ML20037A321
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October 4, 1979 t.\\
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MEMORANDUM FOR: Robert W. Reid, Chief, Operating Reactors Branch #4, 00R FRCM:
D. C. Dilanni, Project Manager, Operating Reactors Branch !4, 00R
SUBJECT:
SPURIOUS REACTOR SCRAM POST TMI Licensees of the Babcock & Wilcox (B&W) designed operating reactor plants were asked to present their operating experiences regarding feedwater transients resulting in reactor scrams (meeting held 3/23/79). As an attendee at this meeting, I feel obliged to express my views on this matter.
Recent operating experience shows that instability in the secondary systems caused spurious reactor scrams by the actuation of the high pressure trip setpoint in the primary system. As a result of TMI, this high pressure trip setpoint was lowered from 2450 to 2300 psig and the power-operated relief valve (PORV) setting was raised'above the high pressure trip setting (2300 psig). Lowering the pressure trip resulted in reducing the pressure spread between the normal operating pressure and the high pressure trip to approximately 100 psi. This change resulted in negating an important
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function of the PORV which is to prevent spurious reactor scrams during plant transients.
It is recomended that these changes in the pressure trip setting and the setting of PORV be considered as an interim measure and the settings should be returned to pre-TMI conditions after upgrading the reliability of the FORV.
Upgrading the reliability of de PORV should be expedited in order that these undesirable pressure settvgs are eliminated.
Experience shows that reactors are more susceptible to spurious scrams when scram settings are set close to the normal operating parameter (aPS00 psi). This experience was brought to the staff's attention by the licensees during the meeting of August 23, 1979.
Furthermore, one could expect that the B&W plants are more susceptible to spurious scrams than the other two PWR reactor vendors because of the faster response of the B&Ws primary system to changes in the secondary system. The transient conditions during a spurious scram does make plant equipment (i.e., valves, cipe vibration, control system, etc.)
prone to malfunction decreasing some of the safety margins during transient periods.
The present pressure setpoint condition also places an excessive stress on the reactor operator since the operating margin is reduced requiring im ediate action by the operator to avoid reactor scrams.
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~1 Assuming that the FORY will be used in the future to assist in the control of primary system pressure, then the staff should develop criterion on an acceptable level of reliability for the PORV to both open and close which has not been covered in detail in NUREG-0578. The development of such a criterion should include the mechanical as well as the control aspects of the valve design. The following is a recommended starting point for this task.
1.
Request for review frem the three NSS vendors the engineering specifications for the PORV that was issued to the valve manufacturers.
2.
The valve manufacturer should be consulte8 as t meeting the requirements of the specifications. Discussions with the vi. ve manufacturer should include a review of the valve design, quality.ssurance/ quality control and testing.
Information from Items 1 and 2 above would assist the staff in detennining area's of design, fabrication, quality assurance / quality control and testing that would require upgrading.
3.
Evaluate the elevation of this valve type to a safety grade valve meeting the requirement of ASME Code,Section III. The ASME Code addresses power i
actuated relief valves which are required for over pressure protection purposes but whether these requirements are adequate for the PORV having the function of a pressure control valve is open to question.
f Valve bench testing criterion should be established which would include 4.
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design flow rates for fluids in all three phases (i.e., liquid, two phase
& steam).. It appears that a fluid supply system for testing should not present a ' problem because of the low capacity of the PORV as compared to5 5 #/hr V.S. safety valves 3.117 x 10 the safety valves (i.e., PORY l x 10
- /hr.).
5.
Valve controls including control circuitry, power supplies, panel indications should be reviewed with the objective of meeting the requirements IEEE 279.
In conclusion, the objective of this memorandum is to bring to your attention the immediate need for upgrading the reliability of the PORV for which adequate priority should be given anc to give an approach in trie resolution of this l
problem.
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D. C. Dilanni, Project Manager Operating Reactors Branch #4 Division of Operating Reactors cc:
W. Gamill G. Ma:etis
- 0. Ross B. Capra 3
T. Novak D. Eisenhut S. Israel R. Vollmer V. Neonan B. Grimes R. Ingram
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