ML20246A017

Fuel Degradation at Westinghouse Plants (Salem 1,Trojan), AEOD Engineering Evaluation Rept

ML20246A017
Person / Time
Site:	Salem, 05000000, Trojan
Issue date:	01/19/1983
From:	Zukor D NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD)
To:
Shared Package
ML20244C040	List: ML20244C037 ML20246A017
References
TASK-AE, TASK-E301 AEOD-E301, NUDOCS 8905080144
Download: ML20246A017 (6)

Text

- _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ - - _ _,

r

• AE0D Engineering Evaluation Report f

Unit: Salem 1 and Trojan Docket Ho: EE Report No. AE0D/E301 Licensee: Date Jar.uary 19, 1983 NSSS/AE: Westinghouse Evalua: ion /

Contact:

Dot Zukor

Subject:

Fuel Degradation at Westinghouse Plants (Salem 1, Trojan)

Evaluation Summary Fuel degradation was discoverad at Salem 1.

It was attributed to fuel lockup and the resultant stress and strain on the clad. Only one pin was affected, '

and it was replaced. This event was considered an isolated occurrence. No other corrective action is scheduled, f

At looseTrojan fuelonpellets.

April 26, 1982 17 assemblies were found with missing rodlets and This degradation was caused by baffle jetting. The f problem has occurred at other U.S. reactors and modifications have been made l or are planned which should solve the problems. j l

4 l

J j

i l

1 I

s9050B01448$$b72 PDR ADOCK O PDR S

7

- i f .

J i

Trojan q

b Discussion On April 26,.1982 at Trojan during a preplanned fuel inspect'on to locate suspected leaking fuel assemblies,17 assemblies were found with degraded fuel cladding. Portions of rodlets were missing and loose fuel pellets ,

were found.

Water-jetting induced vibration of.the fuel pins adjacent to baffle plate joint locations with enlarged gaps caused the fuel damage. Two types of baffle-cap related failures occurred. The first type is the outside corner or center injection jetting failure. (This type occurred at Trojan in 1980.) In this case, the water jet impinges on' the third rod from the

. corner and causes its failure in the lower axial region due to impingement, whirling and vibration. (See Figure 1.) The second type of failure is the inside corner or corner-injection jetting failure. In this case the water

. flows parallel to the fuel bundle perimeter face between the fuel and adjacent baffle plate. The water causes fuel rod whirling and vibration to appear at the first few rod locations. This type of failure propagates. >

Water-jetting-induced rod motion causes rod fretting due to abnormal clad wear against the Inconel grid assemblies.

Findings Holes in the core barrel provide pathways for bypass flow which is diverted from the annulus between the vessel and the core barrel walls: to a downward direction through holes in the Lorizontal "fonner" plate segrx Ets. (See Figure 2.) This small portion of the coolant flow between the baffle plates and the core barrel provides additional cooling for the barrel. However, most of the coolant flow from the vessel cold-leg inlet nozzles is downward ,

through the annulus between the core barrel and the vessel walls, then into a plenum at the bottom of the vessel . It then reverses direction and flows upward through the core. A pressure differential is thereby established between the downward coolant flow in the vessel-barrel annulus and through the "former" plates, and the reversed upward flow through the core inside the barrel. Coolant cross-flow through the enlarged baffle gaps results in high velocity jetting because of this pressure differential. The baffle water-jet then impinges on fuel rods and induces excessive rod motion, producing severe clad degradation.

One attempted solution was to peen the entire joint to reduce the gaps between the baffle plates; however, as evidenced by the event of April 26, 1982 the peening operation on the center-injected joints at the end of Cycle 31981 actually enlarged the gaps in the corner-injection joints. Despite the l l peening, three center-injection assemblies were damaged. i i

! The interim solution to the problem involves using solid stainless steel rods in the assemblies adjacent to the baffle plate joints. These rods are stronger than the ones currently in use and have been used before.

Six of these rods were installed at the end of cycle 2 in assemblies adjacent to baffle corners. No damage was noticed in these rods at the end of Cycle 3 or 4. Three rods will be replaced with stainless steel rods in the center-injection assemblies. In addition to the modified 1

fuel assemblies, partial grids will be used to provide midspan support to fuel in the vulnerable area in addition to increasing the frequencies and decreasing the amplitudes of the fundamental modes of vibration for these rods.

In the United States only Trojan and the Farley Units have a downward directed flow behind the baffle plates which was originally done to decrease the bypass flow by the core and add to plant efficiency.

Some foreign plants have the same flow path. (See Table)

The final corrective action to this problem will be to plug some holes in the core barrel and drill more holes in the upper former plate to change the flow from a downward to an upward direction. Since Westinghouse was not prepared to suggest a permanent solution while Trojan was shutdown for refueling, Farley will be the first plant to be modified, even though no fuel damage has occurred at this plant. The modifications are planned for the mid-January,1981 refueling outage. Trojan will be modified at a later time. KO-RI will be shutdown about one month after Farley to do the same modification.

Conclusions The licensees and Westinghouse appear to have found the root cause of the problem and appropriate action has been taken to prevent similar events in the future.

I i

~ ~- - ~ ~ ~

.D l; p,. ' ,' +, ~ . :i

!,7 I '

• 7; *?

e

.p '

l

.I

~-

'q 1,

1

(.

COOLANT FLOW THROUGH JOINT (ENLARGED GAP)

O (11 CENTER lNJECTION (2)

CORNER lNJECTION JOINT JOINT

,_ 'Pg .'

d 1

, BAFFLE an

- _oo .

O

~

P)P 3 . 2 l FUELROD

'P, PRESSURE I FIGURE 1. BAFF' E WATER. JET IMPlNDEMENT l

i j

l

CORE BARREL UPPER CORJ PLATE

• COOLANT INLET 4 FLOW

)

l' r-1,

~

3 m s Y':

BAFFLE PLATE "Q>:

/,  ;

); ,

FORMER k I J;. .p f o o LOWER CORE PLATE

/ .. -

JI"II"llt! ll ORE SUPPORT PLATE

1. ff/ffM/ -

V i

l FIGURE 2. "DOWNFLOW" BARREL / BAFFLE REGION DESIGN 1

L-Similar Events at Other Plants Date Plant Country Damage 1971-1972 Foreign Plant -

3 pins damaged 1973 Foreign Plant -

1 pin damaged 1975 Foreign Plant -

1 pin damaged 1977 Point Beach United States' 1 pin damaged.

July, 1979 Foreign Plant -

damaged in 10 fuel assemblies November, 1979 Foreign Plant --

damaged in 2 fuel assemblies April, 1980 Trojan -

damaged in 2 fuel assemblies

- J uly , 1981 Foreign Plant -

5 ruptured pins April, 1982. Foreign Plant -

3 damaged fuel assemblies April, 1982 Trojan -

17 damaged assemblies 1

i l References '

Inspection and Enforcemet Circular No. 80-17 LER 50-344/82-006/01T-0 i Inspection and Enforcement Information Notice No. 82-27 4

i l

i

_ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ____________.__.__..______._______...__.______________.________._.__.___.__.___.______J