Technical Specifications for Generic Letter 83-28, Items 4.3 and 4.4 (Generic Letter No. 85-10)
UNITED STATES
NUCLEAR REGULATORY COMMISSION
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.
8505210131
- 2 -
In 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.
- 2 -
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.
- 3 -
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 hours. 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 hours
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 a
- 4 -
reactor 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 hours.
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."
- 5 -
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.
Page Last Reviewed/Updated Tuesday, March 09, 2021