Extract xml value from Clob

I have the following xml stored in a CLOB column in a table. I want to retrieve one value from this xml - ReplacementPersonId.

I tried using the following query but it is not working properly. It returns null lines only but i know there is data in the field.

   SELECT EXTRACTVALUE(xmltype.createxml(transaction_document), '/Transaction/TransCtx/ReplacementPersonId')
FROM hr_api_transactions where LENGTHB(TO_CHAR(SUBSTR(transaction_document,1,4000)))<>0;

The xml data is:

<Transaction>
   <TransCtx>
      <TransactionGroup>ABSENCE_MGMT</TransactionGroup>
      <PrsnJobName>SE.Software Engineer</PrsnJobName>
      <PrsnAsgFlag>Y</PrsnAsgFlag>
      <LoginPrsnNpwFlag>A</LoginPrsnNpwFlag>
      <PrsnBgId>202</PrsnBgId>
      <EmployeeGeneration>A</EmployeeGeneration>
      <PrsnNpwFlag>A</PrsnNpwFlag>
      <ItemType>HRSSA</ItemType>
      <PrsnJobId>35934</PrsnJobId>
      <AsgStartDate dataType="d">2013-11-13</AsgStartDate>
      <PrsnGradeId>22</PrsnGradeId>
      <TransactionRefId dataType="n">36498</TransactionRefId>
      <LoginPrsnLegCode>US</LoginPrsnLegCode>
      <PrsnMgrId>31421</PrsnMgrId>
      <PrsnAssignmentId>32077</PrsnAssignmentId>
      <PrsnLegCode>US</PrsnLegCode>
      <LoginPrsnId>31422</LoginPrsnId>
      <LoginPrsnContextSet dataType="b">true</LoginPrsnContextSet>
      <pNtfSubMsg>HR_ABS_NTF_SUB_MSG</pNtfSubMsg>
      <ProductCode>PER</ProductCode>
      <EffectiveDate dataType="d">2013-12-19</EffectiveDate>
      <LoginPrsnEmpFlag>A</LoginPrsnEmpFlag>
      <LoginPrsnType>E</LoginPrsnType>
      <pCalledId dataType="n">1010344</pCalledId>
      <ReviewTemplateRNAttr>HR_ABS_NTF_SS</ReviewTemplateRNAttr>
      <TransactionId>130479</TransactionId>
      <PrsnLocationId>20795</PrsnLocationId>
      <PrsnKflexStructCode>PEOPLE_GROUP_FLEXFIELD</PrsnKflexStructCode>
      <LoginPrsnMgrName>Ramachandran, Abhijit</LoginPrsnMgrName>
      <PrsnContextSet dataType="b">true</PrsnContextSet>
      <PrsnPositionName>199.Software Engineer</PrsnPositionName>
      <PrsnEmpFlag>A</PrsnEmpFlag>
      <PrsnMgrName>Ramachandran, Abhijit</PrsnMgrName>
      <PrsnOrganizationId>204</PrsnOrganizationId>
      <PrsnPositionId>58470</PrsnPositionId>
      <TxnStatus>W</TxnStatus>
      <LoginWorkerNumber>2110</LoginWorkerNumber>
      <PrsnBgCurrencyCode>USD</PrsnBgCurrencyCode>
      <HeaderType>PER_HEADER</HeaderType>
      <SSHR_WF_BASED dataType="b">true</SSHR_WF_BASED>
      <PrsnSecurityGroupId>0</PrsnSecurityGroupId>
      <LoginPrsnMgrId>31421</LoginPrsnMgrId>
      <PrsnType>E</PrsnType>
      <PerzOrganizationId>202</PerzOrganizationId>
      <LoginPrsnName>Ramachandran, Anoop</LoginPrsnName>
      <CreatorPrsnId dataType="n">31422</CreatorPrsnId>
      <PrsnId>31422</PrsnId>
      <TransactionType>WF</TransactionType>
      <NtfAttachAttr>FND:entity=PQH_SS_ATTACHMENT&amp;pk1name=TransactionId&amp;pk1value=130479</NtfAttachAttr>
      <pApprovalReqd>YD</pApprovalReqd>
      <pAMETranType>SSHRMS</pAMETranType>
      <RelaunchFunction>HR_ABS_ENTRY_PAGE_SS</RelaunchFunction>
      <PerzLocalizationCode>US</PerzLocalizationCode>
      <TransactionRefTable>PER_ABSENCE_ATTENDANCES</TransactionRefTable>
      <TransactionIdentifier>ABSENCES</TransactionIdentifier>
      <pCalledFrom>HR_LOA_SS</pCalledFrom>
      <LoginPrsnBgId>202</LoginPrsnBgId>
      <PerzFunctionName>HR_LOA_SS</PerzFunctionName>
      <ProcessName>HR_GENERIC_APPROVAL_PRC</ProcessName>
      <PrsnPayrollId>153</PrsnPayrollId>
      <PrsnName>Ramachandran, Anoop</PrsnName>
      <CNode name="AbsenceParams" type="Ht">
         <AbsenceAttdId>36498</AbsenceAttdId>
         <AbsenceAction>CreateMode</AbsenceAction>
      </CNode>
      <pAMEAppId>800</pAMEAppId>
      <SSHR_REVIEW_FLOW_MODE>WF_REVIEW_PAGE</SSHR_REVIEW_FLOW_MODE>
   </TransCtx>
   <EoApiMap>
      <EO Name="oracle.apps.per.schema.server.PerAbsenceAttendancesEO">HR_PERSON_ABSENCE_SWI.PROCESS_API</EO>
   </EoApiMap>
   <TransCache>
      <AM MomVer="1044362310593">
         <cd/>
         <TXN Def="0" New="0" Lok="2" pcid="128">
            <EO Name="oracle.apps.per.schema.server.PerAbsenceAttendancesEO">
               <![CDATA[000100000004C3044163]]>
               <PerAbsenceAttendancesEORow PS="0" PK="Y">
                  <AbsenceAttendanceId>36498</AbsenceAttendanceId>
                  <BusinessGroupId>202</BusinessGroupId>
                  <AbsenceAttendanceTypeId>6</AbsenceAttendanceTypeId>
                  <PersonId>31422</PersonId>
                  <ReplacementPersonId>28</ReplacementPersonId>
                  <AbsenceDays>2</AbsenceDays>
                  <DateEnd>2013-12-26</DateEnd>
                  <DateNotification>2013-12-19 10:31:20.0</DateNotification>
                  <DateProjectedEnd null="true"/>
                  <DateProjectedStart null="true"/>
                  <DateStart>2013-12-25</DateStart>
                  <TimeProjectedEnd null="true"/>
                  <TimeProjectedStart null="true"/>
                  <LastUpdateDate>2013-12-19 10:30:56.0</LastUpdateDate>
                  <LastUpdatedBy>1013437</LastUpdatedBy>
                  <LastUpdateLogin>5574319</LastUpdateLogin>
                  <CreatedBy>1013437</CreatedBy>
                  <CreationDate>2013-12-19 10:30:56.0</CreationDate>
                  <ObjectVersionNumber null="true"/>
               </PerAbsenceAttendancesEORow>
            </EO>
            <EO Name="oracle.apps.per.schema.server.TransactionsEO">
               <![CDATA[000100000004C30E0550]]>
               <TransactionsEORow PS="0"/>
            </EO>
         </TXN>
      </AM>
   </TransCache>
</Transaction>

Try like this,

SELECT EXTRACTVALUE(XMLTYPE.createxml(transaction_document), '/Transaction/TransCache/AM/TXN/EO/PerAbsenceAttendancesEORow/ReplacementPersonId')
FROM   hr_api_transactions 
WHERE  LENGTHB(TO_CHAR(SUBSTR(transaction_document,1,4000)))<>0;