LD-87-012, Forwards Generic Design Info in Response to 10CFR50.62, Requirements for Reduction of Risk from ATWS Events for Light Water-Cooled Nuclear Power Plants. Requirements Will Be Met When Existing Supplementary Protection Sys Modified

Forwards Generic Design Info in Response to 10CFR50.62, Requirements for Reduction of Risk from ATWS Events for Light Water-Cooled Nuclear Power Plants. Requirements Will Be Met When Existing Supplementary Protection Sys Modified

ML20207Q808
Person / Time
Site:	05000470
Issue date:	02/27/1987
From:	Scherer A ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY
To:	Miraglia F NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LD-87-012, LD-87-12, NUDOCS 8703100012
Download: ML20207Q808 (3)

Text

,, - .

February 27, 1987 LD-87-012 STN 50-470F Mr. Frank J. Miraglia U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555

Subject:

CESSAR Compliance with the ATWS Rule (10CFR50.62)

Dear Mr. Miraglia:

This letter forwards generic design information which may be referenced by System 80TM plants in responding to 10CFR50.62, " Requirements for Reduction of Risk from Anticipated Transients Without Scram ( ATWS)

Events for Light Water-Cooled Nuclear Power Plants."

The attachment describes System 80's compliance with the ATWS Rule. In summary, System 80 plants will meet the requirements of 10CFR50.62 when the existing Supplementary Protection System (SPS) is modified to include an additional trip actuation device which is diverse and independent from the existing reactor trip breakers.

The above change to the SPS will be incorporated in the next amendment

, to CESSAR. If you have any questions, please feel free to call me or Mr.

! S.E. Ritterbusc:4 of my staff at (203) 285-5206.

Very truly yours, COMBUSTION ENGINEERING, INC.

m l

8703100012 870227 [. E.icherer PDR ADOCK 05000470-A PDR '

Director Nuclear Licensing i 9 l AES:ss S l attachments h

cc

M. Licitra (NRC)

Power Systems 1000 Prospect Hill Road (203) 688-1911 Combustion Engineering. Inc. Post Office Box 500 Telex: 99297 Windsor Connecticut 060954500 l

.+

• Attachment Page 1 of 2 LD-87-012 CESSAR Compliance With The ATWS Rule A C-E PWR must have the following features to meet the ATWS Rule (10CFR50.62):

1. To meet section (c)(1) of 10CFR50.62 (the " mitigation requirement")

the plant must have equipment to automatically initiate emergency feedwater and turbine trip under conditions indicative of an ATWS.

This equipment must function reliably and must be diverse and independent from the reactor trip system.

2. To meet section (c)(2) of 10CFR50.62 (the " prevention requirement")

the plant must have a scram system which is diverse and independent from the existing reactor trip system.

The existing System-80 M design, as described in CESSAR-F, incorporates several safety grade systems designed to protect the plant and mitigate the consequences of various design basis events. These include the following

, features.

Reactor Protective System (RPS) - Initiates a reactor trip to protect the RCS pressure boundary in the event of high pressurizer pressure or low steam generator level (conditions indicative of an ATWS). The system consists of sensors, bistables, bistable relays, matrix relays, initiation relays, and actuation devices.

Core Protection Calculators (CPCs) - Provide inputs to the Reactor Protective System (RPS) by actuating the appropriate RPS bistable relays when cold leg temperature or pressurizer i pressure exceed the allowable range (conditions indicative of an ATWS) .

Engineered Safety Featums Actuation System - Generates an Emergency Feedwater Actuation Signal (EFAS), in the event of low steam generator level. The system utilizes the outputs from RPS l sensors to actuate EFAS specific bistables, histable relays, matrix ,

relays, initiation relays, and actuation devices. )

Supplementary Protection System (SPS) - The SPS augments reactor protection by utilizing an independent and diverse trip logic, relative to the RPS, for initiation of reactor trip. The SPS provides a simple, reliable, and diverse mechanism to increase the reliability of reactor trip when the pressurizer pressure exceeds a predetermined value. The existing SPS is a safety grade system which is independent and diverse from the CPC's, RPS (up to the final actuation device), and the EFAS. The final actuation devices for the SPS safety grade reactor trip are the reactor trip breakers which are also actuated by an RPS trip signal.

5 .. .. ,

. Attachment l Page 2. of 2 '

l LD-87-012 ~

l l

l To comply with the ATWS rule, C-E will modify CESSAR to reflect the I addition of control-grade circuitry to allow the SPS to trip the CEDM motor-generator output load contactors. This trip, with appropriate '

isolation, will be diverse and independent from the RPS actuation of the reactor trip breakers. The isolation devices will maintain the current reliability of the SPS as a safety grade system.

The SPS is diverse and independent from the EFAS (which initiates emergency feedwater) and, also, the current safety grade SPS meets all regulations, standards, etc. for a safety grade reactor trip for ATWS

. conditions. Specifically, in evaluating the CESSAR SPS, the NRC Staff stated the following in the CESSAR SER (NUREG-0852):

"The SPS conforms to the regulations, regulatory guides, and industry standards applicable to the RPS. Furthermore, the CESSAR scope of supply of the SPS meets practical achievable diversity, vis-a-vis the RPS, and hence in the staff's judgment meets the intent of NUREG-0460, Volume 3, Anticipated Transient Without Scram (ATWS)".

The SPS, as modified, provides a turbine trip initiation that is diverse and independent from the reactor trip system. The SPS causes a reactor trip by interrupting power to the Control Element Assembly common power bus.

Upon interruption of this power, undervoltage relays attached to the bus de-energize, causing actuation of the turbine trip circuitry.

Since the EFAS is diverse and independent from the safety grade SPS (which, according to all regulations and standards, is equivalent to an RPS) and since a turbine trip initiation is provided (through the SPS) which is diverse and independent from the reactor trip system, the requirements of 10CFR50.62(C)(1) - ATWS mitigation - are met.

To meet 10CFR50.62(C)(2), the System 80 design must have a reactor trip function which is reliable and which is independent and diverse from the existing reactor trip system. This trip function is provided by the SPS modification described above. Since the SPS, subject to this modification, provides a diverse scram signal from the reactor trip system, the requirements of 10CFR50.62 (c)(2) - ATWS prevention - are met.

Subject to the aforementioned addition to the SPS final actuation device, plants referencing CESSAR should be found to meet the ATWS rule.