ML20235D999
Text
- -.
Rigufatory Filo Cy.
NOR7HERN STATES POWER COMPANY Minneapolis, Minnesota 55401 P
A occKETED 4
\\
September 15, 1971 ET D
SEP2 01971
- I V1, SJ
-2
~
REGULATORY b
MA:L SECTION DOCKET CLERK g
g Director Dr. Peter A, Morris, Licensing 9
Division of Reactor a
y g
United States Atomic Energy Commission
- c Washington, D.C.
20545
Dear Dr. Morris:
MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Inoperability of the High Pressure CoolantInjectionSystem The High Pressure Coolant injection (HPCI) s stem was declared inoperable at the Monticello Nuclear Generating Plant on Se tember 4,1971, and re-mained inoperable until September 10, 1971. This occurrence is being reported Technical Specifications, in accordance with Section 6.6.B.2 of Appendix A, Region lit Compliance of the Provisional Operating License DPR-22. The Office has been notified of the occurrence.
Sumry Dseriotion of Occurrence On Septanber 4,1971, during a monthly operability test of the HPCI systan, the HPCI steam line isolation valves tripped closed from a false high steam flow signal. The HPCI system was declared inoperable and the RCIC, LPCI, and core spray systerns were immediately demonstrated to be operable as required by Section 4.5.D.2 of the Technical Specifications.
Elbow taps with four differential pressure indicating switches are installed on the HPCI steam supply lines to detect high steam flow conditions. Two of the four high flow sensors are connected in a one of two logic array and trip at a steam flow of 150,000 #/hr.
If either of these switches remain tripped for more than 45 seconds, the HPCI steam line will isolate.
(The other two high flow sensors trip at a steam flow of 300,000 #/hr, either sensor causing an instantaneous isolation). Whenever the HPCI system is started, the initial surge of steam flow results in a trip of the 150,000 #/hr flow sensors; however, the rated steam flow of approx-imat ely 100,000 #/hr is established within 45 seconds and no isolation occurs. The flow sensors resei at a value of approximately 125,000 #/hr.
I 8709250442 870921
MENIB7-111 db n>
ja investigation :f the September 4 occurrence revealed that the differential l
pressure measured at the elbow tapsi on the HPCI steam line was higher -
than previous 1;. measured during HPCI testing. Because of the change in the j
indicated differential pressure the 150,000 #/hr flow sensors did not reset'within 4E seconds and the,HPCl isolation was initiated. During the September 4th :estingb00 #/hr.the sensors falsely: indicated the normal flow to
~
be approximately 140, 1
On September 1:,1971, following backflushing of the flow elbow. sensing lines, the system was tested at reactor pressures of 150 psig, 350 psig, and 1000 psig, taps was found to have returned to the values measured during and found to operate properly. The differential pressure at the elbow testing prior to September 4th.
Weekly testing of the HPCI system will be conducted. until such time that th' e Operations Committee is satisfied that the change in the flow elbow differential pressure.is not a recurring problem. Also, flow elbow differential pressures will be recorded 'di. ring all future surveillance tests.
Yours very truly, 20 0-%(e cg
. R.0. Duncan' son, Jr., P. E.
Gen. Supt. of Power Plants-Mechanical Chairman-Monticelle Safety Audit Committee -
ROD /caf n
.h
_-