ML19209B606
| ML19209B606 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 10/05/1979 |
| From: | TOLEDO EDISON CO. |
| To: | |
| Shared Package | |
| ML19209B593 | List: |
| References | |
| NUDOCS 7910100214 | |
| Download: ML19209B606 (11) | |
Text
.
1 DAVIS-BESSE NUCLEAR PGWER STATION UNIT NO. 1 EVALUATION OF POTENTIALLY ADVERSE ENVIRONMENTAL EFFECTS ON NON-SAFETY GRADE CONTPOL SYSTDIS Prepared By:
The Toledo Edison Company and Babcock & Wilcox Company s
October 5,1979 1112 312 7 910100 2/T
TABLE OF CONTENrS Page I.
Introduction 1
II.
Facility Licensing Basis 2
?
III.
Safety Assessment 3
1.
Environmental Effects 2.
Impact on Facility Safety Analysis IV.
Justification for Continued Operation 4
V.
Recommended Follow-Up Action 5
Tables I.
Typical Equipment Response During High Energy Line Breaks II.
Environmental Effects on Nor-Safety Grade Control Systems m
t i
I.
Introduction This report is.in response to Harold R. Denton's letter of September 17, 1979, on the subject of " Potential Unreviewed Safety Question on interaction Between Non-Safety Grade Systems and Safety Grade Systems."
It is intended to serve as a response to the concerns listed in Infor-mation Notice 79-22 and to fulfill the commitment made during our meeting with your staff on September 20,19/9. During that meating, we committed to:
Evaluate impact on Licensing basis accident analyses due to consequential environmental effects on non-safety grade control systems.
- Identify Licensing basis accidents which cause an f
adverse environment for each f acility.
- Define Safety Analysis. inputs and responses used during.Lic ensing basis t idents.
- Verify Safety Analysis conclusions or recommend actions justifying continued operation.
The scope of this response includes a confirmation that the facility's actual equipment actuation and performance are consistant with that used in the Lic ensing basis analysis. A matrix of environmental ef fects on non-safety grade control systems is presented.
Where non-safety grade equipment performance could be af fected by the adverse environ-m en t, a safety assessment has been prepared. The safety assessment was.used to define probinms due to the effects on an adverse environ-ment on non-safety grade control systems.
A justification for continued operation of the f acility is provided based on the safety assessments and risk evaluations. Work beyond the scope of the 20-day response and work to provide a more detailed assess-ment are included in recommended follow-up actions,
~
s 1112 H5 1
II.
Facility Licensing nas,is The facility Licensing basis anal)._s, as presented in the FSAR, were reviewed to define the inputs, assumptions and responacs used for non-safety grade control systems.
This information is summarized in Table I, which lists typical equipment actions and actuation times used in the safety analyses for B&W 177 fuel assembly plants.
The data has been cate-erized to reflect the functional requirements as follows:
A. Reactor Power Control and Shutdown B. Reactor Pressure Control C. Steam Syctem Isolation and Pressure Control D.
Feedwater System Isolation Control This categorization has been developed to focus upon those primary functions whicit have a potential for control system interactica.
The table identifies the range of equipment actions and ctuation times us-d in the facility safety analysis for steam line break, feedwater line brea and large and small LOCA.
I112
?16 2
III.
Safety Assessment 1.
Environment Effects The non-safety-grade control systems have been reviewed to determine if an accident cavironment could adversely affect the analyzed course of the event.
Specifically, the approach taken was to use the safety analysis functions and parameters :from Table I as a basis to identify where potential control system effects could have an impe-t.
The result of this evaluation is summarized in Table II, Environmental Effects on Non-Safety-Grade Control Systems. The matrix identifies, for six accident types, the non-safety-grade control systems which could be adversely affected by the environment caused by the event.
f 2.
Impact on Facility Safety Analysis Environmental effects which could adversely tmpact the facility safety analysis are identified in Table II in the Notes.
For each potential adverse effect, a safety assessment has been prepared to confirm facility safety or identify a potential problem area.
These safety assessmants indicate that the effect on non-safety grade controls and equipment of an adverse environ-ment caused by the Licensing Basis Accidents could not af fect the Safety Analysis results I112 317 3
IV.
Justification for Continued Operation Based on the evaluations'and safety assessments above, we conclude that continued operation is just.ified, particularly in light of the very low probabilities of the high-energy line breaks considered and the conservatisms included in the analyses. One area has been previously identified and is being evaluated under an Inspection and Faforcement ef fort discribed below.
Auxiliary Feedwater Control as a Result of Small LOCA or FULB Inside Containment The only potentially af fected components inside containment are the safety grade steam generator level transmitters whose accuracy could be affected by the elevated temperature (all other components which could r
af fect these controls are outside containment).
This subject has previously been addressed in response to Bulletin 79-21, and the associated ~ operator guidance to accommodate these errors are considered sufficient to Justify continued operation pending any further evaluations and/or corrective actions.
1112 318 4
V.
Recommended Follow-Up Action The 20-day response to Mr. Denton's letter focused upon a confirmation that the fccility's actual equipment actuation and performance are consistent with that used in the licensing basis analyses. The approach taken was to define effects of non-safety-grade control systems in an adverse enviro ment and prepare an assessment to confirm the conclusions reached in the original safety analyses.
Justification for continued operation was then based upon the results of this evaluation.
The scope of the 20-day response did not include potential control systen effects which could impact long-term system response and operator action. A complete assessment of cavironmental effects on non-safety grade control systems should include an evaluation of equipment required to maintain a safety shutdown following accidents which cause an adverse I
environmen t.
To address this issue, a future program is recommended to:
- 1.. Define instrumentation and control functions required for safe shutdown 2.
Identify applicable equipment errors and responses in an adverse environment.
3.
Prepare a safety assessment and recommand corrective action if required.
This ef fort will be closely coupled to the Abnormal Transient Operating Guidelines Program currently underway, and will focus upon additional operator training to recognize and respond to the impact of an adverse environment on non-safety-grade control systems. The schedule for submittal of the Safety Assessment will.,a evasistant with the current schedule for the. Abnormal Transient Operating Guidelines Program (i.e., mid-1980).
I k
111?
319 5
TABLE I
. TYPICAL EQUIPMENT RESIME DURING HIGH ENERGY LINE BREAKS B&W 177 FA PLANTS Steam Line Feedwater Large Small Break Line Break LOCA LOCA I.
Reactor Power Control and Shutdown High 6 or Low High RC Pressure Reactor Trip Low RC Pressure Trip Function Utilized 4
RC Pressure Not Used Time of Reactor Trip 1.1-8.0 sec.
8.2-13.4 sec.
II.
Reactor Pressure Control Time to PORV Actuation PORV Not 4-8 sec.
PORV Response PORV Not Reg'd Actuated for Not Important to Operate Time at Which PORV Closes Steam Line 20 sec.
B rc.ak III.
Steam System Isolation and Pressure Control (1)(2) Steam Line Isolation Time 1.6-8.5 sec.
6.0-12.0 sec.
Code Safety Code Safety Valves are Used Valves are Used (2)
Time to Steam Relief Valve Opening 7.0-16.0 sec.
7.0-7.5 sec.
in the Analyses in the Analyses for Conservatism for Conservatism (2)
Time for Steam Relief Valve Closure 20-30 sec.
25-30 sec.
IV.
Feedwater System Isolation and Control
]l)(2)MainFeedwaterIsolationTime 19-34 sec.
18 sec.
Analysis Con-Not Required servatively pM)
Auxiliary Feedwater Isolation Time 19-34 sec.
18 sec.
Assumes a Loss Not Required of All Feed-S2)
Auxiliary Feedwater Initiation Time 40 sec.
40 sec.
Water 40 sec.
TO 9)
Main or Auxiliary Feedwater Control Maintain SG Maintain SG Level Level Level (1) At tected Steam Generator (2)
Unaffected Steam Generator
TABLE II ENVIRONMENTAL EFFECTS ON NON-SAFETY GRADE CONTROL SYSTFltS
( ) = See notes attached Licensing Basis Accidents SLB Inside SLB Outside FVLB Inside FWLB Outside Large Small LOCA {
Non-Safety Grade Control Systems Containment Containment Con t a ini..en t gita_inment LOCA m
I.
Reactor Power Control and Shutdown N
Cont rol ' Rod Drive Contrdi System (3)
(3)
(3)
(3)
(3)
(3) 1.
Reactor Pressure Control Power Operated Relief Valve (4)
(4)
(4)
(4)
(4)
(4)
Pressurizer lleaters (5)
(10)
(5)
(10)
(5)
(5)
Pressurizer Spray (6)
(6)
(6)
(6)
(6)
(6)
I.
Steam System Isolation and Pressure Control Turbine Trip / Turbine Stop Valves (7)
(11)
(7)
(12)
(7)
(7)
Main Steam Line Isolation Valve (1)(2)
(6)
(6)
(6)
(6)
(6)
(6)
Turbine Bypass Valves (1) (2 )
(8)
(8)
(8)
(8)
(8)
(8)
Atmospheric Vent Valves (2)
(C)
(9)
(9)
(9)
(9)
(9)
V.
Feedwater System Isolation and Control Main Feedwater Cont rol (1)(2)
(9)
(4)
(9)
(9)
(13)
(7)
Main Feedwater Isolation Valves (1)(2)
(6)
(6)
(6)
(6)
(6)
( 6)
Aux iliary Feedwa t er Isolation Valves, (6)
(6)
(6)
(6)
(6)
(6)
( 1 ) (.' )
Auxiliary Feedwater In it iat ion (2)
(6)
(6)
(6)
(6)
(6)
(6)
An y. i i i i r v Feci!wi e r I. eve l cen t r.. I 8 ' 'i (b)
(6)
(G)
(6) to)
(6)
NOTES TO TABLE II 1.
Affected Steam Generator (SG) 2.
Unaffected Steam Generator 3.
The initial reactor power cannot be changed enough by the adverse environment prior to the reactor trip to affect the Safety Analysis reoults.
,4.
All control cables are qualified to withstand the adverse environment both inside and outside the containment. All other controls are located where they will not be subject to the adverse environment.
(switchgear rooms, cab ine t room, or control room).
Since the valve electrical operator has to be energized to 'open, an cdverse environment could not cause a hot short, which would be required to cause the valve to open inadvertantly.
5.
All controls and power supplies for two redundant 126 KW ban.-
of pressurizer heaters are safety grade. All cables are safety grade except for the cables inside the containment, immediately adjacent to the heater. A failure of these cables caused by the adverse environment will not affect the Safety Analysis results.
6.
All controls that can be affected by the adverse environment are safety grade and qualifit '.
7.
Adverse environmental ef fects cannot occur due to the location of equipment being outside the affected area.
- 8. The turbine bypass valves are automatically isolated f rom the SG's by the safety grade closure of the MSIV's.
Therefore, any adverse environment will not affect the Safety Analysis results.
9.
All non-safety grade controls are isolated by safety grade signals.
10.
All controls located outside the containment including cables and power supplies on two redundant 126 KW banks of pressurizer heaters are safety grade and qualified, 11.
If a main steam line break (MSLB) were to occur at the main turbine, the turbine stop valves would not be fully qualified for this environment and a main turbine trip would not be assured.
However, even with a single failure of a safety g.ade main steam line isolation valve (MSIV), the unit would have one unaffected SG and the consequences would be no worse than a steam line break upstream of a iSIV.
If the MSLB were to occur in the auxiliary building, then the main turbine stop, valves anc their control would not be subject to the adverse environment and would therefore close properly.
Ii12 322
(
- 12. Main feedwater lines that are located in the turbine building are located a considerable distance from the main turbine stop valves.
As a result, a main feedwater line break (FWLB) in the turbine building would cause the main turbine to trip with a signal f rom the Safety Grade Steam and Feedwater Rupture Control System (SFRCS) before (d01 second) the adverse environment could reach the main turbine stop valve and controls.
13.
Main feedvater would be isolated from both SG's af ter a large LOCA by a safety grade signal from the safety features actuation system to the safety grade main feedwater isolation valve.
1112 323