Proposed Generic Communication Testing of Safety-Related Logic Circuits

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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