ML20235D252

From kanterella
Jump to navigation Jump to search
Ro:On 710420,determined That Two Air Ejector off-gas Monitors Have Been Inoperable During Startup Testing Program to 25% Power Level.Caused by Improper Hookup of Ejector Sample Chamber Purge Valve.Sys Piped Up Properly
ML20235D252
Person / Time
Site: Monticello, 05000000
Issue date: 04/29/1971
From: Duncanson R
NORTHERN STATES POWER CO.
To: Morris P
US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20235B311 List: ... further results
References
FOIA-87-111 NUDOCS 8709250169
Download: ML20235D252 (3)
v • d • e


Text

, _

'~ ~

! /* . ..

~

'r '"

l NSP "'~5"

NORTHERN STATES POWER COMPANY Minneapolis, Minnesota 55401 cp 9 g g"J5 s Ap ril 29,1971 e + b  !

3

%$' s off l Dr. Peter A. Morris, Director Division of Reactor Licensing

+

g p'{ S cpq=. Oc g 8[ (g g

y82

/g 9 United States Atomic Energy Commission I Washington D.C. 20545 g e c N

Dear. Dr. Morris:

MONTl CELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Inoperability of the Air Ejector Off-Gas System Radiation Monitors On April 20, 1971, it was determined that the two air ejector off-gas monitors have been inoperable during the startup testing program to the 25%

power level. We are reporting this occurrence in accordance with Section 6.6.B.3 of Appendix A, Technical Specifications, of the Provisional Operating License DPR-22.

Summarv Descrintinn or Occurrence During the startup testing program, while initially escalating to each power level, daily grab samples of the air ejector of f-gas are analyzed.

During the initial rise to 15% power, the air ejector activity discharge was approximately 25 uci/see with a corresponding stack release rate of approximately 15 uci/sec. These activity rates existed at the time of the 3-10-71 shutdown from 15% power. Following an extended shutdown the plant was restarted and reached 13% power on 4-19-71 with an air, ejector activity discharge of approximately 120 uci/see with a stack release rate of ap On 4-20-71 during the initial rise to 25% power, proximately the analysis of an off-gas45 grabuci/sec.

sam y activity discharge ,to be approximately 300sec. uci/ple Withshowed the air ejector this analyzed activity, it was expected that the air ejector off-gas monitors should be indicating noticeably above the indication provided by the bug sources. While investigating this concern, it was discovered that the monitor indications increased from 2.8 mr/hr to approximately 9 mr/hr when the Off-Gas Sample Chamber Purge controls were turned to the ON position. It was then recognized that the system was operating normally with the controls indicating a purge condition. The system was operated in this manner until the plant was shutdown.

Further investigation of the problem revealed that the air ejector sample chamber purge valve was hooked up improperly. The valve is a three way valve which should allow purging of the sample chamber when the valve solenoid is energized and provide normal sampling when the valve is de-energized. The valve was found piped up the opposite way and apparently

-71 "O 8709250169 870921 PDR FOIA -M NENZ87-111 PDR r / ? 'l / a

  • a' l 3y,,

4 had been 'in this condition since initial installation. .Following a i the system was piped up croperly and ~

.during plant shutdown a plant restart on on April Ap r25th,il 26th, proper operation of the system was verified. .l The Region til Compliance Office has been previously rotified of' the occurrence in accordance with Section 6.6. A.3 of the Technical Specifications. {

.Yours ver truly,

(

n&.2r

. R.0. Duncanson, Jr., P.E.

Gen; Supt. of Power Plants-Mechanical-Chairman Monticello Safety Audit Committee -

ROD /CEL/caf

)

1 i

'I v)

b g

6f8 #

na 3

tiu.

sgh o ,iti u

m l

d L h 2

l l .- < 8 e . '

20 $

SU $

$[ d r 00 $

e3 (I a. d 5

se <

d

.hI . .

a g3 ti, wc* O ti l se y --

,t v g,,4LfM y gj, b g

W M

W i O!-

8 g

GJg 3 . g , g ,. w w r.. 4 i-

k. A g 0 2

.a .na I"mi+*il

NSF NORTHERN STATES POWER COMPANY Minneapolis, Minnesota 55401 i Regulatory File Cy.

N l Acril 30,1971 'b '

t$

d oocmm USAEC //

"- r i A 1 S. Peter A. Morris, Director  ; MAY 5 1971 *g5 01- 4 v L i Civision of Reactor Licensing g gugY 6

~~

4q y ~ /p q L,1ted States Atomic Energy Commission Doc m CLERK 6 g Art /7

  • f 4ashington, D.C. 20545 g daCr ;7 1  % 3 C. ear Dr. Morris:
  • 4 2 @..- .

MOMTiCELLO NJCLEAR GENERATlNG PLANT Docket No. 50-263 License No. DPR-22 Safety / Relief Valve Settings Exceeding 1080 PSIG A condition occurred at the Monticello Nuclear Generating Plant which is reportable to your office in accordance with the provisions of Appendix A, Technical Specifications, of the Provisional Operating License DPR-22. The cccurrence was classified as an Abnormal Occurrence as defined in Section i. A.1 c' the Technical Specifications and requires reporting in accordance with Section 6.6.B.3 of the Specifications. The Region ll1 Compliance Office has been notified in accordance with the requirements of Section 6.6. A of the Technical Specifications.

Summarv Dencrintion of the Occurrence Analysis of reactor pressure data recorded during the " Loss-c f-Offsite-Power" test performed on pA ril 22, 1971, indicated that the initiation setpoints of the four reactor coolant system safety / relief valves might be above the Technical Specification limit of 1080 psig. Calibration checks were f:ormed on the pressure instrumentation and the settings of the safety /per-relief valves were tested under cold conditions, using nitrogen pressure.

These checks and tests indicated that the settings of three valves were above 1095 psig. The other valve was set at about 1080 psig.

All four valves were adjusted to initiate at less than 1080 psig.

Detailed Description and Analvsis As part of the startup test program, a " Loss-of-Offsite-Power" test was performed at 25% of rated power. This test, as expected, resulted in a reactor pressure transient. The wide range pressure recorder in the control room indicated that reactor pressure had increased to 1087 psig within approximately 24 seconds following the test initiation. At this time safety / relief valve RV-2-71 A opened, as indicated by a drop in pressure, a sharp increase in RV. 2-71 A discharge temperature and indication from an accelerometer mounted on the valve. Pressure was reduced to 1042 psig gjp;c;;; E6f 0

33 Q(

.w c

1

. Y .

within.8 secones and the valve closed. During the next 3[ minutes the pressure increased slowly to a peak value of 1100 psig, as indicated by the wide rari;e recorder. The Disturbance Log, printed by the plant computer, showed a peak pressure of 1104 psig at this time. Then RV-2-71 A opened a second time. Pressure was reduced to 1048 psig within 8 seconds.

~ Pressure then slowly increased to a peak of 1067 psig .followed by a steady decrease.

The indication that the second initiation had occurred at a pressure 13 psi, above.tbe first initiation was puzzling. .Also, since none of the.renaining valves had opened, it seemed that the settings of the remaining valves were even higher.

The first initiation at 1087-psig would'not have been considered unusual by itself. The ASME code requires a setpoint tolerance of one percent.

' This means the ' valves could initiate as much as 11 psig above the nominal 1080 psig setting. Also, considering the various accuracy tolerances associated with the pressure instrumentation, the recorded pressure could be in error by up to z 9 psig. Additional errors can occur due to recorder chart variatior.s. Similarly, the computer Disturbance Log .could be in error by up to 6.5 psig. Even considering all of these possible it appeared that at least three valves were set substantially above errors,ig.

1080 ps Further investigation was therefore considered necessary.

A calibration check of the recorder and the computer point was performed.

. At 1100 psig the recorder error was found to be + 5 psi and the computer error was founc to be + 9 psi. Based on this calibration it appeared '

that the first initiation of RV-2-71 A. occurred at 1082 psig and the second initiation at 1995 psig.

The four safety / relief valves were inspected under the direction of the I manufacturer's representative and the opening pressures of the first stage l pilot valves were tested under ambient temperature conditions using nitrogen pressure. These tests and inspections showed the following:

l l RV-2-71A: The setting was essentially correct.

RV-2-718: The setting of the setpoint adjustment nut was found to be correct. However, an improper length dowel pin was found to have compressed the setpoint adjusting I spring beyond the proper setting when the bonnet cap which covers the adjustment nut was bolted in

, pl ace. This caused the actual initiation pressure to be at least 1110 psig.

RV-2-710: The setting was found to be approximately 1100 psig.

A slight leak in the first stage pilot valve made it RV-2-71 D:

impossible to accurately determine the setpoint without special test equipment. However, it can be inferred that the setting was probably greater than 1095 psig.

'A

The observed 13 psi increase in setpoint for the second initiation of RV-2-71 A is attributed to the effect of temperature on the valve actuating system.' Wher, a valve is initiated, flow through the upper portions of the valve mechanism apparentl setpoint increase.-

y results The in sufficient additional manufacturers heating to representative affect stated thataan temporary approximately 15 increase in ,setpoint would be expected as the valve is heated to. normal operating temperature. This is confirmed by the results of the ambient temperature tests which showed the RV-2-71 A opening, point to be 1070 psig with. nitrogen, whereas it had initially opened during the loss of power test at about 1082 psig.

Correctiv. Actions

, The first stage pilot in RV-2-71D was repaired; the dowel pin in RV-2-71B was shortened to proper length; and all four valves were adjusted, at ambient temperature, to: initiate at less than the equivalent of 1080 psig at normal operating temperature.

Conclusions The manufacturers certification of pressure setting had been obtained for all four valves prior to initial plant operation. However, only one of the four valves was found to be properly set. Two valves were apparently not properly adjusted and one valve was affected by an improper length dowel pin.

There is reasorable confidence that the valves are presently set properly.

The test gauge used to adjust the valve settings was compared with an accurate dead weight test _ set before and after making the adjustments.

During the remainder of the startup test program particular effort will. be made to monitor the safety / relief valve performance during transient tests.

Yours very truly, 744p P.E.

R.O. Duncanson, Gen. Supt. of PowerJr. , Plants-Mechanical Chairman Monticello Safety Audit Committee ROD /fMC/ car k

9 l

Retrieved from "https://kanterella.com/w/index.php?title=ML20235D252&oldid=3192218"