TSTF-514
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1.0 Description
NUREG-1433 Specification 3.4.6, "RCS Leakage Detection Instrumentation," and
NUREG-1434 Specification 3.4.7 of the same title require instrumentation to detect
significant reactor coolant pressure boundary (RCPB) degradation as soon after
occurrence as practical to minimize the potential for propagation to a gross failure. The
Improved Standard Technical Specifications (ISTS) for BWR/4 plants (NUREG-1433)
requires one drywell floor drain sump monitoring system, one channel of either primary
containment atmospheric particulate or atmospheric gaseous monitoring system, and
(optionally) a primary containment air cooler condensate flow rate monitoring system.
The BWR/6 ISTS (NUREG-1434) requires one drywell floor drain sump monitoring
system, one channel of either drywell atmospheric particulate or atmospheric gaseous
monitoring system, and (optionally) a drywell air cooler condensate flow rate monitoring
system.
Questions have been raised regarding the Operability requirements for these instruments.
In particular, improvements in plant fuel integrity have resulted in a reduction of the
Reactor Coolant System (RCS) activity. As a result, the atmospheric radioactivity
monitors may not be capable of promptly detecting an increase in RCS leakage.
The proposed change revises the Bases to clearly define the RCS leakage detection
instrumentation Operability requirements and to modify the Actions to be taken when the
atmospheric gaseous radioactivity monitor is the only Operable monitor to require
additional, more frequent monitoring of other indications of RCS leakage and to shorten
the time allowed to restore another monitor to Operable status.
2.0 Proposed Change
The "RCS Leakage Detection Instrumentation," specification (BWR/4 LCO 3.4.6 and
BWR/6 LCO 3.4.7) is revised to add a new Condition. New Condition D is applicable
when the atmospheric gaseous radioactivity monitor is the only Operable monitor (i.e., all
other monitors are inoperable). The Required Actions require analyzing grab samples of
the primary containment (BWR/4) or drywell (BWR/6) atmosphere and monitoring RCS
leakage using administrative means every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and restoring another monitor to
Operable status within 7 days. The subsequent Conditions are renumbered to reflect in
addition of the new Condition.
The Bases are revised to clearly define the RCS leakage detection instrumentation
Operability requirements in the LCO Bases and to eliminate discussion from the Bases
that could be erroneously construed as Operability requirements. The Bases are also
revised to reflect the changes to the Technical Specifications and to more accurately
reflect the existing Technical Specifications.
Also, the primary containment and drywell air cooler condensate flow rate monitor is
plant-specific, and therefore bracketed in the NUREG. The specifications and Bases are
revised to consistently bracket references to this monitor.
3.0 Background
General Design Criterion (GDC) 30 of Appendix A to 10 CFR 50 requires means for
detecting and, to the extent practical, identifying the location of the source of RCS
Leakage. Regulatory Guide (RG) 1.45, Revision 0, "Reactor Coolant Pressure Boundary
Leakage Detection Systems," May 1973, describes acceptable methods for selecting
leakage detection systems. Revision 1 of RG 1.45 was issued in May 2008. However,
operating nuclear power plants are not committed to Revision 1 of RG 1.45.
NRC Information Notice (IN) 2005-24, "Non-conservatism in Leakage Detection
Sensitivity," (ADAMS Accession No. ML051780073) pointed out that the reactor
coolant activity assumptions used for designing the containment radiation gaseous
radiation monitor may be greater than the RCS radioactivity level present during normal
operation. As a result, the containment gas channel may not be able to detect a 1 gpm
leak within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> at the current RCS radioactivity level.
RG 1.45, Rev. 0, Regulatory Position C.2 states that "Leakage to the primary reactor
containment from unidentified sources should be collected and the flow rate monitored
with an accuracy of one gallon per minute (gpm) or better." Regulatory Position C.3
states, "At least three separate detection methods should be employed and two of these
methods should be (1) sump level and flow monitoring and (2) airborne particulate
radioactivity monitoring. The third method may be selected from the following: a.
monitoring of condensate flow rate from air coolers, b. monitoring of airborne gaseous
radioactivity. Humidity, temperature, or pressure monitoring of the containment
atmosphere should be considered as alarms or indirect indication of leakage to the
containment." Regulatory Position C.5 states, "The sensitivity and response time of each
leakage detection system in regulatory position [C.]3. above employed for unidentified
leakage should be adequate to detect a leakage rate, or its equivalent, of one gpm in less
than one hour." RG 1.45, Rev. 0, states, "In analyzing the sensitivity of leak detection
systems using airborne particulate or gaseous radioactivity, a realistic primary coolant
radioactivity concentration assumption should be used. The expected values used in the
plant environmental report would be acceptable." Many plants pre-date the issuance of
RG 1.45 and their plant-specific licensing basis is described in their UFSAR. In either
case, the appropriate sensitivity of the atmospheric radiation monitors is dependent on the
design assumptions and the plant licensing basis of each licensee.
The ISTS "RCS Leakage Detection Instrumentation" Bases do not clearly define the basis
for Operability for the RCS leakage detection instrumentation. Operability requirements
should be defined in the LCO section of the Bases. However, the current Bases contain
information that could be construed as Operability requirements in the Background,
Applicable Safety Analysis, and LCO sections. In addition, the current Bases do not
accurately describe the Operability of a detector as being based on the design
assumptions and licensing basis for the plant.
Because the atmospheric gaseous radiation monitor cannot always detect an RCS leak at
a rate of 1 gpm within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, some plants have removed the monitor from the Technical
Specification list of required monitors. However, experience has shown that the
containment atmosphere gaseous radiation monitor is useful to detect an increase in RCS
leak rate and provides a diverse means to confirm an RCS leak exists when other
monitors detect an increase in RCS leak rate. Therefore, the preferred solution is to retain
the atmospheric gaseous radiation monitor in the LCO list of required equipment, and to
revise the Actions to require additional monitoring and to provide less time before a plant
shutdown is required when the atmospheric gaseous radiation monitor is the only
Operable monitor.
4.0 Technical Analysis
This change will reduce the number of unnecessary MODE changes and requests for
enforcement discretion by clarifying the Operability requirements for the RCS leakage
detection instrumentation and by allowing a limited time to repair one or more of the
inoperable monitors. A plant shut down solely as a result of the loss of the preferred TS
monitoring capability could be avoided. The use of alternate leakage detection
monitoring for a limited time is an appropriate response to this condition.
The proposed Bases changes will clarify the Operability requirements of the RCS leakage
detection instrumentation. All references to RG 1.45 are revised to reference Revision 0
of the RG. Information in the Background and Applicable Safety Analysis sections of
the Bases that could be construed as Operability requirements is deleted. The LCO
section of the Bases is expanded to provide a detailed discussion of the Operability
requirements for each of the required instruments. For the atmospheric radioactivity
monitors, the Bases clearly relate Operability to the design assumptions and licensing
basis for the plant and a reference to the Final Safety Analysis Report description of the
design basis of the monitors is included.
As described in 10 CFR 50.36(c)(2)(i), the Limiting Condition for Operation and
associated Operability requirements represent the lowest functional capability or
performance levels of equipment required for safe operation of the facility. In practice,
the leakage monitoring instrumentation is typically set to provide the most sensitive
response without distracting the reactor operators with unnecessary alarms.
When the atmospheric gaseous radiation monitor is the only Operable monitor, the
current Technical Specifications require grab samples of the primary containment or
drywell atmosphere once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and restoration of the inoperable monitors within
30 days. The proposed change requires analyzing grab samples from the primary
containment or drywell atmosphere and monitoring RCS leakage by administrative
means once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and restoration of at least one additional monitor within 7 days.
Administrative means of monitoring RCS leakage include monitoring and trending
parameters that may indicate an increase in RCS leakage. There are diverse alternative
mechanisms from which appropriate indicators may be selected based on plant conditions.
It is not necessary to utilize all of these methods, but a method or methods should be
selected considering the current plant conditions and historical or expected sources of
unidentified leakage. The Bases list the plant-specific administrative methods, such as
primary containment and drywell pressure, temperature, and humidity, Component
Cooling Water System outlet temperatures and makeup, Reactor Recirculation System
pump seal pressure and temperature and motor cooler temperature indications, Drywell
cooling fan outlet temperatures, Reactor Building Chiller amperage, Control Rod Drive
System flange temperatures, and Safety Relief Valves tailpipe temperature, flow, or
pressure. These indications, coupled with the atmospheric grab samples, are sufficient to
alert the operating staff to an unexpected increase in unidentified LEAKAGE.
A primary containment or drywell grab sample is comparable to the atmospheric
particulate radiation monitor with respect to the ability to detect RCS leakage. Due to the
time to take and analyze the grab sample, this is not a continuous monitoring method.
However, the frequent performance of the grab samples ensures there is no significant
loss of monitoring capability during the limited time period allowed by the proposed
change. The 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> (once per shift) performance of primary containment or drywell
grab samples and monitoring by administrative means is reasonable given the availability
of the atmospheric gaseous radiation monitor. The 7 day Completion Time to restore
another monitor to Operable status is reasonable given the diverse methods employed in
the Required Actions to detect an RCS leak and the low probability of a large RCS leak
during this period.
5.0 Regulatory Analysis
5.1 No Significant Hazards Consideration
The Technical Specification Task Force (TSTF) has evaluated whether or not a
significant hazards consideration is involved with the proposed generic change by
focusing on the three standards set forth in 10 CFR 50.92, "Issuance of amendment," as
discussed below:
1. Does the proposed change involve a significant increase in the probability or
consequences of an accident previously evaluated?
Response: No.
The proposed change clarifies the Operability requirements for the Reactor
Coolant System (RCS) leakage detection instrumentation and reduces the time
allowed for the plant to operate when the only Operable RCS leakage detection
instrumentation monitor is the atmospheric gaseous radiation monitor. The
monitoring of RCS leakage is not a precursor to any accident previously evaluated.
The monitoring of RCS leakage is not used to mitigate the consequences of any
accident previously evaluated.
Therefore, it is concluded that this change does not involve a significant increase
in the probability or consequences of an accident previously evaluated.
2. Does the proposed change create the possibility of a new or different kind of
accident from any accident previously evaluated?
Response: No.
The proposed change clarifies the Operability requirements for the Reactor
Coolant System (RCS) leakage detection instrumentation and reduces the time
allowed for the plant to operate when the only Operable RCS leakage detection
instrumentation monitor is the atmospheric gaseous radiation monitor. The
proposed change does not involve a physical alteration of the plant (no new or
different type of equipment will be installed) or a change in the methods
governing normal plant operation.
Therefore, it is concluded that this change does not create the possibility of a new
or different kind of accident from any accident previously evaluated.
3. Does the proposed change involve a significant reduction in a margin of safety?
Response: No.
The proposed change clarifies the Operability requirements for the Reactor
Coolant System (RCS) leakage detection instrumentation and reduces the time
allowed for the plant to operate when the only Operable RCS leakage detection
instrumentation monitor is the atmospheric gaseous radiation monitor. Reducing
the amount of time the plant is allowed to operate with only the atmospheric
gaseous radiation monitor Operable increases the margin of safety by increasing
the likelihood that an increase in RCS leakage will be detected before it
potentially results in gross failure.
Therefore, it is concluded that this change does not involve a significant reduction
in a margin of safety.
Based on the above, the TSTF concludes that the proposed change presents no significant
hazards considerations under the standards set forth in 10 CFR 50.92(c), and, accordingly,
a finding of "no significant hazards consideration" is justified.
5.2 Applicable Regulatory Requirements/Criteria
10 CFR 50, Appendix A, "General Design Criteria for Nuclear Power Plants," Criterion
30, "Quality of reactor coolant pressure boundary," requires that means be provided for
detecting and, to the extent practical, identifying the location of the source of reactor
coolant leakage. The specific attributes of the reactor coolant leakage detection systems
are outlined in Regulatory Positions 1 through 9 of Regulatory Guide 1.45, Rev. 0.
10 CFR 50.36, "Technical Specifications," paragraph (c)(2)(ii)(A), specifies that a
Limiting Condition for Operation be established for installed instrumentation that is used
to detect and indicate in the control room a significant abnormal degradation of the
reactor coolant pressure boundary. This instrumentation is required by the "RCS
Leakage Detection Instrumentation" Specification. The modification of the Actions in
the Specification is not in conflict with the 10 CFR 50.36 requirements. The proposed
changes do not adversely impact the ability of the Reactor Coolant System leakage
detection system to function as designed and do not impact conformance to the applicable
GDCs. Therefore, the proposed changes are consistent with all applicable regulatory
requirements or criteria.
Based on the considerations discussed above, (1) there is reasonable assurance that the
health and safety of the public will not be endangered by operation in the proposed
manner, (2) such activities will be conducted in compliance with the Commission’s
regulations, and (3) the approval of the proposed change will not be inimical to the
common defense and security or to the health and safety of the public.
6.0 Environmental Consideration
A review has determined that the proposed change would change a requirement with
respect to installation or use of a facility component located within the restricted area, as
defined in 10 CFR 20, or would change an inspection or surveillance requirement.
However, the proposed change does not involve (i) a significant hazards consideration, (ii)
a significant change in the types or significant increase in the amounts of any effluent that
may be released offsite, or (iii) a significant increase in individual or cumulative
occupational radiation exposure. Accordingly, the proposed change meets the eligibility
criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9). Therefore, pursuant to
10 CFR 51.22(b), no environmental impact statement or environmental assessment need
be prepared in connection with the proposed change.
7.0 References
None.