[Federal Register Volume 60, Number 98 (Monday, May 22, 1995)]
[Notices]
[Pages 27141-27143]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-12468]



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NUCLEAR REGULATORY COMMISSION

Proposed Generic Communication Testing of Safety-Related Logic 
Circuits

AGENCY: Nuclear Regulatory Commission.

ACTION: Notice of opportunity for public comment.

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SUMMARY: The Nuclear Regulatory Commission (NRC) is proposing to issue 
a generic letter concerning problems with the testing of safety-related 
logic circuits. This draft generic letter requests addresses to review 
surveillance procedures to determine whether any of the procedures fail 
to test all required portions of the logic circuitry and, if any 
problems are found, to correct the problems. The NRC is seeking comment 
from interested parties regarding both the technical and regulatory 
aspects of the proposed generic letter presented under the 
Supplementary Information heading. This proposed generic letter and 
supporting documentation were discussed in meeting number 272 of the 
Committee to Review Generic Requirements (CRGR) on April 25, 1995. The 
relevant information that was sent to the CRGR to support their review 
of the proposed generic letter will be made available in the NRC Public 
Document Room. The NRC will consider comments received from interested 
parties in the final evaluation of the proposed generic letter. The 
NRC's final evaluation will include a review of the technical position 
and, when appropriate, an analysis of the value/impact on licensees. 
Should this generic letter be issued by the NRC, it will become 
available for public inspection in the Public Document Rooms.
    The staff recognizes that during implementation of the requested 
actions in the proposed generic letter, licensees may identify 
conditions in violation of their technical specifications or other NRC 
requirements. Consequently, the staff is considering the possibility of 
exercising enforcement discretion under certain circumstances during 
the period of implementation of the requested actions in order to 
encourage licensees to perform effective reviews.

DATES: Comment period expires on July 21, 1995. Comments submitted 
after this date will be considered if it is practical to do so, but 
assurance of consideration cannot be given except for comments received 
on or before this date.

ADDRESSES: Submit written comments to Chief, Rules Review and 
Directives Branch, U.S. Nuclear Regulatory Commission, Washington, DC 
20555. Written comments may also be delivered to 11545 Rockville Pike, 
Rockville, Maryland, from 7:30 am to 4:15 pm, Federal workdays. Copies 
of written comments received may be examined at the NRC Public Document 
Room, 2120 L Street, NW., (Lower Level), Washington, DC.

FOR FURTHER INFORMATION CONTACT:
Hukam Garg, (301) 415-2929.

SUPPLEMENTARY INFORMATION:

NRC Generic Letter No. 95-XX: Testing of Safety-Related Logic Circuits

Addresses

    All holders of operating licenses or construction permits for 
nuclear power reactors.

Purpose

    The U.S. Nuclear Regulatory Commission (NRC) is issuing this 
generic letter to: (1) notify addressees about problems with testing of 
safety-related logic circuits, (2) request that all addresses implement 
the actions described herein, and (3) require that all addressees 
submit a written response to this generic letter regarding 
implementation of the requested actions.
Background

    The Nuclear Regulatory Commission staff had previously issued the 
following information notices (INs) regarding problems with testing of 
safety-related logic circuits: IN 88-83, ``Inadequate Testing of Relay 
Contacts in Safety-Related Logic Circuits,'' dated October 19, 1988; IN 
91-13, ``Inadequate Testing of Emergency Diesel Generators (EDGs),'' 
dated March 4, 1991; IN 92-40, ``Inadequate Testing of Emergency Bus 
Undervoltage Logic Circuitry,'' dated May 27, 1992; IN 93-15, ``Failure 
to Verify the Continuity of Shunt Trip Attachment Contacts in Manual 
Safety Injection and Reactor Trip Switches,'' dated February 18, 1993; 
and IN 93-38, ``Inadequate Testing of Engineered Safety Features 
Actuation Systems,'' dated May 24, 1993. Despite these notices, recent 
events have occurred similar to those described in the INs which 
indicate that licensees have not taken sufficient action to correct 
previously identified problems in logic circuit surveillance testing. 
On March 7, 1995, NRC issued IN 95-15, ``Inadequate Logic Testing of 
Safety-Related Circuits,'' which informed licensees about these recent 
events at Cooper Nuclear Station, Fermi 2, Waterford 3, Grand Gulf 
Nuclear Station, and Arkansas Nuclear One, Unit 1 and Unit 2.

Description of Circumstances

    The NRC has documented a significant number of instances involving 
problems with logic testing of safety-related circuits in the 
information notices described above. These information notices discuss 
events at various pressurized water and boiling water reactors. The 
examples of problems with logic testing cover a wide range of systems 
including safety injection system actuation, containment spray system 
actuation, residual heat removal system actuation, diesel generator 
load sequencing, and rector protection system actuation. In most cases, 
the affected logic circuits functioned properly when testing in 
accordance with technical specification [[Page 27142]] (TS) 
requirements was performed. The NRC has taken enforcement action in 
many of these cases since they resulted in violations. The details of 
these instances are included in the information notices cited above. An 
example of the details associated with this issue at Fermi Station are 
repeated here.
    On July 15, 1994, during a routine review of surveillance 
procedures required by the Fermi Unit 2 TS, the licensee (Detroit 
Edison Company) discovered that neither the procedures used for testing 
the load shedding of the 4160 volt Residual heat Removal (RHR) pumps 
nor the related instrumentation and control (I&C) logic functional test 
procedure provided for the full testing of the RHR pump start logic. 
Also, the test procedures did not include verification that the 
switchgear breaker would not close with an undervoltage signal present 
at the bus.
    After investigating further, the licensee discovered additional 
deficiencies in the undervoltage functional test surveillance 
procedures including the logic functional test surveillance procedures 
for the three other engineered safety buses. Also, the surveillance 
test overlap did not include sufficient overlap of the logic circuit to 
cover the degraded voltage trip input to the non-interruptible air 
supply system isolation logic, the degraded voltage trip input to the 
bus feeder breaker position, and the alternative automatic closure 
circuits for the EDG output breakers. The licensee further determined 
that the 480 volt load shed logic had not been fully tested.
    On September 9, 1994, the licensee identified additional 
surveillance deficiencies and expanded the investigation of its 
surveillance procedures for EDGs and I&C overlap testing. During this 
investigation, the licensee determined that (1) multiple pathways for 
starting an EDG through the emergency core cooling system (ECCS) logic 
were not being tested, (2) emergency equipment cooling water (EECW) 
actuation from the load sequencer was not being differentiated from 
EECW actuation on reactor building closed cooling water low pressure, 
and (3) test acceptance criteria permitted performance outside of the 
TS limits.
    On November 30, 1994, the licensee identified several other test 
deficiencies in its surveillance procedures. These deficiencies were 
related to the core spray system, RHR system, reactor protection 
system, safety relief valves, alternate rod insertion and main steam 
isolation valve leadage control system logic, remote shutdown panel, 
primary containment manual isolation valves, and alternate shutdown 
panel transfer switches.
    To address the above deficiencies, the licensee has taken the 
following correction actions: (1) Reviewed deficient procedures and 
performed required surveillance to establish operability, (2) reviewed 
similar procedures to identify other deficiencies. The licensee has 
taken the following corrective actions: (1) reviewed deficient 
procedures and performed required surveillance to establish 
operability, (2) reviewed similar procedures to identify other 
deficiencies, (3) created electrical overlap drawings, and (4) trained 
authors and technical reviewers of procedures to be fully aware of 
logic surveillance requirements. The NRC staff issued a notice of 
violation to Detroit Edison Company concerning the above issue (NRC 
Inspection Report No. 50-341/94-12).

Discussion

    A number of NRC regulations document the requirements to test 
safety-related systems to ensure that they will function as designed 
when called upon. For example, Title 10 of the Code of Federal 
Regulations (10 CFR), Section 50.36, ``Technical Specifications,'' 
paragraph (c)(3) states that, ``surveillance requirements are 
requirements relating to test, calibration or inspection to assure that 
the necessary quality of systems and components is maintained, that 
facility operation will be within the safety limits, and that the 
limiting conditions of operation will be met.'' surveillance 
requirements to assure continued operability of safety related logic 
circuits have been included in the plant-specific technical 
specifications for all operating nuclear power plants
    Other documents that provide a basis for these requirements 
include:
     10 CFR 50.55a, ``Codes and Standards,'' paragraph (h) 
which includes reference to Institute of Electrical and Electronic 
Engineers (IEEE) Standard 279, ``Criteria for Protection Systems for 
Nuclear Power Generating Stations''
     Appendix A to 10 CFR 50, General Design Criterion (GDC) 
21, `Protection System for Reliability and Testability''
     Appendix A to 10 CFR 50, General Design Criterion (GDC) 
18, ``Inspection and Testing of Electric Power Systems''
     Appendix B to 10 CFR 50, Criterion XI, ``Test Control''
     Regulatory Guide (RG) 1.118, ``Periodic Testing of 
Electric Power and Protection Systems''
     RG 1.32, ``Criteria for Safety-Related Electric Power 
Systems for Nuclear Power Plants''
    As noted above, the NRC staff has issued a number of information 
notices (identified in the ``Background'' section) that document 
identified deficiencies in actuation logic surveillance test programs. 
However, because of the number of more recently identified similar 
deficiencies, the NRC staff has determined that licensees may not have 
yet adequately addressed this issue and further action is necessary.
    The NRC staff finds that the failure to adequately test safety-
related actuation logic circuitry is safety significant in that 
inoperable essential electric components required for automatic 
actuation of post-accident mitigation systems may be undetected for 
extended periods. This is particularly true for the reactor protection 
system, whose unavailability is shown in probabilistic risk assessments 
to be a dominant contributor to potential core damage scenarios. 
Undetected reactor protection system availability/reliability 
degradation is also a potentially significant contributor to overall 
risk. Unavailability of those circuits associated with automatic 
emergency core cooling system (ECCS) actuation, especially in a loss-
of-offsite-power situation, is a lesser contributor to overall risk but 
is important in ensuring post-accident recovery in accordance with 
licensing bases. Failure to automatically actuate safety systems also 
places the additional burden on the operators of having to manually 
actuate required functions and thus increases the chance for operator 
error.
    The NRC staff notes that even in cases where surveillance testing 
of the logic circuits has not been complete, it is likely that only 
very small portions of the circuit have been omitted from the test. 
Further, the NRC staff is not aware of instances of specifically 
identified surveillance inadequacies that resulted in the 
unavailability of the safety system when called on during an event. 
Nevertheless, as indicated above, the NRC staff finds that compliance 
with the plant-specific technical specifications is essential in order 
to maintain the validity of the assumptions in the licensing basis 
accident analyses. On the basis of the recent events, previously issued 
INs, complexity of the logic, and contribution to the core damage 
frequency, the NRC staff has further determined that licensees should 
review their surveillance procedures for the reactor protection system, 
EDG load shedding and sequencing, and actuation logic for the 
engineered safety features systems to ensure that complete testing 
[[Page 27143]] is being performed as required by the technical 
specifications.

Requested Actions

    The NRC staff requests that all holders of operating licenses for 
nuclear power reactors take the following actions:
    (1) Compare electrical schematic drawings and logic diagrams for 
the reactor protection system, EDG load shedding and sequencing and 
actuation logic for the engineered safety features systems against 
technical specification surveillance test procedures to ensure that all 
portions of the logic circuitry, including the parallel logic, 
interlocks, bypasses and inhibit circuits, are adequately covered in 
the surveillance procedures. This review should also include relay 
contacts, control switches, and other relevant electrical components 
within these systems, utilized in the logic circuits.
    (2) Modify the surveillance procedures as necessary for complete 
testing to comply with the technical specifications. Additionally, the 
licensee may request an amendment to the technical specifications if 
relief from certain testing requirements can be justified.
    It is requested the completion of these actions not go beyond the 
first refueling outage commencing 90 days after the issuance of this 
generic letter.

    Note: Some licensees may have already performed the requested 
reviews and taken appropriate corrective actions. These licensees do 
not need to perform any additional review unless modifications have 
been made to the logic circuits for these systems. In these cases 
the modifications should be reviewed.

Required Response

    All addressees, including those who have already completed the 
requested actions, are required to submit a written response to this 
generic letter as follows:
    (1) Within 60 days of the date of this generic letter, a written 
response indicating whether or not the addressee will implement the 
actions requested above. If the addressee intends to implement the 
requested actions, submit a schedule for completing implementation. If 
an addressee chooses not to take the requested actions, submit a 
description of any proposed alternative course of action, the schedule 
for completing the alternative course of action (if applicable), and 
the safety basis for determining the acceptability of the planned 
alternative course of action.
    (2) Within 30 days of completion of the requested actions, a 
response confirming completion.

Backfit Discussion

    The actions requested in this generic letter are considered 
backfits in accordance with NRC procedures. Because established 
regulatory requirements exist but were not satisfied, these backfits 
are necessary to bring the addressees into compliance with existing 
requirements. Therefore, on the basis of 10 CFR 50.109(a)(4)(i), a full 
backfit analysis was not performed.
    An evaluation was performed in accordance with NRC procedures, 
including a statement of the objectives of and reasons for the 
requested actions and the basis for invoking the compliance exception. 
Response to question ix in the CRGR review package contains this 
evaluation.

    Dated at Rockville, Maryland, this 15th day of May, 1995.

    For the Nuclear Regulatory Commission.
Brian K. Grimes,
Director, Division of Project Support, Office of Nuclear Reactor 
Regulation.
[FR Doc. 95-12468 Filed 5-19-95; 8:45 am]
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