ML19347E355
| ML19347E355 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 10/24/1980 |
| From: | Noell P, Stilwell T Franklin Research Ctr |
| To: | Polk P Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19347E354 | List: |
| References | |
| CON-NRC-03-79-118, TAC 12890 TER-C5257-224-R01, NUDOCS 8104270110 | |
| Download: ML19347E355 (7) | |
Text
7 l
g TFilS REPORT SUPERSEDES ISSUE OF AUGUST 22, 1980 i
an v
TECHNICAL EVALUAT!ON REPORT i
i PRIMARY COOLANT SYSTEM PRESSURE ISOLATION VALVES TOLED0 EDISON COMPANY l
DAVIS-BESSE UNIT 1 l-NRC DOCKET NO.
50-346 i
NRC TAC NO.
12890 FRC PROJECT CS257 N RC CONTRACT NO. NRC-03-79-118 FRC TASK 224 Prepared by Franklin Research Center Author:
P. N. Noell The Parkway at Twentieth Street T. C. Stilwell Philadelphia, PA 19103 FRC Group Leader:
P. N. Noell Prepared for Nuclear Regulatory Commission i
l Washington, D.C. 20555 Lead NRC Engineer:
P. J. Polk l
October 24, 1980 This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, or any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third party's use, or the results of such use, of any information, apparatus, product or process i
disclosed in this report, or represents that its use by such third l
party would not infringe privately owned rights.
l A
.. 0. Franklin Research Center A Division of The Franklin Institute The Benjamn Frankl.n Parkway. Phita.. Pa. 19103 (215) 448-1000 810427 ag go e
1.0 INTRODUCTION
The NRC has determined that certain isolation valve configurations in systems connecting the high-pressure Primary Coolant System (PCS) to lower-pressure systems extending outside containment are potentially significant contributors to an intersystem loss-of-coolant accident (LOCA). Such configu-rations have been found to represent a significant factor in the risk computed for core melt accidents.
The sequence of events leading to the core melt is initiated by the con-current failure of two in-series check valves to function as a pressure isola-tion barrier between the high-pressure PCS and a lower-pressure system extend-ing beyond containment. This failure can cause an overpressurization and rup-ture of the low-pressure system, resulting in a LOCA that bypasses containment.
The NRC has determined that the probability of failure of these check valves as a pressure isolation barrier can be significantly reduced if the pressure at each valve is continuously monitored, or if each valve is periodi-cally inspected by leakage testing, ultrasonic examination, or radiographic inspection. The NRC has established a program to provide increased assurance that such multiple isolation barriers are in place in all operating Light Water Reactor plants designated by DOR Generic Implementation Activity B-45.
In a generic letter of February 23, 1980, the NRC requested all licensees to identify the following valve configurations which may exist in any of their plant systems consunicating with the PCS: 1) two check valves in series or 2) two check valves in series with a e stor-operated valve (MOV).
For plants in which valve configurations of concern are found to exist, licensees were further requested to indicate: 1) whether, to ensure integrity of the various pressure isolation check valves, continuous surveillance or periodic testing was currently being conducted, 2) whether any check valves of concern were known to lack integrity, and 3) whether plant procedures should be revised or plant modifications be made to increase reliability.
F: anklin Research Center (FRC) was requested by the NRC to provide tech-nical assistance to NRC's 3-45 activity by reviewing each licensee's submittal.
n---.
r i
against criteria provided by the NRC and by verifying the licensee's reported findings from plant system drawings. This report documents FRC's technical review.
2.0 CRITERIA 2.1 Identification Criteria For a piping system to have a valve configuration of concern, the follow-ing five items must be fulfilled:
I l
- 1) The high-pressure system must be connected to the Primary Coolant System; l
- 2) there must be a high-pressure / low-pressure interface present in the line;
- 3) this same piping must eventually lead outside containment;
- 4) the line must have one of the valve configurations shown in Figure 1; and
- 5) the pipe line must have a diameter greater than 1 inch.
PCS Wovi I
I i
c l
l k
'/
'M 4
i l
'/
l c
I Iwovl
=
Mov l l
HP4
- LP Figure 1.
Valve Configurations Designated by the NRC To Be Included in This Technical Evaluation {
<: q -
2.2 Periodic Testing Criteria For licensees whose plants have valve configurations of concern and choose to institute periodic valve leakage testing, the NRC has established criteria for frequency of testing, test conditions, and acceptable leakage rates.
These criteria may be summarized as follows:
'2. 2.1 Frequency of Testing Periodic hydrostatic leakage tes ting
- on each check valve shall be accom-plished every time the plant is placed in the cold shutdown condition for refueling, each time the plant is placed in a cold shutdown condition for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> if testing has not been accomplished in, the preceding 9 months,
each time any check valve may have moved from the fully closed position (i.e., any time the differen-tial pressure across the valve is less than 100 psig), and prior to returning the valve to service af ter maintenance, repair, or replacement work is performed.
2.2.2 Hydrostatic Pressure Criteria Leakage tests involving pressure differentials lower than function pres-sure differentials are permitted in those types of valves in which service pressure will tend to diminish the overall leakage channel opening, as by pressing the disk into or onto the seat with greater force. Cate valves, check valves, and globe-type valves, having function pressure dif ferential applied over the seat, are examples of valve applications satisfying this requirement. When leakage tests are made in such cases using pressures lower than function maximum pressure differential, the observed leakage l
shall be adjusted to function maximum pressure differential value. This I
adjustment shall be made by calculation appropriate to the test media and the ratio between test and function pressure differential, assuming leak-age to be directly proportional to the pressure differential to the ene-half power.
l 2.2.3 Acceptable Leakage Rates:
Leakage rates less than or equal to 1.0 gpm are considered accept-e able.
l l
e Leakage rates greater than 1.0 gpm but less than or equal to 5 0 l
gpm are considered acceptable if the latest measured rate has not exceeded the rate determined by the previous test by an amount
- To satis fy ALARA requirements, leakage may be measured indirectly (as from the performance of pressure indicators) if accomplished in accordance with approved procedures and supported by computations showing that the method is capable of demonstrating valve compliance with the leakage criteria.
i i
! l
?
4
o t,
that reduces the margin between measured leakage rate and the maximum permissible rate of 5.0 gum by 50% or greater.
Leakage rates greater than 1.0 gpm but less than or equal to 5.0 e
gpa are considered unacceptable if the latest measured rate ex-ceeded the rate determined by the previous test by an amount that reduces the margin between measured leakage rate and the maximum permissible rate of 5.0 gpm by 50% or greater.
Leatage rates greater than 5.0 gpm are considered unacceptable.
e
3.0 TECHNICAL EVALUATION
3.1 Licensee's Response to the Generic Letter In response to NRC's generic letter [Ref.1], the Toledo Edison Company (TEC) stated [Ref. 2] that, "A valve configuration at DB-1 includes two check valves in series with a motor operated valve. This falls under the Event V isolation valve configuration definition of a Class I boundary of high pres-sure piping connecting primary coolant system (PCS) piping to low pressure system piping. The valves involved are CF-31, DR-77, CF-30 and DH-76, and shown on Figure 6-17 of the DB-1 Final Safety Analysis Report (FSAR)."
The Licensee further stated, "As shown on Figure 6-17 of the FSAR, there is a continuous pressure surveillance by a computer alarm which alarms at pressures above 375 psig with both decay heat pumps off. The pressure moni-toring in the two LPI trains are common to this computer alarm. In addition to this alarm, there are pressure indicators PI 2882A and PI 2882B local to the [motorneerated] valves DHIA and DHlB."
It is FRC's understanding that, with TEC's concurrence, the NRC will di-rect TEC to change its Plant Technical Specifications as necessary to ensure that periodic leakage testing (or equivalent testing) is conducted in accor-dance with the criteria of Section 2.2.
3.2 FRC Review of Licensee's Respont FRC has reviewed the licensee's response against the plant-specific Piping and Instrumentation Diagrams (P& ids) [Ref. 3] that might have the valve configurations of concern.
.o
, ~.
A' i
FRC has also reviewed the efficacy of' instituting periodic testing for the
~
check valves involved in this particular application with respect to the _ re-duction of the probability of an intersystem LOCA in the Decay Heat Removal piping ~ 1ine s.
In its review of the P& ids (Ref. 3] for Davis-Besse Unit 1 FRC foundLthe following piping system to be of concern:
The Decay Heat Removal System (DHR) is composed of two piping
. trains, 'each. connected directly to the reactor vessel.. Each i
train has two check vsives and a motor-operated valve in one of the series configurations of concern.- In each train the high-pressure / low-pressure interface ~ is located on the upstream side of the motor-operated valve (MOV). These valves are listed below:
1 Decay Heat Removal System i
Train A high-pressure check valve, CF-30 high pressure check valve, DH-76, locked open i
high-pressure MOV, DHL A, normally opened Train B 1
high-pressure check valve, CF-31 i
i high-pressure check valve, DH-77, locked open high-pressure MOV, DHLB, normally opened In accordance with the criteria of Section 2.0, FRC found no other valve configurations of concern existing in this plant. These findings confirm the j
licensee 's response [ Ref. 2].
i FRC reviewed the effectiveness of instituting periodic leakage testing of the check valves in these lines as a means of reducing the probability of an
)
intersystem LOCA occurring. FRC found that introducing a program of check valve leakage testing in accordance with the criteria summarized in Section 2.0 will be an effectsve measure in substantially reducing the probability of i
l an intersystem LOCA occurring in these lines and a means of increasing the j
probability that these lines will be able to perform their safety-related functions.
It is also a step toward achieving a corresponding reduction in the plant probability of intersystem LOCA in Davis-Besse Unit 1.
1 1
i i
1,
.---.- m
-,.,.,, -,.,,.. -..,,, - -,. -.., _, _ ~.. -... -....,. _ _ -,. - - -, -. - -.. -. - -, - -, -
u v
-y.
~
4.0 CONCLUSION
Davis-Besse Unit I has been determined to have valves in one of the configurations of concern in both trains of the Decay Heat Removal System.
If TEC modifies the Plant Technical Specification for Davis-Besse Unit 1 to incorporate periodic testing, as delineated in Section 2.2, for the check valves itemized in Table 1.0, then FRC considers this an acceptable means of
~
achieving plant compliance with the NRC staff objectives of Reference 1.
Table 1.0 Primary Coolant System Pressure Isolation Valves System Check Valve No.
Allowable Leakage
- Decay Heat Removal Train A CF-30 Train B CF-31
5.0 REFERENCES
[1]. Generic NRC letter, dated 2/23/80, from Mr. D. G. Eisenhut, Department of Operating Reactors (DOR), to Mr. R. P. Crouse, Toledo Edison Company (TEC).
[2]. Toledo Edison Company's response to NRC's letter, dated 3/21/80, from Mr. R. P. Crouse (TEC) to Mr. D G. Eisenhut (DOR).
[3]. List of examined P& ids:
Toledo Edison drawings:
M-030, ( Rev. 15)
M-031, ( Rev. 14) l M-033, (Rev. 21)
M-033, (Rev. 23)
M-034, (Rev. 16)
Fig. 6-12 Fig. 6-19
- To be provided by licensee at a future date in accordance with Section 2.2.3.
l l,
l