movement of fuel or control rods within the reactor vessel), FitzPatricks
TS surveillance requirement 3.3.1.2.2 requires that an operable SRM be located in the core
quadrant where core alterations are being performed and that a second operable SRM be
located in an adjacent core quadrant. FitzPatricks TS bases state that the two required SRMs
provide redundant monitoring of reactivity changes during fuel or control rod movement and give
the control room operators early indication of unexpected subcritical multiplication that could be
indicative of an approach to criticality. The TS bases indicate that while the SRMs have no
safety function and are not assumed to function during any design basis accident or transient
analysis, these instruments provide on-scale monitoring of neutron flux levels during refueling
and startup. The FitzPatricks TS bases also require one operable SRM in the quadrant where
core alterations are being performed and one operable SRM in an adjacent quadrant, which
addresses the local nature of reactivity changes and ensures that core reactivity will be
continuously monitored during alterations. However, the TS currently do not define the term
core quadrant.
The inspectors identified that core quadrant, as defined in FitzPatricks plant procedures, is
based on the axes of the SRM locations rather than the geometric center of the core. This
orientation resulted in quadrant axes that are rotated approximately 16° clockwise from the
arrangement that was described above, and it resulted in quadrant boundaries that bisect
individual fuel assemblies. FitzPatricks personnel determined that such fuel assemblies could
be considered to reside in either of the adjacent quadrants. The inspectors reviewed specific
documents referenced by the plant personnel as support for its definition of core quadrant, and
determined that there did not appear to be any analytical support for the plants definition of core
quadrant as implemented in procedure changes. Additional information is available in TIA
2012-01.
DISCUSSION
Because there was no specific definition of core quadrant found in FitzPatricks TS, technical
requirements manual (TRM), or final safety analysis report, the plant personnel developed and
incorporated into the plant procedures, its own primary and alternate core quadrant definitions, which are designed to minimize the impact of an inoperable SRM on refueling operations.
The two core quadrant definitions, as defined in the plant procedures, are (1) the quadrant
boundaries are rotated around the geometric center of the SRMs 16° clockwise from the
north-south and east-west axes and (2) the alternate definition consists of quadrant boundaries
rotated 70° counterclockwise from the major axis. FitzPatricks licensee claims that these
rotations leave the SRM within the redefined quadrant and that application of these two
definitions simultaneously allows the refueling operations to proceed in any core location with
any single SRM inoperable.
The NRC staff conducted a detailed evaluation of the licensees definition of the core quadrant
issue based on technical, regulatory, and safety criteria using available documents at the NRC
that were obtained from the licensee. The NRC staff, upon evaluating this information, concluded that the SRM quadrant rotation results in asymmetric quadrants with unequal areas.
Due to the asymmetry in quadrants, the NRC staff found that the SRMs ability to monitor
reactivity changes during core alterations will be adversely affected.
In the case described in this IN, the licensee has interpreted the definition of TS core quadrants
without considering seeking a license amendment or obtaining clarification from the NRC to
define the core quadrant. The licensee indicated that the definition of quadrant, in absence of
any specific guidance, is based on engineering judgment. The NRC staff maintains that neither
the plants TS nor its design documents provide authority to the licensee to define the core
quadrants, in a situation(s) when one or more SRMs is found to be inoperable, without
performing a supporting neutronics calculation.
The NRC staff, on evaluation of the licensee documentation supporting the core quadrant
redefinition, concluded that the licensees definition will result in asymmetric core quadrants with
an adverse effect on the SRMs ability to monitor reactivity changes. Furthermore, when the
quadrant axes are rotated, the distance between the SRM and the location of possible core
alterations within the quadrant would be increased, further reducing the SRMs ability to detect
reactivity changes and monitor for unexpected subcritical multiplication during refueling. The
NRC staff also determined that no neutronics calculations were performed by the licensee to
support the licensees position that when one core SRM is found to be inoperable, the functional
SRMs will remain coupled to the area of the core where alterations are being performed and will
be capable of detecting increases in subcritical multiplication.
The NRC staff review of the Licensees 10 CFR 50.59 Screening
As discussed in TIA 2012-01, the NRC staff reviewed the licensees 10 CFR 50.59 screen
control form establishing the licensees definition of core quadrant for FitzPatrick. The NRC
staff identified that the licensee answered the 10 CFR 50.59 screening question: Does the
proposed activity invalidate, render incorrect or otherwise require a change to an existing
Technical Specification or the Facility Operating License? with a NO for TS change and
proceeded to perform the core quadrant rotation during the refueling mode. For questions, Does the proposed activity: (1) Invalidate or render incorrect an existing Technical Specification Bases?, (2) Require a change to Technical Specification Bases?, (3) Affect the
TRM or program described in TRM? the licensee also answered NO. As stated in the TIA,
the NRC staff noted that, (a) the Entergy definition of core quadrant represents a change to the
plant TS that requires prior review and approval by the NRC staff as specified in 10 CFR 50.59 before it could be implemented and is therefore not acceptable, and (b) implementing the
Entergy definition of core quadrant does not satisfy TS 3.3.1.2 SRM operability requirements
during core alterations.
The NRC staff determined that by answering NO to the 10 CFR 50.59 screening questions
described above, the licensee proceeded to define the core quadrants, thereby implementing a
new interpretation of TS, without also performing a supporting neutronics calculation.
Therefore, the NRC staff concluded that the licensees use of the 10 CFR 50.59 process
resulted in the licensee implementing a new definition for the TS plain language meaning of the
term core quadrant. Additional information on the licensees subject 10 CFR 50.59 screening
is available in TIA 2012-01.
CONCLUSION
As documented in TIA 2012-01, the NRC staff found that the licensees definition of core
quadrant that places SRMs near the quadrant edge will increase the distance between the SRM
and reactivity changes due to refueling activities within the quadrant. This distance increase is
compounded by the portion of the definition wherein the center of the quadrant axes is not the
geometric center of the core, resulting in asymmetric quadrants with unequal areas. In the
absence of supporting neutronics calculations, the NRC staff concluded that the asymmetric
definition of quadrants will adversely affect the ability of the SRMs to monitor reactivity changes
in the core. Moreover, the NRC staff concluded in TIA 2012-01 that the licensees definition of
core quadrant is not acceptable, and that implementing the licensees definition of core
quadrant does not comply with the TS 3.3.1.2 SRM operability requirements during core
alterations.
CONTACT
S
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contacts listed below or to the appropriate NRC project manager.
/RA/ /RA/
Lawrence E. Kokajko, Director Laura A. Dudes, Director
Division of Policy and Rulemaking Division of Construction Inspection
Office of Nuclear Reactor Regulation and Operational Programs
Office of New Reactors
Technical Contacts: Reed Anzalone, NRR
(301) 415-5627 E-mail: reed.anzalone@nrc.gov
(301) 415-2987 E-mail: mathew.panicker@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Library.
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