ML19340E444

Forwards Info Re Redundant Parallel Flow Path to Auxiliary Feedwater Pumps Design,In Response to NRC 791022 Request. Bypass Is Provided Around Existing Valve FW-339,which Is Single Feedwater Supply Source to Auxiliary Feedwater Pumps

ML19340E444
Person / Time
Site:	Fort Calhoun
Issue date:	01/09/1981
From:	William Jones OMAHA PUBLIC POWER DISTRICT
To:	Eisenhut D Office of Nuclear Reactor Regulation
References
NUDOCS 8101140513
Download: ML19340E444 (9)

Text

.

4 om H-\

Omaha Public Power District 1623 HARNEY O M AN A. NEsRASMA 68102 TELEPHONE 536-4000 ARE A C ODE er*

January 9, 1981 Mr. Darrell G. Eisenhut, Director U. S. Nuclear Regulatory Comission Office of Nuclear Reactor Regulation Division of Licensing Washington, D.C. 20555

Reference:

Docket No. 50-285

Dear Mr. Eisenhut:

The Omaha Public Power District's letter dated January 14, 1980, provided responses to questions in the Comission's letter dated October 22, 1979, regarding the Fort Calhoun Station auxiliary feedwater system design. The District's January 14, 1980, letter indicated that inform-ation on two issues would be provided at a later date; one being a design description for redundant auxiliary feedwater suction paths and the other being the results of the high energy line break (HELB) evalu-ation and resultant proposed modifications. The auxiliary feedwater suction side design description was provided by telephone on May 1, 1980, in discussions between Mr. Hickle of the District and Mr. LeFave of the Commission. The HELB evaluation results and proposed system modifications were provided to the Commission by telephone on August 21, 1980, in a discussion between Messrs. Hickle, Khan, and Eidem of the District and Messrs. Wagner, LeFave, and Leoung of the Commission. In response to a telephone discussion on January 6, 1981, between Messrs.

Morris, Patterson, and Pirruccello of the District and Messrs. Parr, Wagner, and Leoung of the Commission, the attached supplemental inform-ation is submitted in response to the Commission's original information request of October 22, 1979. If the District can be of further service.

l please advise.

e l

Sincerely,

~

f% *

, .[ . . C . ' _ . _ ,

b W. C. Jones Division fianager Production Operations WCJ/KJM/TLP

jem QQ/

Attachments )

cc: LeBoeuf, Lamb, Leiby & MacRae 1333 New Hampshire Avenue, N.W. ((

l Washington, D.C. 20036 8101140 b D

(

l l

1 X.3.3.3.2 i

Recommendation CL-2 l Licensees with plants in which all (primary and alternate) water sup-plies to the AFW systems pass through valves in a single flow path ,

should install redundant parallel flow paths (piping and valves). l l Response A design description of the Fort Calhoun Station for a redundant parallel suction flow path to the auxiliary feedwater pumps is attached.  !

2 l

l l

l l

l l

I I l i

l l

l l

t 4

1 i

l 1

O FORT CALHOUN STATION UNIT NO. 1 REDUNDANT PARALLEL FLOW PATH TO AUXILIARY FEEDWATER PUMPS DESIGN DESCRIPTION i

n h

DESIGN DESCRIPTION AUXILIARY FEEDWATER SUCTION BYPASS FORT CALHOUN STATION - UNIT 1 OMAHA PUBLIC POWER DISTRICT 1.0 DESIGN BASIS - REQUIREMENTS The auxiliary feedwater suction bypass is required for compliance with NRC Recommendation GL-2 in Docket No. 50-285 dated October 22, 1979. This Recommendation is identified as long-term, and "repre-sent actions that should be implemented by January 1, 1981, or as soon thereafter as is practicable." The Recommendation is as follows:

" Licensees with plants in which all (primary and alternate) water

' supplies to the AFW systems pass through valves in a single flow path should install redundant parallel flow paths (piping and valves)."

Commitment to install redundant parallel flow paths during the 1981 refueling outage was made in OPPD's response to the NRC dated January 14, 1980. A bypass valve piped around existing suction valve FW-339 has been approved as an acceptable solution to Re-commendation GL-2, as discussed by telephone between Mr. Bruce Hickle of OPPD and Mr. Bill LeFave of the NRC.

2.0 TECHNICAL DESCRIPTION

A bypass is provided around existing valve FW-339, which is the

single source of feedwater supply to the auxiliary feedwater pumps.

The valve provided in the bypass is a 150# cast carbon steel gate valve similar to the existing valve and will be locked open.

3.0 SAFETY ANALYSIS The bypass piping and valve are designated as Critical Quality Elements (CQE) and meet or exceed the requirements of the existing piping and valve. It is, therefore, concluded that this modifi-cation does not constitute an unreviewed safety question (10CFR 50.59) for the following reasons:

3.1 It does not create the possibility of an accident or equipment malfunction which is different from those previously analyzed' in the FSAR and its amendments.

3.2 It does not increase the possibility of occurrence or con-sequences of an accident or equipment malfunction which has been previously evaluated in the FSAR and its amendments.

3.3 It does not reduce the margins of safety as defined in the basis for the technical specificat ons i of Fort Calhoun plant.

I l

4.0 STRESS ANALYSIS A stress analysis of the bypass piping and valve W -1316 was conducted. The objective of the analysis was to ensure that the 4

stress in the bypass line would remain within the seismic criteria defined in the Fort Calhoun Station FSAR, Appendix F. The stress

' analysis concluded that, as designed, all stresses in the piping considered are within allowable limits under all loading conditions in accordance with the FSAR criteria.

i e

I l

i l

1 1

l l

l I

b r

4 < 5 c:

~

~

w s I I -

r r< ~

r ~ -

55

- 1 i

. e h.

e r; ( ar w

- ) -

~ ]~ -

e -

_.e e

c .i 7c =

37 w

c =

=

=

-z w

l-m i< w O -

O>2 .

E /'.- AY - k -- 5 c=(JA - d=y .. 5 - -

- 5 e -> >. E <

J __ >g E <._ _ -- . O. .= .= I - N - = . Q<< =  :. fer,olc - m- (,T 3 3 :  ?,5(~TO e= - n 2.,C 3, eee 23 EE e 3 = 0 e =- e l==- l =w z , m w - s

u. s:=

e w n ,I a_ mA ca =- u__. . l e , $ \e 5 I:. JA?.=S. L_ . ':.'JA L ?, 5 < =- e  : l- \) - e ~ cC, w . X5 - '.: DBs2 -- g .E c N  : i ,% ~ j? ' C e [J 24557  % M M}- ~ 3 " - X~ i.- . x :e =.- . ./ .- < - w Ew- "V E I il- - . = - w I , > r E .: E r- .y *g= 6 4d-- l.\ Om J n/ . = w .5 stg C '-  % 4, ,/ e e , ~- N d - .---9 2-2  : x . 4 w-  %. g < x == .. U gy 3 ~- 3? 3 O T M = < .g - = x' -w o eE e .x - l :: E 77E .h

c. 'l: 97 5 e - gt -u a - .-

w "Mw LV>$v2 S =b LJ J W . ysggcw$ - a m *m. - e >~ < a m.

• i C .

0 < e C == I2 1 ( 3 - s< E4( 3 v 3 w= WC- =E ==O

• a h ,

,. m= , - 2 ~ wm m -m E m O ' h% = m e-  :~ _a u e e e ces:- n<% =-i n< W - = I ;. -1 a- x 0 ' s ism -> O a - - = - "- a 3  ;'r-

, 2 >

< a ei ei w .< u < t

• • ' l I 3 C  ? !o

- w * : Ep I \. >

e=! 3--c Y,/,7 z - i G 2 -$hEc. -X-$= 2* a l 3 o ~- N c l ?00R BRIGINAL X.3.3.3.4 Recommendation The licensee should evaluate the following concerns:

a. The discharge lines of both AFW pumps combine into a single header through which all AFW water must flow. A pipe break in this single flow path could result in the loss if the entire AFW system func* ion.

b. The Fort Calhoun AF% system design does not meet the high energy line break crit 0ria in SRP 10.4.9 and Branch Technical Position 10-1; namely, that the AFW system should maintain the capability to supply the required AFW flow to the steam generator (s) assuming a pipe break anywhere in the AFW pump discharge lines concurrent with a single active failure.

The licensee should evaluate the postulated pipe breaks stated above and (1) determine any AFW system design changes or procedures necessary to detect and isolate the break and direct the required feedwater flow to the steam generator (s) before they boil dry or (2) describe how the plant can be brought to a safe shutdown condition by use of other systems which would be available following such postulated events.

Response

a. The discharge from the two auxiliary feedwater pumps do combine into a single header for feeding the steam generators through the auxiliary feedwater nozzles. The District has performed additional evaluation following our earlier response to this concern (ref: OPPD letter, W. C. Jones to D. G.

Eisenhut, dated Januciy 14, 1980). It was determined that a break in this common header would not result in the total loss of auxiliary feedwater system function. If a break occurs in this common header, it can be isolated by the closure of the following valves:

HCV-1107A and/or B HCV-1108A and/or B HCV-1384 and/or FW-169, and/or FW-170 FW-171 and FW' 172 Valves FW-744, FW-745 and FW-746 would then be opened (Note:

FW-746 would already be open, since it is proposed that this valve be locked open in part "b" of this response), and auxiliary feedwater flov would be directed into thu steam generators through the main feedwater lines vis HCV-1385 or HCV-1386; using either FCV-1101/HCV-1103 and FCV-1102/HCV-1104 or the bypass valves, HCV-1105 and HCV-1106,

b. The District has completed its evaluatica of the Fort Calhoun auxiliary feedwater system relative to the high energy line break criteria. To satisfy high energy line break criteria, the auxiliary feedwater system must be capable of supplying water ' to a steam generator in conjunction with the following events:

1. Loss of offsite electrical power.

2. A high energy line break, which corresponds to a passive failure anywhere in the AFW pump discharge lines.

3. A single active component failure in the AFW system.

The auxiliary feedwater system downstream of, and including, valves FW-171, FW-172, FW-744, and FW-745 will meet the above criteria by utilizing the existing main feedwater supply lines to the steam generators as an alternate flow path. A line break in the common AFW discharge header can be isolated, as described in "a" above, and the flow rerouted through the main feedwater piping to the steam generators. The portion of the main feedwater system, which the District proposes to utilize as an alternate AFW flow path, was designed, constructed, and tested in accordance with the criteria listed below:

1. USAS B31.7, Nuclear Power Piping (Draf t USA Standard dated February 1968), for feedwater piping downstream of containment isolation valves HCV-1385 and HCV-1386.

2. USAS B31.1.0, Power Piping, 1967, for feedwater piping upstream of the containment isolation valves.

3. The feedwater system within Containment and the Auxiliary Building is seismically supported.

The reliability of the remaining portion of the AFW system, vulnerable to high energy line break criteria, will be insured by complying with Technical Specification 3.9 and by increasing in-service inspection of appropriate valves and discharge piping.

Detection of an AFW line break can be done by a variety of methods, depending "pon the location of the break. Flow elements FE-1109 and FE-1110 (A2W to steam generators) will inform the operator whether or not AFW is flowing to the steam generators via the AFU piping. Flow elements FE-1368 and FE-1369 (AFW pump suction) will indicate flow through/by the AFW pumps. In the event of an AFW line failure, steam generator level indication in conjunction with FE-1368 and FE-1369 will alert the operator whether or not AFW flow had been established through the main FW lines to the steat generators.

Loss of offsite electrical power could (depending upon line break location) require manual operation of AFW and main feedwater valves to isolate a line break and reroute AFW flow to the steam generators. The District has conducted a time-response test for an operator to perform these manual valve operations. The District's test demonstrated that the maximum time, including travel time, an operator would require to realign the AFW flow path is 7.0 minutes. This would assure that the steam generator would maintain an inventory at all times.

To guarantee the existing AFW system's safety, the District shall implement the following:

1. Valve FW-746 will be maintained in the " locked open" position.

This will insure an alternate AFW flow path to the main feed-water loop, in the event a passive failure occurs in the common AFW discharge header.

2. In-service inspection and testing requirements of check valves FW-173, FW-174, and pump discharge piping up to valves FW-171, FW-172, FW-744 and FW-745 will be increased. The testing and inspection requirements for this portion of the AFW system will be upgraded in accordance with ASME Section XI for Class 3 components. This step, in conjunction with the surveillance requirements of Technical Specification 3.9, will insure the reliability of that portion of the AFW system vulnerable to high energy line break criteria.

3. A new cheek valve will be installed downstream of valves FW-746 and FW-169. The new check valve vill preclude continuous feedwater prassure in the piping from the AFW pumps, through the switchgear room, to the main feedwater lines. This step is not required for high energy line break criteria compliance, but will enhance the safety of the system.

In su= mary, the District , believes that the actions prescribed in this response will enable the safe. operation of the existing AFW system relative to a postulated high energy line break.

.~ , ,, -- - -

, ,