ML20153F367

From kanterella
Jump to navigation Jump to search
Safety Evaluation Accepting Util 870311 Proposed Changes to Tech Spec Tables 2.2.1-1,3.6.1.2-1 & 3.6.3-1 Re MSIV-closure Setpoint
ML20153F367
Person / Time
Site: Nine Mile Point, 05000000
Issue date: 04/30/1987
From:
Office of Nuclear Reactor Regulation
To:
Shared Package
ML20150F672 List:
References
FOIA-88-356 NUDOCS 8809070248
Download: ML20153F367 (7)
v • d • e


Text

' - - -

i

  • * * "%,* UNITED STATES NUCLE AR REGULATORY COMMISSION i ,; WASMNQ TON, D. C. 20m 5., . p ENCLOSURE-1 e

SAFETY EVALL'ATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION MS!V CHANGE TO WYE-PATTERN GLOBE VALVES SUPPORTING AMENDMENT NO-----TO FACILITY OPERATING LICENSE NO.-----

NIAGARA M0 HAWK POWER CORFORATION NINE MILE POINT-UNIT 2 DOCKET NO:50-410

1.0 INTRODUCTION

Cy letter dated March 11, 1987 The Niagara Mohawk Power Corporation (NMPC, licensee) requested changes to the Technical Specifications for Nine Mile Foint Unit #2. These changes are required due to the changing cf the Main Steam Isolation Valves (M51Ys) from hydraulic actuated ball valve to air-operated Wye-pattern globe valves. By letters dated March 16 April 2, and April 28, 1987, NMPC provided additional infertnation as requested by the staff. Changes to the M31Y-closure trip setpoints in the Technical Specifications are required due to the valve change.

2.0 _ EVALUATION The M51V Wye-pattern gicbe valves function in a similar e.anner as the M51V ball valves. The new valves will close in 3 to 5 seconds in accordance with existino technical specifications. The new valves will also be actuated on the same safety related signals as presently used. NMPC has reviewed the effect on overpressurization protection analysis, LOCA analyses and transient and accident analyses due to the MS!V change to Wye-pattern globe valves. The results of the NMPC review are evaluated below.

8809070248 000010 PDR FOIA KUDLICKOO-356 PDR v o y ty r T ~

2 2.1 OvefpressurizationProtection The worst case overpressurization transient, MS!V closure with flux scram, was not affected since failure of direct position scram was assumed in the analysis. Therefore, the proposeci HSIV closure trip setpoint change in the Technical Specifications from " <6% closed" to " <8% closed" and allewable value change from " (7% closed" to "<12% closed" in RPS instrumentation setpoints have no impact on the overpressurization protection analysis.

2.2 Loss of Coolant Accident (LOCA)

The change in MS!V closure characteristics, resulting from the installation of the Vye pattern glove valves, has a negligible effect on the ECCS performance analyses as shown in Table 1. The change to Wye pattern globe valves would cause less than . degree F increase in the peak clad tenerature (PCT) for the most limiting large break and less than 2 degrees F increase for small breaks. Therefore, the acceptance criteria for emergency core cooling systems for light water nuclear power reactors as contained in 10CFR50.46 are satisfied with the globe valves in operation. The modeling of steam flow during MSIV closure remains unchanged from that is described in NE00-19329, page B-9, and has been previously found to be acceptable by the staf f.

In addition to reanalyzing the worst case breaks, the licensee assessed the impact of the change on other postulated breaks. For a recirculation line, feedwater line, or ECCS line break, MSIV closure is conservatively assumed to occur on low-low-low water level (Level 1). A scram would be expected to have already occurred on Low water level (Level 3). Thus, changing the HSly position scram setpoint has no effect on the ECCS performance analyses for these breaks since it was not utilized in these analyses.

1

3 For a steamline break inside the containment, the scram will occur on high dryvell, pressure before MSIV closure occurs. The MS!Y position scram setpoint is not used for the ECCS systen response. For steamline break outside the containeent, the analysis conservatively starts with the water level at the scram trigger point, Low water level (Level 3).

Realistically, a scran is likely tn occur earlier due to MSIV closure on high steam line flow, but this input has been conservatively omitted in the analysis. Thus, the analysis is unaffected by the MS!V position scram setpoint change.

2.3 ANTICIPATED OPERATICN OCCURRENCES The proposed change to the MSIV closure setpoint necessitated by the valve char.ge has been evaluated with respect to the transtant and accident analyses contained in the FSAR. Loss of air or nitrogen, manual closure of all MSIVs pressure regulator controller failure, and other transients and accidents were considered for any significant effect on the margin of sa fety.

The impact of a delayed scran signal due to the new MSIV closure-trip switch setroint on transients has been evaluated. The new setpoint corresponds to an analytical limit cf '85% MSIV open" insteet of the previous '90 P41V open." Two transients which take credit for this scram function are the manual closure of all main steam isolation valves (direct scram event) and the pressure regulator centroller failure (open event).

Of the two events, the manual closure is more limiting. The transient results are more sensitive (limiting) to differences in the allewable range of the Technical Specifications (3 to 5 sec.) speed of MSiv closure (which isn't being changed by this Technica! Specification change) than due to a small scram delay resulting from the setpoint change. Tiie proposed change to the Main Steam Isolation Valve-Closure setpoint was evaluated by reanalyzing the manual closure of all main steam isolation valves transient and there was no change in the critical power ratio (CPR) operating limit.

4 Another event affected by the setpoint change is load tejection without turbine bypass. This event was also reanalyzed. The change in MCPR, as showninTable1,isinsignificant(muchlessthan0.01).

The remaining existing FSAR transient analyses are based upon an analytical model that bounds the closure characteristics (flow area versus time) of either the ball or globe valves. The Wye pattern globe valves have a 10 psi higher pressure differential when full open, than the bal!

valves, due to frictional flow losses, Sensitivity studies. performed by l

GE based upon information from a number of plants have shown that the l larger aP across the steamline volume produces milder transient rNponse.

Larger steam line AP has a dampening effect on the pressure wave ,

following a closure of turbine stop or control valves. Thus, since the previous analyses are based upon a model which conservatively simulates  ;

the Wye pattern valve characteristics, there is no significar,t impact on the other pressurization transients due to the HSIV change.

3.0 CONCLUSION

The preposed change to the HSIV closure setpoint in Technical Specification Table 2.2.1-1 necessitated by the HSIV change was evaluated against affected transient and accident analyses and the proposed change l

has been shown not to involve a significant increase in the probability or consequences of an accident previously evaluated. Table 3.6.1.2-1 has been changed to alter the valve designation to provide consistent notation forthetypeofvalveinstalled,e.g.,anair-operated (A0V) valve. Table 3.6.3-1 has also been changed to alter the valve designation to provide consistent notation. These changes are administrative only. For the reasons discussed in the evaluation, we find the proposed changes in Technical Specification Tables 2.2.1-1, 3.6.1.2-1, and 3.6.3-1 are acceptable.

I i

5 We have concluded, based on the considerations discussed above, that: (1) there is reasonable assurance tha- the health and safety of the public will not' be endangered by operation in the proposed manner, and (2) sucn activities will be conducted in compliance with the Comission's regulations, and issuance of this crendment will not be inimical to the I comon defense and security or to the health and safety of the public.

l l

l 1

l l

l 1

I 1

l

6 TABLE 1 COMPARISON OF LOCA ANALYSIS BALL WYE Operating Limit (1) CPR 1.28 1.28 Limiting Transient (1)6 CPR 0.22 <0.22(2)

Safety Limit MCPR 1.06 1.06 Peak-VesselPressure(psi) 1268 1268 Allow >1e Pressure (psi) 1375 1375 Large Break PCT ( F) 1921 1922 g Small Break PCT ( F) 1522 1524 Allowable PCT (*F) 2200 2200 I

(1) Load rejection without bypass Section 15.2.2 (2) Slightly less due to 10 psi higher a P across Y valves COMPARISON OF TRANSIENT ANALYSIS l

BAlu WYE l

Operating Limit CPR 1.28 1.28 HSIV Closure Event (l' 4)

(15.2.4)(3) A CFFs 0.01 <0.01 Safety Limit MCPR 1.06 1.06 Peak Vessel Pressure (psi) 1268 1271 Allowable Pressure (psi) 1375 1375 (1) Only event affected by setpoint change (2) LoadrejectionwithoutbypassSection15.2usingODYNOptionA (3) Slightly less due to 10 psi higher a P across Wye type valves (4) No change in Limiting Transient

. .I ENCLOSURE 2

, SALP EVALUATION - NMPC Functional Areas

1. Management Involvement The submittal required additional information to permit approval Rating: Category 2
2. Resolution of Technical Issues The initial submittal showed insufficient understanding of the technical l issues involved.

Rating: Category 2

3. Responsiveness to NRC Initiatives Responses to questions were fully acceptable,

.: ting: Category 2

_a

Retrieved from "https://kanterella.com/w/index.php?title=ML20153F367&oldid=3353697"