NRC Generic Letter 85-10, Technical Specification for Generic Letter 83-28, Items 4.3 and 4.4

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WASHINGTON, D. C. 20555

May 23, 1985

TO ALL BABCOCK AND WILCOX PRESSURIZED WATER REACTOR LICENSEES AND APPLICANTS

Gentlemen:

SUBJECT: TECHNICAL SPECIFICATIONS FOR GENERIC LETTER 83-28, ITEMS 4.3 AND 4.4 (Generic Letter 85-10)

Item 4.3 of Generic Letter 83-28, "Required Actions Based on Generic Implications of Salem ATWS Events," established the requirement for the automatic actuation of the shunt trip attachment for B&W plants. Also, licensees are to submit any needed technical specification change requests as soon as practical following staff review and approval of the modified design. Item 4.4 of Generic Letter 83-28 requires that the appropriate .

surveillance and test sections of the technical specifications be revised to include testing of the silicon controlled rectifiers used to interrupt power to control rods.

In the staff's evaluation of the B&W generic design modifications for automatic actuation of the shunt trip attachment, as described in individual letters to all B&W operating reactors, dated September 12, 1983, the staff concluded that technical specification changes should be proposed by licensees and that they would be reviewed on a plant specific basis. In the staff's review of plant specific responses to the generic letter, some licensees have indicated that changes to the technical specifications are not required. In such cases, the staff has found this to be unacceptable and has indicated that proposed technical specification changes should be submitted to reflect independent testing of the shunt and undervoltage trip attachments consistent with the design of the test features provided.

Therefore, licensees are requested to submit proposed technical specification changes which are responsive to the guidance noted in the enclosure. The enclosed guidance will be used to revise the Standard Technical Specifications for B&W plants, and it will be used by the staff as a basis to review changes to technical specifications submitted by licensees and for the review of proposed technical specifications for operating license applications.

For plants which have implemented the shunt trip modifications, a schedule for submittal of proposed technical specification changes should be established through discussions with the individual Project Manager for each facility.

8505210131In addition, discussions with the individual Project Managers should establish a schedule for plants which have not implemented the shunt trip modifications. Proposed technical specifications should be submitted as soon as practical following staff review and approval of modified design. For operating license applicants, proposed technical specifications should include requirements which are responsive to the enclosed guidance.

This request for information was approved by the Office of Management and Budget under clearance number 3150-0011 which expires April 30, 1985. Should you have an questions, the staff contact is R. Karsch. Mr. Karsch can be reached on (301) 492-8563.

Hugh L. Thompson, Jr., Director Division of Licensing

Enclosure:

Sample of Technical Specifications List of Generic Letters

ENCLOSURE

TECHNICAL SPECIFICATION CHANGES FOR REACTOR TRIP BREAKERS (B&W PLANT)

Background

As a consequence of the Salem ATWS event, Item 4.3 of Generic Letter 83-28 established the requirements for the automatic actuation of the shunt trip attachment for reactor trip breakers. Further, licensees are to submit any needed technical specification change requests prior to declaring the modified system operable. A number of the responses from operating reactors have indicated that no technical specification changes are required for this modification.

The staff has reviewed the guidance provided in the Standard Technical Specifications (STS) for B&W Plants, NUREG-0103, and finds that additional clarification of both the limiting conditions of operation and surveillance requirements are appropriate as a result of the design modifications to include automatic actuation of the shunt trip attachments. In addition, Item 4.4 of the generic letter requires that technical specification surveillance requirements be revised to include testing of the silicon controlled rectifiers (SCR). The STS for B&W Plants will be revised to include the changes noted herein. Pending formal revision of the STS, this document provides guidance to licensees and operating license applicants on appropriate technical specifications in response to Items 4.3 and 4.4 of the Generic Letter.Discussion

The operability requirements for the reactor trip breakers are specified in Table 3.3-1 of the STS (see Attachment 2). The specification states that both reactor trip breakers shall be operable in Modes 1 and 2, and when the breakers are in the closed position, the control rod drive system is capable of rod withdrawal, and fuel is in the reactor vessel. The action statement for an inoperable breaker requires that the breaker be placed in a tripped condition within one hour.

With the addition of the automatic actuation of the shunt trip attachment (STA), diverse features exist to effect a reactor trip for each breaker. If one of these diverse trip features is inoperable, a decision would have to be made with regard to the operability status of the reactor trip breaker. The definition of OPERABLE-OPERABILITY in Section 1.0 of the STS states that a component shall be operable or have operability when it is capable of performing its safety function. Since either trip feature being operable would initiate a breaker trip on demand, it would be overly conservative to treat a breaker as inoperable if one of these diverse trip features were inoperable. However, on the other hand the reliability of the reactor trip system would be reduced if each diverse trip feature is not maintained in an operable status.The reactor trip breaker surveillance test should independently verify the operability of the shunt and undervoltage trip features of the reactor trip breaker as part of a single sequential test procedure. Therefore, the surveillance test which identifies a failure of one diverse trip feature also confirms the operability of the other trip feature. As a consequence, there is a higher degree of confidence that this trip feature would be capable of initiating a reactor trip in the next 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. Accordingly, an additional action statement will be included in the STS for the reactor trip breakers as follows:

ACTION - With one of the diverse trip features (undervoltage or shunt trip attachment) inoperable, restore it to OPERABLE status in 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> or place the breaker in trip in the next hour.

In accordance with the requirements of Item 4.4 of the Generic Letter, the SCR relays have also been included in the changes to Table 3.3-1 to define their operability requirements. The reactor trip system design for B&W plants includes two basic configurations; the Oconee design shown in Figure 3.4 and the Davis Besse design shown in Figure 3.5 (see Attachment 1). In the Oconee design the SCR relays for the regulating rods duplicate the trip function of the DC breakers for the safety rods. Therefore, for this design an inoperable channel should be placed in trip as required by action statement 7. However, in the Davis Besse design, the SCR relays provide a third means to insure that power is removed from all rods to initiate areactor trip. Therefore, placing inoperable channels of SCR relays in trip would only increase the potential for inadvertent reactor trips without significantly reducing the potential of an ATWS event, when considering the increased reliability of the reactor trip breaker afforded by the incorporation of diverse trip features. For plants with the Davis Besse design, a new action statement will be included in Table 3.3-1 of the STS as follows:

ACTION - With one or both channels of SCR relays inoperable, restore the channels to OPERABLE status during the next COLD SHUTDOWN exceeding 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

The B&W generic design modification includes test features which permit independent testing to verify the operability of the shunt and undervoltage trip attachments. As noted above, operability as applied to the diverse trip features of breakers may have different degrees of safety significance. In order to be consistent with the intent to the test features provided, the following notation will be included in the surveillance requirements specified in STS Table 4.3-1 for reactor trip breakers (see Attachment 2):

"The CHANNEL FUNCTIONAL TEST shall independently verify the OPERABILITY of the undervoltage and shunt trip attachments of the Reactor Trip Breakers."Consistent with the requirements of Item 4.4 of the Generic Letter, the surveillance requirements for SCR relays will also be included in Table 4.3-1. For plants with the Oconee design, the channel functional test of the SCR-relays will be specified as monthly since the SCR relays used for the regulating rods duplicate the trip function of the DC breakers for the safety rods. For plants with the Davis Besse design, the frequency of the channel functional test of the SCR relays will be specified as at least once per 18 months. The less frequent testing for the SCR relays in the Davis Besse design is due to their less critical, i.e., duplicative, safety function.

Attached are marked-up pages of the applicable STS tables with these changes. Proposed changes to plant specific technical specifications will be evaluated by the staff based on this guidance.